LM3280
BYP
SVIN
LDO3
FB
C3
1 éF
ENBUCK
ENLDO1
ENLDO2
ENLDO3
VCON
SGND
LDO2
LDO1
SW
BYPOUT
C2
4.7 éF
L1
2.2 éH
C5
1 éF
C6
1 éF
C7
1 éF
PA
BAND2
PA
BAND3
PA
BAND1
VIN :
2.7V to 5.5V
PGND
PVIN
C1
10 éF
VOUT :
0.8V to 3.6V
VLDO1 : 2.85V
VLDO2 :2.85V
VLDO3 : 2.85V
VCON :
0.267V to 1.200V
VOUT = 3 x VCON
DAC PA VCC
ON/OFF
ON/OFF
ON/OFF
éPC
ON/OFF VRE
F
VRE
F
VRE
F
LM3280
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LM3280 Adjustable Step-Down DC-DC Converter and 3 LDOs for RF Power Management
Check for Samples: LM3280
1FEATURES DESCRIPTION
The LM3280 is a multi-functional Power Management
2• 2MHz (typ.) PWM Switching Frequency Unit, optimized for low-power handheld applications
• Operates from a Single Li-Ion Cell (2.7V to such as Cellular Phones.
5.5V) The LM3280 incorporates three low-dropout LDO
• Adjustable Output Voltage (0.8V to 3.6V) DC- voltage regulators and one step down PWM DC-DC
DC converter with an internal Bypass FET. The step
• High-Efficiency Synchronous Buck Converter down converter's output voltage can be set using an
analog input (VCON) for optimizing efficiency of the RF
• 300mA Maximum Load Capability (PWM Mode) PA at various power levels. The LDO operates a
• 500mA Maximum Load Capability (Bypass nominal output voltage of 2.85V and maximum load
mode) current capability of 20mA for a reference voltage
• PWM, Forced and Automatic Bypass Mode required by linear RF power amplifiers. The LM3280
additionally features a separate enable pin for each
• 3 Low-Dropout and Fast Transient Response output.
LDOs
• 16-pin DSBGA Package The LM3280 is available in a 16-pin lead free DSBGA
package.
• Current Overload Protection
• Thermal Overload Protection
APPLICATIONS
• Cellular Phones
• Hand-Held Radios
• Battery Powered RF Devices
Typical Application
Figure 1. LM3280 Typical Application
1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 2006–2013, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
4321
A
B
C
D
ENBUCK
BYP
SW
PVIN
SVIN
VCON
ENLDO2
LDO2
LDO1
ENLDO1
LDO3
FB
BYPOUT
SGND
ENLDO3 PGND
Top View
LM3280
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Connection Diagrams
Figure 2. 16–Bump DSBGA Package, Large Bump
See Package Number YZR0016QQA
Pin Descriptions
Pin # Name Description
A1 LDO1 LDO1 Output.
B1 LDO2 LDO2 Output.
C1 LDO3 LDO3 Output.
D1 ENLDO3 LDO3 Enable Input. Set this digital input high to turn on LDO3. (ENBUCK pin must be also set high.) For
turning LDO3 off, set low.
A2 SVIN Analog, Signal, and LDO Supply Input.
B2 FB Buck Converter Feedback Analog Input. Connect to the output at the output filter capacitor.
C2 ENLDO2 LDO2 Enable Input. Set this digital input high to turn on LDO2. (ENBUCK pin must be also set high.) For
turning LDO2 off, set low.
D2 VCON Buck Converter Voltage Control Analog Input. This pin controls VOUT in PWM mode. Set: VOUT = 3 x VCON. Do
not leave floating.
A3 SGND Analog, Signal, and LDO Ground.
B3 ENBUCK Buck Converter Enable Input. Set this digital input high after Vin >2.7V for normal operation. For shutdown,
set low.
C3 ENLDO1 LDO1 Enable Input. Set this digital input high to turn on LDO1. (ENBUCK pin must be also set high.) For
turning LDO1 off, set low.
D3 BYP Forced Bypass Input. Use this digital input to command operation in Bypass mode. Set BYP low (<0.4V) for
normal operation.
A4 BYPOUT Bypass FET Drain. Connect to the output capacitor. Do not leave floating.
B4 PVIN Buck Converter Power Supply Voltage Input to the internal PFET switch and Bypass FET.
C4 SW Buck Converter Switch Node connection to the internal PFET switch and NFET synchronous rectifier.
Connect to an inductor with a saturation current rating that exceeds the maximum Switch Peak Current Limit
of the PWM Buck Converter.
D4 PGND Buck Converter Power Ground.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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Absolute Maximum Ratings(1)(2)
SVIN, PVIN to SGND −0.2V to +6.0V
PGND to SGND −0.2V to +0.2V
ENs, FB, BYP, VCON (SGND −0.2V)
to (SVIN +0.2V)
w/6.0V max
SW, BYPOUT (PGND −0.2V)
to (PVIN +0.2V)
w/6.0V max
PVIN to SVIN −0.2V to +0.2V
Continuous Power Dissipation
(3) Internally Limited
Junction Temperature (TJ-MAX) +150°C
Storage Temperature Range −65°C to +150°C
Maximum Lead Temperature
(Soldering, 10 sec.) +260°C
ESD Rating (4)
Human Body Model 2k V
Machine Model 200 V
(1) Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed
performance limits and associated test conditions, see the Electrical Characteristics tables.
(2) All voltages are with respect to the potential at the GND pins.
(3) Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ= 150°C (typ.) and
disengages at TJ= 125°C (typ.).
(4) The Human body model is a 100pF capacitor discharged through a 1.5kΩresistor into each pin. (MIL-STD-883 3015.7) The machine
model is a 200pF capacitor discharged directly into each pin. National Semiconductor recommends that all integrated circuits be
handled with appropriate precautions. Failure to observe proper ESD handling techniques can result in damage.
Operating Ratings(1)(2)
Input Voltage Range 2.7V to 5.5V
Recommended Load Current
PWM Mode: 0mA to 300mA
Bypass Mode: 0mA to 500mA
LDO: 0mA to 20mA
Junction Temperature (TJ) Range −30°C to +125°C
Ambient Temperature (TA) Range −30°C to +85°C
(3)
(1) Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed
performance limits and associated test conditions, see the Electrical Characteristics tables.
(2) Shutdown current includes leakage current of PFET and Bypass FET.
(3) In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may
have to be de-rated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP =
125°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the
part/package in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).
Thermal Properties
Junction-to-Ambient Thermal Resistance (θJA), DSBGA Package (1) 48 °C/W
(1) Junction-to-ambient thermal resistance (θJA) is taken from thermal measurements, performed under the conditions and guidelines set
forth in the JEDEC standard JESD51-7. A 1" x 1", 4 layer, 1.5oz. Cu board was used for the measurements. The θJA, which is
performed under the 4 layer cellphone board condition, is 86°C/W.
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General Electrical Characteristics(1)(2)(3)
Limits in standard typeface are for TA= TJ= 25°C. Limits in boldface type apply over the full operating ambient temperature
range (−30°C ≤TA= TJ≤+85°C). Unless otherwise noted, specifications apply to the LM3280 with: VIN = ( SVIN = PVIN = )
3.6V, ENBUCK = 3.6V, ENLDO1 = ENLDO2 = ENLDO3 = BYP = 0V, FB = 2V, VCON = 0.267V.
Symbol Parameter Conditions Min. Typ. Max Units
IQShutdown Supply Current ENBUCK = 0V, 0.1 3µA
FB = SW = VCON = 0V,
BYPOUT = 0V
No Load Supply Current ENBUCK = 3.6V, 720 800 µA
BYPOUT = 0V
ENBUCK = 3.6V, 920 1300 µA
BYPOUT = 0V,
ENLDO1 = 3.6V
ENBUCK = BYP = 3.6V 720 800 µA
ENBUCK = BYP = 3.6V, 920 1300 µA
ENLDO1 = 3.6V
VIH Logic High Input Threshold Voltage for FB = 0V 1.2 V
ENx, BYP
VIL Logic Low Input Threshold Voltage for FB = 0V 0.4 V
ENx, BYP
IPDWN Logic Input Pull Down Current for ENx, ENx, BYP = 3.6V 5 10 µA
BYP
THSD Thermal Shutdown Temperature (2) 150 °C
Hysteresis Temperature (2) 25 °C
(1) All voltages are with respect to the potential at the GND pins.
(2) Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the
most likely norm.
(3) The LM3280 is designed for mobile phone applications where turn-on after power-up is controlled by the system controller and where
requirements for a small package size overrule increased die size for internal Under Voltage Lock-Out (UVLO) circuitry. Thus, it should
be kept in shutdown by holding the EN pin low until the input voltage exceeds 2.7V.
Buck Electrical Characteristics(1)(2)(3)
Limits in standard typeface are for TA= TJ= 25°C. Limits in boldface type apply over the full operating ambient temperature
range (−30°C ≤TA= TJ≤+85°C). Unless otherwise noted, specifications apply to the LM3280 with: VIN = ( SVIN = PVIN = )
3.6V, ENBUCK = 3.6V, ENLDO1 = ENLDO2 = ENLDO3 = BYP = 0V, FB = 2V, VCON = 0.267V.
Symbol Parameter Conditions Min. Typ. Max Units
VFB_ MIN Feedback Voltage at Minimum Setting VCON = 0.267V 0.75 0.800 0.85 V
VFB_ MAX Feedback Voltage at Maximum Setting VCON = 1.20V, VIN = 4.2V 3.528 3.600 3.672 V
OVP Over-Voltage Protection Threshold (4) 330 400 mV
VBYPASS−Auto Bypass Detection Negative (5) 160 250 320 mV
Threshold
VBYPASS+ Auto Bypass Detection Positive (5) 350 450 540 mV
Threshold
RDSON (P) Pin-Pin Resistance for PFET ISW = 500mA, FB = 0V 320 450 mΩ
RDSON (N) Pin-Pin Resistance for N-FET ISW = - 200mA 310 450 mΩ
RDSON (BYP) Pin-Pin Resistance for Bypass FET IBYPOUT = 500mA 85 120 mΩ
(1) All voltages are with respect to the potential at the GND pins.
(2) Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the
most likely norm.
(3) Shutdown current includes leakage current of PFET and Bypass FET.
(4) Over-Voltage protection (OVP) threshold is the voltage above the nominal VOUT where the OVP comparator turns off the PFET switch
while in PWM mode.
(5) SVIN is compared to the programmed output voltage (VOUT). When SVIN – VOUT falls below VBYPASS−for longer than TBYP the Bypass
FET turns on and the switching FETs turn off. This is called the Bypass mode. The device comes out of Bypass mode when SVIN –
VOUT exceeds VBYPASS+for longer than TBYP, and PWM mode returns. The hysteresis for the bypass detection threshold VBYPASS+–
VBYPASS−will always be positive and will be approximately 200mV (typ.).
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Buck Electrical Characteristics(1)(2)(3) (continued)
Limits in standard typeface are for TA= TJ= 25°C. Limits in boldface type apply over the full operating ambient temperature
range (−30°C ≤TA= TJ≤+85°C). Unless otherwise noted, specifications apply to the LM3280 with: VIN = ( SVIN = PVIN = )
3.6V, ENBUCK = 3.6V, ENLDO1 = ENLDO2 = ENLDO3 = BYP = 0V, FB = 2V, VCON = 0.267V.
Symbol Parameter Conditions Min. Typ. Max Units
ILIM-PWM Switch Current Limit FB = 0V (6) 700 820 940 mA
ILIM-BYP Bypass FET Current Limit (7) 800 1000 1200 mA
FOSC Internal Oscillator Frequency 1.8 22.2 MHz
Gain VCON to VOUT Gain 0.267V ≤VCON ≤1.20V, 3 V/V
VIN = 4.2V
ICON VCON Input Leakage Current VCON = 1.2V 10 nA
(6) Electrical Characteristic table reflects open loop data (FB = 0V and current drawn from SW pin ramped up until cycle by cycle current
limit is activated). Refer to datasheet curves for closed loop data and its variation with regards to supply voltage and temperature.
Closed loop current limit is the peak inductor current measured in the application circuit by increasing output current until output voltage
drops by 10%.
(7) The current is defined as the load current at which the BYPOUT voltage is 1V lower than PVIN.
Buck System Characteristics(1)(2)
The following spec table entries are guaranteed by design if the component values in the typical application circuit are used.
These parameters are not guaranteed by production testing.
Symbol Parameter Conditions Min Typ Max Units
TRESPONSE Time for VOUT to Rise from VIN = 4.2V, COUT = 4.7µF,
0.8V to 3.4V in PWM Mode RLOAD = 15Ω25 µs
L = 2.2 µH (ISAT > 0.94A)
TSTARTUP Time for VOUT to rise to 3.4V VIN = 4.2V, COUT = 4.7µF,
in PWM Mode RLOAD = 15Ω36 µs
(3) L = 2.2µH (ISAT = 0.94A)
EN = Low to High
CCON VCON Input Capacitance VIN = 3.6V, VCON = 1V, 15 pF
Test Freq. = 100kHz
TON_BYP Bypass FET Turn On Time In VIN = 3.6V, VCON = 0.267V,
Bypass Mode COUT = 4.7µF, RLOAD = 15Ω30 µs
BYP = Low to High
TBYP Auto Bypass Detect Delay (4) 10 15 20 µs
Time
(1) All voltages are with respect to the potential at the GND pins.
(2) Shutdown current includes leakage current of PFET and Bypass FET.
(3) The startup time is the time to reach 90% of 3.4V nominal output voltage from the ENBUCK being low to high.
(4) SVIN is compared to the programmed output voltage (VOUT). When SVIN – VOUT falls below VBYPASS−for longer than TBYP the Bypass
FET turns on and the switching FETs turn off. This is called the Bypass mode. The device comes out of Bypass mode when SVIN –
VOUT exceeds VBYPASS+for longer than TBYP, and PWM mode returns. The hysteresis for the bypass detection threshold VBYPASS+–
VBYPASS−will always be positive and will be approximately 200mV (typ.).
LDO1, 2, and 3 Electrical Characteristics(1)(2)
Limits in standard typeface are for TA= TJ= 25°C. Limits in boldface type apply over the full operating ambient temperature
range (−30°C ≤TA= TJ≤+85°C). Unless otherwise noted, specifications apply to the LM3280 with: VIN = 3.6V, ENBUCK =
3.6V, BYP = 0V, FB = 2V, VCON = 0.267V, ENLDOx = 3.6V (3).
Symbol Parameter Conditions Min Typ Max Units
VLDO LDO Output Voltage VLDO = 2.85V, IOUT = 1mA -1 +1 %
Accuracy -2 +2 %
ΔVLDO Line Regulation VIN = VLDO(nom) + 0.5V to 5.5V, 0.1 %/V
IOUT = 1mA
Load Regulation IOUT = 1mA to 20mA 0.01 0.04 %/mA
(1) All voltages are with respect to the potential at the GND pins.
(2) Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the
most likely norm.
(3) The ENLDOx means that the one of ENLDO1, ENLDO2, and ENLDO3 is set high (> 1.2V) and the others are set 0V.
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LDO1, 2, and 3 Electrical Characteristics(1)(2) (continued)
Limits in standard typeface are for TA= TJ= 25°C. Limits in boldface type apply over the full operating ambient temperature
range (−30°C ≤TA= TJ≤+85°C). Unless otherwise noted, specifications apply to the LM3280 with: VIN = 3.6V, ENBUCK =
3.6V, BYP = 0V, FB = 2V, VCON = 0.267V, ENLDOx = 3.6V (3).
Symbol Parameter Conditions Min Typ Max Units
ILIM_LDO LDO Current Limit (4) 30 40 55 mA
IPU Pull-Up Current (4) 40 60 80 mA
RPD Pull-Down Resistance IOUT = -50mA, 10 13.5 17 Ω
ENBUCK = all ENLDO = 0V
VDROP Dropout Voltage IOUT = 20mA (5) 70 115 mV
(4) The current is defined as the load current at which the LDOx voltage is 1.0V lower than the nominal output voltage.
(5) Dropout voltage is the voltage difference between the input and the output at which the output voltage drops to 100mV below the
nominal voltage.
LDO1, 2, and 3 System Characteristics(1)
The following spec table entries are guaranteed by design if the component values in the typical application circuit are used.
Unless otherwise noted, specifications apply to the LM3280 with: VIN = 3.6V. These parameters are not guaranteed by
production testing.
Symbol Parameter Conditions Min Typ Max Units
PSRR Power Supply Ripple Rejection Test Freq. = 1KHz, VRIPPLE = 0.5Vpp 55 dB
Ratio COUT = 1µF, IOUT = 1mA, BYP = VIN
TLDO_ON Time to reach 90% of VLDO(nom) VIN = ENBUCK = 3V, 50 100 µs
after ENLDO signal goes high. COUT = 1µF,
ENLDOx = Low to High,
RLOAD = 270Ω
VIN = 3V, 80 130 µs
COUT = 1µF,
ENBUCK = ENLDOx = Low to High,
RLOAD = 270Ω
TLDO_OFF Time to reach 0.1V of VLDO after VIN = 3V, 50 200 µs
ENLDO signal goes low. COUT = 1µF,
ENLDOx = High to Low,
IOUT = 0mA
(1) All voltages are with respect to the potential at the GND pins.
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LDO
20 Ps/DIV
500 mV/DIV
5V/DIV
ENLDO
VIN = 3.0V
COUT = 1 éF
RLOAD = 270:
LDO
20 Ps/DIV
500 mV/DIV
5V/DIV
ENBUCK &
ENLDO 500 mV/DIV
VOUT
VIN = 3.0V
COUT = 1 éF
RLOAD = 270:
0.0
0.2
JUNCTION TEMPERATURE (°C)
SHUTDOWN CURRENT (PA)
-40 -20 0 20 40 60 80 100 120 140
0.1
0.3
VIN = 2.7V
VIN = 4.2V
VIN = 5.5V
VIN = 3.6V
0.4
0.5
0.6
0.7
0.8
0.9
1.0
20 Ps/DIV
10 mV/DIV
AC Coupled
3.0 V
VIN
LDO
3.6 V
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
QUIESCENT CURRENT (mA)
0.60
0.64
0.68
0.72
0.80
0.84
0.76
TA = 25oC
TA = -30oC
TA = 85oC
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
QUIESCENT CURRENT (mA)
0.76
0.80
0.84
0.88
0.96
1.00
0.92
TA = 25oC
TA = 85oC
TA = -30oC
LM3280
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SNOSAU4B –OCTOBER 2006–REVISED FEBRUARY 2013
Typical Performance Characteristics
(VIN = ENBUCK = 3.6V, ENLDOx = BYP = 0V, TA= 25°C, unless otherwise noted)
Quiescent Current vs Quiescent Current vs
Supply Voltage Supply Voltage
(VCON = 0.267V, FB = 2V, No Switching, LDO Disabled) (VCON = 0.267V, FB = 2V, No Switching, LDO Enabled)
Figure 3. Figure 4.
Shutdown Current vs
Temperature LDO Line Transient Response
(all EN = BYPOUT = VCON = SW = FB = 0V) (RLOAD = 270Ω, COUT = 1µF)
Figure 5. Figure 6.
LDO Turn ON LDO Turn ON
(ENLDO = Low to High) (ENBUCK = ENLDO = Low to High)
Figure 7. Figure 8.
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0 4 8 12 16 20
OUTPUT CURRENT (mA)
LDO DROPOUT VOLTAGE (mV)
100
80
60
20
0
40
TA = 85oC
TA = 25oC
TA = -30oC
0 10 20 30 40 50 60
OUTPUT CURRENT (V)
LDO VOLTAGE (V)
0.0
TA = -30°C
0.5
1.0
1.5
2.0
2.5
3.0
3.5
TA = 85°C
TA = 25°C
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
LDO VOLTAGE (V)
2.830
IOUT = 1 mA
IOUT = 10 mA
IOUT = 20 mA
2.835
2.840
2.845
2.850
2.855
2.860
2.865
-40 -20 0 20 40 60 80 100
AMBIENT TEMPERATURE (°C)
LDO VOLTAGE (V)
2.830
IOUT = 1 mA
IOUT = 10 mA
IOUT = 20 mA
2.835
2.840
2.845
2.850
2.855
2.860
2.865
LDO
20 Ps/DIV
500 mV/DIV
5V/DIV
ENLDO
VIN = 3.0V
COUT = 1 éF
No Load
10 Ps/DIV
1 mA
10 mV/DIV
AC Coupled
IOUT
LDO
10 mA
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Typical Performance Characteristics (continued)
(VIN = ENBUCK = 3.6V, ENLDOx = BYP = 0V, TA= 25°C, unless otherwise noted)
LDO Turn OFF LDO Load Transient Response
(ENLDO = High to Low) (COUT = 1µF)
Figure 9. Figure 10.
LDO Voltage LDO Voltage
vs vs
Supply Voltage Temperature
Figure 11. Figure 12.
LDO Dropout Voltage LDO Voltage vs
vs Output Current
Output Current (VIN = 3.6V)
Figure 13. Figure 14.
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IL
40 Ps/DIV
200 mA/DIV
3.6V
3.0V
50 mV/DIV
AC Coupled
VIN
VOUT
VOUT = 1.5V
IOUT = 200 mA
20 Ps/DIV
200 mA
250 mA
50 mA
100 mV/DIV
AC Coupled
VIN = 3.6V
VOUT = 1.5V
IL
IOUT
VOUT
IL
100 Ps/DIV
200 mA/DIV
5V/DIV
VSW
VOUT
VIN = 4.2V
1V/DIV
VIN
RLOAD = 15:
VCON = 1.1V
VIN = 3.0V
IL
100 Ps/DIV
200 mA/DIV
5V/DIV
VSW
VOUT
VCON = 0.5V
RLOAD = 15:
BYP
1V/DIV
2V/DIV
ENBUCK 20 Ps/DIV
500 mA/DIV
5V/DIV
1V/DIV
5V/DIV
VOUT
VSW
IL
VIN = 4.2V
VOUT = 3.4V
RLOAD = 15:
IL
100 Ps/DIV
200 mA/DIV
5V/DIV
VSW
VOUT
VIN = 4.2V
VOUT = 3.25V
RLOAD = 15:
EN
2V/DIV
2V/DIV
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SNOSAU4B –OCTOBER 2006–REVISED FEBRUARY 2013
Typical Performance Characteristics (continued)
(VIN = ENBUCK = 3.6V, ENLDOx = BYP = 0V, TA= 25°C, unless otherwise noted)
PWM Startup PWM Shutdown Response
(VCON = 1.13V) (VCON = 1.08V)
Figure 15. Figure 16.
Automatic Bypass Operation Forced Bypass Operation
(VIN = 4.2V to 3.0V) (VIN = 3.0V)
Figure 17. Figure 18.
Line Transient Response Load Transient Response
(VIN = 3.0V to 3.6V) (VCON = 0.5V)
Figure 19. Figure 20.
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0-40 40 80
AMBIENT TEMPERATURE (oC)
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
SWITCHING FREQUENCY VARIATION (%)
20-20 60 100
VIN = 4.2V
VCON = 0.5V
IOUT = 200 mA
VIN = 2.7V
VIN = 3.6V
-40 -20 0 20 40 60 80 100
AMBIENT TEMPERATURE (oC)
60
70
80
90
100
110
120
RDS(ON) (m:)
IBYPOUT = 500 mA
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
50
IL
400 ns/DIV
200 mA/DIV
2V/DIV
VSW
VIN = 3.6V
VOUT = 1.5V
10 mV/DIV
AC Coupled
VOUT
IOUT = 200 mA
IL
400 ns/DIV
200 mA/DIV
2V/DIV
VSW
VIN = 3.57V
VOUT = 3.25V
10 mV/DIV
AC Coupled
VOUT
IOUT = 200 mA
100 Ps/DIV
1.08V
0.5V
VSW
VOUT VIN = 4.2V
RLOAD = 15:
3.25V
2V/DIV
VCON
1.5V
IL
10 Ps/DIV
500 mA/DIV
2V/DIV
VSW
VOUT
VOUT = 1.5V
1V/DIV
RLOAD = 15:
LM3280
SNOSAU4B –OCTOBER 2006–REVISED FEBRUARY 2013
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Typical Performance Characteristics (continued)
(VIN = ENBUCK = 3.6V, ENLDOx = BYP = 0V, TA= 25°C, unless otherwise noted)
VCON Voltage Response Timed Current Limit Response
(VIN = 4.2V, VCON = 0.5V / 1.1V) (Normal Operation to Short Circuit)
Figure 21. Figure 22.
Output Voltage Ripple Output Voltage Ripple in Dropout
(VOUT = 1.5V) (VIN = 3.75V, VOUT = 3.25V, IOUT = 200mA)
Figure 23. Figure 24.
Switching Frequency Variation RDSON
vs vs
Temperature (VOUT = 1.5V) Temperature (Bypass FET)
Figure 25. Figure 26.
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2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE (V)
1.490
1.495
1.500
1.505
1.515
1.520
1.510
IOUT = 300 mA
IOUT = 150 mA
IOUT = 50 mA
-20 0 20 40 60 80 100
AMBIENT TEMPERATURE (oC)
1.490
1.495
1.500
1.510
1.515
1.520
OUTPUT VOLTAGE (V)
-40
IOUT = 50 mA
IOUT = 100 mA
IOUT = 300 mA
1.505
-20 0 20 40 60 80 100
AMBIENT TEMPERATURE (oC)
150
200
300
400
450
500
RDS(ON) (m:)
-40
VIN = 4.2V
ISW = 500 mA
VIN = 2.7V
VIN = 3.6V
350
250
-20 0 20 40 60 80 100
AMBIENT TEMPERATURE (oC)
150
200
300
400
450
500
RDS(ON) (m:)
-40
VIN = 4.2V
ISW = -200 mA
VIN = 2.7V
VIN = 3.6V
250
350
LM3280
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SNOSAU4B –OCTOBER 2006–REVISED FEBRUARY 2013
Typical Performance Characteristics (continued)
(VIN = ENBUCK = 3.6V, ENLDOx = BYP = 0V, TA= 25°C, unless otherwise noted)
RDSON RDSON
vs vs
Temperature (P-FET) Temperature (N-FET)
Figure 27. Figure 28.
PWM Output Voltage vs PWM Output Voltage vs
Supply Voltage Temperature
(VOUT = 1.5V) (VOUT = 1.5V)
Figure 29. Figure 30.
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0.1 0.2 0.3 0.4 0.5
VCON VOLTAGE (V)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
OUTPUT VOLTAGE (V)
0.0
VIN = 5.0V
VIN = 5.5V
VIN = 4.7V
0.4 0.6 0.8 1.0 1.2 1.4
VCON VOLTAGE (V)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
OUTPUT VOLTAGE (V)
0.2
VIN = 3.6V
Bypass Mode
VIN = 3.0V
VIN = 2.7V
VIN = 4.2V
TA = -30°C
TA = 25°C
TA = 85°C
ILIM-BYP
= 965 mA
Max Load
Capability
0 200 400 600 800 1000 1200
OUTPUT CURRENT (mA)
1.0
0.8
0.6
0.4
0.2
0.0
DROPOUT VOLTAGE (V)
500 mA
-40 -20 0 20 40 60 80 100
AMBIENT TEMPERATURE (oC)
760
780
800
820
840
860
CURRENT LIMIT (mA)
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V OPEN LOOP
CLOSED LOOP
VIN = 4.2V
VIN = 2.7V VIN = 3.6V
LM3280
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Typical Performance Characteristics (continued)
(VIN = ENBUCK = 3.6V, ENLDOx = BYP = 0V, TA= 25°C, unless otherwise noted)
Open/Closed Loop Current Limit vs Dropout Voltage vs
Temperature Output Current
(PWM mode) (Bypass mode, VIN = BYP = 3.6V)
Figure 31. Figure 32.
VCON Voltage vs Low VCON Voltage vs
PWM Output Voltage Output Voltage
(IOUT = 200mA) (RLOAD = 15Ω)
Figure 33. Figure 34.
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0 50 100 150 200 250 300 350
OUTPUT CURRENT (mA)
40
50
60
70
80
90
100
EFFICIENCY (%)
VIN = 4.2V
VIN = 3.6V
VIN = 3.9V
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT VOLTAGE (V)
70
75
80
85
90
95
100
EFFICIENCY (%)
RLOAD = 15:
VIN = 3.9V
RLOAD = 10:
0 50 100 150 200 250 300 350
OUTPUT CURRENT (mA)
40
50
60
70
80
90
100
EFFICIENCY (%)
VIN = 4.2V
VIN = 2.7V
VIN = 3.6V
LM3280
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SNOSAU4B –OCTOBER 2006–REVISED FEBRUARY 2013
Typical Performance Characteristics (continued)
(VIN = ENBUCK = 3.6V, ENLDOx = BYP = 0V, TA= 25°C, unless otherwise noted)
Efficiency vs Efficiency vs
Output Voltage Output Current
(VIN = 3.9V) (VOUT = 1.5V)
Figure 35. Figure 36.
Efficiency vs
Output Current
(VOUT = 3.25V)
Figure 37.
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OSCILLATOR
SHUTDOWN
CONTROL
FB
VCON
ENBUCK
PVIN
SW
SGND
SVIN
BYP
ERROR
AMPLIFIER
CURRENT
COMP
MAIN CONTROL
0.15V
VCON Low Voltage
DETECTOR
OVP COMP
BYPOUT
MOSFET
CONTROL
LOGIC
ä
Discharge Control
ENLDOx
LDOx
PGND
0.95V
SVIN
SGND
LDO Control
Charge Control
VREF
-
+
LM3280
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BLOCK DIAGRAM
Figure 38. Functional Block Diagram
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DEVICE INFORMATION
The LM3280 a multi-functional Power Management Unit, optimized for low-power handheld applications such as
Cellular Phones. It incorporates one adjustable voltage PWM DC-DC converter with an internal Bypass FET and
three LDOs. It also provides a separate enable pin for each output. The buck converter output voltage can be
programmed from 0.8V to 3.6V in PWM mode. The buck converter is designed for a maximum load capability of
300mA in PWM mode and 500mA in Bypass mode. Maximum load range may vary from this depending on input
voltage, output voltage and the inductor chosen. The LDO operates a nominal output voltage of 2.85V and
maximum load current capability of 20mA.
The buck converter is designed to allow the RF PA (Power Amplifier) to operate at maximum efficiency over a
wide range of power levels from a single Li-Ion battery cell. It is based on current-mode buck architecture, with
synchronous rectification for high efficiency. It has three of pin-selectable operating modes. Fixed-frequency
PWM operation offers regulated output at high efficiency while minimizing interference with sensitive IF and data
acquisition circuits. Bypass mode (Forced or Automatic) turns on an internal FET bypass switch to power the PA
directly from the battery. This helps the RF PA maintain its operating power during low battery conditions by
reducing the dropout voltage across the buck converter. Shutdown mode turns the device off and reduces battery
consumption to 0.1µA (typ.).
DC PWM mode output voltage precision is +/-2% for 3.6VOUT. Efficiency is typically around 96% for a 120mA
load with 3.2V output, 3.6V input. PWM mode quiescent current is 0.72mA typ. The output voltage is dynamically
programmable from 0.8V to 3.6V by adjusting the voltage on the control pin (VCON) without the need for external
feedback resistors.
An LDO is used to provide a regulated 2.85V reference voltage supply to each RF PA. Since each LDO has its
own enable pin, it can be used to enable or disable its respective PA. The LDO can be enabled only after the
buck converter is activated. The LDO will automatically be disabled whenever the ENBUCK or ENLDOx is disabled.
Single LDO must be turned on at the same time. Each LDO provides an active charge circuit. The LDO output is
pulled to ground potential via an internal resistor when the ENBUCK or ENLDOx pin is low.
Additional features include current overload protection and thermal shutdown. The buck converter also provides
over voltage protection.
The LM3280 is constructed using a chip-scale 16-pin DSBGA package. This package offers the smallest
possible size, for space-critical applications such as cell phones, where board area is an important design
consideration. Use of a DSBGA package requires special design considerations for implementation. (See
DSBGA PACKAGE ASSEMBLY AND USE.) Its fine bump-pitch requires careful board design and precision
assembly equipment. Use of this package is best suited for opaque-case applications, where its edges are not
subject to high-intensity ambient red or infrared light. Also, the system controller should set ENBUCK low during
power-up and other low supply voltage conditions. (See Shutdown Mode.)
Buck Converter
CIRCUIT OPERATION
Referring to Figure 1 and Figure 38, the buck converter operates as follows. During the first part of each
switching cycle, the control block in the buck converter turns on the internal PFET (P-channel MOSFET) switch.
This allows current to flow from the input through the inductor to the output filter capacitor and load. The inductor
limits the current to a ramp with a slope of around (VIN - VOUT) / L, by storing energy in a magnetic field. During
the second part of each cycle, the controller turns the PFET switch off, blocking current flow from the input, and
then turns the NFET (N-channel MOSFET) synchronous rectifier on. In response, the inductor’s magnetic field
collapses, generating a voltage that forces current from ground through the synchronous rectifier to the output
filter capacitor and load. As the stored energy is transferred back into the circuit and depleted, the inductor
current ramps down with a slope around VOUT / L. The output filter capacitor stores charge when the inductor
current is going high, and releases it when inductor current is going low, smoothing the voltage across the load.
The output voltage is regulated by modulating the PFET switch on time to control the average current sent to the
load. The effect is identical to sending a duty-cycle modulated rectangular wave formed by the switch and
synchronous rectifier at SW to a low-pass filter formed by the inductor and output filter capacitor. The output
voltage is equal to the average voltage at the SW pin.
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PWM MODE
While in PWM (Pulse Width Modulation) mode, the output voltage is regulated by switching at a constant
frequency (2MHz typ.) and then modulating the energy per cycle to control power to the load. Energy per cycle is
set by modulating the PFET switch on-time pulse width to control the peak inductor current. This is done by
comparing the PFET drain current to a slope-compensated reference current generated by the error amplifier. At
the beginning of each cycle, the clock turns on the PFET switch, causing the inductor current to ramp up. When
the current sense signal ramps past the error amplifier signal, the PWM comparator turns off the PFET switch
and turns on the NFET synchronous rectifier, ending the first part of the cycle. If an increase in load pulls the
output down, the error amplifier output increases, which allows the inductor current to ramp higher before the
comparator turns off the PFET. This increases the average current sent to the output and adjusts for the increase
in the load. The minimum on-time of PFET in PWM mode is 50ns (typ.).
BYPASS MODE
The buck converter contains an internal PFET switch for bypassing the PWM DC-DC converter during Bypass
mode. In Bypass mode, this PFET is turned on to power the PA directly from the battery for maximum RF output
power. Bypass mode is more efficient than operating in PWM mode at 100% duty cycle because the resistance
of the bypass PFET is less than the series resistance of the PWM PFET and inductor. This translates into higher
voltage available on the output in Bypass mode, for a given battery voltage. The part can be placed in bypass
mode by sending BYP pin high. This is called Forced Bypass Mode and it remains in bypass mode until BYP pin
goes low.
Alternatively the part can go into Bypass mode automatically. This is called Auto-bypass mode or Automatic
Bypass mode. The bypass switch turns on when the difference between the input voltage and programmed
output voltage is less than 250mV (typ.) for more than the bypass delay time of 15µs (typ.). The bypass switch
turns off when the input voltage is higher than the programmed output voltage by 450mV (typ.) for longer than
the bypass delay time. The bypass delay time is provided to prevent false triggering into Automatic Bypass mode
by either spikes or dips in VIN. This method is very system resource friendly in that the Bypass PFET is turned on
automatically when the input voltage gets close to the output voltage, typical scenario of a discharging battery. It
is also turned off automatically when the input voltage rises, typical scenario of a charger connected. Another
scenario could be changes made to VCON voltage causing Bypass PFET to turn on and off automatically. It is
recommended to connect BYPOUT pin directly to the output capacitor with a separate trace and not to the FB
pin.
OPERATING MODE SELECTION CONTROL
The BYP digital input pin is used to select between PWM/Auto-bypass and Bypass operating mode. Setting BYP
pin high (>1.2V) places the device in Forced Bypass mode. Setting BYP pin low (<0.4V) or leaving it floating
places the device in PWM/Auto-bypass mode.
Bypass and PWM operation overlap during the transition between the two modes. This transition time is
approximately 31µs when changing from PWM to Bypass mode, and 15µs when changing from Bypass to PWM
mode. This helps prevent under or overshoots during the transition period between PWM and Bypass modes.
DYNAMICALLY ADJUSTABLE OUTPUT VOLTAGE
The LM3280 buck converter features dynamically adjustable output voltage to eliminate the need for external
feedback resistors. The output can be set from 0.8V to 3.6V by changing the voltage on the analog VCON pin.
This feature is useful in PA applications where peak power is needed only when the handset is far away from the
base station or when data is being transmitted. In other instances, the transmitting power can be reduced. Hence
the supply voltage to the PA can be reduced, promoting longer battery life. See BUCK CONVERTER SETTING
THE OUTPUT VOLTAGE for further details.
OVER VOLTAGE PROTECTION
The buck converter has an over voltage comparator that prevents the output voltage from rising too high, when
the device is left in PWM mode under light-load conditions, during output voltage steps, or during startup. When
the output voltage rises to 330mV over its target, the OVP comparator inhibits PWM operation to skip pulses until
the output voltage returns to the target. During the over voltage protection mode, both the PWM PFET and the
NFET synchronous rectifier are off. When the part comes out of the over voltage protection mode, the NFET
synchronous rectifier remains off for approximately 3.5µs to avoid inductor current going negative.
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INTERNAL SYNCHRONOUS RECTIFICATION
While in PWM mode, the buck converter uses an internal NFET as a synchronous rectifier to reduce rectifier
forward voltage drop and associated power loss. Synchronous rectification provides a significant improvement in
efficiency whenever the output voltage is relatively low compared to the voltage drop across an ordinary rectifier
diode.
With medium and heavy loads, the internal NFET synchronous rectifier is turned on during the inductor current
down slope in the second part of each cycle. The synchronous rectifier is turned off prior to the next cycle. There
is no zero cross detect, which means that the NFET can conduct current in both directions and inductor current is
always continuous. The advantage of this method is that the part remains in PWM mode at light loads or no load
conditions. The NFET has a current limit. The NFET is designed to conduct through its intrinsic body diode
during transient intervals before it turns on, eliminating the need for an external diode.
CURRENT LIMITING
A current limit feature allows the buck converter to protect itself and external components during overload
conditions. In PWM mode, a 940mA (max.) cycle-by-cycle current limit is normally used. If an excessive load
pulls the output voltage down to below approximately 0.375V, indicating a possible short to ground, then the
device switches to a timed current limit mode. In timed current limit mode, the internal PFET switch is turned off
after the current comparator trips, and the beginning of the next cycle is inhibited for 3.5µs to force the
instantaneous inductor current to ramp down to a safe value. After the 3.5µs interval, the internal PFET is turned
on again. This cycle is repeated until the load is reduced and the output voltage exceeds approximately 0.375V.
Therefore, the device may not startup if an excessive load is connected to the output when the device is enabled.
The synchronous rectifier is off in the timed current limit mode. Timed current limit prevents the loss of current
control seen in some products when the output voltage is pulled low in serious overload conditions.
A current limit is also provided for the NFET. This is approximately −500mA. Both the NFET and the PFET are
turned off in negative current limit until the PFET is turned on again at the beginning of the next cycle. The
negative current limit inhibits buildup of excessive negative inductor current.
In the Bypass mode, the bypass current limit is 1000mA (typ.). The output voltage drops when the bypass
current limit kicks in.
LDO
LDO OPERATION
The LDO provides a nominal output voltage of 2.85V. Each LDO can be enabled when the respective enable pin
is set high (>1.2V) after the buck converter has been enabled. The LDO will automatically be disabled whenever
the ENBUCK or ENLDOx is disabled. Only one LDO may be enabled on at a time. A 2µs period of time needs to
occur between disabled one LDO and enabling another. Otherwise, all LDOs are disabled.
CHARGE AND DISCHARGE
Each LDO includes an active charge circuit. 7.5us (typ.) after the LDO is enabled, the current limit of the LDO is
set to 60mA. A 1µF load capacitor will be charged to 90% of the nominal output voltage in approximately 50us
(typ.). (Note: This number is based on the assumption that the PWM loop has been enabled and given time to
stabilize before the LDO is enabled.) The current limit is then reduced to 40mA.
An internal pull-down resistor is also included in each LDO. The LDO discharges the output capacitor through the
pull-down resistor when LDO is disabled.
Shutdown Mode
Setting the ENBUCK digital pin low (<0.4V) places the LM3280 in a 0.1µA (typ.) Shutdown mode. During
shutdown, the PFET switch, NFET synchronous rectifier, reference voltage source, control and bias circuitry of
the LM3280 are turned off. Setting ENBUCK high (>1.2V) enables normal operation.
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ENBUCK should be set low to turn off the LM3280 during power-up and under voltage conditions when the power
supply is less than the 2.7V minimum operating voltage. The LM3280 is designed for compact portable
applications, such as cellular phones. In such applications, the system controller determines power supply
sequencing and requirements for small package size outweigh the benefit of including UVLO (Under Voltage
Lock-Out) circuitry.
Thermal Overload Protection
The LM3280 has a thermal overload protection function to protect the device from short-term misuse and
overload conditions. When the junction temperature exceeds around 150°C, the device inhibits operation. Both
the PFET and the NFET are turned off in PWM mode, and the Bypass PFET is turned off in Bypass mode. The
LDO is also turned off. When the temperature drops below 125°C, normal operation resumes. Prolonged
operation in thermal overload conditions may damage the device.
APPLICATION INFORMATION
BUCK CONVERTER SETTING THE OUTPUT VOLTAGE
The buck converter features a pin-controlled variable output voltage to eliminate the need for external feedback
resistors. It can be programmed for an output voltage from 0.8V to 3.6V by setting the voltage on the VCON pin,
as in the following formula:
VOUT = 3 x VCON (1)
When VCON is between 0.267V and 1.20V, the output voltage will follow proportionally by 3 times of VCON.
If VCON is over 1.20V (VOUT = 3.6V), sub-harmonic oscillation may occur because of insufficient slope
compensation.
If VCON voltage is less than 0.267V (VOUT = 0.8V), the output voltage may not be regulated due to the required
on-time being less than the minimum on-time (50ns). The output voltage can go lower than 0.8V providing a
limited VIN range is used. Refer to the Typical Performance Characteristics (Low VCON Voltage vs. Output
Voltage) for details. This curve is for a typical part and there could be part to part variation for output voltages
less than 0.8V over the limited VIN range. In addition, if the VCON is less than approximately 0.15V, the PWM
mode output is turned off, but the internal bias circuits are still active.
INDUCTOR SELECTION
A 2.2μH inductor with saturation current rating over 940mA is recommended for almost all applications. The
inductor resistance should be less than 0.2Ωfor better efficiency. Table 1 lists suggested inductors and
suppliers.
Table 1. Suggested Inductors and Their Suppliers
Model Size (WxLxH) [mm] Vendor
DO3314-222MX 3.3 x 3.3 x 1.4 Coilcraft
LPS3010-222MLC 3.1 x 3.1 x 1.0 Coilcraft
LPS3008-222MLC 3.1 x 3.1 x 0.8 Coilcraft
MIPSA2520D2R2** 2.5 x 2.0 x 1.2 FDK
KSLI252010AG2R2* 2.5 x 2.0 x 1.0 Hitachi-Metal
VLF3010AT-2R2M1R0 2.6 x 2.8 x 1.0 TDK
NR3010T2R2M 3.0 x 3.0 x 1.0 Taiyo-Yuden
NR3012T2R2M 3.0 x 3.0 x 1.2 Taiyo-Yuden
1117AS-2R2M(DE2810C) 2.8 x 3.0 x 1.0 Toko
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If a higher value inductor is used the LM3280 may become unstable and exhibit large under or over shoot during
line, load and VCON transients. If smaller inductance value is used, slope compensation maybe insufficient
causing sub-harmonic oscillations. The device has been tested with inductor values in the range 1.55μH to 3.1μH
to account for inductor tolerances.
For low-cost applications, an un-shielded bobbin inductor can be used. For noise-critical applications, an un-
shielded or shielded-bobbin inductor should be used. A good practice is to layout the board with footprints
accommodating both types for design flexibility. This allows substitution of an un-shielded inductor, in the event
that noise from low-cost bobbin models is unacceptable. Saturation occurs when the magnetic flux density from
current through the windings of the inductor exceeds what the inductor’s core material can support with a
corresponding magnetic field. This can cause poor efficiency, regulation errors or stress to a DC-DC converter
like the LM3280.
CAPACITOR SELECTION
The LM3280 is designed to be used with ceramic capacitors. Use a 10µF ceramic capacitor for the power input,
a 4.7µF ceramic capacitor for the buck converter output, and a 1µF ceramic capacitor for the LDO and the signal
input. Ceramic capacitors such as X5R, X7R and B are recommended for both filters. These provide an optimal
balance between small size, cost, reliability and performance for cell phones and similar applications. Table 2
lists suggested capacitors and suppliers.
Table 2. Suggested Capacitors and Their Suppliers
Model Size (EIA) Vendor
C1608X5R0J475M 1608 (0603) TDK
C2012X5R0J106M 2012 (0805) TDK
GRM188B10J105KA01 1608 (0603) Murata
LMK107BJ105KA 1608 (0603) Taiyo-Yuden
C1608JB1C105K 1608 (0603) TDK
The DC bias characteristics of the capacitor must be considered when making the selection. If smaller case size
such as 1608 (0603) is selected, the DC bias could reduce the cap value by as much as 40%, in addition to the
20% tolerances and 15% temperature coefficients. Request DC bias curves from manufacturer when making
selection. The buck converter has been designed to be stable with output capacitors as low as 3μF to account
for capacitor tolerances. The LDO has been done with output capacitors as low as 0.5µF. These values include
DC bias reduction, manufacturing tolerances and temp coefficients.
The input filter capacitor supplies AC current drawn by the PFET switch of the LM3280 in the first part of each
cycle and reduces the voltage ripple imposed on the input power source. A 1µF capacitor is also recommended
close to SVIN pin. The output filter capacitor absorbs the AC inductor current, helps maintain a steady output
voltage during transient load changes and reduces output voltage ripple. These capacitors must be selected with
sufficient capacitance and sufficiently low ESR (Equivalent Series Resistance) to perform these functions. The
ESR of the filter capacitors is generally a major factor in voltage ripple.
DSBGA PACKAGE ASSEMBLY AND USE
Use of the DSBGA package requires specialized board layout, precision mounting and careful re-flow
techniques, as detailed in National Semiconductor Application Note 1112. Refer to the section, Surface Mount
Technology (SMD) Assembly Considerations. For best results in assembly, alignment ordinals on the PC board
should be used to facilitate placement of the device. The pad style used with DSBGA package must be the
NSMD (non-solder mask defined) type. This means that the solder-mask opening is larger than the pad size.
This prevents a lip that otherwise forms if the solder-mask and pad overlap, from holding the device off the
surface of the board and interfering with mounting. See Application Note 1112 for specific instructions how to do
this. The 16-Bump package used for the LM3280 has 300 micron solder balls and requires 10.82 mil pads for
mounting on the circuit board. The trace to each pad should enter the pad with a 90° entry angle to prevent
debris from being caught in deep corners. Initially, the trace to each pad should be 6-7 mil wide, for a section
approximately 6 mil long or longer, as a thermal relief. Then each trace should neck up or down to its optimal
width. The important criterion is symmetry. This ensures the solder bumps on the LM3280 re-flow evenly and that
the device solders level to the board. In particular, special attention must be paid to the pads for bumps B4, C4
and D4. Because PVIN and PGND are typically connected to large copper planes, inadequate thermal relief can
result in inadequate re-flow of these bumps.
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The DSBGA package is optimized for the smallest possible size in applications with red or infrared opaque
cases. Because the DSBGA package lacks the plastic encapsulation characteristic of larger devices, it is
vulnerable to light. Backside metallization and/or epoxy coating, along with front-side shading by the printed
circuit board, reduce this sensitivity. However, the package has exposed die edges. In particular, Thin Micro
DSBGA devices are sensitive to light, in the red and infrared range, shining on the package’s exposed die edges.
Do not use or power-up the LM3280 while subjecting it to high intensity red or infrared light; otherwise degraded,
unpredictable or erratic operation may result. Examples of light sources with high red or infrared content include
the sun and halogen lamps. Place the device in a case opaque to red or infrared light.
BOARD LAYOUT CONSIDERATIONS
PC board layout is an important part of DC-DC converter design. Poor board layout can disrupt the performance
of a DC-DC converter and surrounding circuitry by contributing to EMI, ground bounce, and resistive voltage loss
in the traces. These can send erroneous signals to the DC-DC converter, resulting in poor regulation or
instability. Poor layout can also result in re-flow problems leading to poor solder joints between the DSBGA
package and board pads. Poor solder joints can result in erratic or degraded performance. Good layout for the
LM3280 can by implemented by following a few simple design rules.
1. Place the LM3280 on 10.82 mil pads. As a thermal relief, connect to each pad with a 7 mil wide,
approximately 7 mil long traces, and when incrementally increase each trace to its optimal width. The
important criterion is symmetry to ensure the solder bumps on the LM3280 re-flow evenly (see DSBGA
PACKAGE ASSEMBLY AND USE).
2. Place the LM3280, inductor and filter capacitors close together and make the trace short. The traces
between these components carry relatively high switching currents and act as antennas. Following this rule
reduces radiated noise. Place the capacitors and inductor close to the LM3280. The input capacitor should
be placed right next to the device between PVIN and PGND pin.
3. Arrange the components so that the switching current loops curl in the same direction. During the first half of
each cycle, current flows from the input filter capacitor, through the LM3280 and inductor to the output filter
capacitor and back through ground, forming a current loop. In the second half of each cycle, current is pulled
up from ground, through the LM3280 by the inductor, to the output filter capacitor and then back through
ground, forming a second current loop. Routing these loops so the current curls in the same direction,
prevents magnetic field reversal between the two half-cycles and reduces radiated noise.
4. Connect the ground pins of the LM3280, and filter capacitors together using generous component side
copper fill as a pseudo-ground plane. Then connect this to the ground-plane (if one is used) with several
vias. This reduces ground plane noise by preventing the switching currents from circulating through the
ground plane. It also reduces ground bounce at the LM3280 by giving it a low impedance ground connection.
5. Use wide traces between the power components and for power connections to the DC-DC converter circuit.
This reduces voltage errors caused by resistive losses across the traces.
6. Route noise sensitive traces, such as the voltage feedback trace, away from noisy traces and components.
The voltage feedback trace must remain close to the LM3280 circuit and should be routed directly from FB
pin to VOUT at the output capacitor. A good approach is to route the feedback trace on another layer and to
have a ground plane between the top layer and the layer on which the feedback trace is routed. This reduces
EMI radiation on to the DC-DC converter’s own voltage feedback trace.
7. It is recommended to connect BYPOUT pin to VOUT at the output capacitor using a separate trace, instead of
connecting it directly to the FB pin for better noise immunity.
20 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated
Product Folder Links: LM3280
LM3280
www.ti.com
SNOSAU4B –OCTOBER 2006–REVISED FEBRUARY 2013
REVISION HISTORY
Changes from Revision A (February 2013) to Revision B Page
• Changed layout of National Data Sheet to TI format .......................................................................................................... 20
Copyright © 2006–2013, Texas Instruments Incorporated Submit Documentation Feedback 21
Product Folder Links: LM3280
PACKAGE OPTION ADDENDUM
www.ti.com 2-Aug-2018
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead/Ball Finish
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LM3280TL-275/NOPB ACTIVE DSBGA YZR 16 250 Green (RoHS
& no Sb/Br) SNAGCU Level-1-260C-UNLIM -30 to 85 V002
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LM3280TL-275/NOPB DSBGA YZR 16 250 178.0 8.4 2.69 2.69 0.76 4.0 8.0 Q1
PACKAGE MATERIALS INFORMATION
www.ti.com 3-Aug-2018
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM3280TL-275/NOPB DSBGA YZR 16 250 210.0 185.0 35.0
PACKAGE MATERIALS INFORMATION
www.ti.com 3-Aug-2018
Pack Materials-Page 2
MECHANICAL DATA
YZR0016xxx
www.ti.com
TLA16XXX (Rev C)
0.600±0.075 D
E
A
. All linear dimensions are in millimeters. Dimensioning and tolerancing per ASME Y14.5M-1994.
B. This drawing is subject to change without notice.
NOTES:
4215051/A 12/12
D: Max =
E: Max =
2.385 mm, Min =
2.385 mm, Min =
2.325 mm
2.325 mm
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