LM2794/95
C1+
GND
BRGT
D1
D2
VIN POUT
C1-
SD
ISET
RSET
1PF
C2-
C1
CIN 1PF
C2 1PF
CHOLD
1PF
D3
D4
C2+
LED2
LED1
LED3
LED4
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LM2794 /LM2795 Current Regulated Switched Capacitor LED Supply with Analog and
PWM Brightness Control
Check for Samples: LM2794,LM2795
1FEATURES APPLICATIONS
2• Regulated Current Sources with ±0.5% • White LED Display Backlights
Matching between any Two Outputs • White LED Keypad Backlights
• High Efficiency 3/2 Boost Function • 1-Cell Li-Ion Battery-Operated Equipment
• Drives One, Two, Three or four White LEDs Including PDAs, Hand-Held PCs, Cellular
Phones
• 2.7V to 5.5V Input Voltage
• Up to 80mA Output Current DESCRIPTION
• Analog Brightness Control The LM2794/95 is a fractional CMOS charge-pump
• Active-Low or High Shutdown Input ('94/95) that provides four regulated current sources. It
accepts an input voltage range from 2.7V to 5.5V and
• Very Small Solution Size and no Inductor maintains a constant current determined by an
• 2.3µA (typ.) Shutdown Current external sense resistor.
• 325kHz Switching Frequency (min.) The LM2794/5 delivers up to 80mA of load current to
• Constant Frequency Generates Predictable accommodate four White LEDs. The switching
Noise Spectrum frequency is 325kHz. (min.) to keep the conducted
• Thin DSBGA Package: 2.08mm X 2.403mm X noise spectrum away from sensitive frequencies
0.600mm High within portable RF devices.
Basic Application Circuit
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 © 2002–2013, 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.
A1
B2
C1
D2
E1
E3
E5
E7
D6
C7
B6
A7
A5
A3
LM2794, LM2795
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DESCRIPTION (CONTINUED)
Brightness can be controlled by both linear and PWM techniques. A voltage between 0V and 3.0V may be
applied to the BRGT pin to linearly vary the LED current. Alternatively, a PWM signal can be applied to the SD
pin to vary the perceived brightness of the LED. The SD pin reduces the operating current to 2.3µA (typ.) The
LM2794 is shut down when the SD pin is low, and the LM2795 is shut down when the SD pin is high.
The LM2794/95 is available in a DSBGA CSP package.
Connection Diagram
Figure 1. DSBGA Package
Bottom View
PIN DESCRIPTION
Pin(1) Name Function
A1 C1+ Positive terminal of C1
B2 C1−Negative terminal of C1
C1 VIN Power supply voltage input
D2 GND Power supply ground input
E1 C2−Negative terminal of C2
E3,E5,E7,D6 D1−4 Current source outputs. Connect directly to LED
C7 ISET Current Sense Input. Connect 1% resistor to ground to set constant current through LED
B6 BRGT Variable voltage input controls output current
A7 SD The LM2794 has an active-low shutdown pin (LOW = shutdown, HIGH = operating). The LM2795
has an active-high shutdown pin (HIGH = shutdown, LOW = operating) that has a pull-up to VIN.
A5 C2+ Positive terminal of C2
A3 POUT Charge pump output
(1) Note that the pin numbering scheme for the DSBGA package was revised in April, 2002 to conform to JEDEC standard. Only the pin
numbers were revised. No changes to the physical location of the inputs/outputs were made. For reference purpose, the obsolete
numbering had C1+ as pin 1, C1- as pin 2, VIN as pin 3, GND as pin 4, C2- as pin 5, D1-D4 as pin 6,7,8 & 9, Iset as pin 10, BRGT as
pin 11, SD as pin 12, C2+ as pin 13, Pout as pin 14
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)
VIN −0.5 to 6.2V max
SD −0.5 to (VIN+0.3V) w/ 6.2V max
BRGT −0.5 to (VIN+0.3V) w/ 6.2V max
Continuous Power Dissipation (3) Internally Limited
TJMAX(3) 135°C
θJA(3) (4) 125°C/W
Storge Temperature −65°C to +150°C
Lead Temp. (Soldering, 5 sec.) 260°C
ESD Rating (5)
Human Body Model 2kV
Machine Model 200V
(1) Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when
operating the device beyond its rated operating conditions.
(2) Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
(3) Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=150°C (typ.) and
disengages at TJ=140°C (typ.). D1, D2, D3 and D4 may be shorted to GND without damage. POUT may be shorted to GND for 1sec
without damage.
(4) The value of θJA is based on a two layer evaluation board with a dimension of 2in. x1.5in.
(5) In the test circuit, all capacitors are 1.0µF, 0.3Ωmaximum ESR capacitors. Capacitors with higher ESR will increase output resistance,
reduce output voltage and efficiency.
Operating Conditions
Input Voltage (VIN) 2.7V to 5.5V
Ambient Temperature (TA)−30°C to +85°C
Junction Temperature (TJ)−30°C to +100°C
Electrical Characteristics
Limits in standard typeface are for TJ= 25°C and limits in boldface type apply over the full Operating Junction
Temperature Range (−30°C ≤TJ≤+100°C). Unless otherwise specified, C1 = C2 = CIN = CHOLD = 1 µF, VIN = 3.6V, BRGT
pin = 0V; RSET =124Ω; LM2794:VSD = VIN (LM2795: VSD = 0V).
Symbol Parameter Conditions Min Typ Max Units
IDX Available Current at Output Dx 3.0V ≤VIN ≤5.5V 15 16.8 mA
VDX ≤3.8V
BRGT = 50mV
2.7V ≤VIN ≤3.0V 10
VDX ≤3.6V mA
BRGT = 0V
VDX ≤3.8V 20 mA
BRGT = 200mV
VDX Available Voltage at Output Dx 3.0V ≤VIN ≤5.5V 3.8 V
IDX ≤15mA
BRGT = 50mV
IDX Line Regulation of Dx Output 3.0V ≤VIN ≤5.5V 14.18 15.25 16.78 mA
Current VDX = 3.6V
3.0V ≤VIN ≤4.4V 14.18 15.25 16.32 mA
VDX = 3.6V
IDX Load Regulation of Dx Output VIN = 3.6V 14.18 15.25 16.32 mA
Current 3.0V ≤VDX ≤3.8V
ID-MATCH Current Matching Between Any VIN = 3.6V, VDX = 3.6V 0.5 %
Two Outputs
IQQuiescent Supply Current 3.0V ≤VIN ≤4.2V, Active, No Load 5.5 8.2 mA
Current
RSET = OPEN
ISD Shutdown Supply Current 3.0V ≤VIN ≤5.5V, Shutdown 2.3 5µA
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Electrical Characteristics (continued)
Limits in standard typeface are for TJ= 25°C and limits in boldface type apply over the full Operating Junction
Temperature Range (−30°C ≤TJ≤+100°C). Unless otherwise specified, C1 = C2 = CIN = CHOLD = 1 µF, VIN = 3.6V, BRGT
pin = 0V; RSET =124Ω; LM2794:VSD = VIN (LM2795: VSD = 0V).
Symbol Parameter Conditions Min Typ Max Units
IPULL-SD Shutdown Pull-Up Current VIN = 3.6V 1.5 µA
(LM2795)
VCP Input Charge-Pump Mode To Pass 4.7 V
Mode Threshold
VCPH Input Charge-Pump Mode To Pass (1) 250 mV
Mode Hysteresis
VIH SD Input Logic High (LM2794) 3.0V ≤VIN ≤5.5V 1.0 V
SD Input Logic High (LM2795) 0.8VIN
VIL SD Input Logic Low (LM2794) 3.0V ≤VIN ≤5.5V 0.2 V
SD Input Logic Low (LM2795) 0.2VIN
ILEAK-SD SD Input Leakage Current 0V ≤VSD ≤VIN 100 nA
RBRGT BRGT Input Resistance 240 kΩ
ISET ISET Pin Output Current IDX/10 mA
fSW Switching Frequency (2) 3.0V ≤VIN ≤4.4V 325 515 675 kHz
(1) Voltage at which the device switches from charge-pump mode to pass mode or pass mode to charge-pump mode. For example, during
pass mode the device output (Pout) follows the input voltage.
(2) The output switches operate at one eigth of the oscillator frequency, fOSC = 1/8fSW.
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100 300 500 700 900110013001500170019002100
RSET
IDX (mA)
0
2
4
6
8
10
12
14
16
18
20
(Ÿ)
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SNVS168L –JANUARY 2002–REVISED MAY 2013
Typical Performance Characteristics
Unless otherwise specified, C1 = C2 = CIN = CHOLD = 1µF, VIN = 3.6V, BRGT pin = 0V, RSET = 124Ω.
IDIODE IDIODE
vs vs
VIN BRGT
Figure 2. Figure 3.
IDIODE
vs IDIODE
VIN vs
BRGT = 3V RSET
Figure 4. Figure 5.
IDIODE
vs IDIODE
RSET vs
VBRGT = 0V VDIODE
Figure 6. Figure 7.
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2.7 3.2 3.7 4.2 4.7 5.2 5.7
0
1
2
3
4
5
SHUTDOWN SUPPLY CURRENT (µA)
-30°C
25°C
100°C
VIN (V)
2.7 3.2 3.7 4.2 4.7 5.2 5.7
100°C
-30°C
25°C
VIN (V)
0
20
40
60
80
100
120
ISUPPLY (mA)
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Typical Performance Characteristics (continued)
Unless otherwise specified, C1 = C2 = CIN = CHOLD = 1µF, VIN = 3.6V, BRGT pin = 0V, RSET = 124Ω.
VSET Duty Cycle
vs vs.
VBRGT Led Current (LM2794)
RSET = 1KΩIDIODE 1- 4 = 15mA
Figure 8. Figure 9.
Supply Current Supply Current
vs vs
VIN VIN
IDIODE 1-4 = 15mA IDIODE 1-4 = Open
Figure 10. Figure 11.
Shutdown Supply Current Shutdown Threshold
vs vs
VIN VIN
Figure 12. Figure 13.
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Typical Performance Characteristics (continued)
Unless otherwise specified, C1 = C2 = CIN = CHOLD = 1µF, VIN = 3.6V, BRGT pin = 0V, RSET = 124Ω.
Start-Up Response @ VIN = 2.7V (LM2794) Start-Up Response @ VIN = 2.7V (LM2795)
Figure 14. Figure 15.
Start-Up Response @ VIN = 3.6V (LM2794) Start-Up Response @ VIN = 3.6V (LM2795)
Figure 16. Figure 17.
Start-Up Response @ VIN = 4.2V (LM2794) Start-Up Response @ VIN = 4.2V (LM2795)
Figure 18. Figure 19.
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Typical Performance Characteristics (continued)
Unless otherwise specified, C1 = C2 = CIN = CHOLD = 1µF, VIN = 3.6V, BRGT pin = 0V, RSET = 124Ω.
Available Additional Current @ POUT
IDIODE 1−4 = 15mA, RSET = 124 ΩSwitching Frequency
Figure 20. Figure 21.
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LM2794/95
2.7 - 5.5V
CIN
1 …F(3/2)x
Charge Pump
VIN
GND
POUT
CPOUT
1 …F
SD
C2
1 …F
C1
1 …F
Voltage
Reference
Brightness
Control
BRGT
RSET D4
D3
D2
D1
*(Only on
LM2795) 10PA
*
110k:
130k:
330k:
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FUNCTIONAL BLOCK DIAGRAM
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VIN
LM2795
SD
Shutdown
Control
*Only on
LM2795
10PA
*
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APPLICATION INFORMATION
CIRCUIT DESCRIPTION
The LM2794/5 is a 1.5x/1x CMOS charge pump with four matched constant current outputs, each capable of
driving up to 20mA through White LEDs. This device operates over the extended Li-Ion battery range from 2.7V
to 5.5V. The LM2794/5 has four regulated current sources connected to the device's 1.5x charge pump output
(POUT). At input voltages below 4.7V (typ.), the charge-pump provides the needed voltage to drive high forward
voltage drop White LEDs. It does this by stepping up the POUT voltage 1.5 times the input voltage. The charge
pump operates in Pass Mode, providing a voltage on POUT equal to the input voltage, when the input voltage is at
or above 4.7V (typ.). The device can drive up to 80mA through any combination of LEDs connected to the
constant current outputs D1-D4.
To set the LED drive current, the device uses a resistor connected to the ISET pin to set a reference current. This
reference current is then multiplied and mirrored to each constant current output. The LED brightness can then
be controlled by analog and/or digital methods. Applying an analog voltage in the range of 0V to 3.0V to the
Brightness pin (BRGT) adjusts the dimming profile of the LEDs. The digital technique uses a PWM (Pulse Width
Modulation) signal applied to the Shutdown pin (SD). (see ISET AND BRGT PINS).
SOFT START
Soft start is implemented internally by ramping the reference voltage more slowly than the applied voltage.
During soft start, the current through the LED outputs will ramp up in proportion to the rate that the reference
voltage is being ramped up.
SHUTDOWN MODE
The shutdown pin (SD) disables the part and reduces the quiescent current to 2.3µA (typ.).
The LM2795 has an active-high shutdown pin (HIGH = shutdown, LOW = operating). An internal pull-up is
connected between SD and VIN of the LM2795. This allows the use of open-drain logic control of the LM2795
shutdown, as shown in Figure 22. The LM2795 SD pin can also be driven with a rail-to-rail CMOS logic signal.
Figure 22. Open-Drain Logic Shutdown Control
The LM2794 has an active-low shutdown pin (LOW = shutdown, HIGH = operating). The LM2794 SD pin can be
driven with a low-voltage CMOS logic signal (1.5V logic, 1.8V logic, etc). There is no internal pull-up or pull-down
on the SD pin of the LM2794.
CAPACITOR SELECTION
The LM2794/5 requires 4 external capacitors for proper operation. Surface-mount multi-layer ceramic capacitors
are recommended. These capacitors are small, inexpensive and have very low equivalent series resistance
(ESR, ≤15mΩtyp.). Tantalum capacitors, OS-CON capacitors, and aluminum electrolytic capacitors are generally
not recommended for use with the LM2794/5 due to their high ESR, as compared to ceramic capacitors.
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¸
¸
¹
·
¨
¨
©
§
¸
¸
¹
·
¨
¨
©
§
Amps
1
10
*
188 BRGT
V*
+ 385.0.0
SET
R
*
oMirrorRati
OFFSET
V +
BRGT
V 385.0
*
RSET
LED =I
LED =I
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SNVS168L –JANUARY 2002–REVISED MAY 2013
For most applications, ceramic capacitors with X7R or X5R temperature characteristic are preferred for use with
the LM2794/5. These capacitors have tight capacitance tolerance (as good as ±10%), hold their value over
temperature (X7R: ±15% over −55°C to 125°C; X5R: ±15% over −55°C to 85°C), and typically have little voltage
coefficient. Capacitors with Y5V or Z5U temperature characteristic are generally not recommended for use with
the LM2794/5. Capacitors with these temperature characteristics typically have wide capacitance tolerance
(+80%, −20%), vary significantly over temperature (Y5V: +22%, −82% over −30°C to +85°C range; Z5U: +22%,
−56% over +10°C to +85°C range), and have poor voltage coefficients. Under some conditions, a nominal 1µF
Y5V or Z5U capacitor could have a capacitance of only 0.1µF. Such detrimental deviation is likely to cause Y5V
and Z5U capacitors to fail to meet the minimum capacitance requirements of the LM2794/5. Table 1 lists
suggested capacitor suppliers for the typical application circuit.
Table 1. Ceramic Capacitor Manufacturers
Manufacturer Contact
TDK www.component.tdk.com
Murata www.murata.com
Taiyo Yuden www.t-yuden.com
LED SELECTION
The LM2794/5 is designed to drive LEDs with a forward voltage of about 3.0V to 4.0V. The typical and maximum
diode forward voltage depends highly on the manufacturer and their technology. Table 2 lists two suggested
manufacturers. Forward current matching is assured over the LED process variations due to the constant current
output of the LM2794/5.
Table 2. White LED Selection
Manufacturer Contact
Osram www.osram-os.com
Nichia www.nichia.com
ISET AND BRGT PINS
An external resistor, RSET, is connected to the ISET pin to set the current to be mirrored in each of the LED
outputs. The internal current mirror sets each LED output current with a 10:1 ratio to the current through RSET.
The current mirror circuitry matches the current through each LED to within 0.5%.
In addition to RSET, a voltage may be applied to the VBRGT pin to vary the LED current. By adjusting current with
the Brightness pin (BRGT), the brightness of the LEDs can be smoothly varied.
Applying a voltage on BRGT between 0 to 3 volts will linearly vary the LED current. Voltages above 3V do not
increase the LED current any further. The voltage on the VBRGT pin is fed into an internal resistor network with a
ratio of 0.385. The resulting voltage is then summed with a measured offset voltage of 0.188V, which comes
from the reference voltage being fed through a resistor network (See Functional Block Diagram). The brightness
control circuitry then uses the summed voltage to control the voltage across RSET. An equation for approximating
the LED current is:
ILED CURRENT SELECTION PROCEDURES
The following procedures illustrate how to set and adjust output current levels. For constant brightness or analog
brightness control, go to “Brightness control using BRGT”. Otherwise refer to “Brightness control using PWM”.
Brightness Control Using PWM
1. Set the BRGT pin to 0V.
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2. Determine the maximum desired ILED current. Use the ILED equation to calculate RSET by setting BRGT to 0V
or use Table 3 to select a value for RSET when BRGT equals 0V.
3. Brightness control can be implemented by pulsing a signal at the SD pin. LED brightness is proportional to
the duty cycle (D) of the PWM signal. For linear brightness control over the full duty cycle adjustment range,
the PWM frequency (f) should be limited to accommodate the turn-on time (TON = 100µs) of the device.
D × (1/f) > TON
fMAX = DMIN ÷ TON
If the PWM frequency is much less than 100Hz, flicker may be seen in the LEDs. For the LM2794, zero duty
cycle will turn off the LEDs and a 50% duty cycle will result in an average ILED being half of the programmed
LED current. For example, if RSET is set to program 15mA, a 50% duty cycle will result in an average ILED of
7.5mA. For the LM2795 however, 100% duty cycle will turn off the LEDs and a 50% duty cycle will result in
an average ILED being half the programmed LED current.
Brightness Control Using BRGT
1. Choose the maximum ILED desired and determine the max voltage to be applied to the BRGT pin. For
constant brightness, set BRGT to a fixed voltage between 0V to 3V.
2. Use Table 3 to determine the value of RSET required or use the ILED equation above to calculate RSET.
3. Use Table 4 as a reference for the dimming profile of the LEDs, when BRGT ranges from 0V to 3V.
Table 3. RSET Values
LED Current
BRGT 5mA 10mA 15mA 20mA
0.0V 374Ω187Ω124Ω93.1Ω
0.5V 768Ω383Ω255Ω191Ω
1.0V 1.15KΩ576Ω383Ω287Ω
1.5V 1.54KΩ768Ω511Ω383Ω
2.0V 1.91KΩ953Ω624Ω475Ω
2.5V 2.32KΩ1.15KΩ768Ω576Ω
3.0V 2.67KΩ1.33KΩ909Ω665Ω
Table 4. LED Current
RSET Values
BRGT 2.67KΩ1.33KΩ909Ω665Ω
0.0V 0.7mA 1.4mA 2.1mA 2.8mA
0.5V 1.4mA 2.9mA 4.2mA 5.7mA
1.0V 2.1mA 4.3mA 6.3mA 8.6mA
1.5V 2.9mA 5.8mA 8.4mA 11.5mA
2.0V 3.6mA 7.2mA 10.5mA 14.4mA
2.5V 4.3mA 8.7mA 12.7mA 17.3mA
3.0V 5.0mA 10.1mA 14.8mA 20.2mA
CHARGE PUMP OUTPUT (POUT)
The LM2794/5 charge pump is an unregulated switched capacitor converter with a gain of 1.5. The voltage at the
output of the pump (the POUT pin) is nominally 1.5 × VIN. This rail can be used to deliver additional current to
other circuitry. Figure 23 shows how to connect additional LEDs to POUT. A ballast resistor sets the current
through each LED, and LED current matching is dependent on the LED forward voltage matching. Because of
this, LEDs driven by POUT are recommended for functions where brightness matching is not critical, such as
keypad backlighting.
Since POUT is unregulated, driving LEDs directly off POUT is usually practical only with a fixed input voltage. If the
input voltage is not fixed (Li-Ion battery, for example), using a linear regulator between the POUT pin and the
LEDs is recommended. Texas Instruments LP3985-4.5V low-dropout linear regulator is a good choice for such
an application.
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The voltage at POUT is dependent on the input voltage supplied to the LM2794/5, the total LM2794/5 output
current, and the output resistance (ROUT) of the LM2794/5 charge pump. Output resistance is a model of the
switching losses of the charge pump. Resistances of the internal charge pump switches (MOS transistors) are a
primary component of the LM2794/5 output resistance. Typical LM2794/5 output resistance is 3.0Ω. For worst-
case design calculations, using an output resistance of 3.5Ωis recommended. (Worst-case recommendation
accounts for parameter shifts from part-to-part variation and applies over the full operating temperature range).
Figure 23. Keypad LEDs Connected to POUT
Output resistance results in droop in the POUT voltage proportional to the amount of current delivered by the
pump. The POUT voltage is an important factor in determining the total output current capability of an application.
Taking total output current to be the sum of all DXoutput currents plus the current delivered through the POUT pin,
the voltage at POUT can be predicted with the following equations:
ITOTAL = ID1 + ID2 + ID3 + ID4 + IPOUT (1)
VPOUT = 1.5 × VIN −ITOTAL × ROUT (2)
LED HEADROOM VOLTAGE (VHR)
Four current sources are connected internally between POUT and D1-D4. The voltage across each current source,
(VPOUT −VDX), is referred to as headroom voltage (VHR). The current sources require a sufficient amount of
headroom voltage to be present across them in order to regulate properly. Minimum required headroom voltage
is proportional to the current flowing through the current source, as dictated by the equation:
VHR-MIN = kHR × IDX (3)
The parameter kHR, typically 20mV/mA in the LM2794/5, is a proportionality constant that represents the ON-
resistance of the internal current mirror transistors. For worst-case design calculations, using a kHR of 25mV/mA
is recommended. (Worst-case recommendation accounts for parameter shifts from part-to-part variation and
applies over the full operating temperature range). Figure 24 shows how output current of the LM2794/5 varies
with respect to headroom voltage.
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0
2
4
6
8
10
12
14
16
18
0.05 0.20 0.35 0.50 0.65 0.80
IDX (mA)
RSET = 2.67kΩ
RSET = 124Ω
RSET = 475Ω
V
HR (V)
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Figure 24. ILED vs VHR
4 LEDs, VIN = 3.0V
On the flat part of the graph, the currents regulate properly as there is sufficient headroom voltage for regulation.
On the sloping part of the graph the headroom voltage is too small, the current sources are squeezed, and their
current drive capability is limited. Changes in headroom voltage from one output to the next, possible with LED
forward voltage mismatch, will result in different output currents and LED brightness mismatch. Thus, operating
the LM2794/5 with insufficient headroom voltage across the current sources should be avoided.
OUTPUT CURRENT CAPABILITY
The primary constraint on the total current capability is the headroom voltage requirement of the internal current
sources. Combining the VPOUT and VHR equations from the previous two sections yields the basic inequality for
determining the validity of an LM2794/5 LED-drive application:
VPOUT = 1.5 × VIN −ITOTAL × ROUT (4)
VHR-MIN = kHR × IDX (5)
VPOUT −VDX ≥VHR-MIN (6)
1.5 × VIN −ITOTAL × ROUT −VDX ≥(kHR × IDX) (7)
Rearranging this inequality shows the estimated total output current capability of an application:
ITOTAL ≤[(1.5 × VIN-MIN)−VDX-MAX −(kHR × IDX)] ÷ ROUT (8)
Examining the equation above, the primary limiting factors on total output current capability are input and LED
forward voltage. A low input voltage combined with a high LED voltage may result in insufficient headroom
voltage across the current sources, causing them to fall out of regulation. When the current sources are not
regulated, LED currents will be below desired levels and brightness matching will be highly dependent on LED
forward voltage matching.
Typical LM2794/5 output resistance is 3.0Ω. For worst-case design calculations, using an output resistance of
3.5Ωis recommended. LM2794/5 has a typical kHR constant of 20mV/mA. For worst-case design calculations,
use kHR = 25mV/mA. (Worst-case recommendations account for parameter shifts from part-to-part variation and
apply over the full operating temperature range). ROUT and kHR increase slightly with temperature, but losses are
typically offset by the negative temperature coefficient properties of LED forward voltages. Power dissipation and
internal self-heating may also limit output current capability but is discussed in a later section.
PARALLEL Dx OUTPUTS FOR INCREASED CURRENT DRIVE
Outputs D1through D4may be connected together in any combination to drive higher currents through fewer
LEDs. For example in Figure 25, outputs D1and D2are connected together to drive one LED while D3and D4
are connected together to drive a second LED.
14 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated
Product Folder Links: LM2794 LM2795
GND
3.0V
LM2794/95
BRGT
15mA
60mA
POUT CPOUT
1 …F
CIN
1 …F
VIN
C2
1 …F
C1
1 …F
C1- C1+ C2- C2+
RSET D4
D3
D2
D1
124:
GND
POUT CPOUT
1 …F
RSET D4
D3
D2
D1
124:
3.0V
CIN
1 …F
VIN
LM2794/95
BRGT
15mA
30mA
C2
1 …F
C1
1 …F
C1- C1+ C2- C2+
LM2794, LM2795
www.ti.com
SNVS168L –JANUARY 2002–REVISED MAY 2013
Figure 25. Two Parallel Connected LEDs
With this configuration, two parallel current sources of equal value provide current to each LED. RSET and VBRGT
should therefore be chosen so that the current through each output is programmed to 50% of the desired current
through the parallel connected LEDs. For example, if 30mA is the desired drive current for 2 parallel connected
LEDs , RSET and VBRGT should be selected so that the current through each of the outputs is 15mA. Other
combinations of parallel outputs may be implemented in similar fashions, such as in Figure 26.
Figure 26. One Parallel Connected LED
Connecting outputs in parallel does not affect internal operation of the LM2794/95 and has no impact on the
Electrical Characteristics and limits previously presented. The available diode output current, maximum diode
voltage, and all other specifications provided in the Electrical Characteristics table apply to parallel output
configurations, just as they do to the standard 4-LED application circuit.
THERMAL PROTECTION
When the junction temperature exceeds 150°C (typ.), the LM2794/5 internal thermal protection circuitry disables
the part. This feature protects the device from damage due to excessive power dissipation. The device will
recover and operate normally when the junction temperature falls below 140°C (typ.). It is important to have good
thermal conduction with a proper layout to reduce thermal resistance.
Copyright © 2002–2013, Texas Instruments Incorporated Submit Documentation Feedback 15
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3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4
VIN (V)
PIN (mW)
290
310
330
350
370
390
410
430
450
LM2794, LM2795
SNVS168L –JANUARY 2002–REVISED MAY 2013
www.ti.com
POWER EFFICIENCY
Figure 27 shows the efficiency of the LM2794/5. The change in efficiency shown by the graph comes from the
transition from Pass Mode to a gain of 1.5.
Efficiency (E) of the LM2794/5 is defined here as the ratio of the power consumed by LEDs (PLED) to the power
drawn from the input source (PIN). In the equations below, IQis the quiescent current of the LM2794/5, ILED is the
current flowing through one LED, VLED is the forward voltage at that LED current, and N is the number of LEDs
connected to the regulated current outputs. In the input power calculation, the 1.5 represents the switched
capacitor gain configuration of the LM2794/5.
PLED = N × VLED × ILED (9)
PIN = VIN × IIN (10)
PIN = VIN × (1.5 × N × ILED + IQ) (11)
E = (PLED ÷ PIN) (12)
Efficiency, as defined here, is in part dependent on LED voltage. Variation in LED voltage does not affect power
consumed by the circuit and typically does not relate to the brightness of the LED. For an advanced analysis, it is
recommended that power consumed by the circuit (VIN x IIN) be evaluated rather than power efficiency. Figure 28
shows the power consumption of the LM2794/5 Typical Application Circuit.
Figure 27. Efficiency vs VIN
4 LEDs, VLED = 3.6V, ILED = 15mA
Figure 28. PIN vs VIN
4 LEDs, 2.5 ≤VDX ≤3.9V, IDX = 15mA
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SNVS168L –JANUARY 2002–REVISED MAY 2013
POWER DISSIPATION
The power dissipation (PDISSIPATION) and junction temperature (TJ) can be approximated with the equations
below. PIN is the power generated by the 1.5x charge pump, PLED is the power consumed by the LEDs, PPOUT is
the power provided through the POUT pin, TAis the ambient temperature, and θJA is the junction-to-ambient
thermal resistance for the DSBGA package. VIN is the input voltage to the LM2794/5, VDX is the LED forward
voltage, IDX is the programmed LED current, and IPOUT is the current drawn through POUT.
PDISSIPATION = PIN - PLED −PPOUT (13)
= [1.5×VIN×(4IDX + IPOUT)] −(VDX×4IDX)−(1.5×VIN×IPOUT) (14)
TJ= TA+ (PDISSIPATION ×θJA) (15)
The junction temperature rating takes precedence over the ambient temperature rating. The LM2794/5 may be
operated outside the ambient temperature rating, so long as the junction temperature of the device does not
exceed the maximum operating rating of 100°C. The maximum ambient temperature rating must be derated in
applications where high power dissipation and/or poor thermal resistance causes the junction temperature to
exceed 100°C.
DSBGA MOUNTING
The LM2794/5 is a 14-bump DSBGA with a bump size of 300 micron diameter. The DSBGA package requires
specific mounting techniques detailed in Application Note (AN -1112 SNVA009). NSMD (non-solder mask
defined) layout pattern is recommended over the SMD (solder mask defined) since the NSMD requires larger
solder mask openings over the pad size as opposed to the SMD. This reduces stress on the PCB and prevents
possible cracking at the solder joint. For best results during assembly, alignment ordinals on the PC board should
be used to facilitate placement of the DSBGA device. DSBGA is a wafer level chip size package, which means
the dimensions of the package are equal to the die size. As such, the DSBGA package lacks the plastic
encapsulation characteristics of the larger devices and is sensitive to direct exposure to light sources such as
infrared, halogen, and sun light. The wavelengths of these light sources may cause unpredictable operation.
Copyright © 2002–2013, Texas Instruments Incorporated Submit Documentation Feedback 17
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SNVS168L –JANUARY 2002–REVISED MAY 2013
www.ti.com
REVISION HISTORY
Changes from Revision K (May 2013) to Revision L Page
• Changed layout of National Data Sheet to TI format .......................................................................................................... 17
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PACKAGE OPTION ADDENDUM
www.ti.com 2-May-2013
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead/Ball Finish MSL Peak Temp
(3)
Op Temp (°C) Top-Side Markings
(4)
Samples
LM2794TL/NOPB ACTIVE DSBGA YPA 14 250 Green (RoHS
& no Sb/Br) SNAGCU Level-1-260C-UNLIM -30 to 85 LOG
LM2794TLX/NOPB ACTIVE DSBGA YPA 14 3000 Green (RoHS
& no Sb/Br) SNAGCU Level-1-260C-UNLIM -30 to 85 LOG
LM2795TLX/NOPB ACTIVE DSBGA YPA 14 3000 Green (RoHS
& no Sb/Br) SNAGCU Level-1-260C-UNLIM -30 to 85 LOJ
(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) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) Multiple Top-Side Markings will be inside parentheses. Only one Top-Side 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 Top-Side Marking for that device.
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
LM2794TL/NOPB DSBGA YPA 14 250 178.0 8.4 2.29 2.59 0.76 4.0 8.0 Q1
LM2794TLX/NOPB DSBGA YPA 14 3000 178.0 8.4 2.29 2.59 0.76 4.0 8.0 Q1
LM2795TLX/NOPB DSBGA YPA 14 3000 178.0 8.4 2.29 2.59 0.76 4.0 8.0 Q1
PACKAGE MATERIALS INFORMATION
www.ti.com 8-May-2013
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM2794TL/NOPB DSBGA YPA 14 250 210.0 185.0 35.0
LM2794TLX/NOPB DSBGA YPA 14 3000 210.0 185.0 35.0
LM2795TLX/NOPB DSBGA YPA 14 3000 210.0 185.0 35.0
PACKAGE MATERIALS INFORMATION
www.ti.com 8-May-2013
Pack Materials-Page 2
MECHANICAL DATA
YPA0014
www.ti.com
TLP14XXX (Rev D)
A
. All linear dimensions are in millimeters. Dimensioning and tolerancing per ASME Y14.5M-1994.
B. This drawing is subject to change without notice.
4215071/A 12/12
NOTES:
0.600±0.075
E
D
D: Max =
E: Max =
2.454 mm, Min =
2.149 mm, Min =
2.393 mm
2.089 mm
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