General Description
The MAX16903 is a small, synchronous buck converter
with integrated high-side and low-side switches. The
device is designed to deliver 1A with input voltages
from +3.5V to +28V, while using only 25μA quiescent
current at no load. Voltage quality can be monitored by
observing the PGOOD signal. The MAX16903 can
operate in dropout by running at 97% duty cycle, making
it ideal for automotive and industrial applications.
The MAX16903 operates at a 2.1MHz frequency, allow-
ing for small external components and reduced output
ripple. It guarantees no AM band interference. SYNC
input programmability enables three frequency modes
for optimized performance: forced fixed-frequency opera-
tion, skip mode (ultra-low quiescent current of 25μA), and
synchronization to an external clock. The MAX16903 can
be ordered with spread-spectrum frequency modulation,
designed to minimize EMI-radiated emissions due to the
modulation frequency.
The MAX16903 is available in a thermally enhanced,
3mm x 3mm, 10-pin TDFN package or a 16-pin TSSOP
package. The MAX16903 operates over the -40°C to
+125°C automotive temperature range.
Applications
●Automotive
●Industrial
●High-Voltage Input-Power DC-DC Applications
Benets and Features
●Meets Stringent Automotive Quality and Reliability
Requirements
• +3.5V to +28V Input Voltage Range Allows
Operation in “Cold Crank” Conditions
• Tolerates Input-Voltage Transients to +42V
• Enable-Pin Compatible from +3.3V Logic Level to
+42V
• 1A Minimum Output Current with Overcurrent
Protection
• -40°C to +125°C Automotive Temperature Range
• AEC-Q100 Qualified
●Increased Efficiency and Reduced BOM Cost and
Board Space
• Integrated High- and Low-Side FETs
• Fixed Output Voltages (see the Selector Guide
and Contact the Factory for All Available Trimmed
Output-Voltage Options)
• 10-Pin TDFN-EP or 16-Pin TSSOP-EP Packages
●Low Quiescent Current Helps Designers Meet
Stringent OEM Current Requirements
• 25μA Quiescent Current During Skip Mode
Operation
● High Switching Frequency Allows Use of Small,
Low-Cost External Components
• 2.1MHz Switching Frequency with Three Modes of
Operation
• Skip Mode for Efficient, Low-Power Operation
• Forced Fixed-Frequency Operation
• External Frequency Synchronization
● Reduced EMI Emissions at the Switching Frequency
• Optional Spread-Spectrum Frequency Modulation
19-5038; Rev 10; 4/17
Note: Insert the desired suffix letters (from the Selector Guide)
into the blanks to indicate the output voltage. Alternative output
voltages available upon request.
+Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
*EP = Exposed pad.
Ordering Information
PART SPREAD
SPECTRUM
TEMP
RANGE
PIN-
PACKAGE
MAX16903RAUE__/V+ Disabled -40°C to
+125°C 16 TSSOP-EP*
MAX16903RATB__/V+ Disabled -40°C to
+125°C 10 TDFN-EP*
MAX16903SAUE__/V+ Enabled -40°C to
+125°C 16 TSSOP-EP*
MAX16903SATB__/V+ Enabled -40°C to
+125°C 10 TDFN-EP*
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
EVALUATION KIT AVAILABLE
Typical Operating Circuits
MAX16903_50/V+
20kΩ
2.2µF
33kΩ
EN
SYNC
GND
VBAT LEVEL
SIGNAL
PGOOD
BIAS
SUP
*PLACE INPUT SUPPLY CAPACITORS AS CLOSE AS POSSIBLE TO THE SUP PIN. SEE THE APPLICATIONS INFORMATION SECTION FOR MORE DETAILS.
4.7µF
BST
0.1µF
4.7µH
LX
10µF
PGND
5V AT 1A
OUTS
MAX16903_33/V+
20kΩ
2.2µF
33kΩ
EN
SYNC
GND
VBAT LEVEL
SIGNAL
PGOOD
BIAS
SUP
4.7µF
BST
0.1µF
*
*
3.3µH
LX
10µF
PGND
3.3V AT 1A
OUTS
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
www.maximintegrated.com Maxim Integrated
│
2
(Voltages referenced to GND.)
SUP, EN.................................................................-0.3V to +42V
BST to LX..................................................................-0.3V to +6V
LX.............................................................-0.3V to (VSUP + 0.3V)
BST.........................................................................-0.3V to +47V
OUTS......................................................................-0.3V to +12V
SYNC, PGOOD, BIAS............................................-0.3V to +6.0V
PGND to GND .......................................................-0.3V to +0.3V
LX Continuous RMS Current.................................................1.5A
OUTS Short-Circuit Duration......................................Continuous
ESD Protection
Human Body Model .........................................................±2kV
Machine Model ..............................................................±200V
Continuous Power Dissipation (TA = +70°C)
TDFN (derate 24.4 mW/°C above +70°C)..................1951mW
TSSOP (derate 26.1 mW/°C above +70°C) ..............2089mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
TDFN
Junction-to-Ambient Thermal Resistance (θJA)...........41°C/W
Junction-to-Case Thermal Resistance (θJC)..................9°C/W
TSSOP
Junction-to-Ambient Thermal Resistance (θJA)........38.3°C/W
Junction-to-Case Thermal Resistance (θJC)..................3°C/W
(Note 1)
(VSUP = +14V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C, unless otherwise noted.)
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer
board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.
Absolute Maximum Ratings
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Package Thermal Characteristics
Electrical Characteristics
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage Range VSUP (Note 2) 3.5 28 V
t < 1s 42
Supply Current ISUP
EN = low 4 8
µA
EN = high, no load 3.3V and 5V output 25 35
1.8V output 40 65 90
EN = high, continuous, no switching 1 mA
UV Lockout VUVLO Bias rising 2.8 3 3.2 V
VUVLO,HYS Hysteresis 0.4
Bias Voltage VBIAS +5.5V ≤ VSUP ≤ +42V 5 V
Bias Current Limit IBIAS 10 mA
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
www.maximintegrated.com Maxim Integrated
│
3
(VSUP = +14V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C, unless otherwise noted.)
Electrical Characteristics (continued)
BUCK CONVERTER
Voltage Accuracy
VOUT,5V
VOUT = 5V, xed frequency
6V ≤ VSUP ≤ 18V,
ILOAD = 0 to 1A,
TA = 0°C to
+125°C
-2.0% 5 +2.5%
V
VOUT = 5V, SKIP mode (Note 3) -2.0% 5 +4%
VOUT,3.3V
VOUT = 3.3V, xed frequency -2.0% 3.3 +2.5%
VOUT = 3.3V, SKIP mode (Note 3) -2.0% 3.3 +4%
VOUT,1.8V
VOUT = 1.8V, xed frequency -2.0% 1.8 +2.5%
VOUT = 1.8V, SKIP mode (Note 3) -2.0% 1.8 +4.0%
VOUT,5V
VOUT = 5V, xed frequency
6V ≤ VSUP ≤ 18V,
ILOAD = 0 to 1A,
TA = -40°C to
+125°C
-3.0% 5 +2.5%
VOUT = 5V, SKIP mode (Note 3) -3.0% 5 +4%
VOUT,3.3V
VOUT = 3.3V, xed frequency -3.0% 3.3 +2.5%
VOUT = 3.3V, SKIP mode (Note 3) -3.0% 3.3 +4%
VOUT,1.8V
VOUT = 1.8V, xed frequency -3.0% 1.8 +2.5%
VOUT = 1.8V, SKIP mode (Note 3) -3.0% 1.8 +4%
Skip-Mode Peak Current ISKIP 350 mA
High-Side DMOS RDSON RON,HS VBIAS = 5V 400 800 mΩ
Low-Side DMOS RDSON RON,LS 250 450 mΩ
DMOS Peak Current-Limit
Threshold IMAX 1.275 1.5 1.75 A
Soft-Start Ramp Time tSS 7 8 9 ms
LX Rise Time tRISE,LX 5 ns
Minimum On-Time tON 80 ns
PWM Switching Frequency fSW Internally generated 1.925 2.1 2.275 MHz
SYNC Input Frequency
Range fSYNC 1.8 2.6 MHz
Spread-Spectrum Range SS Spread-spectrum option only +6 %
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
www.maximintegrated.com Maxim Integrated
│
4
Note 2: When the typical minimum on-time of 80ns is violated, the device skips pulses.
Note 3: Guaranteed by design; not production tested.
(VSUP = +14V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
PGOOD
PGOOD Threshold VTHR,PGD VOUT rising 88 93 98 %
VTHF,PGD VOUT falling 88 91 94
PGOOD Debounce tDEB 10 µs
PGOOD HIGH Leakage
Current ILEAK,PGD TA = +25°C, VPGD ≤ VOUT 1 µA
PGOOD Output Low Level VOUT,PGD Sinking 1mA 0.4 V
LOGIC LEVELS
EN Level VIH,EN 2.4 V
VIL,EN 0.6
EN Input Current IIN,EN VEN = VSUP = +42V, TA = +25°C 1 µA
SYNC Switching Threshold VIH,SYNC 1.4 V
VIL,SYNC 0.4
SYNC Internal Pulldown RPD,SYNC 200 kΩ
THERMAL PROTECTION
Thermal Shutdown TSHDN 175 °C
Thermal Shutdown
Hysteresis TSHDN,HYS 15 °C
Electrical Characteristics (continued)
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
www.maximintegrated.com Maxim Integrated
│
5
(VSUP = +14V, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE (SKIP MODE)
MAX16903 toc02
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
2624222018161412108
10
20
30
40
50
60
0
6 28
5V PART
3.3V PART
LINE REGULATION
(ILOAD = 1A)
MAX16903 toc03
INPUT VOLTAGE (V)
OUTPUT-VOLTAGE CHANGE (%)
26248 10 12 16 18 2014 22
-3
-2
-1
0
1
2
3
4
-4
6 28
LOAD REGULATION
MAX16903 toc04
LOAD CURRENT (A)
OUTPUT-VOLTAGE CHANGE (%)
0.80.60.2 0.4
-3
-2
-1
0
2
1
3
4
-4
0 1.0
SKIP MODE
FFF MODE
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX16903 toc05
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
2624222018161412108
3
6
9
12
15
0
6 28
STARTUP WAVEFORM (ILOAD = 1A)
MAX16903 toc06
IINDUCTOR
1A/div
PGOOD
5V/div
VOUT
5V/div
EN
5V/div
1ms/div
SHUTDOWN WAVEFORM (ILOAD = 1A)
MAX16903 toc07
IINDUCTOR
1A/div
PGOOD
5V/div
VOUT
5V/div
EN
5V/div
20µs/div
EFFICIENCY vs. LOAD CURRENT
(5V VERSION)
MAX16903 toc01
ILOAD (A)
EFFICIENCY (%)
0.10.010.0010.0001
10
20
30
40
50
60
70
80
90
100
0
0.00001 1
SKIP MODE
FFF MODE
LOAD-TRANSIENT RESPONSE
(FIXED MODE)
MAX16903 toc08
ILOAD
1A/div
PGOOD
5V/div
VOUT
200mV/div
5V
5V
AC
COUPLED
200µs/div
ILOAD = 100mA TO 1A TO 100mA
Maxim Integrated
│
6
www.maximintegrated.com
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
(VSUP = +14V, TA = +25°C, unless otherwise noted.)
Pin Description
Typical Operating Characteristics (continued)
PIN NAME FUNCTION
TDFN TSSOP
1 1 BST Bootstrap Capacitor for High-Side Driver (0.1µF)
2 2, 3 SUP Voltage Supply Input. Connect a 4.7µF ceramic capacitor from SUP to PGND. Place the
capacitor very close to the SUP pin. For the TSSOP-EP package, connect both SUP pins
together for proper operation.
3 4, 5 LX Buck Switching Node. LX is high impedance when the device is off. For the TSSOP package,
connect both LX pins together for proper operation.
4 6, 7 PGND Power Ground. For the TSSOP-EP package, connect both PGND pins together for proper
operation.
Pin Congurations
LOAD-TRANSIENT RESPONSE
(SKIP MODE)
MAX16903 toc09
ILOAD
1A/div
PGOOD
5V/div
VOUT
200mV/div
5V
5V
AC-
COUPLED
200µs/div
ILOAD = 100mA TO 1A TO 100mA
UNDERVOLTAGE PULSE (COLD CRANK)
MAX16903 toc10
VSUP
10V/div
VOUT
5V/div
ILOAD
1A/div
PGOOD
5V/div
14V
3.5V
10ms/div
ILOAD = 500mA
STANDBY CURRENT
vs. LOAD CURRENT
MAX16903 toc11
ILOAD (mA)
I
SUP
(µA)
0.10
50
100
150
200
250
300
350
400
450
500
0
0.01 1.00
MAX16903
+
5 6OUTS PGOOD
4
TOP VIEW
7PGND SYNC
38LX BIAS
29SUP GND
1
TDFN
10BST EN
EP
MAX16903
+
8 9OUTS N.C.
710PGND N.C.
611PGND PGOOD
314SUP GND
215SUP EN
116BST N.C.
512LX SYNC
4
TSSOP
13LX BIAS
EP
Maxim Integrated
│
7
www.maximintegrated.com
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
Pin Description (continued)
Functional Diagram
PIN NAME FUNCTION
TDFN TSSOP
5 8 OUTS Buck Regulator Voltage-Sense Input. Bypass OUTS to PGND with a 10µF or larger X7R
ceramic capacitor.
611 PGOOD Open-Drain Power-Good Output
7 12 SYNC
Sync Input. SYNC allows the device to synchronize to other supplies. When connected to GND
or unconnected, skip mode is enabled under light loads. When connected to a clock source or
BIAS, forced PWM mode is enabled.
8 13 BIAS +5V Internal Logic Supply. Connect a 2.2µF ceramic capacitor from BIAS to GND.
9 14 GND Analog Ground
10 15 EN Enable Input. EN is high-voltage compatible. Drive EN HIGH for normal operation.
— 9, 10, 16 N.C. No Connection. Not internally connected.
— — EP Exposed Pad. Connect EP to PGND. Do not use EP as the only ground connection.
MAX16903
LSD
PWM
EAMP
COMP
HSD
BIAS
LX
PGND
BST
SUP
LOGIC
CONTROL
CURRENT-SENSE
AND
SLOPE COMPENSATION
SOFT-START
OSCBANDGAP
GND
VGOOD
PGOOD
OUTS
BIAS
HVLDO
SYNC
REF
EN
CLK
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
www.maximintegrated.com Maxim Integrated
│
8
Detailed Description
The MAX16903 is a small, current-mode buck convert-
er that features synchronous rectification and requires
no external compensation network. The MAX16903 is
designed for 1A output current. The MAX16903 can stay
in dropout by running at 97% duty cycle. It provides an
accurate output voltage within the input range of +6.5V to
+18V. Voltage quality can be monitored by observing the
PGOOD signal. The MAX16903 operates at 2.1MHz (typ)
frequency, which allows for small external components,
reduced output ripple, and guarantees no AM band inter-
ference.
The MAX16903 features an ultra-low 25μA (typ) quiescent
supply current in standby mode. Standby mode is entered
when load currents are below 5mA and when SYNC
is low. The MAX16903 operates from a +3.5V to +28V
supply voltage and tolerates transients up to +42V,
making it ideal for automotive applications. The MAX16903
is available in factory-trimmed output voltages from 1.8V
to 10.7V in 100mV steps. Contact factory for availability
of voltage options.
Enable (EN)
The MAX16903 is activated by driving EN high. EN
is compatible from a +3.3V logic level to automotive
battery levels. EN can be controlled by microcontrollers
and automotive KEY or CAN inhibit signals. The EN input
has no internal pullup/pulldown current to minimize over-
all quiescent supply current. To realize a programmable
undervoltage lockout level, use a resistor-divider from
SUP to EN to GND.
BIAS/UVLO
The MAX16903 features undervoltage lockout. When the
device is enabled, an internal bias generator turns on. LX
begins switching after VBIAS has exceeded the internal
undervoltage lockout level VUVLO = 3V (typ).
Soft-Start
The MAX16903 features an internal soft-start timer. The
output voltage soft-start ramp time is 8ms (typ). If a short
circuit or undervoltage is encountered, after the soft-start
timer has expired, the device is disabled for 30ms (typ)
and it reattempts soft-start again. This pattern repeats
until the short circuit has been removed.
Oscillator/Synchronization and
Efciency (SYNC)
The MAX16903 has an on-chip oscillator that provides a
switching frequency of 2.1MHz (typ). Depending on the
condition of SYNC, two operation modes exist. If SYNC is
unconnected or at GND, the device must operate in highly
efficient pulse-skipping mode if the load current is below
the SKIP mode current threshold. If SYNC is at BIAS or
has a frequency applied to it, the device is in forced PWM
mode. The MAX16903 offers the best of both worlds. The
device can be switched during operation between forced
PWM mode and SKIP mode by switching SYNC.
SKIP Mode Operation
SKIP mode is entered when the SYNC pin is connected
to ground or is unconnected and the peak load current
is < 350mA (typ). In this mode, the high-side FET is
turned on until the current in the inductor is ramped up
to 350mA (typ) peak value and the internal feedback
voltage is above the regulation voltage (1.2V typ). At this
point, both the high-side and low-side FETs are turned
off. Depending on the choice of the output capacitor and
the load current the high-side FET turns on when OUTS
(valley) drops below the 1.2V (typ) feedback voltage.
Achieving High Efciency at Light Loads
The MAX16903 operates with very low quiescent current
at light loads to enhance efficiency and conserve battery
life. When the MAX16903 enters SKIP mode the output
current is monitored to adjust the quiescent current.
When the output current is < 5mA, the MAX16903 oper-
ates in the lowest quiescent current mode also called the
standby mode. In this mode, the majority of the internal
circuitry (excluding that necessary to maintain regulation)
in the MAX16903, including the internal high-voltage
LDO, is turned off to save current. Under no load and with
SKIP mode enabled, the IC draws only 25μA (typ) current.
For load currents > 5mA, the IC enters normal SKIP mode
still maintaining very high efficiency.
Controlled EMI with Forced-Fixed Frequency
In forced PWM mode, the MAX16903 attempts to operate
at a constant switching frequency for all load currents. For
tightest frequency control, apply the operating frequency
to SYNC. The advantage of this mode is a constant
switching frequency, which improves EMI performance;
the disadvantage is that considerable current can be
thrown away. If the load current during a switching cycle
is less than the current flowing through the inductor, the
excess current is diverted to GND. With no external load
present, the operating current is in the 10mA range.
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
www.maximintegrated.com Maxim Integrated
│
9
Extended Input Voltage Range
In some cases, the MAX16903 is forced to deviate from
its operating frequency independent of the state of SYNC.
For input voltages above 18V, the required duty cycle to
regulate its output may be smaller than the minimum on-
time (80ns, typ). In this event, the MAX16903 is forced to
lower its switching frequency by skipping pulses.
If the input voltage is reduced and the MAX16903 approach-
es dropout the device tries to turn on the high-side FET
continuously. In order to maintain gate charge on the
high-side FET, the BST capacitor must be periodically
recharged. To ensure proper charge on the BST capaci-
tor when in dropout, the high-side FET is turned off every
6.5μs and the low-side FET is turned on for about 150ns.
This gives an effective duty cycle of > 97% and a switching
frequency of 150kHz when in dropout.
Spread-Spectrum Option
The MAX16903 has an optional spread-spectrum version.
If this option is selected, then the internal operating fre-
quency varies by +6% relative to the internally generated
operating frequency of 2.1MHz (typ). Spread spectrum is
offered to improve EMI performance of the MAX16903.
By varying the frequency 6% only in the positive
direction, the MAX16903 still guarantees that the 2.1MHz
frequency does not drop into the AM band limit of 1.8MHz.
Additionally, with the low minimum on-time of 80ns (typ)
no pulse skipping is observed for a 5V output with 18V
input maximum battery voltage in steady state.
The internal spread spectrum does not interfere with the
external clock applied on the SYNC pin. It is active only
when the MAX16903 is running with internally generated
switching frequency.
Power-Good (PGOOD)
The MAX16903 features an open-drain power-good out-
put. PGOOD is an active-high output that pulls low when
the output voltage is below 91% of its nominal value.
PGOOD is high impedance when the output voltage is
above 93% of its nominal value. Connect a 20kΩ (typ)
pullup resistor to an external supply or the on-chip BIAS
output.
Overcurrent Protection
The MAX16903 limits the peak output current to 1.5A
(typ). The accuracy of the current limit is ±15%, which
makes selection of external components very easy.
To protect against short-circuit events, the MAX16903
will shut off when OUTS is below 1.5V (typ) and one
overcurrent event is detected. The MAX16903 attempts
a soft-start restart every 30ms and stays off if the short
circuit has not been removed. When the current limit
is no longer present, it reaches the output voltage by
following the normal soft-start sequence. If the MAX16903
die reaches the thermal limit of 175°C (typ) during the
current-limit event, it immediately shuts off.
Thermal-Overload Protection
The MAX16903 features thermal-overload protection. The
device turns off when the junction temperature exceeds
+175°C (typ). Once the device cools by 15°C (typ), it turns
back on with a soft-start sequence.
Applications Information
Inductor Selection
The nominal inductor value can be calculated using Table
1 based on the nominal output voltage of the device.
Select the nearest standard inductance value to the calcu-
lated nominal value. The nominal standard value selected
should be within ±25% of LNOM for best performance.
Input Capacitor
A low-ESR ceramic input capacitor of 1μF or larger is
needed for proper device operation. This value may need
to be larger based on application input-voltage ripple
requirements.
The discontinuous input current of the buck converter
causes large input ripple current. The switching frequen-
cy, peak inductor current, and the allowable peak-to-peak
input-voltage ripple dictate the input capacitance require-
ment. Increasing the switching frequency or the inductor
Table 1. Nominal Output Voltage Values
Table 2. Examples for Standard Output
Voltages
VOUT (V) LNOM (µH)
1.8 to 3.1 VOUT/0.55
3.2 to 6.5 VOUT/0.96
6.6 to 8.1 VOUT/1.40
8.2 to 10 VOUT/1.75
VOUT (V) CALCULATED
LNOM (µH)
STANDARD
VALUE (µH)
1.8 3.3 3.3
3.3 3.4 3.3
5.0 5.2 4.7
8.0 5.7 5.6
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
www.maximintegrated.com Maxim Integrated
│
10
value lowers the peak-to-average current ratio yielding a
lower input capacitance requirement.
The input ripple comprises mainly of ΔVQ (caused by the
capacitor discharge) and ΔVESR (caused by the ESR of
the input capacitor). The total voltage ripple is the sum of
ΔVQ and ΔVESR. Assume the input-voltage ripple from
the ESR and the capacitor discharge is equal to 50%
each. The following equations show the ESR and capaci-
tor requirement for a target voltage ripple at the input:
ESR
PP
OUT
OUT
IN Q SW
V
ESR I
I2
I D ( 1 D )
CV f
−
∆
=∆

+


×−
=∆×
where:
IN OUT OUT
PP
IN SW
( V V ) V
IV f L
−
−×
∆= ××
and:
OUT
IN
V
DV
=
where IOUT is the output current, D is the duty cycle,
and fSW is the switching frequency. Use additional input
capacitance at lower input voltages to avoid possible
undershoot below the UVLO threshold during transient
loading.
Output Capacitor
To maintain acceptable phase margin, a minimum ceramic
output capacitor value of 10μF is needed with a voltage
rating 2 times the VOUT voltage. Additional output capaci-
tance may be needed based on application-specific output-
voltage ripple requirements.
The allowable output-voltage ripple and the maximum
deviation of the output voltage during step load currents
determine the output capacitance and its ESR. The out-
put ripple comprises of ΔVQ (caused by the capacitor
discharge) and ΔVESR (caused by the ESR of the output
capacitor). Use low-ESR ceramic or aluminum electrolytic
capacitors at the output. For aluminum electrolytic capaci-
tors, the entire output ripple is contributed by ΔVESR. Use
the ESROUT equation to calculate the ESR requirement
and choose the capacitor accordingly. If using ceramic
capacitors, assume the contribution to the output ripple
voltage from the ESR and the capacitor discharge to be
equal. The following equations show the output capaci-
tance and ESR requirement for a specified output-voltage
ripple.
ESR
PP
PP
OUT
Q SW
V
ESR I
I
C8V f
−
−
∆
=∆
∆
=×∆ ×
where:
IN OUT OUT
PP IN SW
OUT_RIPPLE ESR Q
(V V ) V
IV f L
V VV
−
−×
∆= ××
≅∆ +∆
ΔIP-P is the peak-to-peak inductor current as calculated
above and fSW is the converter’s switching frequency.
The allowable deviation of the output voltage during fast
transient loads also determines the output capacitance
and its ESR. The output capacitor supplies the step
load current until the converter responds with a greater
duty cycle. The response time (tRESPONSE) depends
on the closed-loop bandwidth of the converter. The high
switching frequency of the MAX16903 allows for a higher
closed-loop bandwidth, thus reducing tRESPONSE and
the output capacitance requirement. The resistive drop
across the output capacitor’s ESR and the capacitor dis-
charge causes a voltage droop during a step load. Use a
combination of low-ESR tantalum and ceramic capacitors
for better transient load and ripple/noise performance.
Keep the maximum output-voltage deviations below the
tolerable limits of the electronics being powered. When
using a ceramic capacitor, assume an 80% and 20%
contribution from the output capacitance discharge and
the ESR drop, respectively. Use the following equations to
calculate the required ESR and capacitance value:
ESR
OUT STEP
STEP RESPONSE
OUT
Q
V
ESR I
I t
CV
∆
=
×
=∆
where ISTEP is the load step and tRESPONSE is the
response time of the converter. The converter response
time depends on the control-loop bandwidth.
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
www.maximintegrated.com Maxim Integrated
│
11
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching
power losses and clean stable operation. Use a multilayer
board wherever possible for better noise immunity. Refer
to MAX16903 Evaluation Kit for recommended PCB lay-
out. Follow these guidelines for a good PCB layout:
1) The input capacitor (4.7μF, see the applications
schematic in the Typical Operating Circuits) should
be placed right next to the SUP pins (pins 2 and 3 on
the TSSOP-EP package) of the MAX16903. Since the
MAX16903 operates at 2.1MHz switching frequency,
this placement is critical for effective decoupling of
high-frequency noise from the SUP pins.
2) Solder the exposed pad to a large copper plane area
under the device. To effectively use this copper area
as heat exchanger between the PCB and ambient
expose the copper area on the top and bottom side.
Add a few small vias or 1 large via on the copper pad
for efficient heat transfer. Connect the exposed pad
to PGND ideally at the return terminal of the output
capacitor.
3) Isolate the power components and high current paths
from sensitive analog circuitry.
4) Keep the high current paths short especially at the
ground terminals. The practice is essential for stable
jitter-free operation.
5) Connect the PGND and GND together preferably at
the return terminal of the output capacitor. Do not
connect them anywhere else.
6) Keep the power traces and load connections short.
This practice is essential for high efficiency. Use thick
copper PCB to enhance full load efficiency and power
dissipation capability.
7) Route high-speed switching nodes away from
sensitive analog areas. Use internal PCB layers as
PGND to act as EMI shields to keep radiated noise
away from the device and analog bypass capacitor.
ESD Protection
The ESD tolerance for the MAX16903 is rated for Human
Body Model and Machine Model. The Human Body Model
discharge components are CS = 100pF and RD = 1.5kΩ
(Figure 1). The Machine Model discharge components
are CS = 200pF and RD = 0Ω (Figure 2).
Figure 1. Human Body ESD Test Circuit
Figure 2. Machine Model ESD Test Circuit
STORAGE
CAPACITOR
HIGH-
VOLTAGE
DC
SOURCE
DEVICE
UNDER
TEST
CHARGE-CURRENT-
LIMIT RESISTOR
DISCHARGE
RESISTANCE
1MΩ
RD
1.5kΩ
CS
100pF
STORAGE
CAPACITOR
HIGH-
VOLTAGE
DC
SOURCE
DEVICE
UNDER
TEST
CHARGE-CURRENT-
LIMIT RESISTOR
DISCHARGE
RESISTANCE
RD
0Ω
CS
200pF
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
www.maximintegrated.com Maxim Integrated
│
12
Note: All devices operate over the -40°C to +125°C automotive temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
*EP = Exposed pad.
Selector Guide
PART OUTPUT VOLTAGE
(V) PIN-PACKAGE SPREAD-SPECTRUM
SWITCHING FREQUENCY
TOP
MARK
MAX16903RATB50+ 5 10 TDFN-EP*
(3mm x 3mm x 0.75mm) — AZO
MAX16903RATB50/V+ 510 TDFN-EP*
(3mm x 3mm x 0.75mm) —AVU
MAX16903RATB18/V+ 1.8 10 TDFN-EP*
(3mm x 3mm x 0.75mm) Yes —
MAX16903RAUE50+ 516 TSSOP-EP*
(5mm x 4.4mm) — —
MAX16903RAUE50/V+ 516 TSSOP-EP*
(5mm x 4.4mm) — —
MAX16903SATB50+ 5 10 TDFN-EP*
(3mm x 3mm x 0.75mm) Yes AZQ
MAX16903SATB50/V+ 510 TDFN-EP*
(3mm x 3mm x 0.75mm) Yes AVW
MAX16903SATB18/V+ 1.8 10 TDFN-EP*
(3mm x 3mm x 0.75mm) Yes —
MAX16903SAUE50+ 516 TSSOP-EP*
(5mm x 4.4mm) Yes —
MAX16903SAUE50/V+ 516 TSSOP-EP*
(5mm x 4.4mm) Yes —
MAX16903RATB33+ 3.3 10 TDFN-EP*
(3mm x 3mm x 0.75mm) — AZN
MAX16903RATB33/V+ 3.3 10 TDFN-EP*
(3mm x 3mm x 0.75mm) —AVT
MAX16903RAUE33+ 3.3 16 TSSOP-EP*
(5mm x 4.4mm) — —
MAX16903RAUE33/V+ 3.3 16 TSSOP-EP*
(5mm x 4.4mm) — —
MAX16903SATB33+ 3.3 10 TDFN-EP*
(3mm x 3mm x 0.75mm) Yes AZP
MAX16903SATB33/V+ 3.3 10 TDFN-EP*
(3mm x 3mm x 0.75mm) Yes AVV
MAX16903SAUE33+ 3.3 16 TSSOP-EP*
(5mm x 4.4mm) Yes —
MAX16903SAUE33/V+ 3.3 16 TSSOP-EP*
(5mm x 4.4mm) Yes —
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
www.maximintegrated.com Maxim Integrated
│
13
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
Chip Information
PROCESS: BiCMOS
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
10 TDFN-EP T1033+1 21-0137 90-0003
16 TSSOP-EP U16E+3 21-0108 90-0120
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
www.maximintegrated.com Maxim Integrated
│
14
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
010/09 Initial release —
17/10 Updated the General Description, Typical Operating Circuits, Absolute Maximum Ratings,
Electrical Characteristics table, Typical Operating Characteristics, Pin Description, and
Detailed Description
1–10
28/10 Corrected a typo in the TSSOP Pin Conguration (pin 2 is SUP, not N.C.) 6
33/11 Updated the Voltage Accuracy and DMOS Peak Current-Limit Threshold parameters in the
Electrical Characteristics, updated the high-side FET in the Skip Mode Operation section
and the output current in the Inductor Selection section
3, 4, 8, 9
44/13 Replaced the Inductor Selection section, and updated the Input Capacitor, Output
Capacitor, and Selector Guide sections 9–11
59/14 Updated Typical Operating Circuits 2
69/14 Updated PGOOD HIGH leakage current in Electrical Characteristics 4
71/15 Updated Benets and Features section 1
89/15 Updated PGOOD Threshold (VOUT rising) in Electrical Characteristics 4
911/15 Added 1.8V package variants to Electrical Characteristics and Selector Guide tables 3, 12
10 4/17 Removed “Military” from Applications section 1
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2017 Maxim Integrated Products, Inc.
│
15
MAX16903 2.1MHz, High-Voltage,
1A Mini-Buck Converter
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Mouser Electronics
Authorized Distributor
Click to View Pricing, Inventory, Delivery & Lifecycle Information:
Maxim Integrated:
MAX16903RATB33/V+T MAX16903RATB50/V+T MAX16903RAUE33/V+ MAX16903RAUE33/V+T
MAX16903RAUE50/V+ MAX16903RAUE50/V+T MAX16903SATB33/V+T MAX16903SATB50/V+T
MAX16903SAUE33/V+ MAX16903SAUE33/V+T MAX16903SAUE50/V+ MAX16903SAUE50/V+T
MAX16903RAUE33+ MAX16903RAUE50+ MAX16903RATB18/V+T