EVALUATION KIT AVAILABLE
MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
General Description
Benefits and Features
The MAX16903 operates at a 2.1MHz frequency, allowing 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 operation, 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.
●● 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
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.
●● 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
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.
●● Low Quiescent Current Helps Designers Meet
Stringent OEM Current Requirements
• 25μA Quiescent Current During Skip Mode
Operation
Applications
●● 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
●● Automotive
●● Industrial
●● High-Voltage Input-Power DC-DC Applications
Ordering Information
SPREAD
TEMP PINSPECTRUM RANGE PACKAGE
-40°C to
MAX16903RAUE__/V+ Disabled
16 TSSOP-EP*
+125°C
-40°C to
MAX16903RATB__/V+
Disabled
10 TDFN-EP*
+125°C
-40°C to
MAX16903SAUE__/V+
Enabled
16 TSSOP-EP*
+125°C
-40°C to
MAX16903SATB__/V+
Enabled
10 TDFN-EP*
+125°C
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.
PART
19-5038; Rev 10; 4/17
●● Reduced EMI Emissions at the Switching Frequency
• Optional Spread-Spectrum Frequency Modulation
MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
Typical Operating Circuits
4.7µF
*
SUP
EN
33kΩ
VBAT LEVEL
SIGNAL
MAX16903_50/V+
SYNC
BST
GND
0.1µF
4.7µH
5V AT 1A
LX
PGOOD
10µF
PGND
BIAS
OUTS
4.7µF
*
20kΩ
2.2µF
SUP
EN
33kΩ
VBAT LEVEL
SIGNAL
MAX16903_33/V+
SYNC
BST
0.1µF
3.3µH
3.3V AT 1A
LX
GND
PGOOD
10µF
PGND
OUTS
BIAS
20kΩ
2.2µF
*PLACE INPUT SUPPLY CAPACITORS AS CLOSE AS POSSIBLE TO THE SUP PIN. SEE THE APPLICATIONS INFORMATION SECTION FOR MORE DETAILS.
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Maxim Integrated │ 2
MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
Absolute Maximum Ratings
(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
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 (Note 1)
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: 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.
Electrical Characteristics
(VSUP = +14V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C, unless otherwise noted.)
PARAMETER
Supply Voltage Range
SYMBOL
VSUP
CONDITIONS
(Note 2)
MIN
3.5
ISUP
EN = high, no load
42
3.3V and 5V output
1.8V output
40
EN = high, continuous, no switching
UV Lockout
VUVLO
VBIAS
Bias Current Limit
IBIAS
4
8
25
35
65
90
1
2.8
VUVLO,HYS Hysteresis
Bias Voltage
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Bias rising
MAX
28
t < 1s
EN = low
Supply Current
TYP
3
0.4
+5.5V ≤ VSUP ≤ +42V
5
10
UNITS
V
µA
mA
3.2
V
V
mA
Maxim Integrated │ 3
MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
Electrical Characteristics (continued)
(VSUP = +14V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C, unless otherwise noted.)
BUCK CONVERTER
VOUT,5V
VOUT,3.3V
VOUT,1.8V
Voltage Accuracy
VOUT,5V
VOUT,3.3V
VOUT,1.8V
Skip-Mode Peak Current
ISKIP
High-Side DMOS RDSON
RON,HS
Low-Side DMOS RDSON
RON,LS
DMOS Peak Current-Limit
Threshold
IMAX
tSS
Soft-Start Ramp Time
LX Rise Time
VOUT = 5V, fixed frequency
-2.0%
5
+2.5%
VOUT = 5V, SKIP mode (Note 3)
-2.0%
5
+4%
-2.0%
3.3
+2.5%
-2.0%
3.3
+4%
6V ≤ VSUP ≤ 18V,
VOUT = 3.3V, fixed frequency
ILOAD = 0 to 1A,
VOUT = 3.3V, SKIP mode (Note 3) TA = 0°C to
+125°C
VOUT = 1.8V, fixed frequency
-2.0%
1.8
+2.5%
VOUT = 1.8V, SKIP mode (Note 3)
-2.0%
1.8
+4.0%
VOUT = 5V, fixed frequency
-3.0%
5
+2.5%
VOUT = 5V, SKIP mode (Note 3)
-3.0%
5
+4%
VOUT = 3.3V, fixed frequency
-3.0%
3.3
+2.5%
-3.0%
3.3
+4%
-3.0%
1.8
+2.5%
-3.0%
1.8
+4%
6V ≤ VSUP ≤ 18V,
ILOAD = 0 to 1A,
VOUT = 3.3V, SKIP mode (Note 3) TA = -40°C to
+125°C
VOUT = 1.8V, fixed frequency
VOUT = 1.8V, SKIP mode (Note 3)
350
VBIAS = 5V
V
mA
400
800
mΩ
250
450
mΩ
1.275
1.5
1.75
A
7
8
9
ms
tRISE,LX
5
ns
Minimum On-Time
tON
80
ns
PWM Switching Frequency
fSW
SYNC Input Frequency
Range
Spread-Spectrum Range
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Internally generated
fSYNC
SS
1.925
2.1
1.8
Spread-spectrum option only
+6
2.275
MHz
2.6
MHz
%
Maxim Integrated │ 4
MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
Electrical Characteristics (continued)
(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
PGOOD Debounce
VTHR,PGD
VOUT rising
88
93
98
VTHF,PGD
VOUT falling
88
91
94
tDEB
10
PGOOD HIGH Leakage
Current
ILEAK,PGD
TA = +25°C, VPGD ≤ VOUT
PGOOD Output Low Level
VOUT,PGD
Sinking 1mA
%
µs
1
µA
0.4
V
LOGIC LEVELS
EN Level
EN Input Current
SYNC Switching Threshold
SYNC Internal Pulldown
VIH,EN
2.4
VIL,EN
IIN,EN
0.6
VEN = VSUP = +42V, TA = +25°C
VIH,SYNC
1
1.4
VIL,SYNC
0.4
V
µA
V
RPD,SYNC
200
kΩ
Thermal Shutdown
TSHDN
175
°C
Thermal Shutdown
Hysteresis
TSHDN,HYS
15
°C
THERMAL PROTECTION
Note 2: When the typical minimum on-time of 80ns is violated, the device skips pulses.
Note 3: Guaranteed by design; not production tested.
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Maxim Integrated │ 5
MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
Typical Operating Characteristics
(VSUP = +14V, TA = +25°C, unless otherwise noted.)
60
50
40
30
20
0
0.00001 0.0001
0.01
0.1
30
20
3.3V PART
8 10 12 14 16 18 20 22 24 26 28
2
1
0
-1
-2
-3
-4
8 10 12 14 16 18 20 22 24 26 28
6
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
LOAD REGULATION
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
STARTUP WAVEFORM (ILOAD = 1A)
1
0
FFF MODE
-1
6
3
ILOAD (A)
SKIP MODE
2
0
1
-2
15
SUPPLY CURRENT (µA)
3
0.001
MAX16903 toc04
4
OUTPUT-VOLTAGE CHANGE (%)
5V PART
10
10
MAX16903 toc06
12
EN
5V/div
IINDUCTOR
1A/div
9
6
PGOOD
5V/div
3
-3
-4
40
4
OUTPUT-VOLTAGE CHANGE (%)
FFF MODE
LINE REGULATION
(ILOAD = 1A)
MAX16903 toc05
EFFICIENCY (%)
70
50
SUPPLY CURRENT (µA)
SKIP MODE
80
60
MAX16903 toc02
90
MAX16903 toc01
100
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE (SKIP MODE)
MAX16903 toc03
EFFICIENCY vs. LOAD CURRENT
(5V VERSION)
0
0.2
0.4
0.6
0.8
1.0
0
VOUT
5V/div
6
LOAD CURRENT (A)
8 10 12 14 16 18 20 22 24 26 28
1ms/div
INPUT VOLTAGE (V)
LOAD-TRANSIENT RESPONSE
(FIXED MODE)
SHUTDOWN WAVEFORM (ILOAD = 1A)
MAX16903 toc07
MAX16903 toc08
ILOAD
1A/div
EN
5V/div
IINDUCTOR
1A/div
PGOOD
5V/div
VOUT
5V/div
20µs/div
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VOUT
200mV/div
AC
COUPLED
5V
PGOOD
5V/div
5V
ILOAD = 100mA TO 1A TO 100mA
200µs/div
Maxim Integrated │ 6
MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
Typical Operating Characteristics (continued)
(VSUP = +14V, TA = +25°C, unless otherwise noted.)
UNDERVOLTAGE PULSE (COLD CRANK)
MAX16903 toc09
3.5V
VOUT
200mV/div
ACCOUPLED
400
350
VOUT
5V/div
PGOOD
5V/div
PGOOD
5V/div
5V
450
VSUP
10V/div
ISUP (µA)
ILOAD
1A/div
5V
500
MAX16903 toc10
14V
ILOAD = 500mA
ILOAD = 100mA TO 1A TO 100mA
200µs/div
STANDBY CURRENT
vs. LOAD CURRENT
MAX16903 toc11
LOAD-TRANSIENT RESPONSE
(SKIP MODE)
300
250
200
150
100
50
ILOAD
1A/div
0
10ms/div
0.01
0.10
1.00
ILOAD (mA)
Pin Configurations
TOP VIEW
BST
1
SUP
2
LX
3
PGND
4
OUTS
5
+
MAX16903
EP
TDFN
10
EN
9
GND
8
BIAS
7
SYNC
6
PGOOD
+
BST
1
SUP
2
15 EN
SUP
3
14 GND
LX
4
LX
5
12 SYNC
PGND
6
11 PGOOD
PGND
7
10 N.C.
OUTS
8
16 N.C.
MAX16903
EP
13 BIAS
9
N.C.
TSSOP
Pin Description
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
4
6, 7
PGND
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Buck Switching Node. LX is high impedance when the device is off. For the TSSOP package,
connect both LX pins together for proper operation.
Power Ground. For the TSSOP-EP package, connect both PGND pins together for proper
operation.
Maxim Integrated │ 7
MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
Pin Description (continued)
PIN
NAME
FUNCTION
TDFN
TSSOP
5
8
OUTS
6
11
PGOOD
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
—
9, 10, 16
N.C.
—
—
EP
Buck Regulator Voltage-Sense Input. Bypass OUTS to PGND with a 10µF or larger X7R
ceramic capacitor.
Open-Drain Power-Good Output
Enable Input. EN is high-voltage compatible. Drive EN HIGH for normal operation.
No Connection. Not internally connected.
Exposed Pad. Connect EP to PGND. Do not use EP as the only ground connection.
Functional Diagram
SYNC
EN
HVLDO
REF
BANDGAP
OSC
BST
BIAS
SUP
CLK
SOFT-START
OUTS
LOGIC
CONTROL
PWM
EAMP
VGOOD
HSD
CURRENT-SENSE
AND
SLOPE COMPENSATION
COMP
LX
BIAS
LSD
MAX16903
PGND
PGOOD
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GND
Maxim Integrated │ 8
MAX16903
Detailed Description
The MAX16903 is a small, current-mode buck converter 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 interference.
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 overall 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.
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2.1MHz, High-Voltage,
1A Mini-Buck Converter
Oscillator/Synchronization and
Efficiency (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 Efficiency 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 operates 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.
Maxim Integrated │ 9
MAX16903
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 ontime (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 approaches 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 capacitor 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 frequency 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 output. 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
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2.1MHz, High-Voltage,
1A Mini-Buck Converter
Table 1. Nominal Output Voltage Values
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
Table 2. Examples for Standard Output
Voltages
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
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 calculated 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 frequency, peak inductor current, and the allowable peak-to-peak
input-voltage ripple dictate the input capacitance requirement. Increasing the switching frequency or the inductor
Maxim Integrated │ 10
MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
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 capacitor requirement for a target voltage ripple at the input:
∆VESR
∆IP−P
I OUT + 2
× D(1 − D)
I
C IN = OUT
∆VQ × f SW
ESR =
where:
(VIN − VOUT )× VOUT
∆IP−P =
VIN × f SW ×L
and:
D=
VOUT
VIN
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 capacitance may be needed based on application-specific outputvoltage 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 output 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 capacitors, the entire output ripple is contributed by ΔVESR. Use
the ESROUT equation to calculate the ESR requirement
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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 capacitance and ESR requirement for a specified output-voltage
ripple.
∆VESR
ESR =
∆IP−P
C OUT =
∆IP−P
8 × ∆VQ × f SW
where:
(VIN − VOUT ) × VOUT
∆IP−P =
VIN × f SW ×L
VOUT_RIPPLE ≅ ∆VESR + ∆VQ
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 discharge 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 =
∆VESR
I STEP
I
×t
C OUT = STEP RESPONSE
∆VQ
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.
Maxim Integrated │ 11
MAX16903
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 layout. 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.
2.1MHz, High-Voltage,
1A Mini-Buck Converter
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).
1MΩ
HIGHVOLTAGE
DC
SOURCE
CHARGE-CURRENTLIMIT RESISTOR
CS
100pF
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.
DISCHARGE
RESISTANCE
DEVICE
UNDER
TEST
STORAGE
CAPACITOR
Figure 1. Human Body ESD Test Circuit
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.
RD
1.5kΩ
RD
0Ω
HIGHVOLTAGE
DC
SOURCE
CHARGE-CURRENTLIMIT RESISTOR
CS
200pF
DISCHARGE
RESISTANCE
DEVICE
UNDER
TEST
STORAGE
CAPACITOR
Figure 2. Machine Model ESD Test Circuit
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.
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Maxim Integrated │ 12
MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
Selector Guide
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+
5
10 TDFN-EP*
(3mm x 3mm x 0.75mm)
—
AVU
MAX16903RATB18/V+
1.8
10 TDFN-EP*
(3mm x 3mm x 0.75mm)
Yes
—
MAX16903RAUE50+
5
16 TSSOP-EP*
(5mm x 4.4mm)
—
—
MAX16903RAUE50/V+
5
16 TSSOP-EP*
(5mm x 4.4mm)
—
—
MAX16903SATB50+
5
10 TDFN-EP*
(3mm x 3mm x 0.75mm)
Yes
AZQ
MAX16903SATB50/V+
5
10 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+
5
16 TSSOP-EP*
(5mm x 4.4mm)
Yes
—
MAX16903SAUE50/V+
5
16 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
—
PART
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.
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Maxim Integrated │ 13
MAX16903
Chip Information
PROCESS: BiCMOS
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2.1MHz, High-Voltage,
1A Mini-Buck Converter
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.
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
Maxim Integrated │ 14
MAX16903
2.1MHz, High-Voltage,
1A Mini-Buck Converter
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
0
10/09
Initial release
1
7/10
Updated the General Description, Typical Operating Circuits, Absolute Maximum Ratings,
Electrical Characteristics table, Typical Operating Characteristics, Pin Description, and
Detailed Description
2
8/10
Corrected a typo in the TSSOP Pin Configuration (pin 2 is SUP, not N.C.)
3
3/11
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
4
4/13
Replaced the Inductor Selection section, and updated the Input Capacitor, Output
Capacitor, and Selector Guide sections
5
9/14
Updated Typical Operating Circuits
2
6
9/14
Updated PGOOD HIGH leakage current in Electrical Characteristics
4
7
1/15
Updated Benefits and Features section
1
8
9/15
Updated PGOOD Threshold (VOUT rising) in Electrical Characteristics
4
9
11/15
Added 1.8V package variants to Electrical Characteristics and Selector Guide tables
10
4/17
Removed “Military” from Applications section
DESCRIPTION
—
1–10
6
3, 4, 8, 9
9–11
3, 12
1
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.
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 specifications 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
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