MAX16903RAUE33/V+T - Maxim

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 oper-

ate 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

operation, skip mode (ultra-low quiescent current of

25μA), and synchronization to an external clock. The

MAX16903 can be ordered with spread-spectrum fre-

quency 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

Military

High-Voltage Input-Power DC-DC Applications

Features

♦Wide +3.5V to +28V Input Voltage Range

♦Tolerates Input Voltage Transients to +42V

♦1A Minimum Output Current with Overcurrent

Protection

♦Fixed Output Voltages (+3.3V and +5V)

♦2.1MHz Switching Frequency with 3 Modes of

Operation

25µA Ultra-Low Quiescent Current Skip Mode

Forced Fixed-Frequency Operation

External Frequency Synchronization

♦Optional Spread-Spectrum Frequency Modulation

♦Power-Good Output

♦Enable-Pin Compatible from +3.3V Logic Level to

+42V

♦Thermal Shutdown Protection

♦-40°C to +125°C Automotive Temperature Range

♦10-Pin TDFN-EP or 16-Pin TSSOP-EP Packages

♦AEC-Q100 Qualified

MAX16903

2.1MHz, High-Voltage, 1A Mini-Buck Converter

________________________________________________________________

Maxim Integrated Products

19-5038; Rev 3; 3/11

EVALUATION KIT

AVAILABLE

PART SPREAD

SPEC T R UM

TEMP

RANGE

PIN-

PACKAGE

MAX16903RAUE__/V+

Disabled

-40°C to

+125°C

16 TS S OP - E P *

MAX16903RATB__/V+

Disabled

-40°C to

+125°C

10 TD FN -E P*

MAX16903SAUE__/V+

Enabled

-40°C to

+125°C

16 TS S OP - E P *

MAX16903SATB__/V+

Enabled

-40°C to

+125°C

10 TD FN -E P*

Ordering Information

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

Note: Insert the desired suffix letters (from Selector Guide) into

the blanks to indicate the output voltage. Alternative output volt-

ages available upon request.

Denotes a lead(Pb)-free/RoHS-compliant package.

/V denotes an automotive qualified part.

EP = Exposed pad.

MAX16903

2.1MHz, High-Voltage, 1A Mini-Buck Converter

2 _______________________________________________________________________________________

MAX16903_50/V+

20kΩ

2.2μF

33kΩ

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

10μF

PGND

5V AT 1A

OUTS

MAX16903_33/V+

20kΩ

2.2μF

33kΩ

SYNC

GND

VBAT LEVEL

SIGNAL

PGOOD

BIAS

SUP

4.7μF

BST

0.1μF

3.3μH

10μF

PGND

3.3V AT 1A

OUTS

Typical Operating Circuits

MAX16903

2.1MHz, High-Voltage, 1A Mini-Buck Converter

_______________________________________________________________________________________ 3

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VSUP = +14V, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C, unless otherwise noted.)

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.

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.maxim-ic.com/thermal-tutorial.

(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

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

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

(Note 2) 3.5 28

Supply Voltage Range VSUP t < 1s 42 V

EN = low 4 8

EN = high, no load 25 35 μA

Supply Current ISUP

EN = high, continuous, no switching 1 mA

VUVLO Bias rising 2.8 3 3.2

UV Lockout VUVLO,HYS Hysteresis 0.4 V

Bias Voltage VBIAS +5.5V  VSUP  +42V 5 V

Bias Current Limit IBIAS 10 mA

BUCK CONVERTER

VOUT = 5V, fixed frequency -2.0% 5 +2.5%

VOUT,5V VOUT = 5V, SKIP mode (Note 3) -2.0% 5 +4%

VOUT = 3.3V, fixed frequency -2.0% 3.3 +2.5%

VOUT,3.3V VOUT = 3.3V, SKIP mode (Note 3)

6V  VSUP  18V,

ILOAD = 0 to 1A,

TA = 0°C to

+125°C -2.0% 3.3 +4%

VOUT = 5V, fixed frequency -3.0% 5 +2.5%

VOUT,5V VOUT = 5V, SKIP mode (Note 3) -3.0% 5 +4%

VOUT = 3.3V, fixed frequency -3.0% 3.3 +2.5%

Voltage Accuracy

VOUT,3.3V VOUT = 3.3V, SKIP mode (Note 3)

6V  VSUP  18V,

ILOAD = 0 to 1A,

TA = -40°C to

+125°C -3.0% 3.3 +4%

MAX16903

2.1MHz, High-Voltage, 1A Mini-Buck Converter

4 _______________________________________________________________________________________

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

Skip-Mode Peak Current ISKIP 350 mA

High-Side DMOS RDSON R

ON,HS V

BIAS = 5V 400 800 m

Low-Side DMOS RDSON R

ON,LS 250 450 m

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 %

PGOOD

VTHR,PGD V

OUT rising 93

PGOOD Threshold VTHF,PGD V

OUT falling 88 91 94 %

PGOOD Debounce tDEB 10 μs

PGOOD HIGH Leakage Current ILEAK,PGD T

A = +25°C 1 μA

PGOOD Output Low Level VOUT,PGD Sinking 1mA 0.4 V

LOGIC LE V EL S

VIH,EN 2.4

EN Level VIL,EN 0.6 V

EN Input Current IIN,EN V

EN = VSUP = +42V, TA = +25°C 1 μA

VIH,SYNC 1.4

SYNC Switching Threshold VIL,SYNC 0.4 V

SYNC Internal Pulldown RPD,SYNC 200 k

THERMAL PROTECTION

Thermal Shutdown TSHDN 175 °C

Thermal Shutdown Hysteresis TSHDN,HYS 15 °C

Note 2: When the typical minimum on-time of 80ns is violated, the device skips pulses.

Note 3: Guaranteed by design; not production tested.

MAX16903

2.1MHz, High-Voltage, 1A Mini-Buck Converter

_______________________________________________________________________________________ 5

EFFICIENCY vs. LOAD CURRENT

(5V VERSION)

MAX16903 toc01

ILOAD (A)

EFFICIENCY (%)

0.10.010.0010.0001

100

0.00001 1

SKIP MODE

FFF MODE

NO-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE (SKIP MODE)

MAX16903 toc02

INPUT VOLTAGE (V)

SUPPLY CURRENT (µA)

2624222018161412108

628

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

-4

628

LOAD REGULATION

MAX16903 toc04

LOAD CURRENT (A)

OUTPUT-VOLTAGE CHANGE (%)

0.80.60.2 0.4

-3

-2

-1

-4

0 1.0

SKIP MODE

FFF MODE

SHUTDOWN SUPPLY CURRENT

vs. INPUT VOLTAGE

MAX16903 toc05

INPUT VOLTAGE (V)

SUPPLY CURRENT (µA)

2624222018161412108

628

STARTUP WAVEFORM (ILOAD = 1A)

MAX16903 toc06

IINDUCTOR

1A/div

PGOOD

5V/div

VOUT

5V/div

1ms/div

SHUTDOWN WAVEFORM (ILOAD = 1A)

MAX16903 toc07

IINDUCTOR

1A/div

PGOOD

5V/div

VOUT

5V/div

20µs/div

LOAD-TRANSIENT RESPONSE

(FIXED MODE)

MAX16903 toc08

ILOAD

1A/div

PGOOD

5V/div

VOUT

200mV/div

COUPLED

200µs/div

ILOAD = 100mA TO 1A TO 100mA

Typical Operating Characteristics

(VSUP = +14V, TA= +25°C, unless otherwise noted.)

MAX16903

2.1MHz, High-Voltage, 1A Mini-Buck Converter

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VSUP = +14V, TA= +25°C, unless otherwise noted.)

LOAD-TRANSIENT RESPONSE

(SKIP MODE)

MAX16903 toc09

ILOAD

1A/div

PGOOD

5V/div

VOUT

200mV/div

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)

ISUP (µA)

0.10

100

150

200

250

300

350

400

450

500

0.01 1.00

Pin Description

TDFN TSSOP

NAME FUNCTION

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.

MAX16903

5 6OUTS PGOOD

TOP VIEW

7PGND SYNC

38LX BIAS

29SUP GND

TDFN

10BST EN

MAX16903

8 9OUTS N.C.

710PGND N.C.

6 11PGND PGOOD

314SUP GND

215SUP EN

116BST N.C.

512LX SYNC

TSSOP

13LX BIAS

Pin Configurations

MAX16903

2.1MHz, High-Voltage, 1A Mini-Buck Converter

_______________________________________________________________________________________ 7

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 compo-

nents, reduced output ripple, and guarantees no AM

band interference.

Pin Description (continued)

TDFN TSSOP

NAME FUNCTION

5 8 OUTS

Buck Regulator Voltage-Sense Input. Bypass OUTS to PGND with a 10μF or larger X7R

ceramic capacitor.

6 11 PGOOD

Open-Drain Power-Good Output. External pullup resistor required for automatic SKIP mode

operation.

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.

Functional Diagram

MAX16903

LSD

PWM

EAMP

COMP

HSD

BIAS

PGND

BST

SUP

LOGIC

CONTROL

CURRENT-SENSE

AND

SLOPE COMPENSATION

SOFT-START

OSCBANDGAP

GND

VGOOD

PGOOD

OUTS

BIAS

HVLDO

SYNC

REF

CLK

MAX16903

The MAX16903 features an ultra-low 25μA (typ) quies-

cent 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 volt-

ages from 1.8V to 10.7V in 100mV steps. Please con-

tact 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 bat-

tery levels. EN can be controlled by microcontrollers

and automotive KEY or CAN inhibit signals. The EN

input has no internal pullup/pulldown current to mini-

mize overall quiescent supply current. To realize a pro-

grammable 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 inter-

nal 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 pat-

tern repeats until the short circuit has been removed.

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 oper-

ate 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 (val-

ley) 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 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 oper-

ate at a constant switching frequency for all load cur-

rents. 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.

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

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 period-

ically 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 fre-

quency varies by +6% relative to the internally generated

2.1MHz, High-Voltage, 1A Mini-Buck Converter

8 _______________________________________________________________________________________

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 gen-

erated 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 volt-

age 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 over-

current event is detected. The MAX16903 attempts a

soft-start restart every 30ms and stays off if the short cir-

cuit has not been removed. When the current limit is no

longer present, it reaches the output voltage by follow-

ing the normal soft-start sequence. If the MAX16903 die

reaches the thermal limit of 175°C (typ) during the cur-

rent-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

Three key inductor parameters must be specified for

operation with the MAX16903: inductance value (L),

peak inductor current (IPEAK), and inductor saturation

current (ISAT). The minimum required inductance is a

function of operating frequency, input-to-output voltage

differential, and the peak-to-peak inductor current

(ΔIP-P). Higher ΔIP-P allows for a lower inductor value,

while a lower ΔIP-P requires a higher inductor value. A

lower inductor value minimizes size and cost, improves

large-signal and transient response, but reduces effi-

ciency due to higher peak currents and higher peak-to-

peak output-voltage ripple for the same output

capacitor. On the other hand, higher inductance

increases efficiency by reducing the ripple current.

Resistive losses due to extra wire turns can exceed the

benefit gained from lower ripple current levels especial-

ly when the inductance is increased without also allow-

ing for larger inductor dimensions. A good compromise

is to choose ΔIP-P equal to 30% of the full load current.

Use the following equation to calculate the inductance:

VIN and VOUT are typical values so that efficiency is

optimum for typical conditions. The switching frequency

is ~2.1MHz. The peak-to-peak inductor current, which

reflects the peak-to-peak output ripple, is worse at the

maximum input voltage. See the

Output Capacitors

section to verify that the worst-case output ripple is

acceptable. The inductor saturation current is also

important to avoid runaway current during continuous

output short circuit. The output current may reach

1.75A since this is the maximum current limit. Choose

an inductor with a saturation current of greater than

1.75A to ensure proper operation and avoid runaway.

Input Capacitor

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

requirement. Increasing the switching frequency or the

inductor 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 ΔVQand 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 rip-

ple at the input:

ESR V

CIDD

ESR

OUT PP

IN OUT

⎛

⎝

⎜⎞

⎠

⎟

=×−

−

1( ))

ΔVf

QSW

LVVV

Vf I

OUT IN OUT

IN SW P P

=−

××

−

()

MAX16903

2.1MHz, High-Voltage, 1A Mini-Buck Converter

_______________________________________________________________________________________ 9

MAX16903

where:

and

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 pos-

sible undershoot below the UVLO threshold during tran-

sient loading.

Output Capacitor

The allowable output-voltage ripple and the maximum

deviation of the output voltage during step load cur-

rents 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 alu-

minum electrolytic capacitors at the output. For alu-

minum electrolytic capacitors, the entire output ripple is

contributed by ΔVESR. Use the ESROUT equation to cal-

culate 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 capacitance and ESR

requirement for a specified output-voltage ripple.

where:

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 capaci-

tance 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 convert-

er. The high switching frequency of the MAX16903

allows for a higher closed-loop bandwidth, thus reduc-

ing tRESPONSE and the output capacitance require-

ment. 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 tran-

sient 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% contribu-

tion from the output capacitance discharge and the

ESR drop, respectively. Use the following equations to

calculate the required ESR and capacitance value:

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.

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 ambi-

ent expose the copper area on the top and bottom

side. Add a few small vias or 1 large via on the cop-

per 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.

ESR V

CIt

OUT ESR

STEP

OUT STEP RESPONSE

=×

ΔIVV V

Vf L

PP IN OUT OUT

IN SW

OUT RIPPLE

−=−×

××

()

_≅≅+ΔΔVV

ESR Q

ESR V

ESR

OUT PP

QSW

=××

−

Δ8

OUT

ΔIVV V

Vf L

PP IN OUT OUT

IN SW

−=−×

××

()

2.1MHz, High-Voltage, 1A Mini-Buck Converter

10 ______________________________________________________________________________________

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 sensi-

tive 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 com-

ponents are CS= 200pF and RD= 0Ω(Figure 2).

MAX16903

2.1MHz, High-Voltage, 1A Mini-Buck Converter

______________________________________________________________________________________ 11

Figure 1. Human Body ESD Test Circuit

STORAGE

CAPACITOR

HIGH-

VOLTAGE

SOURCE

DEVICE

UNDER

TEST

CHARGE-CURRENT-

LIMIT RESISTOR

DISCHARGE

RESISTANCE

1MΩ

1.5kΩ

100pF STORAGE

CAPACITOR

HIGH-

VOLTAGE

SOURCE

DEVICE

UNDER

TEST

CHARGE-CURRENT-

LIMIT RESISTOR

DISCHARGE

RESISTANCE

0Ω

200pF

Figure 2. Machine Model ESD Test Circuit

Selector Guide

PART OUTPUT VOLTAGE

(V) PIN-PACKAGE SPREAD-SPECTRUM

SWITCHING FREQUENCY

TOP

MARK

MAX16903RATB50/V+ 5 10 TDFN-EP*

(3mm x 3mm x 0.75mm)

⎯AVU

MAX16903RAUE50/V+ 5 16 TSSOP-EP*

(5mm x 4.4mm) ⎯⎯

MAX16903SATB50/V+ 5 10 TDFN-EP*

(3mm x 3mm x 0.75mm)

Yes AVW

MAX16903SAUE50/V+ 5 16 TSSOP-EP*

(5mm x 4.4mm) Yes ⎯

MAX16903RATB33/V+ 3.3 10 TDFN-EP*

(3mm x 3mm x 0.75mm)

⎯AVT

MAX16903RAUE33/V+ 3.3 16 TSSOP-EP*

(5mm x 4.4mm) ⎯⎯

MAX16903SATB33/V+ 3.3 10 TDFN-EP*

(3mm x 3mm x 0.75mm)

Yes AVV

MAX16903SAUE33/V+ 3.3 16 TSSOP-EP*

(5mm x 4.4mm) Yes ⎯

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.

MAX16903

2.1MHz, High-Voltage, 1A Mini-Buck Converter

12 ______________________________________________________________________________________

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

Package Information

For the latest package outline information and land patterns

(footprints), go to www.maxim-ic.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.

MAX16903

2.1MHz, High-Voltage, 1A Mini-Buck Converter

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________

Revision History

REVISION

NUMBER

REVISION

DATE DESCRIPTION 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

1–10

2 8/10 Corrected a typo in the TSSOP Pin Configuration (pin 2 is SUP, not N.C.) 6

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

3, 4, 8, 9