MAX26402/MAX26403

36V, 2.5A/3.5A, Fully Integrated Synchronous

Silent Switcher Buck Converters

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SYNC

External Clock Synchronization Input. Connect an external clock in the given frequency range to enable

external clock synchronization. Connect SYNC to low to enable skip mode. Connect SYNC to high to

enable FPWM mode.

Detailed Description

The MAX26402/MAX26403 are small, synchronous buck converters with integrated high-side and low-side switches.

These devices are designed to deliver up to 2.5A/3.5A for input voltages of 3V to 36V. They offer fixed output voltage

options of 5V and 3.3V, or adjustable output voltage options from 0.8V to 12V. Output voltage quality can be monitored

by observing the PGOOD signal. The devices can operate in dropout by running at 99% duty cycle, making them ideal

for industrial applications. Contact factory for additional options not listed in ordering table.

Frequency is internally fixed at 3MHz/2.1MHz/400kHz, which allows for small external components and reduced output

ripple, and guarantees no AM interference. These converters automatically enter skip mode at light loads with ultra-low

quiescent current of 10μA (typ) at no load when SYNC is pulled low. They feature spread-spectrum frequency modulation

to minimize EMI-radiated emissions. The average current-mode architecture allows much better noise rejection of the

current loop and very short minimum on-time.

Linear Regulator Output (BIAS)

The devices include a 1.8V linear regulator (VBIAS) that provides power to the internal circuit blocks. Connect a 2.2μF

ceramic capacitor from BIAS to GND. For the internal feedback version, the bias regulator draws power from the SUP

input during startup and switches over to the output after the startup is complete.

System Enable (EN)

An enable control input (EN) activates the device from low-power shutdown mode. EN is compatible with inputs from the

operating level down to 3V. Drive EN high to turn on the internal linear BIAS LDO. Once VBIAS is above the internal

lockout threshold of 1.63V (typ), the converter is enabled and the output voltage ramps up with the programmed soft-start

time.

A logic-low at EN shuts down the device. During shutdown, the BIAS regulator and gate drivers turn off, and the quiescent

current is reduced to 2.75μA (typ).

Synchronization Input (SYNC)

SYNC is a logic-level input used for operation-mode selection and frequency control. Connect SYNC to BIAS to enable

forced fixed-frequency operation (FPWM) or to GND to enable automatic skip-mode operation for light load efficiency.

SYNC can also be connected to an external clock, enabling forced-frequency operation. The device synchronizes with an

external clock in two cycles, synchronizing at the rising edge of the signal applied. See the external clock frequency limits

specified in the Electrical Characteristics table. When the external clock signal at SYNC is absent for more than two clock

cycles, the IC switches to use the internal clock.

Soft-Start

The devices include a fixed, internal soft-start time. Soft-start time limits start-up inrush current by forcing the output

voltage to ramp up toward its regulation point. The soft-start ramp rate is set at 2.5ms (typ).

Power-Good (PGOOD) Output

The MAX26402/MAX26403 feature an open-drain, PGOOD output to monitor output voltage quality. PGOOD is an active-

high output signal that pulls low when VOUT falls below 93% (typ) of its nominal value or rises above 105% (typ) of its

nominal value. Connect a 20kΩ (typ) pull-up resistor to an external supply or the on-chip BIAS output.

Spread Spectrum

The devices feature a spread-spectrum option. When the SPS pin is pulled high, the spread-spectrum feature is enabled

and the internal operating frequency is varied by ±6% relative to the internally generated operating frequency. The

modulation signal is a triangular wave with a period of 1.25ms at 400kHz (200μs at 2.1MHz). Spread spectrum is disabled

if the device is synchronized to an external clock.

Overcurrent and Short-Circuit Protection

The MAX26402/MAX26403 feature a current limit that protects them against short-circuit and overload conditions at the

output. In the event of a short-circuit or overload condition, the high-side switch remains on until the inductor current

reaches the specified LX current-limit threshold. The converter then turns the high-side switch off and the low-side switch