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MAX16935
(Rev.:2014)

36V, 3.5A, 2.2MHz Step-Down Converter with 28µA Quiescent Current

Maxim Integrated 

MAX16935

36V, 3.5A, 2.2MHz Step-Down Converter

with 28µA Quiescent Current

Pin Descriptions (continued)

PIN

12

13, 14

15

16

—

NAME

SUPSW

LX

PGND

PGOOD

EP

FUNCTION

Internal High-Side Switch Supply Input. SUPSW provides power to the internal switch. Bypass SUPSW

to PGND with 0.1FF and 4.7FF ceramic capacitors.

Inductor Switching Node. Connect a Schottky diode between LX and AGND.

Power Ground

Open-Drain, Power-Good Output. PGOOD asserts when VOUT is above 95% regulation point. PGOOD

goes low when VOUT is below 92% regulation point.

Exposed Pad. Connect EP to a large-area contiguous copper ground plane for effective power

dissipation. Do not use as the only IC ground connection. EP must be connected to PGND.

Detailed Description

The MAX16935 is a 3.5A current-mode step-down

converter with integrated high-side and low-side

MOSFETs designed to operate with an external Schottky

diode for better efficiency. The low-side MOSFET

enables fixed-frequency forced-PWM (FPWM) operation

under light-load applications. The device operates with

input voltages from 3.5V to 36V, while using only 28FA

quiescent current at no load. The switching frequency

is resistor programmable from 220kHz to 2.2MHz and

can be synchronized to an external clock. The output

voltage is available as 5V fixed or adjustable from 1V

to 10V. The wide input voltage range along with its abil-

ity to operate at 98% duty cycle during undervoltage

transients make the device ideal for automotive and

industrial applications.

Under light-load applications, the FSYNC logic input

allows the device to either operate in skip mode for

reduced current consumption or fixed-frequency FPWM

mode to eliminate frequency variation to minimize EMI.

Fixed frequency FPWM mode is extremely useful for

power supplies designed for RF transceivers where

tight emission control is necessary. Protection

features include cycle-by-cycle current limit, over-

voltage protection, and thermal shutdown with auto-

matic recovery. Additional features include a power-

good monitor to ease power-supply sequencing

and a 180N out-of-phase clock output relative to the

internal oscillator at SYNCOUT to create cascaded power

supplies with multiple devices.

Wide Input Voltage Range

The device includes two separate supply inputs (SUP and

SUPSW) specified for a wide 3.5V to 36V input voltage

range. VSUP provides power to the device and VSUPSW

provides power to the internal switch. When the device

is operating with a 3.5V input supply, conditions such as

cold crank can cause the voltage at SUP and SUPSW to

drop below the programmed output voltage. Under such

conditions, the device operates in a high duty-cycle mode

to facilitate minimum dropout from input to output.

In applications where the input voltage exceeds 25V,

output is ≤ 5V, operating frequency is ≥ 1.8MHz and

the IC is selected to be in FPWM mode by either forcing

the FSYNC pin high, or using an external clock, pulse

skipping is observed on the LX pin. This happens due

to insufficient minimum on time. Under certain load con-

ditions (typically < 1A), a filter circuit from LX to GND is

required to maintain the output voltage within the expect-

ed data sheet limits. A typical filter value of RFILTER = 1I,

CFILTER = 220pF (see the Typical Application Circuit) is

sufficient to filter out the noise and maintain the output

voltage within data sheet limits. This extra filter on the LX

pin of the IC has no impact on efficiency.

Linear Regulator Output (BIAS)

The device includes a 5V linear regulator (BIAS) that

provides power to the internal circuit blocks. Connect a

1FF ceramic capacitor from BIAS to AGND.

Power-Good Output (PGOOD)

The device features an open-drain power-good output,

PGOOD. PGOOD asserts when VOUT rises above 95%

of its regulation voltage. PGOOD deasserts when VOUT

drops below 92% of its regulation voltage. Connect

PGOOD to BIAS with a 10kI resistor.

Maxim Integrated

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