MAX16935CAUES/V 데이터 시트보기 (PDF) - Maxim Integrated

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MAX16935CAUES/V

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

Maxim Integrated 

MAX16935/MAX16939

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

with 28µA Quiescent Current

Pin Descriptions (continued)

PIN

TQFN

TSSOP

10

11

11

12, 13

14

15

12

13, 14

15

16

—

—

NAME

SUP

SUPSW

LX

PGND

PGOOD

EP

FUNCTION

Voltage Supply Input. SUP powers up the internal linear regulator. Bypass SUP to

PGND with a 4.7FF ceramic capacitor. It is recommended to add a placeholder for

an RC filter to reduce noise on the internal logic supply (see the Typical Application

Circuit)

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, Active-Low 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/MAX16939 are 3.5A current-mode step-

down converters 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 devices operate 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 3.3V/5V fixed or adjustable from

1V to 10V. The wide input voltage range along with its

ability to operate at 98% duty cycle during undervoltage

transients make the devices ideal for automotive and

industrial applications.

Under light-load applications, the FSYNC logic input

allows the devices 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,

overvoltage 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 devices include 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 operate 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 conditions (typically

< 1A), a filter circuit from LX to GND is required to maintain

the output voltage within the expected 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 devices include a 5V linear regulator (BIAS) that

provides power to the internal circuit blocks. Connect a

1FF ceramic capacitor from BIAS to AGND.

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