MAX1952ESA 데이터 시트보기 (PDF) - Maxim Integrated

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MAX1952ESA

1MHz, All-Ceramic, 2.6V to 5.5V Input, 2A PWM Step-Down DC-to-DC Regulators

Maxim Integrated 

1MHz, All-Ceramic, 2.6V to 5.5V Input,

2A PWM Step-Down DC-to-DC Regulators

VCC

COMP

POSITIVE AND NEGATIVE CURRENT LIMITS

OSC

CLOCK

CURRENT SENSE

PWM

CONTROL

RAMP GEN SLOPE

COMP

CLAMP

ERROR

SIGNAL

THERMAL

SHUTDOWN

gm

SOFT-START/

UVLO

DAC

REF

2V

MAX1951

BANDGAP

REF

1.25V

IN

LX

PGND

FB

REF

GND

Figure 1. Functional Diagram

through the high-side MOSFET body diode, back to the

input, until the beginning of the next cycle or until the

inductor current drops to zero. The MAX1951/MAX1952

utilize a pulse-skip mode to prevent overheating during

short-circuit output conditions. The device enters pulse-

skip mode when the FB voltage drops below 300mV, lim-

iting the current to 3A (typ) and reducing power

dissipation. Normal operation resumes upon removal of

the short-circuit condition.

VCC Decoupling

Due to the high switching frequency and tight output

tolerance (1%), decouple VCC with a 0.1µF capacitor

connected from VCC to GND, and a 10Ω resistor con-

nected from VCC to IN. Place the capacitor as close to

VCC as possible.

Soft-Start

The MAX1951/MAX1952 employ digital soft-start circuitry

to reduce supply inrush current during startup conditions.

When the device exits undervoltage lockout (UVLO), shut-

down mode, or restarts following a thermal-overload

event, or the external pulldown on COMP is released, the

digital soft-start circuitry slowly ramps up the voltages at

REF and FB (see the Soft-Start Waveforms in the Typical

Operating Characteristics).

Undervoltage Lockout

If VCC drops below 2.25V, the UVLO circuit inhibits

switching. Once VCC rises above 2.35V, the UVLO

clears, and the soft-start sequence activates.

Compensation

and Shutdown Mode

The output of the internal transconductance voltage

error amplifier connects to COMP. The normal operation

voltage for COMP is 1V to 2.2V. To shut down the

MAX1951/MAX1952, use an NPN bipolar junction

transistor or a very low output capacitance open-drain

MOSFET to pull COMP to GND. Shutdown mode causes

the internal MOSFETs to stop switching, forces LX to a

high-impedance state, and shorts REF to GND.

Release COMP to exit shutdown and initiate the soft-

start sequence.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipation

in the device. When the junction temperature exceeds TJ

= +160°C, a thermal sensor forces the device into shut-

down, allowing the die to cool. The thermal sensor turns

the device on again after the junction temperature cools

by 15°C, resulting in a pulsed output during continuous

overload conditions. Following a thermal-shutdown condi-

tion, the soft-start sequence begins.

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