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

Pin Description

PIN NAME

FUNCTION

1

VCC

Supply Voltage. Bypass VCC with 0.1µF

capacitor to ground and 10Ω resistor to IN.

2 REF Reference Bypass. Bypass REF with 0.1µF

capacitor to ground.

3 GND Ground

Feedback Input. Connect FB to the output to

regulate using the internal feedback resistor

4

FB

string (MAX1952). Connect an external resistor-

divider from the output to FB and GND to set

the output to a voltage between 0.8V and VIN

(MAX1951).

Regulator Compensation. Connect series RC

network from COMP to GND. Pull COMP below

5 COMP 0.17V to shut down the regulator. COMP =

GND when VIN is less than 2.25V (see the

Compensation and Shutdown Mode section)

Power Ground. Internally connected to GND.

6 PGND Keep power ground and signal ground planes

separate.

7

LX

Inductor Connection. Connect an inductor

between LX and the regulator output.

Power-Supply Voltage. Input voltage range

8

IN

from 2.6V to 5.5V. Bypass IN with a 10µF (min)

ceramic capacitor to GND and a 10Ω resistor

to VCC.

Detailed Description

The MAX1951/MAX1952 high-efficiency switching regula-

tors are small, simple, DC-to-DC step-down converters

capable of delivering up to 2A of output current. The

devices operate in pulse-width modulation (PWM) at a

fixed frequency of 1MHz from a 2.6V to 5.5V input voltage

and provide an output voltage from 0.8V to VIN, making

the MAX1951/MAX1952 ideal for on-board postregula-

tion applications. The high switching frequency allows

for the use of smaller external components, and internal

synchronous rectifiers improve efficiency and eliminate

the typical Schottky free-wheeling diode. Using the on-

resistance of the internal high-side MOSFET to sense

switching currents eliminates current-sense resistors,

further improving efficiency and cost. The MAX1951

total output error over load, line, and temperature (0°C

to +85°C) is less than 1%.

Controller Block Function

The MAX1951/MAX1952 step-down converters use a

PWM current-mode control scheme. An open-loop com-

parator compares the integrated voltage-feedback signal

against the sum of the amplified current-sense signal and

the slope compensation ramp. At each rising edge of the

internal clock, the internal high-side MOSFET turns on

until the PWM comparator trips. During this on-time, cur-

rent ramps up through the inductor, sourcing current to

the output and storing energy in the inductor. The current-

mode feedback system regulates the peak inductor cur-

rent as a function of the output voltage error signal. Since

the average inductor current is nearly the same as the

peak inductor current (<30% ripple current), the circuit

acts as a switch-mode transconductance amplifier. To

preserve inner-loop stability and eliminate inductor stair-

casing, a slope-compensation ramp is summed into the

main PWM comparator. During the second half of the

cycle, the internal high-side p-channel MOSFET turns off,

and the internal low-side n-channel MOSFET turns on.

The inductor releases the stored energy as its current

ramps down while still providing current to the output. The

output capacitor stores charge when the inductor current

exceeds the load current, and discharges when the

inductor current is lower, smoothing the voltage across

the load. Under overload conditions, when the inductor

current exceeds the current limit (see the Current Limit

section), the high-side MOSFET does not turn on at the

rising edge of the clock and the low-side MOSFET

remains on to let the inductor current ramp down.

Current Sense

An internal current-sense amplifier produces a current

signal proportional to the voltage generated by the

high-side MOSFET on-resistance and the inductor cur-

rent (RDS(ON) x ILX). The amplified current-sense signal

and the internal slope compensation signal are

summed together into the comparator’s inverting input.

The PWM comparator turns off the internal high-side

MOSFET when this sum exceeds the output from the

voltage-error amplifier.

Current Limit

The internal high-side MOSFET has a current limit of 3.1A

(typ). If the current flowing out of LX exceeds this limit,

the high-side MOSFET turns off and the synchronous

rectifier turns on. This lowers the duty cycle and causes

the output voltage to droop until the current limit is no

longer exceeded. A synchronous rectifier current limit of

-0.6A (typ) protects the device from current flowing into

LX. If the negative current limit is exceeded, the synchro-

nous rectifier turns off, forcing the inductor current to flow

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