MAX1820 Просмотр технического описания (PDF) - Maxim Integrated

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производитель

MAX1820

WCDMA Cellular Phone 600mA Buck Regulators

Maxim Integrated 

WCDMA Cellular Phone 600mA

Buck Regulators

BATT

VOLTAGE 1.25V TO

REFERENCE

IC BIAS

GND

ERROR SIGNAL

SLOPE COMP

PWM

COMPARATOR

CURRENT SENSE

PWM CONTROL

TRANSIMPEDANCE

AND

OUT

ERROR AMP

SKIP

COMPARATOR

SKIP LOGIC

REF

CLAMP

SKIP THRESHOLD

MAX1820

÷13 OR

÷18

1MHz

OSCILLATOR

LX

PGND

Figure 1. MAX1820 Simplified Functional Diagram (No SYNC for MAX1820Z)

BATT

VOLTAGE 1.25V

REFERENCE

GND

TO

IC BIAS

TRANSIMPEDANCE

OUT

ERROR AMP

CLAMP

REF

ERROR SIGNAL

SLOPE COMP

CURRENT SENSE

SKIP THRESHOLD

MAX1821

PWM

COMPARATOR

SKIP

COMPARATOR

PWM CONTROL

AND

SKIP LOGIC

1MHz

OSCILLATOR

LX

PGND

Figure 2. MAX1821 Simplified Functional Diagram (No SYNC for MAX1821)

ing each cycle, using the PWM comparator. The power

transferred to the load is adjusted by changes in the

inductor peak current limit during the first half of each

cycle, based on the output error voltage.

A new cycle begins at each falling edge of the internal

oscillator. The controller turns on the P-channel MOS-

FET to increase the inductor current, and the slope

compensation block initiates a new reference current

ramp that is summed with the internal P-channel MOS-

FET current (Figures 1 and 2).

The second half of the cycle begins when the reference

ramp is greater than the error voltage. The P-channel

MOSFET is turned off, the synchronous rectifier is

turned on, and inductor current continues to flow to the

output capacitor. The output capacitor stores charge

when the current is high and releases it when the

inductor current is low, smoothing the voltage across

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