MAX8772 datasheet(20/47 Pages) MAXIM

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MAX8770/MAX8771/MAX8772 Dual-Phase, Quick-

PWM Controller for IMVP-6+ CPU Core Power Supplies

______________________________________________________________________________________

CONFIDENTIAL INFORMATION – RESTRICTED TO INTEL® IMVP-6 LICENSEES

TRIG

ONE-SHOT

PGND1

DL1

BST1

DH1

LX1

CCV

TON

CSP1

CSN1

MINIMUM

OFF-TIME

VCC

REF

GND

PWRGD

5ms

STARTUP

DELAY

TARGET

- 300mV

TARGET

+ 200mV

REF

(2.0V)

SHDN

TRIG

ONE-SHOT

PHASE 1

ON-TIME

CSP2

CSN2

TRIG

ONE-SHOT

PHASE 2

ON-TIME

PHASE CONTROL

VDD

CSP2

CSN2

CSN1

CSP1

CCI

BLANK

BST2

DH2

LX2

DL2

CSP1

CSN1

2.5mV

MAIN PHASE

DRIVERS

Gm(CCV)

Gm(CCI)

CSP_

CSN_

Gm(FB)

D0–D6

22.5mV

CLKEN

VRHOT

THRM

0.3 x VCC

GNDS

PHASEGD

CURRENT-

BALANCE-

FAULT

POUT

POWER

MONITOR

CSP1 - CSN1

CSN1 - GNDS

CSP2 - CSN2

PGND2

µs

STARTUP

DELAY

Gm(CCI)

DAC

R-TO-I

CONVERTER

TIME

FAULT

REF

DPRSLPVR

DPRSTP

5ms

STARTUP

DELAY

BLANK

SECONDARY

PHASE DRIVERS

MAX8770

MAX8771

MAX8772

Figure 2. Functional Block Diagram

MAX8770/MAX8771/MAX8772

Detailed Description

Free-Running, Constant On-Time PWM

Controller with Input Feed-Forward

The Quick-PWM control architecture is a pseudo-fixed-

frequency, constant-on-time, current-mode regulator

with voltage feed-forward (Figure 2). This architecture

relies on the output filter capacitor’s ESR to act as the

current-sense resistor, so the output ripple voltage pro-

vides the PWM ramp signal. The control algorithm is sim-

ple: the high-side switch on-time is determined solely by

a one-shot whose period is inversely proportional to

input voltage, and directly proportional to output voltage

or the difference between the main and secondary

inductor currents (see the On-Time One-Shot section).

Another one-shot sets a minimum off-time. The on-time

one-shot triggers when the error comparator goes low,

the inductor current of the selected phase is below the

valley current-limit threshold, and the minimum off-time

one-shot times out. The controller maintains 180

° out-of-

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