Rainbow-electronics MAX1636 Manual do Utilizador descarregar pdf (Página 12)

PWM Controller

The heart of the current-mode PWM controller is a

multi-input, open-loop comparator that sums four sig-

nals: the output voltage error signal with respect to the

reference voltage, the current-sense signal, the inte-

grated voltage-feedback signal, and the slope-

compensation ramp (Figure 3).

The PWM controller is a direct-summing type, lacking a

traditional error amplifier and the phase shift associat-

ed with it. This direct-summing configuration approach-

es ideal cycle-by-cycle control over the output voltage

(Figure 4).

When SKIP = low, Idle Mode circuitry automatically

optimizes efficiency throughout the load-current range.

Idle Mode dramatically improves light-load efficiency

MAX1636

Low-Voltage, Precision Step-Down

Controller for Portable CPU Power

12 ______________________________________________________________________________________

Low Light Idle

LOAD

CURRENT

Pulse-skipping,

discontinuous inductor

current

MODE DESCRIPTION

PWM

High Light PWM

Constant-frequency PWM,

continuous inductor current

PWMHigh Heavy

Constant-frequency PWM,

continuous inductor current

Low Heavy

Constant-frequency PWM,

continuous inductor current

SSKKIIPP

Table 3.

SSKKIIPP

PWM Table

SHOOT-

THROUGH

CONTROL

30mV

LEVEL

SHIFT

OSC

LEVEL

SHIFT

CURRENT

LIMIT

SYNCHRONOUS

RECTIFIER CONTROL

SHDN

-100mV

CSH

CSL

REF

BST

VGG

PGND

SLOPE

COMPENSATION

SKIP

COUNTER

DAC

SOFT-START

Figure 3. PWM Controller Functional Diagram

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 22 23

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