MAX1636 Datasheet, PDF (12/24 Pages) Maxim Integrated Products – Low-Voltage, Precision Step-Down Controller for Portable CPU Power

Low-Voltage, Precision Step-Down
Controller for Portable CPU Power
Table 3. SKIP PWM Table
SKIP
LOAD
CURRENT
MODE
DESCRIPTION
Pulse-skipping,
Low
Light
Idle discontinuous inductor
current
Low
Heavy
PWM
Constant-frequency PWM,
continuous inductor current
High
Light
PWM
Constant-frequency PWM,
continuous inductor current
High
Heavy
PWM
Constant-frequency PWM,
continuous inductor current
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
SKIP
SHDN
30mV
SLOPE
COMPENSATION
DAC
CK
COUNTER
SOFT-START
CSH
1X
CSL
FB
2X
REF
CC
gm
R
Q
S
OSC
BST
LEVEL
SHIFT
DH
LX
CURRENT
LIMIT
SHOOT-
THROUGH
CONTROL
-100mV
SYNCHRONOUS
RECTIFIER CONTROL
RQ
S
LEVEL
SHIFT
VL
DL
PGND
Figure 3. PWM Controller Functional Diagram
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