MAX1636 Maxim, MAX1636 Datasheet - Page 12

• Manufacturer Part Number: MAX1636
• Description: Low-Voltage / Precision Step-Down Controller for Portable CPU Power
• Manufacturer: Maxim

Low-Voltage, Precision Step-Down
Controller for Portable CPU Power
12
Table 3. S S K K I I P P PWM Table
Figure 3. PWM Controller Functional Diagram
S S K K I I P P
High
High
Low
Low
______________________________________________________________________________________
CURRENT
LOAD
Heavy
Heavy
Light
Light
-100mV
SHDN
SKIP
MODE
PWM
PWM
PWM
Idle
30mV
Pulse-skipping,
discontinuous inductor
current
Constant-frequency PWM,
continuous inductor current
Constant-frequency PWM,
continuous inductor current
Constant-frequency PWM,
continuous inductor current
SOFT-START
COUNTER
SLOPE
COMPENSATION
DESCRIPTION
DAC
CK
RECTIFIER CONTROL
SYNCHRONOUS
R
S
Q
CURRENT
LIMIT
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
1X
gm
R
S
Q
OSC
2X
THROUGH
CONTROL
SHOOT-
LEVEL
LEVEL
SHIFT
SHIFT
CSH
CSL
FB
REF
CC
DH
BST
LX
VL
DL
PGND
PWM Controller