MAX1715 Maxim, MAX1715 Datasheet - Page 12

• Manufacturer Part Number: MAX1715
• Description: Ultra-High Efficiency / Dual Step-Down Controller for Notebook Computers
• Manufacturer: Maxim

Ultra-High Efficiency, Dual Step-Down
Controller for Notebook Computers
Figure 2. Functional Diagram
12
current-limit threshold, and the minimum off-time one-
shot has timed out.
The heart of the PWM core is the one-shot that sets the
high-side switch on-time for both controllers. This fast,
low-jitter, adjustable one-shot includes circuitry that
varies the on-time in response to battery and output
voltage. The high-side switch on-time is inversely pro-
portional to the battery voltage as measured by the V+
OUTPUT1
1.8V
5V INPUT
______________________________________________________________________________________
V
DD
V+
V
DD
OUT1
FB1
SKIP
ON1
ON2
TON
P
V
LX1
BST1
DL1
GOOD
DD
DH1
On-Time One-Shot (TON)
V
DD
V
CC
5µA
CROSSING
CURRENT
I
LIM_
ZERO
LIMIT
9R
R
4.5V TO 28V
BATTERY
(SEE FIGURE 3)
CONTROLLER
PWM
MAX1715
V+
V+
(SEE FIGURE 3)
CONTROLLER
input, and proportional to the output voltage. This algo-
rithm results in a nearly constant switching frequency
despite the lack of a fixed-frequency clock generator.
The benefits of a constant switching frequency are
twofold: first, the frequency can be selected to avoid
noise-sensitive regions such as the 455kHz IF band;
second, the inductor ripple-current operating point
remains relatively constant, resulting in easy design
methodology and predictable output voltage ripple.
The on-times for side 1 are set 15% higher than the
V
CC
PWM
5µA
ZERO
CROSSING
CURRENT
LIMIT
I
LIM_
R
9R
REF
2V
V
DD
BST2
PGND
AGND
OUT2
DH2
LX2
DL2
V
FB2
REF
CC
V
DD
V+
20Ω
OUTPUT2
V
DD
2.5V