Rainbow Electronics MAX1715 - Manual (Page 10)

MAX1715
Ultra-High Efficiency, Dual Step-Down
Controller for Notebook Computers
10 ______________________________________________________________________________________
V DD = 5V
BIAS SUPPLY
PINS 15, 23, 28 = N.C.
POWER-GOOD
INDICATOR
MAX1715
V CC
OUTPUT1
1.8V
V IN
4.5V TO 28V
D3
CMPSH-3A
ILIM1
ON1
DL1
TON
OUT1
AGND
C3 C4 D1
N2 N4
N3 N1
LX1
DH1
C5
0.1 µF
C6
0.1
µF
C7
0.22 µF
FB1
V DD
C8
1 µF
C1
20
21
25
26
27
24
5
1
9
2
8
10
11
18
17
16
19
22
14
6
13
7
C2
C11
1
µF
L1
12
3
L2
BST1
ILIM2
REF
ON1
ON2
DL2
PGND
+5V
100k
OUT2
LX2
DH2
FB2
PGOOD
V+
4
BST2
SKIP
C9
4.7 µF
R1
20
Ω
OUTPUT2
2.5V
D2
ON/OFF
CONTROLS
Figure 1. Standard Application Circuit
Standard Application Circuit
The standard application circuit (Figure 1) generates
two low-voltage rails for general-purpose use in note-
book computers (I/O supply, fixed CPU core supply,
DRAM supply). This DC-DC converter steps down a
battery or AC adapter voltage to voltages from 1.0V to
5.5V with high efficiency and accuracy.
See Table 1 for a list of components for common appli-
cations. Table 2 lists component manufacturers.
Detailed Description
The MAX1715 buck controller is designed for low-volt-
age power supplies for notebook computers. Maxim’s
proprietary Quick-PWM pulse-width modulator in the
MAX1715 (Figure 2) is specifically designed for han-
dling fast load steps while maintaining a relatively con-
stant operating frequency and inductor operating point
over a wide range of input voltages. The Quick-PWM
architecture circumvents the poor load-transient timing
problems of fixed-frequency current-mode PWMs while
also avoiding the problems caused by widely varying
switching frequencies in conventional constant-on-time
and constant-off-time PWM schemes.
+5V Bias Supply (V CC and V DD )
The MAX1715 requires an external +5V bias supply in
addition to the battery. Typically, this +5V bias supply
is the notebook’s 95% efficient +5V system supply.
Keeping the bias supply external to the IC improves
efficiency and eliminates the cost associated with the
+5V linear regulator that would otherwise be needed to
supply the PWM circuit and gate drivers. If stand-alone
capability is needed, the +5V supply can be generated
with an external linear regulator such as the MAX1615.