ltc3557-ltc3557-1 Linear Technology Corporation, ltc3557-ltc3557-1 Datasheet - Page 21

• Manufacturer Part Number: ltc3557-ltc3557-1
• Description: Usb Power Manager With Li-ion Charger And Three Step-down Regulators
• Manufacturer: Linear Technology Corporation

External HV Buck Control Through the V
The WALL, ACPR and V
with an external high voltage buck regulator such as the
LT
to the V
shown in Figures 3-5 (consult the factory for a complete
list of approved high voltage buck regulators). When the
WALL pin voltage exceeds 4.3V, V
is enabled and drives the V
LT3505. The V
APPLICATIONS INFORMATION
®
3480, LT3481 or LT3505 to provide power directly
OUT
pin through a power P-channel MOSFET as
C
pin control circuitry is designed so that no
(TRANSIENTS
8V TO 34V
8V TO 38V
TO 60V)
C
HV
HV
pins can be used in conjunction
C
IN
IN
pin of the LT3480, LT3481 or
4.7μF
4.7μF
BUCK CIRCUITRY
BUCK CIRCUITRY
HIGH VOLTAGE
HIGH VOLTAGE
Figure 3. LT3480 Buck Control Using V
Figure 4. LT3481 Buck Control Using V
C
LT3480
LT3481
pin control circuitry
68nF
68nF
C
Pin
40.2k
60.4k
NC
150k
150k
10
10
4
5
7
6
4
5
6
V
RUN/SS
R
NC
NC
V
RUN/SS
R
GND
GND
IN
IN
T
T
LT3480
LT3481
11
11
BOOST
BOOST
V
BIAS
V
V
V
SW
C
SW
C
C
C
BD
BD
9
26
9
26
FB
FB
LTC3557-1
LTC3557-1
WALL ACPR
WALL ACPR
LTC3557
LTC3557
2
3
1
8
2
3
7
1
8
3
3
compensation components are required on the V
The voltage at the V
(BAT + 300mV) or 3.6V as shown in Figures 6 and 7. The
feedback network of the high voltage regulator should be
set to generate an output voltage higher than 4.4V (be sure
to include the output voltage tolerance of the buck regula-
tor). The V
V
once the V
independent of the buck regulator feedback network.
C
0.47μF
0.47μF
control of the external high voltage buck. Therefore,
25
25
GATE
V
GATE
V
BAT
OUT
BAT
OUT
DFLS240L
DFLS240L
C
C
6.8μH
6.8μH
(800kHz Switching)
(800kHz Switching)
23
21
22
23
21
22
C
C
control is enabled, the output voltage is set
control of the LTC3557 overdrives the local
499k
549k
100k
200k
Si2333DS
Si2333DS
LTC3557/LTC3557-1
OUT
22μF
22μF
pin is regulated to the larger of
Si2333DS
(OPT)
+
Si2333DS
(OPT)
+
UP TO
2A
UP TO
2A
35571 F03
35571 F04
Li-Ion
Li-Ion
C
C
OUT
OUT
V
BAT
V
BAT
OUT
OUT
21
C
node.
35571fa