15585 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'15585' PDF : 20 Pages View PDF
LTC1558-3.3/LTC1558-5
TYPICAL APPLICATIONS
LTC1558-3.3 Low Main Battery Voltage (4.5V to 10V) Application
R14
14k
RESET
PUSHBUTTON
BACKUP +
BATTERY
1.2V
NiCd
L11†
22µH
C11
1
47µF
SW
7
6.3V
VCC
3
8
CTL VBAK
2 LTC1558-3.3 5
GND RESET
4
6
FB BACKUP
+
C12
1µF
RESET
BACKUP
MAIN
BATTERY
4.5V TO 10V
Q11
R11
P-CHANNEL
Si4431DY
221k
1%
R12
100k
1%
R13
100k
*SUMIDA CDRH125-10
**IRC LR2D1D-01-RQ33-F
†SUMIDA CD54-220
CC2
51pF
+ C2
1µF
CC
330pF
RC
10k
CSS
0.1µF
COSC
68pF
13
16
+
Q1
N-CHANNEL
Si4412DY
CIN
22µF
35V
×2
VIN
9
EXTVCC
TG
14
SW
4
SFB
15
BOOST
6
LTC1435
12
VOSENSE INTVCC
3
ITH
SENSE + 8
C4
0.1µF
D1 CMDSH-3
L1*
10µH
RSENSE**
0.033Ω
+
2 RUN/SS SENSE – 7
C5
1000pF
1
11
COSC
BG
Q2
D2
SGND PGND
5
10
+ C3
4.7µF
16V
N-CHANNEL
MBRS140T3
Si4412DY
R5
20k
1%
CIN
100µF
10V
×2
R1
35.7k
1%
C6
100pF
VOUT
3.3V
3A
C1
100pF
1558 TA03
Typical “Low Voltage” Application
The maximum main battery voltage is less than the maxi-
mum VBAK pin voltage (12V). This configuration has the
lowest number of external components.
The LTC1435’s minimum input voltage is 3.5V. The VBAK
voltage, set by R11 and R12, is programmed to 3.8V.
Therefore, the main battery’s lowest voltage should be
3.8V + 1 body diode drop = 4.5V. This will enable a fresh
main battery to turn on the external P-channel MOSFET
and power up the system out of UVLO during cold power
boot or out of backup mode when the LTC1558 is power-
ing up the system.
A 100k pull-up resistor enables the open-drain BACKUP
pin to turn the external P-channel MOSFET off when VBAK
is higher than VCC.
15
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