15585 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'15585' PDF : 20 Pages View PDF
LTC1558-3.3/LTC1558-5
TYPICAL APPLICATIONS
LTC1558-5 Medium Main Battery Voltage (7V to 18V) Application
RESET
PUSHBUTTON
MAIN
BATTERY
7V TO 18V
L11†
22µH
BACKUP + C11
1
R14
BATTERY
14k
1.2V
47µF
6.3V
SW
7
VCC
NiCd
3
8
CTL VBAK
2 LTC1558-5 5
GND RESET
4
6
FB BACKUP
+
C12
1µF
D11
1N5818
R13
100k
Q11
R11
P-CHANNEL
422k
Si4431DY
1%
R12
100k
1%
*SUMIDA CDRH125-10
**IRC LR2D1D-01-RQ33-F
†SUMIDA CD54-220
RESET
BACKUP
+ C2
1µF
13
16
+
Q1
N-CHANNEL
Si4412DY
CIN
22µF
35V
×2
VIN
9
EXTVCC
TG
14
SW
4
SFB
15
BOOST
6
LTC1435
12
C4
0.1µF
L1*
10µH
RSENSE**
0.033Ω
VOUT
CC2
51pF
CC
330pF
RC
10k
CSS
0.1µF
COSC
68pF
VOSENSE INTVCC
3
ITH
SENSE + 8
2 RUN/SS SENSE – 7
1
COSC
11
BG
D1 CMDSH-3
C5
1000pF
SGND PGND
+ C3
Q2
N-CHANNEL
Si4412DY
D2
MBRS140T3
5V
+
COUT
100µF
3A
10V
×2
R1
35.7k
1%
R6
C6
5
10
4.7µF
16V
11k
100pF
1%
C1
100pF
1558 TA04
Typical “Medium Voltage” Application
The maximum main battery voltage is more than the
maximum VBAK pin voltage (12V). This configuration is
needed for most notebook computers that have 3-cell or
4-cell series connected lithium battery packs.
The Schottky diode D11 (1N5818) prevents the main
battery’s high terminal voltage from overstressing the
LTC1558’s VBAK pin during nonbackup conditions. An
internal Zener inside the LTC1558 will clamp VBAK to 12V
when the 1N5818’s reverse bias leakage current
increases at high temperature.
A 100k pull-up resistor enables the LTC1558’s open-drain
BACKUP pin to turn the external P-channel MOSFET off
during backup mode, even when VBAK is higher than VCC.
The main battery pack should have an internal control to
shut itself down once its energy is used up. This prevents
the lithium cells from deep discharge damage. Once the
main battery shuts down, the FB voltage drops and the
LTC1558 switches to backup mode.
16
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