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 High Main Battery Voltage (48V) Application
Q12
2N3906
R16
100k
R15
100k
Z11
12V
D11
MBR170
BACKUP +
R14
BATTERY
14k
1.2V
NiCd
RESET
PUSHBUTTON
L11†
22µH
C11
1
47µF
SW
7
6.3V
VCC
3
8
CTL VBAK
LTC1558-5 5
RESET
2
6
GND BACKUP
FB
4
+
C12
1µF
RESET
BACKUP
Q11
R11
P-CHANNEL 422k
MTD2955E 1%
MAIN
R12
BATTERY 100k
48V
1%
D1
1N4148
C1
0.047µF
+
C3
3.3µF
C4
470pF
D2
1N4148
C2
0.068µF
RC
1k
CC
3300pF
1
PGATE
16
CAP
2
VIN
SHUTDOWN 2 15
3
VCC
14
RGND
4
P-DRIVE
NGATE 13
5
VCC
LTC1149-5
PGND
12
6
CT
SGND 11
7
ITH
SHUTDOWN 1 10
8 SENSE–
SENSE+ 9
*HURRICANE LAB HL-KI168M
**IRC LR2512-01-RO40-5
†SUMIDA CD54-220
+
Q1
P-CHANNEL
MTD2955E
L1*
68µH
CIN
100µF
100V
C6
0.1µF
RSENSE**
0.04Ω
VOUT
5V
2.5A
Q2
N-CHANNEL
IRFZ34
D3
MBR380
+
COUT
220µF
10V
OS-CON
SHUTDOWN
R3
100Ω
C5
1000pF
R4
100Ω
1558 TA05
Typical “High Voltage” Application
The maximum main battery voltage is 48V.
The Schottky diode D11 (MBR170) 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 MBR170’s reverse bias leakage current
increases at high temperature.
As shown above, the design must ensure that VBAT does
not force the external P-channel MOSFET’s VGS above its
maximum rating (15V for the MTD2955E) shown during
nonbackup mode.
During nonbackup mode, the LTC1558’s open-drain
BACKUP pin is low. The external 12V Zener and 2N3906
conduct and the MTD2955E’s VGS is clamped at approxi-
mately 12V. During backup, the BACKUP pin floats and the
2N3906’s base voltage is pushed nearer to VBAK. The
MTD2955E is effectively turned off, isolating the main
battery from VBAK during backup.
The main battery pack should have an internal control to
shut itself down once its energy is used up. This prevents
it from deep discharge damage.
17
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