LT8705
APPLICATIONS INFORMATION
Supercapacitor Backup Supply
TO
LOADS
L1
2.2µH
D
IN
25mΩ
25mΩ
M4
M1
V
V
IN
12V
OUT
15V
+
+
C
C
IN2
×3
C
C
IN1
M2
M3
OUT1
OUT2
×2
×2
×3
TO
DIODE D
TO
DIODE D
B1
0.22µF
B2
C
1.2k
SC
×6
0.22µF
×6
3mΩ
2Ω
2Ω
115k
TG1 BOOST1 SW1 BG1 CSP CSN
CSNIN
CSPIN
GND BG2 SW2 BOOST2 TG2
CSPOUT
CSNOUT
V
EXTV
CC
IN
SHDN
SWEN
LDO33
MODE
FBIN
RT
FBOUT
INTV
10k
CC
CC
100k
4.7µF
B2
GATEV
LT8705
4.7µF
SRVO_FBIN
SRVO_FBOUT
SRVO_IIN
4Ω
D
D
B1
TO
TO
15V
1µF
113k
71.5k
20k
SS
SRVO_IOUT
IMON_IN
BOOST1 BOOST2
2N3904
20k
IMON_OUT
V
CLKOUT
SYNC
C
24k
1k
124k
14.3k
100nF
100nF
47.5k
350kHz
4.7µF
1µF
220pF
15nF
8705 TA02a
C
C
C
, C
: 100µF, 20V SANYO OS-CON 205A100M
: 22µF, 25V, TDK C4532X741E226M
D
D
: APPROPRIATE 2A SCHOTTKY DIODE OR IDEAL
DIODE SUCH AS LTC4358, LTC4412, LTC4352, ETC.
B1 B2
IN1 OUT2
IN
, C
IN2 OUT1
: 60F, 2.5V COOPER BUSSMAN HB1840-2R5606-R
, D : CENTRAL SEMI CMMR1U-02-LTE
SC
L1: 2.2µH, VISHAY IHLP-5050CE-01-2R2-M-01
M1-M4: FAIRCHILD FDMS7698
12V LOADS
LOADS
113k
POWER FLOW
POWER FLOW
25mΩ
D
IN
D
IN
25mΩ
25mΩ
25mΩ
0V
INPUT
12V
INPUT
C
C
1.2k
1.2k
1.2k
1.2k
1.2k
1.2k
SC
C
C
1.2k
1.2k
1.2k
1.2k
1.2k
1.2k
8705 TA02
SC
LIMIT
INPUT CURRENT
IN EXCESS OF 2A
WILL DRAW FROM
SUPER CAPS
115k
10k
113k
20k
CAPACITOR
CHARGING
CURRENT
TO 1A
REGULATE LOADS
TO 8V
20k
SC
SC
SC
SC
SC
SC
115k
C
C
C
C
C
C
C
C
REGULATE CAPACITORS
TO 15V
10k
SC
SC
SC
SC
8705 TA02
Charging VOUT to 15V
with 1A Current
Remove VIN. Loads (4A Draw)
Regulated to 8V from Supercaps
V
OUT
15V
5V/DIV
V
IN
5V/DIV
V
V
IN
8V
5V/DIV
OUT
5V/DIV
I
I
L
L
5A/DIV
5A/DIV
8705 TA02d
8705 TA02e
20SEC/DIV
3SEC/DIV
8705p
41
For more information www.linear.com/8705
Linear [ Linear ]
