Datasheet

LT8705
40
8705fb
For more information www.linear.com/LT8705
Supercapacitor Backup Supply
D
IN
12V
INPUT
25mΩ
POWER FLOW
12V LOADS
INPUT CURRENT
IN EXCESS OF 2A
WILL DRAW FROM
SUPER CAPS
25mΩ
LIMIT
CAPACITOR
CHARGING
CURRENT
TO 1A
113k
20k
115k
REGULATE CAPACITORS
TO 15V
1.2kC
SC
C
SC
C
SC
C
SC
C
SC
C
SC
10k
1.2k
1.2k
1.2k
1.2k
1.2k
8705 TA02b
D
IN
0V
INPUT
25mΩ
POWER FLOW
LOADS
25mΩ
113k
20k
115k
1.2k
REGULATE LOADS
TO 8V
C
SC
C
SC
C
SC
C
SC
C
SC
C
SC
10k
1.2k
1.2k
1.2k
1.2k
1.2k
8705 TA02c
V
OUT
5V/DIV
V
IN
5V/DIV
I
L
5A/DIV
20SEC/DIV
8705 TA02d
V
OUT
5V/DIV
V
INP
5V/DIV
I
L
5A/DIV
3SEC/DIV
15V
8705 TA02e
8V
Charging V
OUT
to 15V
with 1A Current
Remove V
IN
. Loads (4A Draw)
Regulated to 8V from Supercaps
8705 TA02a
CSPOUT
CSNOUT
EXTV
CC
FBOUT
INTV
CC
GATEV
CC
SRVO_FBIN
SRVO_FBOUT
SRVO_IIN
SRVO_IOUT
IMON_IN
IMON_OUT
47.5k
SYNCCLKOUT
V
C
14.3k
350kHz
CSNIN
TG1 BOOST1
0.22µF 0.22µF
TO
DIODE D
B1
L1
2.2µH
TO
LOADS
TO
DIODE D
B2
M2
M1
25mΩ
M4
M3
SW1 BG1 CSP CSN
LT8705
GND BG2 SW2 BOOST2
V
OUT
15V
V
IN
12V
TG2
CSPIN
V
IN
SHDN
SWEN
LDO33
MODE
FBIN
RT
SS
15nF
C
IN1
, C
OUT2
: 100µF, 20V SANYO OS-CON 205A100M
C
IN2
, C
OUT1
: 22µF, 25V, TDK C4532X741E226M
C
SC
: 60F, 2.5V COOPER BUSSMAN HB1840-2R5606-R
D
IN
: APPROPRIATE 2A SCHOTTKY DIODE OR IDEAL
DIODE SUCH AS LTC4358, LTC4412, LTC4352, ETC.
D
B1
, D
B2
: CENTRAL SEMI CMMR1U-02-LTE
L1: 2.2µH, VISHAY IHLP-5050CE-01-2R2-M-01
M1-M4: FAIRCHILD FDMS7698
220pF
124k
71.5k
20k1k
1µF
1µF15V
4.7µF
10k
115k
C
IN1
×2
D
IN
V
INP
C
IN2
×3
C
OUT1
×3
C
SC
×6
1.2k
×6
C
OUT2
×2
4Ω
D
B1
D
B2
4.7µF
TO
BOOST1
100k
4.7µF
113k
2Ω 2Ω
3mΩ
20k
1k
+ +
TO
BOOST2
100nF
*INPUT SIDE OVERVOLTAGE PROTECTION WHEN CONVERTER
IS DRAWING CURRENT FROM THE SUPER CAPACITORS
100nF
25mΩ
2N3904*
24k
Typical applicaTions