LTC3703-5
17
37035fa
Figure 9a. V
CC
Generated from 5V < V
OUT
< 15V
APPLICATIO S I FOR ATIO
W
U
U
U
V
CC
DRV
CC
V
IN
TG
SW
BG
BGRTN
LTC3703-5
V
OUT
5V TO
15V
+
C
OUT
37035 F09a
+
C
IN
+
1
µ
F
V
IN
L1
D1
5.1V
R1
Q1
V
CC
DRV
CC
V
IN
TG
SW
BG
BGRTN
LTC3703-5
V
OUT
<5V
+
C
OUT
3703 F09b
+
C
IN
C9
4.7
µ
F
6.3V
V
IN
L1
D1
5.1V
Q1
R1
C10
1
µ
F
10V
V
IN
SW
GND
SHDN
FB
R17
37.4k
1%
R17
12.1k
1%
LT1613
D2
ZHCS400
L2
4.7
µ
H
Figure 9b. V
CC
Generated from V
OUT
< 5V
current to flow at full reverse voltage. If the reverse
current times reverse voltage exceeds the maximum
allowable power dissipation, the diode may be damaged.
For best results, use an ultrafast recovery diode such as
the MMDL770T1.
An internal undervoltage lockout (UVLO) monitors the
voltage on DRV
CC
to ensure that the LTC3703-5 has
sufficient gate drive voltage. If the DRV
CC
voltage falls
V
CC
DRV
CC
FCB
GND
V
IN
TG1
SW
BG1
BGRTN
LTC3703-5
V
OUT
V
SEC
+
C
OUT
+
1
µ
F
3703 F09c
R1
V
IN
T1
OPTIONAL V
CC
CONNECTION
5V < V
SEC
< 15V
R2
+
C
IN
R1
Q1
N
1
D1
5.1V
V
CC
DRV
CC
V
IN
TG
SW
BG
BGRTN
LTC3703-5
V
OUT
+
C
OUT
3703 F09d
+
+
C
IN
V
IN
(<40V)
L1
1
µ
F
Q1
R1
BAT85
BAT85
BAT85
VN2222LL
0.22
µ
F
D1
5.1V
Figure 9c. Secondary Output Loop and V
CC
Connection
Figure 9d. Capacitive Charge Pump for V
CC
(V
IN
< 40V)
below the UVLO threshold, the LTC3703-5 shuts down
and the gate drive outputs remain low.
Bottom MOSFET Source Supply (BGRTN)
The bottom gate driver, BG, switches from DRV
CC
to BGRTN
where BGRTN can be a voltage between ground and –5V.
Why not just keep it simple and always connect BGRTN to
ground? In high voltage switching converters, the switch
