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| LTC3703-5_15 Datasheet, PDF (17/32 Pages) Linear Technology – 60V Synchronous Switching Regulator Controller | |||
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LTC3703-5
APPLICATIO S I FOR ATIO
VIN
+
1µF
VIN
LTC3703-5
TG
VCC
SW
DRVCC
BG
+
CIN
L1
R1
Q1
D1
5.1V
VOUT
5V TO
15V
+
COUT
VIN
R1
Q1
+
D1 CIN
5.1V
VIN
LTC3703-5
TG
VCC
SW
DRVCC
BG
D2
ZHCS400
L2
4.7µH
C10
1µF R17
10V
37.4k
1%
SW
LT1613
VIN
FB
SHDN
R17
GND
12.1k
1%
L1
+
COUT
C9
4.7µF
6.3V
VOUT
<5V
BGRTN
37035 F09a
Figure 9a. VCC Generated from 5V < VOUT < 15V
VIN
OPTIONAL VCC
CONNECTION
5V < VSEC < 15V
VIN
LTC3703-5
VCC
TG1
DRVCC
R1
FCB
R2
GND
SW
BG1
BGRTN
+
CIN
R1
Q1
D1
5.1V
N
T1
1
+ VSEC
1µF
VOUT
+
COUT
3703 F09c
Figure 9c. Secondary Output Loop and VCC Connection
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 DRVCC to ensure that the LTC3703-5 has
sufficient gate drive voltage. If the DRVCC voltage falls
BGRTN
3703 F09b
Figure 9b. VCC Generated from VOUT < 5V
VIN (<40V)
+
1µF
+
CIN
VIN
LTC3703-5
TG
VCC
SW
DRVCC
BG
R1
BAT85
Q1
D1
5.1V
BAT85
0.22µF
VN2222LL
BAT85
VOUT
L1
+
COUT
BGRTN
3703 F09d
Figure 9d. Capacitive Charge Pump for VCC (VIN < 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 DRVCC to BGRTN
where BGRTN can be a voltage between ground and â5V.
Why not just keep it simple and always connect BGRTN to
ground? In high voltage switching converters, the switch
37035fa
17
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