Datasheet

LT3504
19
3504fa
For more information www.linear.com/LT3504
Overvoltage Transient Protection
Figure 9 shows the complete application circuit for a
4-output step-down regulator with 100% duty cycle
operation that withstands 180V surges. Under normal
operating conditions (V
IN
< 33V), the V
SKY
rail supplies
gate drive to MOSFET Q1, providing the LT3504 with a low
applicaTions inForMaTion
resistance path to V
SUPPLY
. In the event that a supply surge
occurs, Zener diode D1 clamps Q1’s gate voltage to 36V.
The source-follower configuration prevents V
IN
from rising
any further than about 33V (a V
GS
below the Zener clamp
voltage ). Figure 10 shows the LT3504 regulating all four
channels through a 180V surge event without interruption.
SW4
DA4
FB4
SW3
DA3
FB3
SW2
DA2
FB2
SW1
DA1
FB1
SW5
EN/UVLO
V
IN
V
IN
V
IN
V
IN
RUN/SS1
RUN/SS2
RUN/SS3
RUN/SS4
RT/SYNC
5V/1A
L4
8.2µH
D3
D4
D5
D6
D7
53.6k
R2
100k
10.2k
10µF
3.3V/1A
L3
8.2µH
L5
10µH
31.6k
10.2k
R3
1k
10Ω
10µF
2.2µF
C1
0.1µF
V
SUPPLY
3.2V to 30V
SURGE PROTECTION TO 180V
0.1µF
C2
22µF
1µF
×4
2.5V/1A
L2
4.2µH
21.5k
10.2k
22µF
22pF
D2
6.8V
D1
36V
Q1
43pF
82pF
100pF
1.8V/1A
L1
4.2µH
12.7k
10.2k
18.2k
f
SW
= 1MHz
22µF
GND
LT3504
+
SKY
V
IN
C1: Sanyo 50CE22BS
D1: BZT52C36-7-F
D2: BZT52C6V8-7-F
D3: BAT54-7-F
D4–D7: ON SEMI MBRM140T3
L3, L4: SUMIDA CDRH5D28-8R2 (8.2µH)
L1, L2: CDRH5D28-4R2 (4.2µH)
L5: TAIYO YUDEN CBC2016T100M (10µH)
Q1: FQB34N20L
3504 F09
3504 F10
100ms/DIV
V
OUT1,2,3,4
2V/DIV
V
SUPPLY
50V/DIV
V
IN
50V/DIV
Figure 9. Complete Quad Buck Regulator with 180V Surge Protection
Figure 10. Overvoltage Protection Withstands 180V Surge