Datasheet
LT3514
21
3514fa
For more information www.linear.com/LT3514
APPLICATIONS INFORMATION
pins (Pins 10, 27) are provided near the V
IN
pins so that
the V
IN
pins can be bypassed to these ground pins. The
SW nodes should be kept as small as possible and kept
far away from the RT/SYNC and FB nodes. Keep the RT/
SYNC node and FB nodes small so that the ground pin
and ground traces will shield them from the SW nodes. If
the user plans on using a SYNC signal to set the oscillator
frequency then the RT/SYNC node should be kept away
from the FB nodes. Include vias near the exposed pad of
the LT3514 to help transfer heat from the LT3514 to the
ground plane. Keep the SW5 pad/trace as far away from
the FB pads as possible.
Overvoltage Transient Protection
Figure 9 shows the complete application circuit for a 3-out
-
put 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 LT3514 with a low resistance
path to V
SUPPLY
. In the event that a supply surge occurs,
3514 F09
8.2µH
CSKY
2.2µF
VSKY
PG
2.2µF
×2
D3
L5
10µH
V
SUPPLY
3.2V TO 30V
SURGE PROTECTION TO 180V
Q1: FQB34N20L
D1: BZT52C36-7-F
D2: BZT52C6V8-7-F
D3: BAT54-7-F
L1: CDRH5D28-4R2
L3: CDRH8D28-4R7
L4: CDRH5D28-8R2
L5: CBC2016100M
0.1µF
18.2k
GND
LT3514
D1
36V
C1
0.1µF
22µF
SKY
SW5
V
IN
V
IN
V
IN
EN/UVLO
PG
RUN/SS1
RUN/SS3
RUN/SS4
RT/SYNC
SW1
DA1
FB1
2.5V/1A
82pF
21.5k
10.2k
22µF
SW3
DA3
FB3
3.3V/2A
47pF
31.6k
10.2k
47µF
SW4
DA4
FB4
5V/1A
22pF
53.6k
10.2k
22µF
4.2µH
L3
L4
L1
4.7µH
+
D2
6.8V
R3
1k
R2
100k
R1
10Ω
Q1
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 LT3514 regulating all three channels
through a 180V surge event without interruption.
Figure 9. Complete Triple Buck Regulator with 180V Surge Protection
Figure 10. Overvoltage Protection Withstands 180V Surge
100ms/DIV
3514 F10
V
OUT1,3,4
2V/DIV
V
SUPPLY
50V/DIV
V
IN
50V/DIV