LTC1645 Linear Technology, LTC1645 Datasheet - Page 17

• Manufacturer Part Number: LTC1645
• Description: Dual-Channel Hot Swap Controller/Power Sequencer
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
Using the LTC1645 as a Linear Regulator
This application uses the LTC1645 to Hot Swap one
primary supply and generate a secondary low dropout
regulated supply. Figure 19 shows how to switch a 5V
supply and create a 3.3V supply using the spare compara-
tor and one additional transistor. The COMP
to monitor the 3.3V output. As the voltage on the gate of
Q2 increases, the 3.3V output increases. At the 3.3V
threshold the spare comparator trips. The COMPOUT pin
V
5V
IN
U
10
4
10k
ON
FAULT
U
V
CC1
0.01 *
1A/DIV
0.1V/DIV
14
TIMER
I
SENSE1
OUT2
V
OUT2
13
11
2.5A
0.5A
Figure 20. Load Transient Response and Voltage Ripple
0.33 F
W
IRF7413
GATE1
Q1
(14-LEAD)
LTC1645
10
12
Figure 19. Switching 5V and Generating 3.3V
V
CC2
0.1 F
25V
0.01 *
+
1
SENSE2
pin is used
U
GND
2
7
COMPOUT
IRFZ24
COMP
GATE2
RESET
Q2
3
BOTH CURRENT LIMITS: 5A
10
FB
+
8
9
6
5
goes high which turns on Q3. This lowers the voltage on
the gate of Q2. This feedback loop is compensated by
capacitors C1 and C2 and resistor R1. When power is first
applied, the FB pin is low and RESET holds one side of C2
low, slowing the ramp-up of V
2.75V, RESET releases to allow improved loop transient
response. Figure 20 shows the load transient response
and voltage ripple of the generated supply.
Q3
PN2222
R1
200k
**
*
LRF1206-01-R010-J (IRC)
T510X477K006AS (KEMET)
1M
C2
0.1 F
25V
2.49k
1%
1.5k
1%
+
C1
0.033 F
+
470 F**
6V
C
2
LOAD1
OUT2
12.1k
1%
10k
1%
1645 F19
V
5V
2.5A
V
3.3V
2.5A
. As V
OUT1
OUT2
LTC1645
OUT2
exceeds
17