LTC1645CS View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTC1645CS Datasheet PDF : 24 Pages
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LTC1645
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+ pin is used
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
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 VOUT2. As VOUT2 exceeds
2.75V, RESET releases to allow improved loop transient
response. Figure 20 shows the load transient response
and voltage ripple of the generated supply.
Q1
VIN
0.01Ω* IRF7413
5V
10Ω
BOTH CURRENT LIMITS: 5A
+
CLOAD1
VOUT1
5V
2.5A
0.1µF
25V
Q2
1M
0.01Ω* IRFZ24
VOUT2
3.3V
+ 470µF**
2.5A
6V
10k
10Ω
×2
14 13
12
12
3
VCC1 SENSE1 GATE1
10
ON
VCC2 SENSE2 GATE2
COMP+ 8
LTC1645
9
COMPOUT
4
FAULT
TIMER
(14-LEAD)
6
FB
5
RESET
GND
11
7
0.33µF
C2
R1
0.1µF
2.49k
200k
25V
1%
C1
0.033µF
Q3
PN2222
1.5k
1%
*LRF1206-01-R010-J (IRC)
**T510X477K006AS (KEMET)
12.1k
1%
10k
1%
1645 F19
Figure 19. Switching 5V and Generating 3.3V
VOUT2
0.1V/DIV
2.5A
IOUT2
1A/DIV
0.5A
Figure 20. Load Transient Response and Voltage Ripple
17
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