LTC1422C データシートの表示（PDF） - Linear Technology
部品番号
コンポーネント説明
メーカー
LTC1422C Datasheet PDF : 16 Pages
| |||
LTC1422
APPLICATIONS INFORMATION
R1
Q1
VCC
+
VOUT
CLOAD
R2
ON/RESET
8
10k 10k
10k
VCC
2 ON
Q4
Q3
REF
TIMER
Q2
3
C2
Q2: 2N7002LT1
Q3, Q4: MMBT3904LT1
7
6
SENSE GATE FB 5
LOGIC
+
COMP 5
–
1
LTC1422
4
C1
R3
R4
RESET
1422 F09
Figure 9. ON Pin Circuitry
5V OUT
3.3V OUT
VIN
3.3V
CURRENT LIMIT: 5A
VIN
5V
R2
0.01Ω
5%
LTC1422
RESET 1 RESET VCC 8
ON 2 ON SENSE 7
3 TIMER GATE 6
C1
0.33µF
16V
4 GND
FB 5
Q1
1/2 Si9436
R3
10Ω
5%
R1
10k
5%
C3
0.047µF
25V
Q2
1/2 Si99436
R7
10Ω
5%
D1
1N4148
VOUT
+
3.3V
CLOAD
VOUT
+
5V
CLOAD
R6
R4
1M
2.74k
5%
1%
C2
0.022µF
25V
TRIP POINT: 4.6V
R5
1k
1%
1422 F10
Figure 10. Switching 5V and 3.3V
and C3 are used to set the rise and fall delays on the 5V
supply. Next, the 3.3V supply ramps up with a 20ms delay
set by R6 and C2. On the falling edge, the 3.3V supply
ramps down first because R6 is bypassed by the diode D1.
Using the LTC1422 as a Linear Regulator
The LTC1422 can be used to Hot Swap the primary supply
and generate a secondary low dropout regulated supply.
Figure 11 shows how to switch a 5V supply and create a
3.3V supply using the reset comparator and one addi-
tional transistor. The FB pin is used to monitor the 3.3V
output. When the voltage on the gate of Q2 increases, the
3.3V increases. At the 3.3V threshold, the reset compara-
tor will trip. The RESET pin goes high which turns on Q3.
This lowers the voltage on the gate of Q2. This feedback
loop is compensated by the capacitor C1 and the resistors
R6 and R7.
Hot Swapping 48V DC/DC Module with
Active Low On/Off Control Signal
Using a 7.5V Zener and a resistor, the LTC1422 can switch
supplies much greater than the 12V VCC pin rating. As
shown in Figure 12, the switching FET Q1 is connected as
a common source driver rather than the usual source
follower used in previous applications. This allows the
ground of the LTC1422 to sit at the negative terminal of the
48V input. The clamp circuit of R5 and D1 provides power
to the LTC1422. The resistive divider R1 and R2 at the ON
pin monitors the input supply. The switching FET Q1 is
prevented from turning on until the input supply is at least
38V. Using the reset comparator to monitor the gate
voltage allows the module to be turned on after the gate
has reached a minimum level plus one timing cycle. A high
voltage transistor Q2 is used to translate the RESET signal
to the module On/Off input.
10
Share Link: 