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
ON
2V/DIV
VREGIN
2V/DIV
VREGOUT
2V/DIV
VOUT2
2V/DIV
VOUT1
2V/DIV
RESET
5V/DIV
Figure 24. Switching Regulator Hot Swap
its FB or SENSE pin. In the case of the LTC1649, large peak
currents result if the FB pin is at ground and not connected
directly to the output inductor and capacitors. To keep the
peak currents under control, R1, R2 and D1 hold the FB pin
above ground but below its normal regulated value until
VOUT2 ramps up and D1 reverse-biases.
Power N-Channel Selection
The RDS(ON) of the external pass transistors must be low
enough so that the voltage drop across them is 100mV or
less at full current. If the RDS(ON) is too high, the voltage
drop across the transistor can cause the output voltage to
trip the reset circuit. The transistors listed in Table 1 or
other similar transistors are recommended for use with
the LTC1645.
Low voltage applications may require the use of logic-level
FETs; ensure their maximum VGS rating is sufficient for the
application. GATE voltage as a function of VCC is illustrated
in the Typical Performance curves. If lower GATE drive is
desired, connect a diode in series with a zener between
GATE and VCC or between GATE and VOUT as shown in
Figure 25.
Table 1. N-Channel Selection Guide
CURRENT
LEVEL
PART
NUMBER
MANUFACTURER
1A to 2A NDH8503N
Fairchild
1A to 2A
Si6928DQ
Siliconix
2A to 5A
Si4920DY
Siliconix
2A to 5A
IRF7313
5A to 10A
Si4420
International
Rectifier
Siliconix
5A to 10A
FDS6680
Fairchild
5A to 10A
IRF7413
International
Rectifier
5A to 10A MMSF3300 ON Semiconductor
10A to 20A FDB8030L
Fairchild
10A to 20A SUD75N03-04
Siliconix
DESCRIPTION
Dual N-Channel
RDS(ON) = 0.033
SuperSOT-8
Dual N-Channel
RDS(ON) = 0.035
TSSOP-8
Dual N-Channel
RDS(ON) = 0.025
SO-8
Dual N-Channel
RDS(ON) = 0.029
SuperSOT-8
Single N-Channel
RDS(ON) = 0.009
SO-8
Single N-Channel
RDS(ON) = 0.01
SO-8
Single N-Channel
RDS(ON) = 0.011
SO-8
Single N-Channel
RDS(ON) = 0.0125
SO-8
Single N-Channel
RDS(ON) = 0.0035
TO-263AB
Single N-Channel
RDS(ON) = 0.004
D2PAK
R1
Q1
VCC
VOUT
D2
D1* 1N4148
D2
1N4148 D4*
*USER SELECTED VOLTAGE CLAMP
1N4688 (5V)
1N4692 (7V): LOGIC-LEVEL MOSFET
1N4695 (9V)
1N4702 (15V): STANDARD-LEVEL MOSFET
Figure 25. Optional Gate Clamp
1645 F25
21
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