LT3742 Просмотр технического описания (PDF) - Linear Technology
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LT3742 Datasheet PDF : 26 Pages
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LT3742
Applications Information
Power Good Indicators
The PG pin is the open-collector output of an internal
window comparator that is pulled low whenever the FB
pin is not within ±10% of the 800mV internal reference
voltage. Tie the PG pin to any supply less than 30V with
a pull-up resistor that will supply less than 200µA. This
pin will be open when the LT3742 is placed in shutdown
mode regardless of the voltage at the FB pin. The power
good indication is valid only when the LT3742 is enabled
(RUN/SS is high) and VIN is 4V or greater.
Output Sequencing and Tracking
The RUN/SS and PG pins can be used together to sequence
the two outputs of the LT3742. Figure 3 shows three
circuits to do this. For the first two cases, controller 1
starts first.
In Figure 2a, controller 2 turns on only after controller
1 has reached within 10% of its final regulation voltage.
A larger value for the soft-start capacitor on RUN/SS2
will provide additional delay between the outputs. One
SHDN
LT3742
RUN/SS1
4.7nF
PG1
RUN/SS2
4.7nF
SHDN (REFERENCE)
VOUT1
5V/DIV
VOUT2
10V/DIV
5ms/DIV
3742 F02a
Figure 2a. Supply Sequencing with Controller 2 Delayed Until After Controller 1 is in Regulation
SHDN
LT3742
RUN/SS1
4.7nF
RUN/SS2
10nF
SHDN (REFERENCE)
VOUT1
5V/DIV
VOUT2
10V/DIV
5ms/DIV
3742 F02b
Figure 2b. Supply Sequencing with Controller 2 Having a Fixed Delay Relative to Controller 1
SHDN
10
LT3742
RUN/SS1
10nF
RUN/SS2
SHDN (REFERENCE)
VOUT1
5V/DIV
VOUT2
10V/DIV
5ms/DIV
Figure 2c. Both Conditions Start Up Together with Ratiometic Tracking
3742 F02c
3742fa
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