Datasheet LT3742 (Analog Devices) - 10

LT3742
applicaTions inForMaTion Power Good Indicators Output Sequencing and Tracking
The PG pin is the open-collector output of an internal The RUN/SS and PG pins can be used together to sequence window comparator that is pulled low whenever the FB the two outputs of the LT3742. Figure 3 shows three pin is not within ±10% of the 800mV internal reference circuits to do this. For the first two cases, controller 1 voltage. Tie the PG pin to any supply less than 30V with starts first. a pull-up resistor that will supply less than 200µA. This In Figure 2a, controller 2 turns on only after controller pin will be open when the LT3742 is placed in shutdown 1 has reached within 10% of its final regulation voltage. mode regardless of the voltage at the FB pin. The power A larger value for the soft-start capacitor on RUN/SS2 good indication is valid only when the LT3742 is enabled will provide additional delay between the outputs. One (RUN/SS is high) and VIN is 4V or greater. LT3742 RUN/SS1 SHDN (REFERENCE) SHDN 4.7nF VOUT1 5V/DIV PG1 VOUT2 RUN/SS2 10V/DIV 4.7nF 5ms/DIV 3742 F02a
Figure 2a. Supply Sequencing with Controller 2 Delayed Until After Controller 1 is in Regulation
LT3742 RUN/SS1 SHDN 4.7nF SHDN (REFERENCE) VOUT1 5V/DIV RUN/SS2 VOUT2 10V/DIV 10nF 3742 F02b 5ms/DIV
Figure 2b. Supply Sequencing with Controller 2 Having a Fixed Delay Relative to Controller 1
LT3742 RUN/SS1 SHDN (REFERENCE) SHDN 10nF VOUT1 5V/DIV V RUN/SS2 OUT2 10V/DIV 3742 F02c 5ms/DIV
Figure 2c. Both Conditions Start Up Together with Ratiometic Tracking
3742fa 10 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Related Parts