SS/TRK

R1

R2

EN

LM20343

External

Power Supply

- 1

EN

LM20343

External

Power Supply

LM20343

www.ti.com

SNVS559B – MAY 2008 – REVISED APRIL 2013

Figure 29. Sequencing LM20343 with Precision Enable

resistor will be selected to be between 10 k

be solved using the equation below to set the desired turn-on voltage.

(10)

The LM20343 features an open drain power good (PGOOD) pin to sequence external supplies or loads and to

the PGOOD tolerance window. Typical values for this resistor range from 10 k

Ω to 100 kΩ.

TRACKING AN EXTERNAL SUPPLY

By using a properly chosen resistor divider network connected to the SS/TRK pin, as shown in Figure 30, the

output of the LM20343 can be configured to track an external voltage source to obtain a simultaneous or

ratiometric start up.

Figure 30. Tracking an External Supply

10 k

Ω to minimize the errors in the tracking output. Once a value for R2 is selected the value for R1 can be

calculated using appropriate equation in Figure 31, to give the desired start up. Figure 30 shows two common

start up sequences; the top waveform shows a simultaneous start up while the waveform at the bottom illustrates

a ratiometric start up.

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Product Folder Links: LM20343