TIME

TIME

SIMULTANEOUS START UP

RATIOMETRIC START UP

=

1

R

VOUT2

OUT1

2

OUT

V

x

8

.

0

<

V

(

) x

-1

=

1

R

2

R

V

1

OUT

2

R

x

-1

V

2

OUT

V

8

.

0

¸

¹

·

¨

©

§

¸

¨

LM20133, LM20133Q

SNVS526F – OCTOBER 2007 – REVISED MARCH 2013

www.ti.com

Figure 36. Common Start Up Sequences

A simultaneous start up is preferred when powering most FPGAs, DSPs, or other microprocessors. In these

simultaneous start up provides a more robust power up for these applications since it avoids turning on any

parasitic conduction paths that may exist between the core and the I/O pins of the processor.

The second most common power on behavior is known as a ratiometric start up. This start up is preferred in

applications where both supplies need to be at the final value at the same time.

Similar to the Soft-Start function, the fastest start up possible is 1 ms regardless of the rise time of the tracking

voltage. When using the track feature the final voltage seen by the SS/TRACK pin should exceed 1V to provide

sufficient overdrive and transient immunity.

20

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