TPS51200-Q1

SLUS984A – NOVEMBER 2009 – REVISED APRIL 2012

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APPLICATION INFORMATION

VIN CAPACITOR

Add a ceramic capacitor, with a value between 1.0-

μF and 4.7-μF, placed close to the VIN pin, to stabilize the

bias supply (2.5- V rail or 3.3- V rail) from any parasitic impedance from the supply.

VLDO INPUT CAPACITOR

Depending on the trace impedance between the VLDOIN bulk power supply to the device, a transient increase of

source current is supplied mostly by the charge from the VLDOIN input capacitor. Use a 10-

μF (or greater)

ceramic capacitor to supply this transient charge. Provide more input capacitance as more output capacitance is

OUTPUT CAPACITOR

For stable operation, the total capacitance of the VO output terminal must be greater than 20

μF. Attach three,

10-

μF ceramic capacitors in parallel to minimize the effect of equivalent series resistance (ESR) and equivalent

series inductance (ESL). If the ESR is greater than 2 m

Ω, insert an R-C filter between the output and the VOSNS

input to achieve loop stability. The R-C filter time constant should be almost the same as or slightly lower than

the time constant of the output capacitor and its ESR.

Low VIN Applications

TPS51200 can be used in an application system where either a 2.5-V rail or a 3.3-V rail is available. If only a 5-V

rail is available, TPS51100 can be used instead. The TPS51200 minimum input voltage requirement is 2.375 V.

If a 2.5-V rail is used, ensure that the absolute minimum voltage (both DC and transient) at the device pin is be

2.375 V or greater. The voltage tolerance for a 2.5-V rail input is between –5% and 5% accuracy, or better.

S3 and Pseudo-S5 Support

The TPS51200 provides S3 support by an EN function. The EN pin could be connected to an SLP_S3 signal in

the end application. Both REFOUT and VO are on when EN = high (S0 state). REFOUT is maintained while VO

is turned off and discharged via an internal discharge MOSFET when EN = low (S3 state). When EN = low and

the REFIN voltage is less than 0.390 V, TPS51200 enters pseudo-S5 state. Both VO and REFOUT outputs are

turned off and discharged to GND through internal MOSFETs when pseudo-S5 support is engaged (S4/S5

state). Figure 1 shows a typical startup and shutdown timing diagram for an application that uses S3 and

pseudo-S5 support.

Tracking Startup and Shutdown

The TPS51200 also supports tracking startup and shutdown when EN is tied directly to the system bus and not

used to turn on or turn off the device. During tracking startup, VO follows REFOUT once REFIN voltage is

greater than 0.39 V. REFIN follows the rise of VDDQ rail via a voltage divider. The typical soft-start time for the

VDDQ rail is approximately 3 ms, however it may vary depending on the system configuration. The SS time of

the VO output no longer depends on the OCL setting, but it is a function of the SS time of the VDDQ rail.

PGOOD is asserted 2 ms after VO is within ±20% of REFOUT. During tracking shutdown, VO falls following

REFOUT until REFOUT reaches 0.37 V. Once REFOUT falls below 0.37 V, the internal discharge MOSFETs are

turned on and quickly discharge both REFOUT and VO to GND. PGOOD is deasserted once VO is beyond the

±20% range of REFOUT. Figure 2 shows the typical timing diagram for an application that uses tracking startup

and shutdown.

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Product Folder Link(s): TPS51200-Q1