Microcontroller

TPS720xx

TPS62xxx

VIN

EN

SW

FB

IN

OUT

BIAS

EN

GND

2.2mF

10mF

10mH

2.5Vto5.5V

Controltoturnon/offthedc/dc

Outputofdc/dcisfloatingwhen

theTPS62xxxENpinislow

GND

14

TPS720

SBVS100E – JUNE 2008 – REVISED SEPTEMBER 2015

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Product Folder Links: TPS720

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Copyright © 2008–2015, Texas Instruments Incorporated

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

8.1.1 Input and Output Capacitor Requirements

Although an input capacitor is not required for stability on the IN pin, it is good analog design practice to connect

a 0.1-μF to 1-μF low equivalent series resistance (ESR) capacitor across the IN pin input supply near the

regulator. This capacitor counteracts reactive input sources and improves transient response, noise rejection,

and ripple rejection. A higher-value capacitor may be necessary if large, fast rise-time load transients are

anticipated, or if the device is located close to the power source. If source impedance is not sufficiently low, a

0.1-μF input capacitor may be necessary to ensure stability.

The BIAS pin does not require an input capacitor because it does not source high currents. However, if source

impedance is not sufficiently low, then TI recommends a small 0.1-μF bypass capacitor.

The TPS720 is designed to be stable with standard ceramic capacitors with values of 2.2 μF or larger at the

output. X5R- and X7R-type capacitors are best because they have minimal variation in value and ESR over

temperature. Maximum ESR should be less than 250 m

Ω.

8.1.2 Output Regulation With IN Pin Floating

The TPS720 supports a novel feature in which the output of the LDO regulates under light loads when the IN pin

is left floating. Under normal conditions, when the IN pin is connected to a power source, the BIAS pin draws

only tens of milliamperes. However, when the IN pin is floating, an innovative circuit is used that allows a

maximum current of 500 μA to be drawn by the load through the BIAS pin, while maintaining the output in

regulation. This feature is particularly useful in power-saving applications where a DC-DC converter connected to

the IN pin is disabled, but the LDO is required to regulate the output voltage to a light load.

Figure 27 shows an application example where a microcontroller is not turned off (to maintain the state of the

internal memory), but where the regulated supply (shown as the TPS62xxx) is turned off to reduce power. In this

case, the TPS720 BIAS pin provides sufficient load current to maintain a regulated voltage to the microcontroller.

Figure 27. Example of Floating IN Pin Regulation