TPS2149

TPS2159

SLVS401 – AUGUST 2001

12

www.ti.com

TYPICAL CHARACTERISTICS

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

–40 –25 –10

5

20

35

50

65

UNDERVOLTAGE LOCKOUT

vs

JUNCTION TEMPERATURE

TJ – Junction Temperature – °C

Rising

Falling

80

95 110

Figure 16

APPLICATION INFORMATION

external capacitor requirements on power lines

A ceramic bypass capacitor (0.01-

µF to 0.1-µF) between VIN and GND, close to the device, is recommended

to improve load transient response and noise rejection.

A bulk capacitor (4.7-

µF ) between VIN and GND is also recommended, especially if load transients in the

hundreds of milliamps with fast rise times are anticipated.

A 66-

µF bulk capacitor is recommended from OUTx to ground, especially when the output load is heavy. This

precaution helps reduce transients seen on the power rails. Additionally, bypassing the outputs with a 0.1-

µF

ceramic capacitor improves the immunity of the device to short-circuit transients.

LDO output capacitor requirements

Stabilizing the internal control loop requires an output capacitor connected between LDO_OUT and GND. The

minimum recommended capacitance is a 4.7

µF with an ESR value between 200 mΩ and 10 Ω. Solid tantalum

electrolytic, aluminum electrolytic, and multilayer ceramic capacitors are all suitable, provided they meet the

ESR requirements.

overcurrent

A sense FET is used to measure current through the device. Unlike current-sense resistors, sense FETs do not

increase the series resistance of the current path. When an overcurrent condition is detected, the device

maintains a constant output current. Complete shut down occurs only if the fault is present long enough to

activate thermal limiting.

Three possible overload conditions can occur. In the first condition, the output is shorted before the device is

enabled or before VIN has been applied. The TPS2149 and TPS2159 sense the short and immediately switches

to a constant-current output.