TPS2145, TPS2147

TPS2155, TPS2157

SLVS333 − AUGUST 2001

15

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 17

APPLICATION INFORMATION

external capacitor requirements on power lines

Ceramic bypass capacitors (0.01-

µ to 0.1-µ) between VIN/SWIN1 and GND and SWIN2 and GND, close to the

device, are recommended to improve load transient response and noise rejection.

Bulk capacitors ( 4.7-

µF) between VIN/SWIN1 and GND and between SWIN2 and GND are 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.

The adjustable LDO (for voltages lower than 3 V) requires a bypass capacitor across the feedback resistor as

shown in Figure 18. The value of this capacitor is determined by using the following equation:

C

f

+

1

2

3.14

R1)

* 4pf

where R1 is derived by programming the adjustable LDO (see programming the adjustable LDO regulator

section shown below).

(1)