Datasheet

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SLVS401 − AUGUST 2001
12
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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
UVLO − Undervoltage Lockout − V
UNDERVOLTAGE LOCKOUT
vs
JUNCTION TEMPERATURE
T
J
− 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.