S1172 Datasheet, PDF (16/35 Pages) Seiko Instruments Inc – HIGH RIPPLE-REJECTION LOW DROPOUT

HIGH RIPPLE-REJECTION LOW DROPOUT HIGH OUTPUT CURRENT CMOS VOLTAGE REGULATOR
S-1172 Series
Rev.2.2_01
5. Thermal shutdown circuit
The S-1172 Series has a thermal shutdown circuit to protect the device from damage due to overheat. When the
junction temperature rises to 150°C typ., the thermal shutdown circuit operates to stop regulating. When the
junction temperature drops to 120°C typ., the thermal shutdown circuit is released to restart regulating.
Due to self-heating of the S-1172 Series, if the thermal shutdown circuit starts operating, it stops regulating so that
the output voltage drops. When regulation stops, the S-1172 Series does not itself generate heat so that the IC’s
temperature drops. When the temperature drops, the thermal shutdown circuit is released to restart regulating, thus
the S-1172 Series generates heat again. Repeating this procedure makes waveform of the output voltage pulse-like
form. Stop or restart of regulation continues unless decreasing either or both of the input voltage and the output
current in order to reduce the internal power consumption, or decreasing the ambient temperature.
Table 9
Thermal Shutdown Circuit
Operation: 150°C typ.^*1
Release: 120°C typ.^*1
*1. Junction temperature
VOUT Pin Voltage
V_SS level
Set value
6. Inrush current limit circuit
The S-1172 Series has a built-in inrush current limit circuit to limit the inrush current generated at power-on or at
the time when the ON/OFF pin is set to ON. This circuit limits the inrush current (500 mA, typ.) immediately after
power-on or from the time when the ON/OFF pin is set to ON until the specified time (100 μs min.) which is set
internally.
Caution
The junction temperature drops to 120°C typ. by the operation of thermal shutdown circuit, after
stopping regulation, the circuit is released to restart regulation; in this case, note that the period
to limit inrush current may become shorter (10 μs min.).
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Seiko Instruments Inc.