S-1137 Datasheet, PDF (20/47 Pages) Seiko Instruments Inc – HIGH RIPPLE-REJECTION LOW DROPOUT SOFT-START FUNCTION CMOS VOLTAGE REGULATOR

HIGH RIPPLE-REJECTION LOW DROPOUT SOFT-START FUNCTION CMOS VOLTAGE REGULATOR
S-1137 Series
Rev.2.1_01
4. Discharge shunt function (S-1137 Series A / B types)
The S-1137 Series A / B types have a built-in discharge shunt circuit to discharge the output capacitance. When the
ON / OFF pin is set to OFF level, turns the output transistor off, and turns the discharge shunt circuit on so that the
output capacitor discharges. These types allow for the VOUT pin reach the VSS level faster than the S-1137 Series C /
D types that does not have a discharge shunt circuit.
Output transistor : OFF
*1
VIN
S-1137 Series
VOUT
Discharge shunt circuit
: ON
ON / OFF
ON / OFF circuit
ON / OFF Pin: OFF
*1
Current flow
Output
capacitor
(C_L)
VSS
*1. Parasitic diode
Figure 19
GND
5. Overcurrent protection circuit
The S-1137 Series has an overcurrent protection circuit having the characteristics shown in “(1) Output Voltage vs.
Output Current (When Load Current Increases) (Ta = 25°C)” in “ Characteristics (Typical Data)”, in order to
protect the output transistor against an excessive output current and short circuiting between the VOUT and VSS pins.
The current when the output pin is short-circuited (Ishort) is internally set at approx. 150 mA typ., and the normal value is
restored for the output voltage, if releasing a short circuit once.
Caution This overcurrent protection circuit does not work as for thermal protection. If this IC long keeps
short circuiting inside, pay attention to the conditions of input voltage and load current so that,
under the usage conditions including short circuit, the loss of the IC will not exceed power
dissipation of the package.
6. Pull-down resistor (S-1137 Series A / C types)
In the S-1137 Series A / C types, the ON / OFF pin is internally pulled down to the VSS pin in the floating status, so the
VOUT pin is set to the VSS level.
IC’s current consumption increases as much as current flows into the pull-down resistor of 2.2 MΩ typ. when the ON /
OFF pin is connected to the VIN pin and the S-1137 Series A / C types is operating.
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