S-1317A10-M5T1U4 Datasheet, PDF (12/31 Pages) Seiko Instruments Inc – Built-in overcurrent protection circuit

5.5 V INPUT, 100 mA CMOS VOLTAGE REGULATOR WITH 0.35 μA SUPER LOW CURRENT CONSUMPTION
S-1317 Series
Rev.1.0_00
 Operation
1. Basic operation
Figure 9 shows the block diagram of the S-1317 Series to describe the basic operation.
The error amplifier compares the feedback voltage (V_fb) whose output voltage (V_OUT) is divided by the feedback
resistors (R_s and R_f) with the reference voltage (V_ref). The error amplifier controls the output transistor,
consequently, the regulator starts the operation that holds V_OUT constant without the influence of the input voltage
(V_IN).
VIN
Current
Supply
V_ref
Error amplifier
−
+
Reference voltage
circuit
*1
R_f
V_fb
R_s
VOUT
VSS
*1. Parasitic diode
Figure 9
2. Output transistor
In the S-1317 Series, a low on-resistance P-channel MOS FET is used between the VIN pin and the VOUT pin as
the output transistor. In order to keep V_OUT constant, the ON resistance of the output transistor varies appropriately
according to the output current (I_OUT).
Caution Since a parasitic diode exists between the VIN pin and the VOUT pin due to the structure of the
transistor, the IC may be damaged by a reverse current if V_OUT becomes higher than V_IN.
Therefore, be sure that V_OUT does not exceed V_IN + 0.3 V.
3. Overcurrent protection circuit
The S-1317 Series has a built-in overcurrent protection circuit to limit the overcurrent of the output transistor.
When the VOUT pin is shorted to the VSS pin, that is, at the time of the output short-circuit, the output current is
limited to 60 mA typ. due to the overcurrent protection circuit operation. The S-1317 Series restarts regulating
when the output transistor is released from the overcurrent status.
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.
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