POWER MONITORING OUTPUT, 5.5 V INPUT, 100 mA CMOS VOLTAGE REGULATOR WITH 0.5 μA SUPER LOW CURRENT CONSUMPTION
1. Regulator block
1. 1 Basic operation
Figure 15 shows the block diagram of the regulator block to describe the basic operation.
The error amplifier compares the feedback voltage (Vfb) whose output voltage (VOUT) is divided by the feedback
resistors (Rs and Rf) with the reference voltage (Vref). The error amplifier controls the output transistor,
consequently, the regulator starts the operation that holds VOUT constant without the influence of the input
*1. Parasitic diode
1. 2 Output transistor
In the S-1740/1741 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 VOUT constant, the ON resistance of the output transistor
varies appropriately according to the output current (IOUT).
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 VOUT becomes higher than VIN.
Therefore, be sure that VOUT does not exceed VIN + 0.3 V.
1. 3 Overcurrent protection circuit
The S-1740/1741 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-1740/1741
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. For example,
when the output transistor keeps the overcurrent status long at the time of output short-
circuit or due to other reasons, pay attention to the conditions of the input voltage and the
load current so as not to exceed the power dissipation.