HIGH RIPPLE-REJECTION AND LOW DROPOUT CMOS VOLTAGE REGULATOR
S-L2980 Series
Rev.4.1_00
Operation
1. Basic Operation
Figure 11 shows the block diagram of the S-L2980 Series.
The error amplifier compares the reference voltage (Vref) with the Vfb, which is the output voltage
resistance-divided by the feedback resistors Rs and Rf. It supplies the output transistor with the gate
voltage necessary to ensure certain output voltage free of any fluctuations of input voltage and
temperature.
VIN
*1
Current source
Error
VOUT
amplifier
Vref
–
Rf
+
Vfb
Reference voltage circuit
Rs
VSS
*1. Parasitic diode
Figure 11
2. Output Transistor
The S-L2980 Series uses a low on-resistance P-channel MOS FET as the output transistor.
Be sure that VOUT does not exceed VIN+0.3 V to prevent the voltage regulator from being broken due to
inverse current flowing from VOUT pin through a parasitic diode to VIN pin.
11
Seiko Instruments Inc.
SII [ SEIKO INSTRUMENTS INC ]
