Rev.4.1
_00
HIGH RIPPLE-REJECTION AND LOW DROPOUT CMOS VOLTAGE REGULATOR
S-L2980 Series
Operation
1. Basic Operation
Figure 11
shows the block diagram of the S-L2980 Series.
The error amplifier compares the reference voltage (V
ref
) with the V
fb
, which is the output voltage
resistance-divided by the feedback resistors R
s
and R
f
. 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
amplifier
V
ref
–
+
R
f
VOUT
V
fb
Reference voltage circuit
R
s
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 V
OUT
does not exceed V
IN
+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.
Seiko Instruments Inc.
11
SII [ SEIKO INSTRUMENTS INC ]
