S1172 Datasheet, PDF (14/35 Pages) Seiko Instruments Inc – HIGH RIPPLE-REJECTION LOW DROPOUT

HIGH RIPPLE-REJECTION LOW DROPOUT HIGH OUTPUT CURRENT CMOS VOLTAGE REGULATOR
S-1172 Series
Rev.2.2_01
 Operation
1. Basic operation
Figure 13 shows the block diagram of the S-1172 Series.
The error amplifier compares the reference voltage (V_ref) with feedback voltage (V_fb), which is the output voltage
resistance-divided by feedback resistors (R_s and R_f). It supplies the gate voltage necessary to maintain the constant
output voltage which is not influenced by the input voltage and temperature change, to the output transistor.
VIN
Current
supply
V_ref
Error
amplifier
−
+
Reference voltage
circuit
*1
R_f
V_fb
R_s
VOUT
VSS
*1. Parasitic diode
Figure 13
2. Output transistor
In the S-1172 Series, a low on-resistance P-channel MOS FET is used as the output transistor.
Be sure that V_OUT does not exceed V_IN + 0.3 V to prevent the voltage regulator from being damaged due to reverse
current flowing from the VOUT pin through a parasitic diode to the VIN pin, when the potential of V_OUT became
higher than V_IN.
14
Seiko Instruments Inc.