S1206 Datasheet, PDF (12/35 Pages) Seiko Instruments Inc – ULTRA LOW CURRENT CONSUMPTION AND

ULTRA LOW CURRENT CONSUMPTION AND LOW DROPOUT CMOS VOLTAGE REGULATOR
S-1206 Series
Rev.3.2_00
 Operation
1. Basic Operation
Figure 11 shows the block diagram of the S-1206 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 11
2. Output Transistor
In the S-1206 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.
3. Overcurrent Protection Circuit
The S-1206 Series includes an overcurrent protection circuit having the characteristics shown in “1. Output Voltage
vs. Output Current (Ta = 25°C)” in “ Characteristics (Typical Data)”, in order to protect the output transistor
against an excessive output current and short circuiting between the VOUT and VSS pins. The current when the
output pin is short-circuited (I_SHORT) is internally set at approx. 130 mA (typ.) (1.2 V ≤ V_OUT < 2.3 V) or approx. 100 mA
(typ.) (2.3 V ≤ V_OUT ≤ 5.2 V), and the normal value is restored for the output voltage, if releasing a short circuit
once.
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 of the package.
12
Seiko Instruments Inc.