S-818_1 Datasheet, PDF (13/32 Pages) Seiko Instruments Inc – LOW DROPOUT CMOS VOLTAGE REGULATOR

Rev.2.1_00
LOW DROPOUT CMOS VOLTAGE REGULATOR
S-818 Series
3. ON/OFF pin (Shutdown pin)
This pin activates and inactivates the regulator.
When the ON/OFF pin is switched to the shutdown level, the operation of all internal circuit stops, the
built-in Pch MOS FET output transistor between VIN and VOUT pin is switched off, suppressing current
consumption. The VOUT pin goes to the Vss level due to internal divided resistance of several MΩ
between VOUT pin and VSS pin.
The structure of the ON/OFF pin is shown in Figure 13. Since the ON/OFF pin is neither pulled down nor
pulled up internally, do not keep it in the floating state. Current consumption increases if a voltage of
0.3 V to V_IN−0.3 V is applied to the ON/OFF pin. When the shutdown pin is not used, connect it to the VIN
pin for product type "A" and to the VSS pin for product type "B".
Product type
A
A
B
B
Table 6 ON/OFF pin function by product type
ON/OFF pin
“H”: Power on
“L”: Shutdown
“H”: Shutdown
“L”: Power on
Internal circuit
Operating
Stop
Stop
Operating
VOUT pin voltage
Set value
VSS level
VSS level
Set value
Current consumption
I_ss1
I_ss2
I_ss2
I_ss1
VIN
ON/OFF
VSS
Figure 13 The structure of the ON/OFF Pin
„ Selection of Output Capacitor (C_L)
The S-818 Series needs an output capacitor between VOUT pin and VSS pin for phase compensation. A
small ceramic or an OS electrolyte capacitor of 2 µF or more can be used. When a tantalum or an
aluminum electrolyte capacitor is used, the capacitance must be 2 µF or more and the ESR must be 10 Ω
or less.
Attention should be paid not to cause an oscillation due to increase of ESR at low temperatures when an
aluminum electrolyte capacitor is used.
Evaluate the performance including temperature characteristics before prototyping the circuit.
Overshoot and undershoot characteristics differ depending upon the type of the output capacitor. Refer
to the “C_L dependence” data in “„ Transient Response Characteristics”.
Seiko Instruments Inc.
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