S1155 Datasheet, PDF (14/28 Pages) Seiko Instruments Inc – HIGH RIPPLE-REJECTION LOW DROPOUT

HIGH RIPPLE-REJECTION LOW DROPOUT HIGH OUTPUT CURRENT CMOS VOLTAGE REGULATOR
S-1155 Series
Rev.2.1_01
3. ON/OFF pin
This pin starts and stops the regulator.
When the ON/OFF pin is set to OFF level, the entire internal circuit stops operating, and the built-in P-channel MOS
FET output transistor between the VIN pin and the VOUT pin is turned off, reducing current consumption
significantly. The VOUT pin is set to the V_SS level by the internal dividing resistor of several hundred kΩ between
the VOUT pin and the VSS pin.
Note that the current consumption increases when a voltage of 0.3 V to 1.0 V is applied to the ON/OFF pin.
The ON/OFF pin is configured as shown in Figure 12. Since the ON/OFF pin is neither pulled down nor pulled up
internally, do not use it in the floating status. When not using the ON/OFF pin, connect it to the VSS pin in the
product A type, and connect it to the VIN pin in B type.
Table 6
Product Type
A
A
B
B
ON/OFF Pin
“L”: ON
“H”: OFF
“L”: OFF
“H”: ON
Internal Circuit
Operate
Stop
Stop
Operate
VOUT Pin Voltage
Set value
V_SS level
V_SS level
Set value
Current Consumption
I_SS1
I_SS2
I_SS2
I_SS1
VIN
ON/OFF
VSS
Figure 12
4. Overcurrent protection circuit
The S-1155 Series includes an overcurrent protection circuit having the characteristics shown in “1. Output
Voltage vs. Output Current (When load current increases) (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 pin
and the VSS pin. The current when the output pin is short-circuited (I_SHORT) is internally set at approx. 200 mA typ.,
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 the load current so
that, under the usage conditions including short circuit, the loss of the IC will not exceed power
dissipation of the package.
14
Seiko Instruments Inc.