S1131 Datasheet, PDF (14/30 Pages) Seiko Instruments Inc – HIGH RIPPLE-REJECTION AND LOW DROPOUT

HIGH RIPPLE-REJECTION LOW DROPOUT MIDDLE OUTPUT CURRENT CMOS VOLTAGE REGULATOR
S-1131 Series
Rev.4.1_00
3. ON/OFF pin
In case of product with ON/OFF circuit, 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 becomes the Vss level due to the internally divided
resistance of several hundreds kΩ between the VOUT pin and the VSS pin.
The structure of the ON/OFF pin is as shown in Figure 14. Since the ON/OFF pin is neither pulled down
nor pulled up internally, do not use it in the floating states. In addition, note that the current consumption
increases if a voltage of 0.3 V to V_IN – 0.3 V is applied to the ON/OFF pin. 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.
Product Type
A
A
B
B
ON/OFF Pin
“L”: ON
“H”: OFF
“L”: OFF
“H”: ON
Table 7
Internal Circuit VOUT Pin Voltage
Operate
Set value
Stop
Stop
Operate
V_SS level
V_SS level
Set value
Current Consumption
I_SS1
I_SS2
I_SS2
I_SS1
VIN
ON/OFF
VSS
Figure 14
„ Selection of Output Capacitor (C_L)
The S-1131 Series performs phase compensation using the internal phase compensator in the IC and the
ESR (Equivalent Series Resistance) of the output capacitor to enable stable operation independent of
changes in the output load. Therefore, always place a capacitor (C_L) of 2.2 μF or more between the VOUT
pin and the VSS pin.
For stable operation of the S-1131 Series, it is essential to employ a capacitor whose ESR is within an
optimum range. Using a capacitor whose ESR is outside the optimum range (approximately 0.5 Ω to 5 Ω),
whether larger or smaller, may cause an unstable output, resulting in oscillation. For this reason, a tantalum
electrolytic capacitor is recommended.
When a ceramic capacitor or an OS capacitor with a low ESR is used, it is necessary to connect an
additional resistor that serves as the ESR in series with the output capacitor. The required resistance value
is approximately 0.5 Ω to 5 Ω, which varies depending on the usage conditions, so perform sufficient
evaluation for selection. Ordinarily, around 1.0 Ω is recommended.
Note that an aluminum electrolytic capacitor may increase the ESR at a low temperature, causing
oscillation. When using this kind of capacitor, perform thorough evaluation, including evaluation of
temperature characteristics.
14
Seiko Instruments Inc.