S812C Datasheet, PDF (8/26 Pages) Seiko Instruments Inc – HIGH OPERATING VOLTAGE CMOS VOLTAGE REGULATOR

HIGH OPERATING VOLTAGE CMOS VOLTAGE REGULATOR
S-812C Series
Rev.1.0
3. Power-off function (ON/OFF pin)
The ON/OFF pin controls the start and stop of the regulation operation.
When the ON/OFF pin is set to power-off level, halting whole internal circuit and turning off the Pch MOSFET
between VIN and VOUT, current consumption is drastically reduced. The voltage of the VOUT pin becomes
VSS level due to the internal resistance divider of several MΩ between VOUT and VSS.
The ON/OFF pin should not be left afloat since no pull-up nor pull-down is made internally as shown in figure
10. Note that the current consumption increases if a voltage between 0.3V and VIN-0.3V is applied to the
ON/OFF pin. When the power-off function is not used, connect the pin to the VIN pin in case of positive logic
and to the VSS pin in case of negative logic.
VIN
Table 8 Power-off function
Product
type
B
B
ON/OFF pin
“H” : Power on
“L” : Power off
Internal
circuit
Operate
Halt
VOUT pin
voltage
Set value
VSS level
Current
consumption
I_ss
I_ss2
ON/OFF
VSS
When a regulation operation at light load less than 100uA is halted, output voltage
Figure 10
may increase. If the increase of the output voltage should be avoided, pull down the VOUT pin to the V_SS level
as soon as ON/OFF pin goes to the power-down level.
4. Short-circuit protection
Installation of the short-circuit protection which protects the output transistor against short-circuit between
VOUT and VSS can be selected in the S-812C series. The short-circuit protection controls output current as
shown in the typical characteristics, (1) OUTPUT VOLTAGE versus OUTPUT CURRENT, and suppresses
output current at about 40 mA even if VOUT and VSS pins are short-circuited.
The short-circuit protection can not at the same time be a thermal protection. Attention should be paid to the
Input voltage and the load current under the actual condition so as not to exceed the power dissipation of the
package including the case for short-circuit.
When the output current is large and the difference between input and output voltage is large even if not
shorted, the short-circuit protection may work and the output current is suppressed to the specified value.
Products without short-circuit protection can provide comparatively large current by removing a short-circuit
protection.
„ Selection of External Components
Output Capacitor (C_L)
The S-812C series can provide stable operation without output capacitor (C_L) since the regulator has an
internal phase compensation circuit to stabilize operation when the load changes. The transient response of
the regulator, however, changes with the output capacitor and the magnitude of overshoot and undershoot on
output voltage accordingly changes. Please refer to C_L dependence data in “Transient Response
Characteristics” to select suitable value for the capacitor. .
When a tantalum or an aluminum electrolytic capacitor is used, the ESR of the capacitor shall be 10Ω or less.
When an aluminum electrolytic capacitor is used attention should be especially paid to since the ESR of the
aluminum electrolytic capacitor increases at low temperature and possibility of oscillation becomes large.
Sufficient evaluation including temperature characteristics is indispensable.
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Seiko Instruments Inc.