HIGH OPERATING VOLTAGE CMOS VOLTAGE REGULATOR

Rev.1.0

S-812C Series

8

Seiko Instruments Inc.

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 M

Ω 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.

Table 8 Power-off function

Product

type

ON/OFF pin

Internal

circuit

VOUT pin

voltage

Current

consumption

B

“H” : Power on

Operate

Set value

B

“L” : Power off

Halt

When a regulation operation at light load less than 100uA is halted, output voltage

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

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

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 10

Ω 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.

VIN

ON/OFF

VSS

Figure 10