Load

Transient

Line

Transient

NOM

~90%

~85%

Power-Up

~2.25V

~1.55V

~1.25V

~2.50V

Power-Down

1.80V

LP38512-1.8

www.ti.com

SNOSAU7E – NOVEMBER 2007 – REVISED MARCH 2009

ENABLE OPERATION

The Enable ON threshold is typically 1.2V, and the OFF threshold is typically 1.0V. To ensure reliable operation

threshold. The Enable threshold has typically 200mV of hysteresis to improve noise immunity.

The Enable pin (EN) has no internal pull-up or pull-down to establish a default condition and, as a result, this pin

must be terminated either actively or passively.

pull-down resistor to ground, will be required for proper operation. A 1 k

Ω to 100 kΩ resistor can be used as the

pull-up or pull-down resistor to establish default condition for the EN pin. The resistor value selected should be

appropriate to swamp out any leakage in the external single ended device, as well as any stray capacitance.

If the Enable pin is driven from a source that actively pulls high and low (such as a CMOS rail to rail comparator

output), the pull-up, or pull-down, resistor is not required.

pin.

The status of the Enable pin also affects the behavior of the ERROR Flag. While the Enable pin is high the

regulator control loop will be active and the ERROR Flag will report the status of the output voltage. When the

Enable pin is taken low the regulator control loop is shutdown, the output is turned off, and the ERROR Flag pin

is immediately forced low.

ERROR FLAG OPERATION

When the LP38512 Enable pin is high, the ERROR Flag pin will produce a logic low signal when the output

drops by more than 15% (typical) from the nominal output voltage. The drop in output voltage may be due to low

input voltage, current limiting, or thermal limiting. This flag has a built in hysteresis. The output voltage will need

to rise to within 10% (typical) of the nominal output voltage for the ERROR Flag to return to a logic high state. It

should also be noted that when the Enable pin is pulled low, the ERROR Flag pin is forced to be low as well.

The internal ERROR flag comparator has an open drain output stage. Hence, the ERROR pin requires an

external pull-up resistor. The value of the pull-up resistor should be in the range of 10 k

Ω to 1 MΩ. The ERROR

parasitic diode may cause unexpected behavior. The ERROR Flag must be connected to ground if this function

is not used.

The timing diagram in Figure 23 shows the relationship between the ERROR flag and the output voltage.

Figure 23. ERROR Flag Operation, see Typical Application

Copyright © 2007–2009, Texas Instruments Incorporated

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