LP2986 Datasheet, PDF (14/33 Pages) National Semiconductor (TI) – Micropower, 200 mA Ultra Low-Dropout Fixed or Adjustable Voltage Regulator

LP2986
SNVS137I – MARCH 1999 – REVISED SEPTEMBER 2015
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Feature Description (continued)
7.3.2 Error Detection Comparator Output
The LP2989 will generate a logic low output whenever its output falls out of regulation by more than
approximately 5% below nominal. Because the ERROR comparator has an open-collector output, an external
pull-up resistor is required to pull the output up to V_OUT or another supply voltage (up to 16 V). The output of the
comparator is rated to sink up to 300 µA. If ERROR pin is not used, it can be left open.
Because the ERROR comparator has an open-collector output, an external pull-up resistor is required to pull the
output up to VOUT or another supply voltage (up to 16 V). The output of the comparator is rated to sink up to
300 µA. If ERROR pin is not used, it can be left open.
7.3.3 Thermal Protection
The device contains a thermal shutdown protection circuit to turn off the output current when excessive heat is
dissipated in the LDO. The circuitry is not intended to replace proper heat sinking. Continuously running the
device into thermal shutdown degrades its reliability.
7.3.4 Short-Circuit Protection (Current Limit)
The internal current limit circuit is used to protect the LDO against high-load current faults or shorting events. The
LDO is not designed to operate in a steady-state current limit. During a current-limit event, the LDO sources
constant current. Therefore, the output voltage falls when load impedance decreases. Note also that if a current
limit occurs and the resulting output voltage is low, excessive power may be dissipated across the LDO, resulting
in a thermal shutdown of the output.
7.4 Device Functional Modes
7.4.1 Shutdown Mode
The LP2986 is shut off by driving the shutdown input low, and turned on by pulling it high. If this feature is not to
be used, the SHUTDOWN input should be tied to V_IN to keep the regulator output on at all times.
To assure proper operation, the signal source used to drive the SHUTDOWN input must be able to swing above
and below the specified turnon/turnoff voltage thresholds listed as V_H and V_L, respectively (see Typical
Characteristics).
Since the SHUTDOWN input comparator does not have hysteresis, It is also important that the turnon (and
turnoff) voltage signals applied to the SHUTDOWN input have a slew rate which is not less than 40 mV/µs when
moving between the V_H and V_L thresholds.
CAUTION
The regulator output state (either On or Off) cannot be specified if a slow-moving AC
(or DC) signal is applied that is in the range between V_H and V_L.
7.4.2 Fixed or Adjustable Regulated Output
A unique feature of the LP2986 device is its ability to output either a fixed voltage or an adjustable voltage,
depending on the external pin connections. To output the internally programmed fixed voltage, tie the SENSE pin
to the OUTPUT pin and the FEEDBACK pin to the TAP pin.
Alternatively, a user-programmable voltage ranging from the internal reference to a 16-V maximum can be set by
using an external resistor divider pair. The resistor divider is tied to V_OUT, and the divided-down voltage is tied
directly to FEEDBACK for comparison against the internal voltage reference. To satisfy the steady-state condition
in which its two inputs are equal, the error amplifier drives the output to equal to Equation 1. For detailed
information see Application and Implementation.
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