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LP3991

SNVS296J – DECEMBER 2006 – REVISED JUNE 2016

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Copyright © 2006–2016, Texas Instruments Incorporated

Feature Description (continued)

7.3.2 Maximum Supply Voltage and Thermal Considerations

Maximum recommended input voltage is 3.6 V. The device may be operated at 4-V VIN if proper care is given to

the board design in regard to thermal dissipation. As a guide, refer to Table 1 for ambient temperature at two

input voltages and two load currents for the example board types.

Table 1. Example Board Ambient Temperatures

RθJA

VIN

VOUT

IOUT

PD

AMBIENT TEMPERATURE

189ºC/W

3.6 V

2.8 V

160 mA

0.13 W

100ºC

250 mA

0.20 W

87ºC

4 V

2.8 V

160 mA

0.19 W

89ºC

250 mA

0.30 W

68ºC

160ºC/W

3.6 V

2.8 V

160 mA

0.13 W

104ºC

250 mA

0.20 W

93ºC

4 V

2.8 V

160 mA

0.19 W

94ºC

250 mA

0.30 W

77ºC

7.4 Device Functional Modes

7.4.1 Enable Control

The LP3991 features an active high enable (EN) pin, which turns the device on when pulled high. When not

enabled the regulator output is off and the device typically consumes 2 nA.

If the application does not require the enable switching feature, the EN pin must be tied to VIN to keep the

regulator output permanently on.

To ensure proper operation, the signal source used to drive the EN input must be able to swing above and below

the specified turnon/off voltage thresholds listed in Typical Characteristics under VIL and VIH.