MCP1711 datasheet(21/36 Pages) MICROCHIP

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DS20005415C-page 21

MCP1711

4.5

Shutdown Input (SHDN)

The MCP1711 internal circuitry can be shut down via

the signal from the SHDN pin. The SHDN input is an

active-low input signal that turns the LDO on and off.

The shutdown threshold is a fixed voltage level. The

minimum value of this shutdown threshold required to

turn the output on is 0.91V. The maximum value

required to turn the output off is 0.38V.

In Shutdown mode, the VOUT pin will be pulled down to

the ground level via, parallel to feedback resistors and

COUT discharge resistance RDCHG. In this state, the

application is protected from a glitch operation caused

by the electric charge at the output capacitor. More-

over, the discharge time of the output capacitor is set by

the COUT auto-discharge resistance (RDCHG) and the

output capacitor COUT. By setting the time constant of a

COUT auto-discharge resistance value (RDCHG) and the

output capacitor value (COUT) as  =COUT x RDCHG,

the output voltage after discharge via the internal

switch is calculated using Equation 4-1:

EQUATION 4-1:

4.6

Dropout Voltage

Dropout Voltage is defined as the input-to-output volt-

age differential at which the output voltage drops 2%

below the nominal value that was measured with a

VR + 1.0V differential applied. See Section 1.0 “Elec-

trical Characteristics”, for minimum and maximum

voltage specifications.

Note:

The RDCHG depends on VIN; when VIN is

high the RDCHG is low.

VOUT t



VOUT e





–





Where:

VOUT(t) = The output voltage during discharging

VOUT = The initial output voltage

t = Discharge time

 =COUT x RDCHG

 ln



VOUT VOUT t







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