LM4817 datasheet(11/21 Pages) NSC

11 / 21 page

LDO Typical Performance Characteristics Unless otherwise specified, V

IN =VOUT + 0.5V, CIN =

COUT = 2.2µF, CCC = 33nF, TJ = 25˚C, VSHDN =VIN. (Continued)

Power-Up Response

Power-Down Response

200781B4

200781B5

External Components Description

(Refer to Figure 1 ).

Components

Functional Description

The Inverting input resistance, along with R

f, set the closed-loop gain. Ri, along with Ci, form a high pass

filter with f

c = 1/(2

πR

iCi).

The input coupling capacitor blocks DC voltage at the amplifier’s input terminals. C

i, along with Ri, create a

highpass filter with f

c = 1/(2

πR

iCi). Refer to the section, SELECTING PROPER EXTERNAL

COMPONENTS, for an explanation of determining the value of C

The feedback resistance, along with R

i, set the closed-loop gain.

The supply bypass capacitor. Refer to the POWER SUPPLY BYPASSING section for information about

properly placing, and selecting the value of, this capacitor.

The capacitor, C

B, filters the half-supply voltage present on the BYPASS pin. Refer to the SELECTING

PROPER EXTERNAL COMPONENTS section for information concerning proper placement and selecting

B’s value.

Combined with R

2, sets the LDO’s output voltage according to the following equation:

1 =R2 ((VOUT / 1.25V) -1)

Combined with R

1, sets the LDO’s output voltage according to the following equation:

2 = (1.25V x R1)/(VOUT - 1.25V)

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