SI91821DH-AD-T1-E3 datasheet(6/10 Pages) VISHAY

No de pièce	SI91821DH-AD-T1-E3

Description	Micropower 300-mA CMOS LDO Regulator With Error Flag

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Fabricant	VISHAY [Vishay Siliconix]

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Si91821

Vishay Siliconix

www.vishay.com

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Document Number: 71614

S-51147–Rev. E, 20-Jun-05

DETAILED DESCRIPTION

The Si91821 is a low drop out, low quiescent current, and very

linear regulator with very fast transient response. It is primarily

designed for battery powered applications where battery run

time is at a premium. The low quiescent current allows

extended standby time while low drop out voltage enables the

system to fully utilize battery power before recharge. The

Si91821 is a very fast regulator with bandwidth exceeding

50 kHz while maintaining low quiescent current at light load

conditions. With this bandwidth, the Si91821 is the fastest

LDO available today. The Si91821 is stable with any output

capacitor type from 1 mF to 10.0 mF. However, X5R or X7R

ceramic capacitors are recommended for best output noise

and transient performance.

VIN

VIN is the input supply pin. The bypass capacitor for this pin

is not critical as long as the input supply has low enough source

impedance. For practical circuits, a 1.0-mF or larger ceramic

capacitor is recommended. When the source impedance is

not low enough and/or the source is several inches from the

Si91821, then a larger input bypass capacitor is needed. It is

required that the equivalent impedance (source impedance,

wire, and trace impedance in parallel with input bypass

capacitor impedance) must be smaller than the input

impedance of the Si91821 for stable operation. When the

source impedance, wire, and trace impedance are unknown,

it is recommended that an input bypass capacitor be used of

a value that is equal to or greater than the output capacitor.

VOUT

VOUT is the output voltage of the regulator. Connect a bypass

capacitor from VOUT to ground. The output capacitor can be

any value from 1.0 mF to 10.0 mF. A ceramic capacitor with

X5R or X7R dielectric type is recommended for best output

noise, line transient, and load transient performance.

GND

Ground is the common ground connection for VIN and VOUT.

It is also the local ground connection for CNOISE, SET, and SD.

SET

SET is not connected internally for the fixed voltage version.

Therefore, it can be connected to GND optionally. For the

adjustable output version, use a resistor divider R1 and R2,

connect R1 from VOUT to SET and R2 from SET to ground. R2

should be in the 25-kW to 150-kW range for low power

consumption, while maintaining adequate noise immunity.

The formula below calculates the value of R1, given the

desired output voltage and the R2 value.

R1 +

VOUT * VSET R2

VSET

(1)

VSET is nominally 1.215 V.

SHUTDOWN (SD)

SD controls the turning on and off of the Si91821. VOUT is

guaranteed to be on when the SD pin voltage equals or is

greater than 1.5 V. VOUT is guaranteed to be off when the SD

pin voltage equals or is less than 0.4 V. During shutdown

mode, the Si91821 will draw less than 2-mA current from the

source. To automatically turn on VOUT whenever the input is

applied, tie the SD pin to VIN.

ERROR

ERROR is an open drain output that goes low when VOUT is

less than 5% of its normal value. As with any open drain output,

an external pull up resistor is needed. This function is active

in shutdown.

The ERROR pin must be left opened if not used.

CNOISE

For low noise application, connect a high frequency ceramic

capacitor from CNOISE to ground. A 0.01-mF or a 0.1-mF X5R

or X7R is recommended.

Numéro de pièce similaire - SI91821DH-AD-T1-E3

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	SI91822DB	119Kb / 10P	Micropower 300-mA CMOS LDO Regulator With Error Flag/Power-On-Reset Rev. A, 15-Oct-01
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Fabricant	No de pièce	Fiches technique	Description
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