Elektronische Bauelemente

STP1117Sxx Series

1.0A Low Dropout Positive

Adjustable or Fixed-Mode Regulator

27-Jun-2017 Rev. B

Page 6 of 6

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Any changes of specification will not be informed individually.

APPLICATION INFORMATION

Output Voltage

The STP1117S develops a 1.25V reference Voltage

Between the output and the adjust terminal. By placing

A resistor between these two terminals, a constant current

Is cause to flow through R1 and down through R2 to set the

Overall output voltage. Normally, this current is chosen to be

the specified minimum load current of 10mA . For fixed voltage

devices R1 and R2 are included in the device.

Load Regulation

When the adjustable regulator is used, load regulation

will be limited by the resistance of the wire connecting the

regulator to the load. The data sheet specification foe load

regulation is measured at the output pin of the device.

Best load regulation is obtained when the top of the

resistor divider (R1) is tied directly to the output pin of the

device not to the load. For fixed voltage, devices the top

of R1 is internally connected to the output, and the ground

pin can be connected to low side of the load. If R1 is

the effective resistance between the regulator and the load

would be:

Input Capacitor

An input capacitor of 10µF or greater is recommended.

Tantalum or aluminum electrolytic capacitors can be used for

bypassing. Larger Values will improve ripple rejection by

bypassing the input to the regulator.

Output Capacitor

The STP1117S requires an output capacitor to maintain stability and improve transient response. Proper

capacitor selection is important to ensure proper operation. The STP1117S output capacitor selection is dependent

upon the ESR (equivalent series resistance) of the output capacitor to maintain stability. When the output

capacitor is 10µF or greater, the output capacitor should have an ESR less than 1 . This will improve transient

response as well as promote stability. A low-ESR solid tantalum capacitor works extremely well and provides

good transient response and stability over temperature.

Aluminum electrolytics can also be used, as long as the ESR of the capacitor is <1 . The value of the output

capacitor can be increased without limit. Higher capacitance values help to improve transient response and ripple

rejection and reduce output noise.

Ripple Rejection

The curves for Ripple Rejection were generated using an adjustable device with the adjust pin bypassed.

With a 25µF bypassing capacitor, 75dB ripple rejection is obtainable at any output level. The impedance of

the adjust pin capacitor, at the ripple frequency, should be <R1. R1 is normally in the range of 100W to

200W. The size of the required adjust pin capacitor is the function of the input ripple frequency. At 120Hz,

with R1=100 ,the adjust pin capacitor should be 13µF. For fixed voltage devices and adjustable devices

without an adjust pin capacitor, the output ripple will increase as the ratio of the output voltage to the reference