STP1117SXX Datasheet, PDF (6/6 Pages) SeCoS Halbleitertechnologie GmbH – 1.0A Low Dropout Positive Adjustable or Fixed-Mode Regulator

Elektronische Bauelemente
STP1117Sxx Series
1.0A Low Dropout Positive
Adjustable or Fixed-Mode Regulator
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
connected to the load, R_P is multiplied by the divider ratio,
the effective resistance between the regulator and the load
would be:
R_P × (1 + R2/R1), R_P = Parasitic Line Resistance
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 1Ω. 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 <1Ω. 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=100Ω,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
voltage (V_OUT /V_REF).
http://www.SeCoSGmbH.com/
27-Jun-2017 Rev. B
Any changes of specification will not be informed individually.
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