Preliminary
EP1117
Figure 2. Connections for Best Load Regulation
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 EP1117 requires an output capacitor to maintain stability and improve transient response. The EP1117
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 electrolytes can also be used, as long as the ESR of the capacitor is less than 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
22μF 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 100Ω-200Ω. The size of the
required adjust pin capacitor is a function of the input ripple frequency. At 120Hz, with R1=100Ω, the adjust pin
capacitor should be 13mF. 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
).
Rev.01
6/8
ETC [ ETC ]
