XB1117
Series
■OPERATIONAL
EXPLANATION
1. Output voltage adjustment
The XB1117 series provide a stable output by comparing the output voltage to an internal reference voltage. With the
adjustable XB1117K type, a 1.25V reference voltage (V
REF
) is fixed between the V
OUT
pin and the ADJ pin and the external
resistors R1 and R2 are used to set the output voltage. The resistance values of R1 and R2 should be set so as to provide a
minimum load current of 10mA. The output voltage is given by the following equation.
V
OUT
=V
REF
(1+R2/R1)+I
ADJ
x R2
The output voltage of the XB1117P type is internally fixed to 1.8V, 2.5V, 3.3V, and 5.0V so external resistors are not
necessary.
2. Stability and load regulation
The XB1117 series requires a load capacitor between the V
OUT
pin and the GND pin to provide phase compensation thereby
ensuring stability of the output voltage. Either a tantalum capacitor of more than 10μF (TYP.) or an aluminum electrolytic
capacitor of more than 50μF (TYP.) should be connected.
(Note : The capacitor's ESR value should not exceed 0.5Ω.)
The output capacitor does not have a theoretical upper limit so increasing its value will increase stability. C
L
=100μF or
more is typical for high current regulator design.
In order to avoid any reductions in output voltage accuracy with the XB1117K type, we recommend not to place a parasitic
resistor (Rp) between the V
OUT
pin and the divider resistor R1. The parasitic resistor (Rp) does not influence the output
however if the divider resistor R1 is directly connected to the V
OUT
pin.
With the XB1117P type, although external resistor (R1) is internally connected to the V
OUT
pin, stability can be maintained by
not wiring a parasitic resistor to the GND pin.
7/13
TOREX [ TOREX SEMICONDUCTOR ]
