NCV4276, NCV4276A
Setting the Output Voltage (Adjustable Version)
The output voltage range of the adjustable version can be
set between 2.5 V and 20 V. This is accomplished with an
external resistor divider feeding back the voltage to the IC
back to the error amplifier by the voltage adjust pin VA.
The internal reference voltage is set to a temperature stable
reference of 2.5 V.
The output voltage is calculated from the following
formula. Ignoring the bias current into the VA pin:
VQ + [(R1 ) R2) * Vref]ńR2
Use R2 < 50 k to avoid significant voltage output errors
due to VA bias current.
Connecting VA directly to Q without R1 and R2 creates
an output voltage of 2.5 V.
Designers should consider the tolerance of R1 and R2
during the design phase.
The input voltage range for operation (pin 1) of the
adjustable version is between (VQ + 0.5 V) and 40 V.
Internal bias requirements dictate a minimum input voltage
of 4.5 V. The dropout voltage for output voltages less than
4.0 V is (4.5 V − VQ).
http://onsemi.com
16