10

www.irf.com

HTH27022S

PRELIMINARY

Output Voltage Adjust - For Higher or Lower Output Voltage

In addition to permitting close voltage regulation of remotely located loads, the converter has a Vadj Pin allowing the users

to trim its output voltage up or down for their applications. The adjustment range is limited to +10% , -20% maximum. The

adjustments are intended as a means to “trim” the output to a voltage setting for certain design application, but are not

intended to create a variable output converter. an adjustable output converter. The output voltage is done by connecting

a resistor with an appropriate value between the Vadj Pin and either +Sense and or -Sense Pins while as shown in Fig. 9

below. The resistance value for a desired output voltage can be determined by formulae described below.

Voltage Trimming Procedure:

(1) Nominal Output Voltage with Vadj Pin (Pin 11) Open: 22V

(2) Trimming Up Output Voltage by installing a trimming resistor Radj (1/4W, 1%) between the Vadj Pin (Pin 11)

and -SENSE Pin (Pin 9):

Radj = [ 1950 / [10 * (Vout - 2.5) - 195 ] ] - 50; Radj in k

Example: To trim Vout up to 24V

Radj = [ 1950 / [10 * (24 - 2.5) -195 ] ] - 50 = [ 1950 / 20 ] - 50 = 47.5 (k

Thus, Vout can be trimmed up to 24V by installing a 1/4W, 1%, 47.5k

and the -SENSE Pin (Pin 9).

(3) Trimming Down Output Voltage by installing a trimming resistor Radj (1/4W, 1%) between the Vadj Pin (Pin 11)

and +SENSE Pin (Pin 10)

Radj = [ 780 * (Vout - 2.5) ] / [ 195 - 10 * (Vout - 2.5 ) ] ; Radj in k

Example: To trim Vout down to 20V

Radj = [ 780 * (20 - 2.5) ] / [ 195 - 10 * (20 - 2.5 ) ] = 13650 / 20 = 682.5 (k

Thus, Vout can be trimmed down to 20V by installing a 1/4W, 1% 682.5k

and the +SENSE Pin (Pin 10).