Technical Reference Note (APC08)

MODEL: APC08 SERIES

SHEET 9 OF 23

OCTOBER 4, 2004 - REVISION 03

Method 1: External Trim Resistor (continued)

whichever is lower. By connecting an external resistor across P4 and P2, Vo is adjusted to a lower value. Only small

reductions, 2%, in voltage are recommended, as adjustment to lower voltages tends to affect the loop compensation of the

module.

Full range adjustment (from 0.9V to 3.6V) can be obtained from a module with the lowest Vo setpoint (0.9Vo).

To adjust Vo to a higher value, please refer to

Figure 4. The required resistor value (Rt) can be

determined through Equation (1) where Vo is the

voltage on P2 before the adjustment and Vot is the

voltage of P2 after Rt is connected.

1

R

Vo

Vot

Vref

Rt

−

=

Equation (1)

Please refer to related constants given in TABLE 1 to calculate the Equation.

TABLE 1. CONSTANTS

Version

0.9V

1.2V

1.5V

1.8V

2.5V

3.3V

R1

APC08X03

R2

97.6k

8.45k

4.32k

2.94k

1.69k

1.13k

3.09k

APC08X08

R2

210k

17.4k

9.09k

6.04k

3.48k

2.32k

6.49k

0.87V

Be aware that the maximum Vo allowed is 3.6V (for APC08x08 series). Please refer to Centauri datasheet.

Example:

Module version: APC08J03-9 (1.8 to 6.0Vin, 0.9Vo).

Based on Equation (1), Rt can be determined as 3.0k

Ω.

To adjust Vo to a lower value, Rt should be connected between P4 and P2. Equation (2) provides the calculation for Rt.

2

)

(

)

)(

(

R

V

V

V

V

V

V

V

Rt

ot

o

ref

ref

ot

ref

o

−

−

−

=

Equation (2)

Note: minimum Vo = 0.9V

Figure 4. Output Voltage Trim Setup.