Technical Reference Note (APC08)
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.
Rt
=
Vref
R
1
Vot
−
Vo
Equation (1)
Figure 4. Output Voltage Trim Setup.
Please refer to related constants given in TABLE 1 to calculate the Equation.
APC08X03
APC08X08
V
r
/ V
ref
Version
R2
R2
0.87V
0.9V
97.6k
210k
TABLE 1. CONSTANTS
1.2V
1.5V
1.8V
8.45k
4.32k
2.94k
17.4k
9.09k
6.04k
2.5V
1.69k
3.48k
3.3V
1.13k
2.32k
R1
3.09k
6.49k
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).
Requiring to adjust output voltage from Vo = 0.9V to Vot = 1.8V. V
ref
= 0.875V and R
1
= 3.09kΩ (from TABLE 1).
Based on Equation (1), Rt can be determined as 3.0kΩ.
To adjust Vo to a lower value,
Rt should be connected between P4 and P2. Equation (2) provides the calculation for Rt.
Rt
=
(
V
o
−
V
ref
)(
V
ot
−
V
ref
)
V
ref
(
V
o
−
V
ot
)
R
2
Equation (2)
Note: minimum Vo = 0.9V
MODEL: APC08 SERIES
OCTOBER 4, 2004 - REVISION 03
SHEET 9 OF 23
ASTEC [ Astec America, Inc ]
