APC08F08 datasheet(10/23 Pages) ASTEC

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Technical Reference Note (APC08)

MODEL: APC08 SERIES

SHEET 10 OF 23

OCTOBER 4, 2004 - REVISION 03

Method 1: External Trim Resistor (continued)

Example

Module version: APC08F03-9 (4.0 to 6.Vin, 3.3Vo).

Requiring to adjust the output voltage from Vo = 3.3V to Vot = 3.3 (1-0.02) = 3.234V.

Vo = 3.3V, Vot = 3.234V, Vref = 0.875V, R2 = 1.13kΩ (from TABLE 1).

Based on Equation (1), Rt can be determined as 111.9k

Ω.

Trim Function (continued)

Method 2: External DC Source

By connecting an external DC supply across P4 (Enable) and P3 (GND) through a limiting resistor Rt, (see Figure 5), output

voltage adjustment can also be achieved. Equation 3 provides the relationship between the External DC supply, Vt, and Vo

(where Vo is the desired output voltage).

Given: Rt = 10k

Ω

Vo Adjustment to Lower Voltages. This method does not limit the recommended lower Vo adjustment to 2% as mentioned

on previous sections re: Vo adjustment through external trim resistor.

Example:

Module version: APC08G03-9 (3V to 6Vin, 2.5Vo).

Requiring to adjust the output voltage from Vo = 2.5V to 1.8V

Vo = 1.8V, Vr = 0.87V, R1 = 3.09kΩ, R2 = 1.69kΩ (from Table 1). Based on Equation (3), Vt = 3.0V.

Example:

Module version: APC08G03-9 (3V to 6Vin, 2.5Vo).

Requiring to adjust the output voltage from Vo = 2.5V to 0.9V

Vo = 0.9V, Vr = 0.87V, R1 = 3.09kΩ, R2 = 1.69kΩ (from Table 1). Based on Equation (3), Vt = 5.9V.

−













Equation (3)

Figure 5. External DC source for output trim adjust.

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