AN2798 datasheet(13/38 Pages) STMICROELECTRONICS

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AN2798

Configuration

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Configuration

The PM6670AS board allows the user to choose the desired mode of operation using four

jumpers (JP1, JP2, JP3 and JP5) and two resistors. Refer to the following configuration

description.

5.1

JP3 fixed or adjustable output voltage (MODE pin)

The JP3 jumper is used to choose between fixed output voltage (1.5 V or 1.8 V) and a user-

defined output voltage in the range 0.9 V to 2.6 V. When connected in the lower position, the

fixed output voltage is selected and the voltage depends on the setting of the DDRSEL pin

(see Section 5.2).

If JP3 is in the upper position, the output voltage is given by:

Both the R8 and R9 resistors are set to 39 k

Ω (1.8 V by default) and can be changed by the

user.

5.2

JP1 DDR2/DDR3 or power-saving mode (DDRSEL pin)

The JP1 jumper allows different options depending on the JP3 configuration. If the fixed

output voltage is selected (JP3 in the lower position), the user can choose between 1.8 V

(DDR2) or 1.5 V (DDR3), connecting JP1 as shown in Figure 10, and the pulse-skip mode is

set by default.

When the adjustable output voltage is selected (JP3 in the upper position), the same jumper

allows choosing between forced PWM, pulse-skip and non-audible pulse-skip modes as

shown in Figure 10 on page 14.

R8 + R9

VDDQ

ADJ

R8 + R9

VDDQ

ADJ

Figure 9.

JP3 (MODE) setting

Fixed Output Voltage

(default position)

Adjustable Output Voltage

Fixed Output Voltage

(default position)

Adjustable Output Voltage

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