PMBus 6-Channel Power-Supply Manager

27

VOUT_MARGIN_LOW (26h)

The VOUT_MARGIN_LOW command loads the device with the voltage to which the power-supply output is to be

changed when the OPERATION command is set to margin low. If the power supply is already operating at margin low,

changing VOUT_MARGIN_LOW has no effect on the output voltage. The device only adjusts the power supply to the

new VOUT_MARGIN_LOW voltage after receiving a new margin low OPERATION command. The 2 data bytes are in

DIRECT format. If the device cannot successfully close-loop margin the power supply, the device keeps attempting to

margin the supply and does the following:

1) Sets the NONE OF THE ABOVE bit in STATUS_BYTE.

2) Sets the NONE OF THE ABOVE and MFR bits in STATUS_WORD.

3) Sets the MARGIN_FAULT bit in STATUS_MFR_SPECIFIC.

4) Notifies the host through ALERT assertion (if enabled in MFR_MODE).

VOUT_SCALE_MONITOR (2Ah)

VOUT_SCALE_MONITOR is used in applications where the measured power-supply voltage is not equal to the voltage

at the ADC input. For example, if the ADC input expects a 1.0V input for a 12V output, VOUT_SCALE_MONITOR =

1.0V/12V = 0.0833. In applications where the power-supply output voltage is greater than the device input range, the

output voltage of the power supply is sensed through a resistive voltage-divider. The resistive voltage-divider reduces

or scales the output voltage. The PMBus commands specify the actual power-supply output voltages and not the input

voltage to the ADC. To allow the device to map between the power-supply voltage (such as 12V) and the voltage at

the ADC input, the VOUT_SCALE_MONITOR command is used. The 2 data bytes are in DIRECT format. This value is

dimensionless. For example, if the required scaling factor is 0.0833, then VOUT_SCALE_MONITOR should be set to

0AABh (2731/32,767 = 0.0833).

IOUT_CAL_GAIN (38h)

The IOUT_CAL_GAIN command is used to set the ratio of the voltage at the ADC input to the sensed current. The units

of the IOUT_CAL_GAIN factor are 0.1mI. The 2 data bytes are in DIRECT format. For example, if a 10mI sense resis-

tor is used with a 50V/V current-sense amplifier, the IOUT_CAL_GAIN should be set to 500mI or 1388h.

USER NOTE: On the device, the full-scale ADC voltage is 1.225V. The value of the sense resistor and current-

sense amplifier gain must be scaled appropriately.

Table 13. VOUT_SCALE_MONITOR

Note: On the device, the full-scale ADC voltage is 1.225V. A scaling factor where a 1.0V ADC input represents a nominal 100%

voltage level is recommended.

NOMINAL VOLTAGE LEVEL

MONITORED (V)

NOMINAL ADC INPUT VOLTAGE

LEVEL (V) (SEE NOTE)

RESISTIVE VOLTAGE-

DIVIDER RATIO

VOUT_SCALE_MONITOR

VALUE (HEX)

1.2

1.0

0.833

6AAAh

1.5

1.0

0.667

5555h

1.8

1.0

0.555

470Ah

2.5

1.0

0.4

3333h

3.3

1.0

0.303

26C8h

5

1.0

0.2

1999h

12

1.0

0.0833

0AABh