Rainbow Electronics MAX34440 - Manual (Page 27)

PMBus 6-Channel Power-Supply Manager
MAX34440
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