Datasheet
MAX34446
PMBus Power-Supply Data Logger
20Maxim Integrated
Table 7. VOUT_SCALE_MONITOR
VOUT_MODE (20h)
The VOUT_MODE command is used to report the device’s data format. The device uses the DIRECT format for all the
voltage-related commands. The value returned is 40h, indicating DIRECT data format. This command is read-only. If
a host attempts to write this command, the CML status bit is asserted. See Table 3 for the m, b, and R values for the
various commands.
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 voltage is greater than the device’s input range, the 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 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). See Table 7.
USER NOTE: The device’s full-scale ADC voltage is 1.225V. A scaling factor where a 1.0V ADC input represents
a nominal 100% voltage level is recommended.
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 in conjunction with a 50V/V current sense amplifier, the IOUT_CAL_GAIN should be set to 500mI or 1388h.
USER NOTE: The device’s full-scale ADC voltage is 1.225V. The value of the sense resistor and current sense
amplifier gain must be scaled appropriately.
VOUT_OV_FAULT_LIMIT (40h)
The VOUT_OV_FAULT_LIMIT command sets the value of the output voltage that causes an output overvoltage fault.
The monitored voltage must drop by at least 2% below the limit before the fault is allowed to clear. This fault is masked
until the output voltage is below this limit for the first time. The 2 data bytes are in DIRECT format. In response to the
VOUT_OV_FAULT_LIMIT being exceeded, the device does the following:
1) Sets the VOUT_OV bit in STATUS_BYTE.
2) Sets the VOUT_OV and VOUT bits in STATUS_WORD.
3) Sets the VOUT_OV_FAULT bit in STATUS_VOUT.
4) Responds as specified in the MFR_FAULT_RESPONSE.
NOMINAL VOLTAGE LEVEL
MONITORED (V)
NOMINAL ADC INPUT VOLTAGE
LEVEL (V) (SEE USER 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