Rainbow Electronics MAX34440 - Manual (Page 20)

PMBus 6-Channel Power-Supply Manager
MAX34440
20
Sending a DIRECT Format Value
To send a value, the host must use the below equation
to solve for Y:
Y = (mX + b) x 10 R
where Y is the 2-byte, two’s complement integer to be
sent to the unit; m is the slope coefficient; X is the real
world value, in units such as volts, to be converted for
transmission; b is the offset; and R is the exponent.
The following example demonstrates how the host can
send and retrieve values from the device. Table 4 shows
the coefficients used in the following parameters.
If a host wants to set the device to change the power-
supply output voltage to 3.465V (or 3465mV), the cor-
responding VOUT_MARGIN_HIGH value is:
Y = (1 x 3465 + 0) x 10 0 = 3465 (decimal) = 0D89h (hex)
Conversely, if the host received a value of 0D89h on a
READ_VOUT command, this is equivalent to:
X = (1/1) x (0D89h x 10 -(-0) - 0) = 3465mV = 3.465V
Power supplies and power converters generally have
no way of knowing how their outputs are connected to
ground. Within the power supply, all output voltages are
most commonly treated as positive. Accordingly, all out-
put voltages and output voltage-related parameters of
PMBus devices are commanded and reported as posi-
tive values. It is up to the system to know that a particular
output is negative if that is of interest to the system. All
output-voltage-related commands use 2 data bytes.
Table 3. PMBus Command Code Coefficients
Table 4. Coefficients for DIRECT Format
Value
PARAMETER COMMANDS UNITS RESOLUTION MAX m b R
Voltage
VOUT_MARGIN_HIGH
VOUT_MARGIN_LOW
VOUT_OV_FAULT_LIMIT
VOUT_OV_WARN_LIMIT
VOUT_UV_WARN_LIMIT
VOUT_UV_FAULT_LIMIT
POWER_GOOD_ON
POWER_GOOD_OFF
READ_VOUT
MFR_VOUT_PEAK
MFR_VOUT_MIN
mV 1 32,767 1 0 0
Voltage Scaling VOUT_SCALE_MONITOR — 1/32,767 1 32,767 0 0
Current
IOUT_OC_WARN_LIMIT
IOUT_OC_FAULT_LIMIT
READ_IOUT
MFR_IOUT_PEAK
mA 1 32,767 1 0 0
Current Scaling IOUT_CAL_GAIN mI 0.1 3276.7 1 0 1
Temperature
OT_FAULT_LIMIT
OT_WARN_LIMIT
READ_TEMPERATURE_1
MFR_TEMPERATURE_PEAK
N
C 0.01 327.67 1 0 2
Timing
TON_DELAY
TON_MAX_FAULT_LIMIT
TOFF_DELAY
MFR_FAULT_RETRY
ms 1 32,767 1 0 0
COMMAND
CODE
COMMAND NAME m b R
25h VOUT_MARGIN_HIGH 1 0 0
8Bh READ_VOUT 1 0 0