MAX34460
PMBus 12-Channel Voltage Monitor and Sequencer
output is available to be configured as a GPO. Also, for
these channels, POWER_GOOD_ON should be set to
0000h to force power-good assertion since this channel
is not measuring voltage (Figure 10). The current-sense
amplifier must have a source impedance of less than the
value as constrained by the selection of the ADC_TIME
bits in MFR_MODE and the output from the amplifier must
not exceed the maximum input-voltage limits of the device.
The 100Iseries resistor is required to protect the device if
the current-sense amplifier can be active when the system
manager is powered off.
Configuration Port
Some applications require the ability to configure the
device when it has been mounted on a PCB. In such
applications, a 3- or 4-wire header can be added to allow
2
access to the slave I C pins.
Resistor-Dividers and Source
Impedance for RSn Inputs
The maximum full-scale voltage on the ADC inputs is
2.048V (nom). A resistor-divider must be used to measure
voltages greater than 1.8V. The maximum source imped-
ance to the RSn inputs is determined by the ADC_TIME
bits in MFR_MODE. See the Recommended Operating
Conditions table for more information.
The VOUT_SCALE_MONITOR command can be used to
properly scale the external sense element and current-
sense amplifier gain so that the READ_VOUT command
reports current instead of voltage. Normally VOUT_SCALE_
MONITOR scales voltage from 0 to 32.767V in 1mV steps.
For channels used to measure current instead of voltage,
the VOUT_SCALE_MONITOR command can be configured
to report current from 0A to 32.767A in 1mA steps by using
the following formula. Table 41 provides some examples.
Note that VOUT_SCALE_MONITOR cannot exceed a ratio
of 1. System designs should avoid RG combinations with a
value greater than 1.
Protecting Input Pins
In applications where voltages can be applied to the RSn
pins when V
is grounded, a series 100Iresistor is rec-
DD
ommended on these pins to protect the device by limiting
power dissipation. In applications where voltage can be
applied to any other pin when V
resistor of 100Ior greater is recommended on these pins
is grounded, a series
DD
to protect the device by limiting power dissipation.
Current Measurement on RSn Inputs
The RSn inputs normally measure voltages, but with the
addition of an external current-sense amplifier the device
can also be configured to measure current. Any of the RSn
inputs can be configured to measure current. On chan-
nels that measure current, the sequencing for that channel
should be disabled by setting TON_MAX_FAULT_LIMIT =
8000h to FFFFh. On these channels, the associated PSENn
VOUT_SCALE_MONITOR = R x G x 32,767
Exposed Pad Grounding
The device uses the exposed pad of the TQFN package
as the common ground (V ) for the entire device. The
SS
exposed pad must be connected to the local ground plane.
3V MAXIMUM OUTPUT VOLTAGE
1kI MAXIMUM OUTPUT IMPEDANCE
CURRENT-
SENSE
AMPLIFIER
GAIN (G)
100I
SENSE
ELEMENT
(R)
CURRENT
MAX34460
RSn
VOUT_SCALE_MONITOR = R x G x 32,767
TON_MAX_FAULT_LIMIT = 8000h TO FFFFh
POWER_GOOD_ON = 0000h
MAX4376 (SINGLE)
MAX4377 (DUAL)
MAX4378 (QUAD)
Figure 10. Current-Measuring Circuit
Table 41. Scale Current-Gain Example
VOUT_SCALE_MONITOR VALUE
R
G
V/A RATIO
SENSE ELEMENT (mI)
AMPLIFIER GAIN (V/V)
R x G (I)
Dec
3276
6553
3276
2621
1638
Hex
0CCC
1999
0CCC
0A3D
0666
1
2
100
100
50
0.1
0.2
2
0.1
4
20
0.08
0.05
0.5
100
Maxim Integrated
62