Datasheet

Analog
Inputs
(14)
Internal
2.5Vref
0.5%
Fast Digital
Comparators
MON1 – MON6
MON1
MON2
MON13
.
.
.
.
12-bit
SAR ADC
200ksps
M
U
X
MON1 – MON13
Glitch
Filter
Internal
Temp
Sense
UCD90124A
www.ti.com SLVSAN8 –JANUARY 2012
VOLTAGE MONITORING
Up to 12 rail voltages can be monitored using the analog input pins. The input voltage range is 0 V–2.5 V for
MON pins 1-6, 59, 62 and 63. Pins 50, 52, 54 and 56 can measure down to 0.2 V. Any voltage between 0 V and
0.2 V on these pins is read as 0.2 V. External resistors can be used to attenuate voltages higher than 2.5 V.
The ADC operates continuously, requiring 3.89 μs to convert a single analog input. Each rail is sampled by the
sequencing and monitoring algorithm every 400 μs. The maximum source impedance of any sampled voltage
should be less than 4 kΩ. The source impedance limit is particularly important when a resistor-divider network is
used to lower the voltage applied to the analog input pins.
MON1 - MON6 can be configured using digital hardware comparators, which can be used to achieve faster fault
responses. Each hardware comparator has four thresholds (two UV (Fault and Warning) and two OV (Fault and
Warning)). The hardware comparators respond to UV or OV conditions in about 80 μs (faster than 400 µs for the
ADC inputs) and can be used to disable rails or assert GPOs. The only fault response available for the hardware
comparators is to shut down immediately.
An internal 2.5-V reference is used by the ADC. The ADC reference has a tolerance of ±0.5% between 0°C and
125°C and a tolerance of ±1% between –40°C and 125°C. An external voltage divider is required for monitoring
voltages higher than 2.5 V. The nominal rail voltage and the external scale factor can be entered into the Fusion
GUI and are used to report the actual voltage being monitored instead of the ADC input voltage. The nominal
voltage is used to set the range and precision of the reported voltage according to Table 3.
Figure 10. Voltage Monitoring Block Diagram
Although the monitor results can be reported with a resolution of about 15 μV, the real conversion resolution of
610 μV is fixed by the 2.5-V reference and the 12-bit ADC.
CURRENT MONITORING
Current can be monitored using the analog inputs. External circuitry, see Figure 11, must be used in order to
convert the current to a voltage within the range of the UCD90124A MONx input being used.
If a monitor input is configured as a current, the measurements are smoothed by a sliding-average digital filter.
The current for 1 rail is measured every 200μs. If the device is programmed to support 10 rails (independent of
current not being monitored at all rails), then each rail's current will get measured every 2ms. The current
calculation is done with a sliding average using the last 4 measurements. The filter reduces the probability of
false fault detections, and introduces a small delay to the current reading. If a rail is defined with a voltage
monitor and a current monitor, then monitoring for undercurrent warnings begins once the rail voltage reaches
POWER_GOOD_ON. If the rail does not have a voltage monitor, then current monitoring begins after
TON_DELAY.
The device supports multiple PMBus commands related to current, including READ_IOUT, which reads external
currents from the MON pins; IOUT_OC_FAULT_LIMIT, which sets the overcurrent fault limit;
IOUT_OC_WARN_LIMIT, which sets the overcurrent warning limit; and IOUT_UC_FAULT_LIMIT, which sets the
undercurrent fault limit. The UCD90xxx Sequencer and System Health Controller PMBus Command Reference
contains a detailed description of how current fault responses are implemented using PMBus commands.
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