Datasheet

UCD9248
www.ti.com SLVSA33A –JANUARY 2010–REVISED AUGUST 2012
Current Foldback Mode
When the measured output current exceeds the value specified by the IOUT_OC_FAULT_LIMIT command, the
UCD9248 attempts to continue to operate by reducing the output voltage in order to maintain the output current
at the value set by IOUT_OC_FAULT_LIMIT. This continues indefinitely as long as the output voltage remains
above the minimum value specified by IOUT_OC_LV_FAULT_LIMIT. If the output voltage is pulled down to less
than that value, the device shuts down, if programmed to do so by the IOUT_OC_LV_FAULT_RESPONSE
command.
Input Voltage and Current Monitoring
The Vin/Iin pin on the UCD9248 monitors the input voltage and current. To measure both input voltage and input
current, an external multiplexer is required, see Figure 4. If measurement of only the input voltage, and not input
current, is desired, then a multiplexer is not needed. The multiplexer is switched between voltage and current
using the TMUX-0 signal. (This signal is the LSB of the temperature mux select signals, so the TMUX-0 signal is
connected both to the temperature multiplexer as well as the voltage/current multiplexer). When TMUX-0 is low
the V
in
/I
in
pin will be sampled for V
in
. When TMUX-0 is high the V
in
/I
in
pin will be sampled for I
in
. The V
in
/I
in
pin is
monitored using the internal 12-bit ADC and so has a dynamic range of 0 to VADC_RANGE. The fault thresholds
for the input voltage are set using the VIN_OV_FAULT_LIMIT and VIN_UV_FAULT_LIMIT commands. The
scaling for V
in
is set using the VIN_SCALE_MONITOR command, and the scaling for I
in
is set using the
IIN_SCALE_MONITOR command.
Input UV Lockout
The input supply lock-out voltage thresholds are configured with the VIN_ON and VIN_OFF commands. When
input supply voltage drops below the value set by VIN_OFF, the device starts a normal soft stop ramp. When the
input supply voltage drops below the voltage set by VIN_UV_FAULT_LIMIT, the device performs per the
configuration using the VIN_UV_FAULT_RESPONSE command. For example, when the bias supply for the
controller is derived from another source, the response code can be set to "Continue" or "Continue with delay,"
and the controller attempts to finish the soft stop ramp. If the bias voltages for the controller and gate driver are
uncertain below some voltage, the user can set the UV fault limit to that voltage and specify the response code
to be "shut down immediately" disabling all DPWM and SRE outputs. If VIN_OFF sets the voltage at which the
output voltage soft-stop ramp is initiated, and VIN_UV_FAULT_LIMIT sets the voltage where power conversion is
stopped.
Temperature Monitoring
Both the internal device temperature and up to eight external temperatures are monitored by the UCD9248. The
controller supports multiple PMBus commands related to temperature, including READ_TEMPERATURE_1,
which reads the internal temperature, READ_TEMPERATURE_2, which reads the external power stage
temperatures, OT_FAULT_LIMIT, which sets the over temperature fault limit, and OT_FAULT_RESPONSE,
which defines the action to take when the configured limit is exceeded.
If more than one external temperature is to be measured, the UCD9248 provides analog multiplexer select pins
(TMUX0-2) to allow up to 8 external temperatures to be measured. The output of the multiplexer is routed to the
Temperature pin. The controller cycles through each of the power stage temperature measurement signals. The
signal from the external temperature sensor is expected to be a linear voltage proportional to temperature. The
PMBus commands TEMPERATURE_CAL_GAIN and TEMPERATURE_CAL_OFFSET are used to scale the
measured temperature-dependent voltage to °C.
The inputs to the multiplexer are mapped in the order that the outputs are assigned using the PHASE_INFO
PMBus command. For example, if only one power stage is wired to each DPWM, the four temperature signals
should be wired to the first four multiplexer inputs.
The UCD9248 monitors temperature using the 12-bit monitor ADC, sampling each temperature in turn with an
100 ms sample period. These measurements are smoothed by a digital filter, similar to that used to smooth the
output current measurements. The filter has a time constant 15.5 times the sample interval, or 1.55 s (15.5 × 0
ms = 1.55 seconds). This filtering reduces the probability of false fault detections.
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