Datasheet

UCD9244
www.ti.com SLVSAL6A –NOVEMBER 2010–REVISED FEBRUARY 2011
The worst case response time to an over-current condition is the sum of the sampling interval (Table 8) and the
smoothing filter lag, t
lag
from Equation 11.
Current Foldback Mode
When the measured output current exceeds the value specified by the IOUT_OC_FAULT_LIMIT command, the
UCD9244 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 responds as programmed by the IOUT_OC_LV_FAULT_RESPONSE command.
Input Voltage Monitoring
The VinMon pin on the UCD9244 monitors the input voltage. The VinMon pin is monitored using the internal
12-bit ADC which has a dynamic range of 0 to 2.5V. The fault thresholds for the input voltage are set using the
VIN_OV_FAULT_LIMIT and VIN_UV_FAULT_LIMIT commands. The scaling for Vin is set using the
VIN_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 as configured
by 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 outputs. 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
The UCD9244 monitors temperature using the 12-bit ADC. The ADC12 is read every 100us and combined into a
running sum. At the end of each 100ms monitoring interval, the ~1000 sample in the running sum are averaged
together and the running sum is restarted. These averaged values are used to calculate the temperature from
external temperature sensors. These same values may be read directly using the READ_AUX_ADCS PMBus
command.
The averaged values are passed through an additional digital smoothing filter to further reduce the chance of
reporting false over-temperature events. The smoothing filter has a time constant of 1.55 seconds.
Auxiliary ADC Input Monitoring
Unused external temperature sensor inputs may be used for general-purpose analog monitoring. The
READ_AUX_ADCS PMBus command returns a block of four 16-bit values, each of which is the average of
multiple raw measurements from the Temp/AuxADC inputs. A value of 0 corresponds to 0.00V and a value of
65535 corresponds to 2.50V. Unlike many other variables that can be monitored via PMBus, no mechanism is
provided for adjusting the gain or offset of the Aux ADC measurements.
When using the temperature sensor inputs as Auxiliary ADCs, the temperature warning and faults should be
disabled to prevent shut-downs due to non-existent over-temperature conditions.
Soft Start, Soft Stop Ramp Sequence
The UCD9244 performs soft start and soft stop ramps under closed-loop control.
Performing a start or stop ramp or tracking is considered a separate operational mode. The other operational
modes are normal regulation and light load regulation. Each operational mode can be configured to have an
independent loop gain and compensation. Each set of loop gain coefficients is called a "bank" and is configured
using the CLA_GAINS PMBus command.
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