Datasheet

UCD9222

SLVSAL7A – NOVEMBER 2010– REVISED FEBRUARY 2011

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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 UCD9222 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 AuxADC inputs. These AuxADC inputs share usage with other signals such

as Temp1, Temp2, Vtrack, and IinMon. 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 UCD9222 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.

Start ramps are performed by waiting for the configured start delay TON_DELAY and then ramping the internal

reference toward the commanded reference voltage at the rate specified by the TON_RISE time and

VOUT_COMMAND. The DPWM outputs are enabled when the internal ramp reference equals the preexisting

voltage (pre-bias) on the output and the calculated DPWM pulse width exceeds the pulse width specified by

DRIVER_MIN_PULSE. This ensures that a constant ramp rate is maintained, and that the ramp is completed at

the same time it would be if there had not been a pre-bias condition.

Figure 16 shows the operation of soft-start ramps and soft-stop ramps.

Product Folder Link(s) :UCD9222