Migrating from UCD9220, UCD , UCD to UCD9224, UCD9246, UCD9248

Transcription

1 Migration from UCD9220, UCD9240 Lit# October 28, 2009 Migrating from UCD9220, UCD , UCD to UCD9224, UCD9246, UCD9248 Eric Oettinger PMP Digital Power Abstract The UCD92xx family, introduced in late 2008, was updated with several changes that must be considered when migrating designs to take advantage of the new features. This paper presents an overview of the changes made and what steps a user should make to ensure a smooth transition. Contents Abstract...1 Contents Difference summary: UCD9240 vs. UCD PMBus address selection Sequencing Other various improvements New commands Removed commands Migration steps References

2 1 Difference summary: UCD9240 family vs. UCD9246 family The updated firmware corrected several shortcomings in the original releases; additionally several new features were added, and a few less popular ones were removed. In the following sections UCD9240 family refers to the original devices (UCD9220, UCD and UCD ) and UCD9246 family likewise refers to the updated UCD9224, UCD9246 and UCD9248 devices. The relationship between the two families of parts is given in Table 1. For additional detail on all modifications please refer to the datasheet and command reference. UCD9240 Family UCD9246 Family Number of Pins Number of Output Rails Number Of Phases UCD9220 UCD UCD UCD UCD UCD Table 1. Members of the 9240 and 9246 families of devices 1.1 PMBus address selection The algorithm used to detect the PMBus address was improved to compensate for temperature and allow more settling time in the A/D conversion. The changes result in very consistent address detection across a wider range of resistors. With these improvements the resistor selection table was re-generated based on standard resistor values. The new table and decode algorithm will require resistor changes when migrating from UCD9240 family to UCD9246 family designs. 1.2 Sequencing The largest firmware changes involved modifying the sequencing operation. Largely driven by numerous requests to support the ability to turn rails off in the reverse order in which they were turned on, outputdependencies in the UCD9240 family have been replaced by turn-on-dependencies and stay-ondependencies in the UCD9246 family. This allows a configuration such as for turn-on and for turn-off, and also permits better fault coordination across multiple UCD92xx devices. A bug was fixed that may have caused DPWM pins intended for GPIO use to be improperly configured. All supported GPIO pins now perform as expected. Sequencing requirements now supersede an ALWAYS_CONVERTING configuration. This provides more flexibility, allowing a sequencing input to function more closely to a page-dedicated control pin. The ability for rails to shut down in either a soft or immediate fashion when stay-on dependencies are deasserted was added. To make room for more sequencing input options, the number of sequencing outputs has been decreased from eight to six; systems that made use of more than six sequencing outputs must be re-designed. To obtain the identical behavior to that of the UCD9240 family devices, both turn-on and stay-on dependencies should be set to the UCD9240 family output-dependencies. Please see the PMBus Command Reference and the UCD9224, UCD9246, UCD9248 Sequencing Application Report for detailed explanation of the modified function. 1.3 Other improvements Here is a list of additional improvements made in the UCD9224, UCD9246, and UCD9248 devices compared to the UCD9240 family devices that one should be aware of: 2

3 The initial ramp up profile was significantly improved. The ramp is more consistent with less overshoot across a wider range of loads. Switching between controller coefficients was streamlined to occur more quickly and with reduced disturbance to the output while minimizing the time when faults are masked Improvements in both ramp and the switch between ramping and regulation modes provide more accurate TON_DELAY / TON_RISE times with fewer flat-spots observed when ramps on multiple rails are initiated simultaneously. A new phase add/drop algorithm was implemented that reduces glitches significantly. The time between DPWM and SRE enables were minimized and ordered such that SRE is consistently first on and last off. New temperature filtering was implemented that gives more accurate and smoother measurements. Faster switching in and out of light-load was implemented. During light-load switches, the order in which gains and the number of enabled phases are switched was changed to improve stability. Improvements in initial duty cycle estimation when starting into a pre-bias were implemented. A glitch on open-drain sequencing outputs pins at startup was fixed. The Watch Dog timer is now enabled. A fault is now correctly posted if an attempt is made to start a rail with no phases assigned to it. The devices now allow current balance in tracking mode if VOUT exceeds power good. Faster DFlash write / erase operations have been implemented; this allows smaller hold-up caps. The ADC12 and DPWM have been synchronized to reduce injected noise into the EADC. The power-good signal gets updated more quickly. The soft-reset timing variation was fixed. The 9240 could take 1.2 second to recognize a reset; the 9246 will respond consistently in 10 msec. Faster Vin droop detection was implemented. The READ_DUTY_CYCLE calculation now takes the third compensation pole into effect. A timing bug encountered if page is configured with only B-phases was fixed. Error reporting on factory fresh part left with flash test pattern was fixed. The firmware was improved to gracefully handle the case where both Dflash banks are invalid. The resetting of retry counters on one rail when another rail was turned on was fixed. Power consumption was reduced by driving unbonded signals low. Power stage measurement (aka TFA) now injects at the filter output to measure just the plant; this provides much higher resolution at all frequencies. If the GUI is used for measurements, this change should be transparent in operation. If alternate methods are used to invoke power stage measurements, proceed with caution using smaller injection levels. 1.4 New commands Here is a list of new PMBus commands supported on the UCD9224, UCD9246, and UCD9248 devices that are not supported on the UCD9240 or UCD9220. DRIVER_CONFIG Determines how the controller interacts with the driver. It allows selection of the fault-detected polarity, determines the controller behavior at startup with a fault pending, and controls how the DPWM and SRE outputs are driven at shutdown. For 9240 equivalent operation DRIVER_CONFIG should be set to 0x0. This command was implemented to support future driver devices. SYNC_OFFSET For arbitrary alignment of the timing of output phases between rails SYNC_OFFSET can be used to specify the offset from the SYNC_IN pin. The UCD9224, UCD9246, UCD9248 Sync Application Report should be referred to for impact on phase margin and other considerations of utilizing SYNC_OFFSET. PHASE_DROP_CAL Significant improvements in the transient performance when adding and dropping phases (primarily used for light-load operation) were made for the When dropping phases the time between disabling the DPWM and SRE outputs has a large impact on the voltage excursions. The optimal delay is strongly dependent on the power stage, and therefore left to the user to determine.

4 The default of 1.0 provides 1.0 switching cycle of delay for each Amp of current in the phase being dropped and will show appreciable improvement in many designs. To remove any delay set PHASE_DROP_CAL to 0. By using an oscilloscope to monitor the output voltage excursions at various load conditions while exercising phase drop operations (see PHASE_ENABLE in the command reference) one can quickly see an improvement in transient performance with larger delays. Faults will be held off during the delay, however, so extremely long delays are not recommended. USER_DATA_00 A buffer in which a 32-bytes of data can be stored is now available. The GUI provides an ASCII text editor interface to this command, but your host microcontroller could use this for arbitrary data storage. This command, like most other PMBus commands, will be stored to data flash if the STORE_DEFAULT_ALL command is executed after writing to USER_DATA_ Removed commands Here is a list of PMBus commands not supported on the UCD9224, UCD9246, and UCD9248 devices that are supported on the UCD9240 or UCD9220. MAX_DUTY Due to the architecture of the digital controller, if the control effort ever exceeded MAX_DUTY, a very large slow transient resulted. The MAX_DUTY is now 100% and not modifiable. MIN_DUTY Similarly, pulses less than MIN_DUTY caused large slow voltage excursions. The command DRIVER_MIN_PULSE which specifies a minimum controller reference threshold should be used instead; it does not provide an absolute minimum pulse, but for startups and shutdowns will give similar outputs as the obsolete MIN_DUTY. PAGE_ISOLATED All pages are now assumed to be isolated. PREBIAS_GAIN / PREBIAS_OFFSET These somewhat obscure commands have been rendered obsolete and unnecessary due to improvements in the ramp algorithm. All FAN-related commands (PWM, TACH and STATUS) were removed to free memory for new features. 2 Migration steps The following steps should be taken to ensure expected system behavior after upgrading to the UCD9246 family of devices. Verify PMBus address resistors are still in range given the new table. If the specific address (and to guarantee that the address will not shift with temperature) is important, new resistor values will be required. The resistor changes are the only hardware modification required; all remaining changes are most easily made using the Fusion GUI. The steps covert a project file depend on whether the target IC is starting with UCD9240 family or UCD9246 family code Conversion of a project file if the target IC has not been upgraded: 1. Launch the GUI, connect to UCD9240 or UCD9220 device. 2. If you don t already have a project file, save the current configuration into a project file. 3. Select Tools->Firmware Download to download the UCD9246 or UCD9224 FW, erasing the data flash. 4

5 4. When the GUI restarts, the device will have the firmware data flash default values. 5. Go to File>Import Project and import the UCD9240 or UCD9220 project file. 6. Save the configuration as a UCD9246 or UCD9224 project file; be sure to review the settings for all the new commands. Conversion of a project file if the device is already a UCD9246 or UCD9224 device: 1. Connect online to UCD9246 or UCD9224 device 2. Select File->Import Project, select UCD9240 or UCD9220 project, import 3. Select File->Save As to save a snapshot of the new device configuration; this project is now a UCD9246 or UCD9224 project At this point the device is a UCD9246 (or UCD9224) with a valid UCD9246 (or UCD9224) project. If editing your device in offline mode, please ensure you edit the new UCD9246/UCD9224 project file. Edits should no longer be made to the UCD9240/UCD9220 project file. In addition to the above conversion steps, you should: Consider the desired sequencing behavior especially given the enhanced options provided by the turnon / stay-on distinction. GPIOs, turn on dependencies, turn off dependencies, and fault shutdown slaves should all be reviewed. As of this writing, the GUI does not import these items due to changes in the GPIO_SEQ_CONFIG command. Verify values for new commands DRIVER_CONFIG, SYNC_OFFSET, and PHASE_DROP_CAL. 3 References UCD9240 Digital PWM System Controller Data Sheet. (SLUS766) UCD92xx Digital PWM System Controller PMBus Command Reference.(SLUU337) Fusion Digital Power designer software (SLVC118)