SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
There are several enable bits related to cycle by cycle current limit:
DPWMCTRL0 contains:
CBC_PWM_C_EN
CBC_PWM_AB_EN
CBC_ADV_CNT_EN
CBC_SYNC_CUR_LIMIT_EN
CBC_BSIDE_ACTIVE_EN
All of these bits, except for CBC_BSIDE_ACTIVE_EN also occur in the AMS registers.
The first two, CBC_PWM_C_EN and CBC_PWM_AB_EN simply enable cycle by cycle current limit for their respective signals. In all modes, CBC_PWM_EN has an independent effect on DPWMC.
The other bits have no effect on DPWMC The other three bits have different effects in different modes. Here are the effects:
Normal Mode
In normal mode, a CBC event will cause DPWMA to go low before the time dictated by the CLA. The dead time for DPWMB will be preserved, so the rising edge of DPWMB will be moved forward by the same amount as the falling edge of DPWMA.
There are only two options for setting the CBC bits in normal mode:
CBC_BSIDE_ACTIVE_EN has no effect. Normal mode has some support for negative dead times, as does the CBC logic. Even negative dead times will be preserved. As seen in Figure 2-14, if there is a negative dead time, the minimum pulse width on DPWMA will be equivalent to the dead time. To preserve a negative dead time, the CBC will trigger a rising edge on DPWMB. After the dead time is expired, then DPWMA will fall.
With a positive dead time, of course, DPWMA will fall with the CBC event, and DPWMB will rise after the dead time:
Even if DPWMB is being used as a GPIO, it is important to program Event 3 for dead times with CBC.
Resonant/Multi Mode
In resonant/multi mode, the systems are often symmetrical. In this case, DPWMB may need to be controlled by the Cycle by Cycle Fault logic as well. Sometimes a shortened on time on one DPWM pin needs to be followed by an equal length on time on the other DPWM pin to prevent an offset from building up in a capacitor or inductor. In this case, it is possible to enable duty cycle matching in these two modes. If DPWMA or DPWMB is cut short by a CBC event, the next pulse, on the other DPWM pin, will also be shortened to the same length.
Here are the states for resonant and multi modes:
CBC_PWM_AB_EN | CBC_ADV_CNT_EN | CBC_BSIDE_ACTIVE_EN | CBC A | CBC B | Duty Match |
---|---|---|---|---|---|
0 | x | x | 0 | 0 | 0 |
1 | 0 | 0 | 1 | 1 | 0 |
1 | 1 | 0 | 1 | M | B matches A |
1 | 1 | 1 | 1 | 1 | both match |
CBC_SYNC_CUR_LIM_EN is used to control the slave sync. If this bit is set, the slave sync is advanced during current limit. This is not used in any topology configuration at this time. If this bit is set, the sync out pulse from the DPWM will occur if the CBC fault occurs. If the CBC fault does not occur during a period, the sync pulse will occur according to the normal setting of the sync control bit fields.
For more information on cycle by cycle current limit, refer to Chapter 6.