User Manual
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V 1.0
2021-08-25
XDPP1100 technical reference manual
Digital power controller
Current sense (IS)
The reconstructed current from the CE drives the AFE DAC in order to center the quantizer at the currently
estimated current value. It is also processed downstream by the ISP to be used by the telemetry and fault
processing functions. In addition, this current is applied in PCMC to compare against the reference current to
determine the PWM turn-off time.
A simplified block diagram of the CE was shown in
, where it is emphasized with dashed lines. It has
four main functions:
•
PWM state delay function
•
Slope estimator
•
Error tracking function
•
Parasitic inductance L
trace
The following subsections describe the PWM state and slope estimator, as well as error tracking and parasitic
inductance estimation in more detail, emphasizing the user-definable parameters. In this section, various CE-
related register names begin as
ceX_
, where the X is:
•
X = 0 for ISEN/IREF input pins
•
X = 1 for BISEN/BIREF input pins
Thus, depending on which current sensing pins are used, the programming needs to be performed accordingly.
3.2.2.1
PWM state
The XDPP1100 controller continuously predicts the current phase and ripple based on the state of the PWM
pulse. Therefore, the PWM state is critical to both slope estimation and error tracking, because it is used to
determine the equation for voltage across the inductor in order to estimate the inductor current slope.
The PWM has three states with respect to the inductor current cycle for a buck-derived isolated topology, as
illustrated in
. These states are:
•
On-state: inductor current rising slope when the PWM FET is on
•
Off-state: inductor current falling slope when the PWM FET is off and the SR FET is on
•
High impedance (HIZ) state: inductor current slope when both switches are off; in case of positive current,
the slope is falling toward the zero and for negative current the slope is increasing toward the zero
Figure 21
PWM state definition with respect to the inductor current cycle
In the actual system, there is delay between the internal PWM state and the actual PWM state observed from
the output inductor. In order to better align the internal state to the sensed current waveform, the internal
PWM can be delayed. This is possible via register
ce_pwmwin_dly
. While adjusting this parameter, all possible
delay sources (e.g., controller output latency, isolator latency, driver latency) within the system should be
considered. It should be noted that an exact unit-by-unit delay match is not required, as the error tracking
corrects minor timing mismatches at the PWM state transitions.
PWM
SR
Inductor current
ON
ON
OFF
HIZ