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User Manual
295 of 562
V 1.0
2021-08-25
XDPP1100 technical reference manual
Digital power controller
Current balance (IBAL)
Figure 90
Simplified current balance block diagram
The circuit receives as its input the cycle-averaged current outputs from ISP1 and ISP2, which correspond to the
ISEN and BISEN sensed currents. The difference between these current inputs is computed and used as the
input to a PI compensation filter. The filter output, ibal_duty_adj, is capable of providing up to ±25 percent
duty-cycle adjustment on the PWM ramp0. Since the difference is computed as (BISEN
–
ISEN) and the
adjustment is provided on ramp0 only, it is required that:
•
ramp0 is used to generate the PWM outputs associated with the phase whose current is sensed by ISEN
•
ramp1 is used to generate the PWM outputs associated with the phase whose current is sensed by BISEN
In case of concern about current sense accuracy at low currents, register
ibal_en_thresh
makes it possible to
dynamically disable the current balance at low currents. The programming of this register is shown in
A setting to always enable the current balance is also provided.
Table 72
Current balance current enable threshold programming
ibal_en_thresh
Current balance enable threshold
0, 1
Always enabled
2
3 A
3
5 A
11.2
Current balance PI filter
The difference between ISEN and BISEN sensed currents is processed by the PI filter. It consists of:
•
a proportional term, which operates on the instantaneous current error
•
an integral term, which operates on the accumulated current error.
The integral term sets the low-frequency gain and the proportional term sets the high-frequency gain of the
filter. The magnitude response of the filter is defined by Equations (11.1) to (11.4).
|𝐻
𝑃𝐼
(𝑓)| = √𝐾
𝑃
2
+ (
𝐾
𝐼
2𝜋∙𝑇
𝑆𝐴𝑀𝑃𝐿𝐸
∙𝑓
)
2
(11.1)
𝐾
𝑃
= (8 + 𝑘𝑝_𝑖𝑏𝑎𝑙[2: 0]) ∙ 2
(𝐾
𝑃
_𝑖𝑏𝑎𝑙[5:3]−14)
(11.2)
𝐾
𝐼
= (8 + 𝑘𝑖_𝑖𝑏𝑎𝑙[2: 0]) ∙ 2
(𝐾
𝐼
_𝑖𝑏𝑎𝑙[5:3]−20)
(11.3)
𝑇
𝑆𝐴𝑀𝑃𝐿𝐸
=
1
𝐹
𝑆𝑊𝐼𝑇𝐶𝐻
(11.4)
Register values
kp_ibal
and
ki_ibal
larger than 55 are clamped to 55. Setting either of these registers to zero
individually disables the proportional or integral component of the filter. It should be noted that when the
integral component of the filter is disabled (either through
ki_ibal
= 0 or the current dropping below the value
isp2_iout_cavg
BISEN, S8.4
isp1_iout_cavg
ISEN, S8.4
-
+
S9.4
PI Filter
clk_fsw
ibal_duty_adj
S-1.9
To PWM Ramp 0
kp_ibal
ki_ibal
0
1
ibal_fw_adj
S-1.9
ibal_fw_en
S