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User Manual
52 of 562
V 1.0
2021-08-25
XDPP1100 technical reference manual
Digital power controller
Current sense (IS)
•
ceX_ktrack_on
, for on-state
•
ceX_ktrack_off
, for off-state
•
ceX_ktrack_hiz
, for high impedance state
In addition, register
ceX_iterm
defines an integral coefficient which is applied across all states if set to a non-
zero value. Setting this current sense tracking error integrator coefficient to 0 disables the error accumulation.
The PWM transition might cause noise on the current sense signal. Therefore, certain parameters exist that are
used to blank the ADC feedback. The following registers can be used to define the transition time windows:
•
ceX_blank_ne_dly
defines the time subsequent to the PWM on-state negative edge during which the error
tracking output is blanked to 0 (i.e., the gain is set to 0)
•
ceX_blank_pe_dly
defines the time after a PWM on-state positive edge during which the error tracking
output is blanked to 0
3.2.2.4
Trace inductance of the PCB current sensing
The PCB trace resistance can be used for current sensing. In the ideal case the parasitic inductance would be
zero, and the current sense voltage shape would be a clear sawtooth waveform. However, in practice this trace
inductance is not zero and it introduces a step to the current sense waveform, as indicated by Equation (3.9).
𝑉
𝑆𝐸𝑁
= 𝑅
𝑃𝐶𝐵
∗ 𝐼 + 𝐿
𝑃𝐶𝐵
∗
𝑑𝐼
𝑑𝑡
(3.9)
Where
𝑑𝐼
𝑑𝑡
is a function of V
RECT
, V
OUT
and L
OUT
shows the current sense voltage waveforms for the
theoretical case L = 0 (V
RPCB
in red) and L ≠ 0 (V
SEN
in blue).
Figure 29
PCB trace inductance
Register
ce_ltrace
is provided to compensate for this step in the input to the AFE DAC. The compensation value
is obtained according to Equation (3.10), where the parameter ce_ltrace_real is defined in Equation (3.11).
𝑐𝑒_𝑙𝑡𝑟𝑎𝑐𝑒 = 𝐼𝑁𝑇 (
𝑐𝑒_𝑙𝑡𝑟𝑎𝑐𝑒_𝑟𝑒𝑎𝑙
2𝐻/Ω𝑠𝑒𝑐
)
,
(3.10)
𝑐𝑒_𝑙𝑡𝑟𝑎𝑐𝑒_𝑟𝑒𝑎𝑙 =
𝐿
𝑃𝐶𝐵
(𝐻)
(2∗𝑅
𝑃𝐶𝐵
(Ω)∗10𝑒−8𝑠𝑒𝑐)
,
(3.11)
3.3
Current sense processor
The main purpose of the ISP is to convert digitally reconstructed inductor current waveform from ADC codes
into a digital representation of amps. A simplified block diagram of the ISP is shown in
L
PCB
R
PCB
I
+ V
RPCB
-
+ V
SEN
-
V
SEN
V
RPCB