C. tune i, An368 – Cirrus Logic AN368 User Manual
Page 26
AN368
26
AN368REV2
c. Tune I
PK(FB)
Compensations for Optimum Linear Performance
To achieve high accuracy for the output current, it is essential to obtain a highly accurate peak current I
PK(FB)
.
Time T1 compensation T1
comp
is used to factor in the peak overshoot of the inductor current due to the current
sense comparator delay and other path delays involved in turning ‘OFF’ the FET. If I
PKx(REF)
is the desired
peak current, the actual peak can be adjusted using the CS_DELAY[2:0] bits in register Config60 at Address
92. The optimized peak current is given by Equation 51.
where,
T1
comp
= CS_DELAY[2:0]
50ns
CS_DELAY[2:0] = dT and is measured as shown in Figure 8b
Figure 8a and 8b illustrate the tuning of I
PKx(FB)
using T1 compensation.
I
PKx FB
I
PKx REF
1 T1
comp
+
T1
measured
----------------------------
=
[Eq. 51]
Figure 8a. Tuning I
PKx(FB)
Using T1 Compensation
Figure 8b. I
PKx(FB)
Compensation
CS1630/31
GD
FBSENSE
Q5
R27
13
+
-
11
R21
To Digital
Digital GD
FBSENSE Blanking
I
PK(REF)
S
R
_
Q
Q
DAC
Peak Current
GND
T1
I
PK(REF)
I
PK
dT
T2
iL
GD