Datasheet

ADP1882/ADP1883
Rev. 0 | Page 21
Although the ADP1882/ADP1883 have only four discrete current-
sense gain settings for a given R
ON
variable, Table 6 and Figure 71
outline several available options for the valley current setpoint
based on various R
ON
values.
The valley current limit is programmed as outlined in Tabl e 6
and Figure 71. The inductor chosen must be rated to handle the
peak current, which is equal to the valley current from Tabl e 6
plus the peak-to-peak inductor ripple current (see the Inductor
Selection section). In addition, the peak current value must be
used to compute the worst-case power dissipation in the
MOSFETs (see Figure 72).
Table 6. Valley Current Limit Program
1
R
ON
(mΩ)
Valley Current Level
47 kΩ 22 kΩ Open 100 kΩ
A
CS
= 3.4 V/V A
CS
= 6.6 V/V A
CS
= 26.7 V/V A
CS
= 13.4 V/V
1.5 38.5
2 28.8
2.5 23.1
3 38.46 19.2
3.5 32.97 16.5
4.5 25.64 12.8
5 23.08 11.5
5.5 20.98 10.5
10 23.08 11.54 5.77
15 30.769 15.38 7.692 3.85
of 40
18 25.641 12.82 6.41 3.21
1
Refer to Figure 71 for more information and a graphical representation.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
VALLEY CURRENT LIMIT (A)
R
ON
(m)
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
RES = 47k
A
CS
= 6.6V/V
RES = 22k
A
CS
= 3.4V/V
RES = 100k
A
CS
= 13.4V/V
RES = OPEN
A
CS
= 26.7V/V
08901-070
Figure 71. Valley Current-Limit Value vs. R
ON
of the Lower-Side MOSFET
for Each Programming Resistor (RES)
INDUCTOR
CURRENT
VALLEY CURRENT-LIMIT
THRESHOLD (SET FOR 25A)
I = 33%
OF 30A
COMP
OUTPUT
SWING
COMP
OUTPUT
2.4V
0.9V0A
35A
30A
32.25A
37A
49
A
39.5A
I = 65%
OF 37A
I = 45%
OF 32.25A
MAXIMUM DC LOAD
CURRENT
08901-071
Figure 72. Valley Current-Limit Threshold in Relation to Inductor Ripple Current
HICCUP MODE DURING SHORT CIRCUIT
A current-limit violation occurs when the current across
the source and drain of the lower-side MOSFET exceeds the
current-limit setpoint. When 32 current-limit violations are
detected, the controller enters the idle mode and turns off the
MOSFETs for 6 ms, allowing the converter to cool down. Then,
the controller reestablishes soft start and begins to cause the
output to ramp up again (see Figure 73). While the output
ramps up, COMP is monitored to determine if the violation is
still present. If it is still present, the idle event occurs again,
followed by the full-chip power-down sequence. This cycle
continues until the violation no longer exists. If the violation
disappears, the converter is allowed to switch normally,
maintaining regulation.
HS
CLIM
ZERO
CURRENT
REPEATED CURRENT-LIMIT
VIOLATION DETECTED
A PREDE
OF PULS
ALLO
TO
TERMINED NUMBER
ES IS COUNTED TO
W THE CONVERTER
COOL DOWN
SOFT START IS
REINITIALIZED TO
MONITOR IF THE
VIOLATION
STILL EXISTS
08901-072
Figure 73. Idle Mode Entry Sequence Due to Current-Limit Violations