Analog Devices ADP1878 Evaluation Board ADP1878-1.0-EVALZ ADP1878-1.0-EVALZ データシート
製品コード
ADP1878-1.0-EVALZ
ADP1878/ADP1879
Data
Sheet
Rev. B | Page 20 of 40
When the desired valley current limit (I
CLIM
) has been determined,
the current sense gain can be calculated as follows:
1.4 V
where:
R
R
ON
is the channel impedance of the low-side MOSFET.
A
CS
is the current sense gain multiplier (see Table 6 and Table 7).
Although the
have only four discrete current
sense gain settings for a given R
ON
variable, Table 7 and Figure 71
outline several available options for the valley current setpoint
based on various R
based on various R
ON
values.
Table 7. Valley Current Limit Program (See Figure 71)
R
ON
(mΩ)
Valley Current Level (A)
47 kΩ,
22 kΩ,
Open,
100 kΩ,
A
CS
= 3 V/V
A
CS
= 6 V/V
A
CS
= 12 V/V
A
CS
= 24 V/V
1.5
38.9
2
29.2
2.5
23.3
3
39.0
19.5
3.5
33.4
16.7
4.5
26.0
13
5
23.4
11.7
5.5
21.25
10.6
10
23.3
11.7
5.83
15
31.0
15.5
7.75
3.87
18
26.0
13.0
6.5
3.25
1
Blank cells are not applicable.
Figure 71. Valley Current-Limit Value vs. R
ON
of the Low-Side MOSFET
for Each Programming Resistor (RES)
The valley current limit is programmed as listed in Table 7 and
shown in Figure 71. The inductor that is chosen must be rated
to handle the peak current, which is equal to the valley current
from Table 7 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).
shown in Figure 71. The inductor that is chosen must be rated
to handle the peak current, which is equal to the valley current
from Table 7 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).
Figure 72. Valley Current-Limit Threshold in Relation to Inductor Ripple Current
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
V
AL
L
E
Y
CUR
RE
NT
L
IM
IT
(
A
)
R
ON
(mΩ)
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
37
35
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
7
5
3
RES = 47kΩ
A
CS
= 3V/V
RES = 22kΩ
A
CS
= 6V/V
RES = NO RES
A
CS
= 12V/V
RES = 100kΩ
A
CS
= 24V/V
09
44
1-
07
1
INDUCTOR
CURRENT
VALLEY CURRENT-LIMIT
THRESHOLD (SET FOR 25A)
∆I = 33%
OF 30A
CS AMP
OUTPUT
SWING
CURRENT
SENSE
AMPLIFIER
OUTPUT
2.4V
1V
0A
35A
30A
32.25A
37A
49A
39.5A
∆I = 45%
OF 32.25A
∆I = 65%
OF 37A
MAXIMUM DC LOAD
CURRENT
09
441
-0
72