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IRF7811 Datasheet(PDF) 20 Page - Analog Devices

Part No. IRF7811
Description  Synchronous Buck Controller
Download  40 Pages
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Manufacturer  AD [Analog Devices]
Direct Link  http://www.analog.com
Logo AD - Analog Devices

IRF7811 Datasheet(HTML) 20 Page - Analog Devices

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ADP1878/ADP1879
Data Sheet
Rev. A | Page 20 of 40
When the desired valley current limit (ICLIM) has been determined,
the current sense gain can be calculated as follows:
1.4V
where:
RON is the channel impedance of the low-side MOSFET.
ACS is the current sense gain multiplier (see Table 6 and Table 7).
Although the ADP1878/ADP1879 have only four discrete current
sense gain settings for a given RON variable, Table 7 and Figure 71
outline several available options for the valley current setpoint
based on various RON values.
Table 7. Valley Current Limit Program (See Figure 71)
RON
(mΩ)
Valley Current Level (A)1
47 kΩ,
22 kΩ,
Open,
100 kΩ,
ACS = 3 V/V
ACS = 6 V/V
ACS = 12 V/V
ACS = 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
7.5
18
26.0
13.0
6.5
3.25
1 Blank cells are not applicable.
Figure 71. Valley Current-Limit Value vs. RON 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).
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
RON (mΩ)
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
RES = 47kΩ
ACS = 3V/V
RES = 22kΩ
ACS = 6V/V
RES = NO RES
ACS = 12V/V
RES = 100kΩ
ACS = 24V/V
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


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