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| MC34652 Datasheet, PDF (20/25 Pages) Freescale Semiconductor, Inc – 2.0 A Negative Voltage Hot Swap Controller with Enhanced Programmability | |||
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TYPICAL APPLICATIONS
The low charging current value of ICHG is intended to limit
the temperature increase during the load capacitor charging
process, and the gradual rise to ICHG is to prevent transient
dips in the input voltage due to sharp increases in the limit
current. This prevents the input voltage from drooping due to
current steps acting on the input line inductance, and that in
turn prevents a premature activation of the UV detection
circuit.
Choosing the External Resistor RICHG Value
The user can change the value of the charging current limit
by adding a resistor (RICHG) between the ICHG and VIN
terminals, as shown in Figure 19, page 17. The charging
current value ranges between 50 mA and 500 mA, with a
default value of 100 mA. Table 7 lists examples of RICHG for
different values of ICHG and Figure 21 shows a plot of RICHG
versus ICHG. It is recommended that the closest 1% standard
resistor value to the actual value be chosen.
Note Accuracy requirements are application dependent.
To calculate the value of the RICHG resistor we use the
following equations:
ICHG(A) = [RICHG(kâ¦) + 1.4 kâ¦] / 335
RICHG(kâ¦) = 335 * ICHG(A) - 1.4 kâ¦
Table 7. RICHG Values for Some Desired ICHG Values
ICHG (A)
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
RICHG (kâ¦)
15.35
32.10
48.85
65.60
82.35
99.10
115.85
135.60
149.35
166.10
180
160
140
120
100
80
60
40
20
0
0
0.1 0.2 0.3 0.4 0.5 0.6
ICCHHGG (AA)
Figure 21. External Resistor (RICHG) Value Versus
Charging Current Limit Value (ICHG)
Choosing the External Capacitor CICHG Value
The user can also change the charging current rise time by
adding a capacitor (CICHG) between the ICHG and VIN
terminals, as shown in Figure 19, page 17. The charging
current rise time ranges between 1.0 ms (default value) and
a recommended maximum of 10 ms. Table 8 lists examples
of CICHG for different values of tICHGR and Figure 22 shows a
plot of CICHG versus tICHGR.
To calculate the value of the CICHG capacitor we use the
following equation:
CICHG(nF) = 1000 * tICHGR(ms) / [3 * RICHG(kâ¦)]
Table 8. CICHG Values for Some Desired tICHGR Values
at a Specific ICHG Value
t ICHGR (ms)
CICHG (nF)
ICHG = 0.05 A
CICHG (nF)
ICHG = 0.1 A
CICHG (nF)
ICHG = 0.5 A
1.0
21.72
10.38
2.01
2.0
43.43
20.77
4.01
3.0
65.15
31.15
6.02
4.0
86.86
41.54
8.03
5.0
108.58
51.92
10.03
6.0
130.29
62.31
12.04
7.0
152.01
72.69
14.05
8.0
173.72
83.07
16.05
9.0
195.44
93.46
18.06
10
217.16
103.84
20.07
34652
20
Analog Integrated Circuit Device Data
Freescale Semiconductor
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