34652 datasheet(21/26 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34652

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 pins,

as shown in Figure 19, page 18. 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(kΩ) + 1.4 kΩ] / 335

RICHG(kΩ) = 335 * ICHG(A) - 1.4 kΩ

Table 7. RICHG Values for Some Desired ICHG Values

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 pins,

as shown in Figure 19, page 18. 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(kΩ)]

ICHG(A)

RICHG(kΩ)

0.05

15.35

0.1

32.10

0.15

48.85

0.2

65.60

0.25

82.35

0.3

99.10

0.35

115.85

0.4

135.60

0.45

149.35

0.5

166.10

Table 8. CICHG Values for Some Desired tICHGR Values

at a Specific ICHG Value

tICHGR(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

217.16

103.84

20.07

100

120

140

160

180

0.1

0.2

0.3

0.4

0.5

0.6

ICHG (A)

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