BQ24750_07 Datasheet, PDF (30/38 Pages) Texas Instruments – Host-controlled Multi-chemistry Battery Charger with Integrated System Power Selector and AC Over-Power Protection

bq24750
SLUS735 – DECEMBER 2006
www.ti.com
APPLICATION INFORMATION (continued)
For a typical notebook charger application, the total stray inductance of the adapter output wire and the PCB
connections is normally 5–12 µH, and the total effective resistance of the input connections is 0.15–0.5 Ω.
Figure 37(a) demonstrates that a higher Ci helps to damp the voltage spike. Figure 37(b) demonstrates the
effect of the input stray inductance Li on the input voltage spike. The dashed curve in Figure 37(b) represents
the worst case for Ci=40 µF. Figure 37(c) shows how the resistance helps to suppress the input voltage spike.
35
Ci = 20 mF
30
Ci = 40 mF
25
Ri = 0.21 W,
Li = 9.3 mH
35
Li = 5 mF
30
Li = 12 mF
25
Ri = 0.15 W,
Ci = 40 mF
20
20
15
15
10
10
5
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Time - ms
(a) Vc with various Ci values
5
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Time - ms
(b) Vc with various Li values
35
Ri = 0.15 W
30
Ri = 0.50 W
25
Li = 9.3 mH,
Ci = 40 mF
20
15
10
5
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Time - ms
(c) Vc with various Ri values
Figure 37. Parametric Study Of The Input Voltage
Minimizing the input stray inductance, increasing the input capacitance and using high-ESR input capacitors
helps to suppress the input voltage spike.
30
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