BQ24751B Datasheet, PDF (29/38 Pages) Texas Instruments – Host-Controlled Multi-Chemistry Battery Charger with Low Iq and System Power Selector

Not Recommended For New Designs
bq24751B
www.ti.com .......................................................................................................................................................... SLUS835A – JULY 2008 – REVISED MARCH 2009
Figure 38 (a) demonstrates a higher Ci helps dampen the voltage spike. Figure 38 (b) demonstrates the effect of
the input stray inductance Li upon the input voltage spike. Figure 38 (c) shows how increased resistance helps to
suppress the input voltage spike.
35
C_i = 20 mF
30
C_i = 40 mF
25
R_i = 0.21 W
L_i = 9.3 mH
35
L_i = 5 mH
30
L_i = 12 mH
25
R_i = 0.15 W
C_i = 40 mF
20
20
15
15
10
10
5
5
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Time - ms
(a) V_c with various C_i values
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Time - ms
(b) V_c with various L_i values
35
R_i = 0.15 W
30
R_i = 0.5 W
25
L_i = 9.3 mH
C_i = 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) V_c with various R_i values
Figure 38. Parametric Study Of The Input Voltage
As shown in Figure 38, minimizing the input stray inductance, increasing the input capacitance, and adding
resistance (including using higher ESR capacitors) helps suppress the input voltage spike. However, a user often
cannot control input stray inductance and increasing capacitance can increase costs. Therefore, the most
efficient and cost-effective approach is to add an external resistor.
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