BQ40Z60_16 Datasheet, PDF (33/47 Pages) Texas Instruments – Programmable Battery Management Unit

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bq40z60
SLUSAW3C – DECEMBER 2014 – REVISED JULY 2015
MOSFET gate-driver power loss contributes to the dominant losses on the controller IC when the buck converter
is switching. The combined high side and low side MOSFET gate charge, Q_{g_total}, is proportional to the power
dissipation of the IC, as shown in Equation 12:
P_{ICLoss_driver} = V_IN × Q_{g_total} × f_s
(12)
Choosing FETs with a lower Q_{g_total} will reduce power loss.
10.2.2.5 Input Filter Design
During adaptor hot plug-in, the parasitic inductance and input capacitor from the adaptor cable form a second-
order system. The voltage spike at the VCC pin may be beyond the IC maximum voltage rating and damage the
IC. The input filter must be carefully designed and tested to prevent an overvoltage event on the VCC pin.
There are several methods for damping or limiting the overvoltage spike during adaptor hot plug-in. An
electrolytic capacitor with high ESR as an input capacitor can damp the overvoltage spike well below the IC
maximum pin voltage rating. A high-current-capability TVS Zener diode can also limit the overvoltage level to an
IC safe level. However, these two solutions may not have low cost or small size.
Figure 9 shows a cost-effective and small size solution. The R1 and C1 are composed of a damping RC network
to damp the hot plug-in oscillation. As a result, the overvoltage spike is limited to a safe level. D1 is used for
reverse voltage protection for the VCC pin (it can be the body diode of input ACFET). C2 is a VCC pin-
decoupling capacitor and it should be placed as close as possible to the VCC pin. R2 and C2 form a damping
RC network to further protect the IC from high dv/dt and high-voltage spike. The C2 value should be less than
the C1 value so R1 can be dominant over the ESR of C1 to get enough of a damping effect for hot plug-in. The
R1 and R2 packages must be sized to handle inrush-current power loss according to the resistor manufacturer’s
datasheet. The filter component values always must be verified with the real application, and minor adjustments
may be needed to fit in the real application circuit.
Adapter
connector
D1
R1
2Ω
C1
2.2 µF
(2010)
R2 ⁽¹²⁰⁶⁾
1Ω
VCC pin
C2
0.1-1 µF
Figure 9. Input Filter
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