DRV8300-Q1
ZHCSPF5 –APRIL 2022
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9.2.1 Design Requirements
表9-1 lists the example design input parameters for system design.
表9-1. Design Parameters
EXAMPLE DESIGN PARAMETER
REFERENCE
EXAMPLE VALUE
MOSFET
-
CSD19532Q5B
12 V
Gate Supply Voltage
Gate Charge
VGVDD
QG
48 nC
9.2.2 Bootstrap Capacitor and GVDD Capacitor Selection
The bootstrap capacitor must be sized to maintain the bootstrap voltage above the undervoltage lockout for
normal operation. 方程式1 calculates the maximum allowable voltage drop across the bootstrap capacitor:
¿8$56: = 8)8&& F8$116&F8
$5678
(1)
=12 V –0.85 V –4.5 V = 6.65 V
where
• VGVDD is the supply voltage of the gate drive
• VBOOTD is the forward voltage drop of the bootstrap diode
• VBSTUV is the threshold of the bootstrap undervoltage lockout
In this example the allowed voltage drop across bootstrap capacitor is 6.65 V. It is generally recommended that
ripple voltage on both the bootstrap capacitor and GVDD capacitor should be minimized as much as possible.
Many of commercial, industrial, and automotive applications use ripple value between 0.5 V to 1 V.
The total charge needed per switching cycle can be estimated with 方程式2:
+.$5_64#05
3616 = 3) +
B
59
(2)
=48 nC + 220 μA/20 kHz = 50 nC + 11 nC = 61 nC
where
• QG is the total MOSFET gate charge
• ILBS_TRAN is the bootstrap pin leakage current
• fSW is the is the PWM frequency
The minimum bootstrap capacitor an then be estimated as below assuming 1V ΔVBSTx
:
3
%
=
616W
$56_/+0
¿8
$56:
(3)
= 61 nC / 1 V = 61 nF
The calculated value of minimum bootstrap capacitor is 61 nF. It should be noted that, this value of capacitance
is needed at full bias voltage. In practice, the value of the bootstrap capacitor must be greater than calculated
value to allow for situations where the power stage may skip pulse due to various transient conditions. It is
recommended to use a 100 nF bootstrap capacitor in this example. It is also recommenced to include enough
margin and place the bootstrap capacitor as close to the BSTx and SHx pins as possible.
%
)8&&
R 10 × %$56:
(4)
= 10*100 nF= 1 μF
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