DRV3201-Q1_16 Datasheet, PDF (41/60 Pages) Texas Instruments – DRV3201-Q1 3 Phase Motor Driver-IC for Automotive Safety Applications

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DRV3201-Q1
SLVSBD6D – MAY 2012 – REVISED AUGUST 2015
Typical Application (continued)
The switching current formed by charging the gates of the external FETs at the given PWM frequency can be
calculated as follows:
I_boost,qg = f_PWM g #FETs g Q_gate
(2)
I_boost = I_boost,sw + I_boost,qg
(3)
Calculation example 1:
f_PWM = 25 kHz
Q_gate = 250 nC
Number of FETs = 6
I_boost,sw = 25 kHz • 6 • 3 mA / 30 kHz • 6 = 2.5 mA
I_boost,qg = 25 kHz • 6 • 250 nC = 37.5 mA
I_boost = 2.5 mA + 37.5 mA = 40 mA
Using the IBOOST = 40 mA from Figure 14 and Figure 15, the total current consumption from VS is 130 mA at
T_A = 25°C and for T_A = 125°C. This gives a total power consumption of 1.82 Watt at T_A = 25°C and at
T_A = 125°C for VS = 14 V.
Calculation example 2:
f_PWM = 20kHz
Q_gate = 200nC
Number of FETs = 6
I_boost,sw = 20 kHz • 6 • 3 mA / 30 kHz • 6 = 2 mA
I_boost,qg = 20 kHz • 6 • 200 nC = 24 mA
I_boost = 2 mA + 24 mA = 27 mA
To estimate the total current consumption from the VS battery supply, the curve IBOOST = 30 mA from
Figure 14 and Figure 15 can be used. From this curve, it follows that for VS = 14 V, the total current consumption
from VS is 105 mA at T_A = 25°C respectively 107 mA at T_A = 125°C. This gives a total power consumption of
1.47 Watt at T_A = 25°C respectively, 1.50 Watt at T_A = 125°C for VS = 14 V.
From these examples, it can be seen how the gate-charge and the PWM frequency impact the load current for
the boost converter and the total battery current consumption in Figure 14 and Figure 15. The total power
consumption can be calculated from this.
8.2.1.2.2 Boost Converter
The output current capability of the boost converter can be configured with the external Rshunt_boost resistor to
0.1 V/Rshunt_boost (note that this resistor must be able to conduct the boost switching current). The output
current capability can be dimensioned to the needed current determined by the PWM switching frequency and
the gate-charge of the external power FETs. TI recommends choosing a coil having a current saturation level of
at least 30% above the current limit level set with the resistor Rboost_shunt. The operation principle of the boost
converter is based on a burst mode fixed frequency controller. During the on-time, the internal low-side boost
FET is turned on until the current limit level is detected. The off-time is calculated proportionally from a 2.5 MHz
time-reference by sensing the supply voltage VS and the output voltage VBOOST. The formula for the calculated
off-time is given in Equation 4, with f_boost = 2.5 MHz.
VS
t_off = _{VBOOST g fBOOST}
(4)
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