DRV8320_17 Datasheet, PDF (61/89 Pages) Texas Instruments – 6 to 60-V Three-Phase Smart Gate Driver

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Typical Application (continued)
9.2.1.1 Design Requirements
Table 21 lists the example input parameters for the system design.
DRV8320, DRV8320R
DRV8323, DRV8323R
SLVSDJ3A – FEBRUARY 2017 – REVISED APRIL 2017
EXAMPLE DESIGN PARAMETER
Nominal supply voltage
Supply voltage range
MOSFET part number
MOSFET total gate charge
MOSFET gate to drain charge
Target output rise time
Target output fall time
PWM Frequency
Buck regulator output voltage
Maximum motor current
ADC reference voltage
Winding sense current range
Motor RMS current
Sense resistor power rating
System ambient temperature
Table 21. Design Parameters
REFERENCE
V_VM
Q_g
Q_gd
t_r
t_f
ƒ_PWM
V_VCC
I_max
V_VREF
I_SENSE
I_RMS
P_SENSE
T_A
EXAMPLE VALUE
24 V
8 V to 45 V
CSD18536KCS
83 nC (typical) at V_VGS = 10 V
14 nC (typical)
100 to 300 ns
50 to 150 ns
45 kHz
3.3 V
100 A
3.3 V
–40 A to +40 A
28.3 A
2W
–20°C to +105°C
9.2.1.2 Detailed Design Procedure
9.2.1.2.1 External MOSFET Support
The DRV832x family of devices MOSFET support is based on the charge-pump capacity and output PWM
switching frequency. For a quick calculation of MOSFET driving capacity, use Equation 9 and Equation 10 for
three phase BLDC motor applications.
Trapezoidal 120° Commutation: I_VCP > Q_g ׃_PWM
(9)
Sinusoidal 180° Commutation: I_VCP > 3 × Q_g ׃_PWM
where
• ƒ_PWM is the maximum desired PWM switching frequency.
• I_VCP is the charge pump capacity, which depends on the VM pin voltage.
• The multiplier based on the commutation control method, may vary based on implementation.
(10)
9.2.1.2.1.1 Example
If a system at V_VM = 8 V (I_VCP = 15 mA) uses a maximum PWM switching frequency of 45 kHz, then the charge-
pump can support MOSFETs using trapezoidal commutation with a Q_g < 167 nC, and MOSFETs with sinusoidal
commutation Q_g < 56 nC.
9.2.1.2.2 IDRIVE Configuration
The gate drive current strength, I_DRIVE, is selected based on the gate-to-drain charge of the external MOSFETs
and the target rise and fall times at the outputs. If I_DRIVE is selected to be too low for a given MOSFET, then the
MOSFET may not turn on completely within the t_DRIVE time and a gate drive fault may be asserted. Additionally,
slow rise and fall times will lead to higher switching power losses. TI recommends adjusting these values in
system with the required external MOSFETs and motor to determine the best possible setting for any application.
The I_DRIVEP and I_DRIVEN current for both the low-side and high-side MOSFETs are independently adjustable on
SPI devices through the SPI registers. On hardware interface devices, both source and sink settings are selected
simultaneously on the IDRIVE pin.
For MOSFETs with a known gate-to-drain charge Q_gd, desired rise time (t_r), and a desired fall time (t_f), use
Equation 11 and Equation 12 to calculate the value of I_DRIVEP and I_DRIVEN (respectively).
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