DRV8307_15 Datasheet, PDF (16/34 Pages) Texas Instruments – DRV8307 Brushless DC Motor Controller

DRV8307
SLVSCK2 – APRIL 2014
HS drive
xHS
15 µs
High Z
Low
Z
High Z
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Low Z
High Z
15 µs
High Z Low Z
High Z
High Z
LS drive
Low
Z
xLS
Figure 8. Gate Control Behavior
The peak drive current of the pre-drivers is fixed at 30 mA.
When changing the state of the output, the peak current is applied for a short period of time (15 μs) to charge the
gate capacitance. After this time, a weak current source is used to keep the gate at the desired state.
During high-side turn-on, the low-side gate is held low with a low impedance. This prevents the gate-source
capacitance of the low-side FET from inducing turn-on. Similarly, during low-side turn-on, the high-side gate is
held off with a low impedance.
The pre-driver circuits include enforcement of a dead time in analog circuitry, which prevents the high-side and
low-side FETs from conducting at the same time.
8.3.7 Current Limit
The current limit circuit activates if the voltage detected across the low-side sense resistor exceeds V_LIMITER.
Note that the current limit circuit is ignored immediately after the PWM signal goes active for a short blanking
time, to prevent false trips of the current limit circuit.
If current limit activates, the high-side FET is disabled until the beginning of the next PWM cycle. If synchronous
rectification is enabled when the current limit activates, the low-side FET is activated while the high-side FET is
disabled.
8.3.8 Charge Pump
Since the output stages use N-channel FETs, a gate drive voltage higher than the VM power supply is needed to
fully enhance the high-side FETs. The DRV8307 device integrates a charge pump circuit that generates a
voltage approximately 10 V more than the VM supply for this purpose.
The charge pump requires two external capacitors for operation. For details on these capacitors (value,
connection, and so forth), refer to Figure 9.
The charge pump is shut down when in standby mode (ENABLEn inactive).
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