DRV8305-Q1_16 Datasheet, PDF (22/54 Pages) Texas Instruments – Three-Phase Automotive Gate Driver

DRV8305-Q1
SLVSD12A – MAY 2015 – REVISED MARCH 2016
www.ti.com
The gate drivers are implemented as temperature compensated, constant current sources up to the 80 mA
(sink)/70 mA (source) current settings in order to maintain the accuracy required for precise slew rate control.
The current source architecture helps eliminate the temperature, process, and load-dependent variation
associated with internal and external series limiting resistors. Beyond that, internal switches are adjusted to
create the desired settings up to the 1.25 A (sink)/1 A (source) settings. For higher currents, internal series
switches are used to minimize the power losses associated with mirroring such large currents.
Control of the gate current during the MOSFET Miller region is a key component for adjusting the MOSFET V_DS
rise and fall times. MOSFET V_DS slew rates are a critical parameter for optimizing emitted radiations, energy and
duration of diode recovery spikes, dV/dt related turn on leading to shoot-through, and voltage transients related
to parasitics.
When a MOSFET is enhanced, three different charges must be supplied to the MOSFET gate. The MOSFET
drain to source voltage will slew primarily during the Miller region. By controlling the rate of charge to the
MOSFET gate (gate drive current strength) during the Miller region, it is possible to optimize the VDS slew rate
for the reasons mentioned.
1. Q_GS = Gate-to-source charge
2. Q_GD = Gate-to-drain charge (Miller charge)
3. Remaining Q_G
Drain
Level
Shifter
Gate
CGD
CGS
Source
Figure 10. MOSFET Charge Example
7.3.5.2 TDRIVE: Gate Driver State Machine
The DRV8305-Q1 gate driver uses an integrated state machine (TDRIVE) in the gate driver to protect against
excessive current on the gate drive outputs, shoot-through in the external MOSFET, and dV/dt turn on due to
switching on the phase nodes. The TDRIVE state machine allows for the design of a robust and efficient motor
drive system with minimal overhead.
The state machine incorporates internal handshaking when switching from the low to the high-side external
MOSFET or vice-versa. The handshaking is designed to prevent the external MOSFETs from entering a period
of cross conduction, also known as shoot-through. The internal handshaking uses the V_GS monitors of the
DRV8305-Q1 to determine when one MOSFET has been disabled and the other can be enabled. This allows the
gate driver to insert an optimized dead time into the system without the risk of cross conduction. Any deadtime
added externally through the MCU or SPI register will be inserted after the handshake process.
The state machine also incorporates a gate drive timer to ensure that under abnormal circumstances such as a
short on the MOSFET gate or the inadvertent turn on of a MOSFET V_GS clamp, the high peak current through
the DRV8305-Q1 and MOSFET is limited to a fixed duration. This concept is visualized in the figure below. First,
the DRV8305-Q1 receives a command to enable or disable the MOSFET through INHx or INLx inputs. Second,
the gate driver is enabled and a strong current is applied to the MOSFET gate and the gate voltage begins to
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