DRV8870_16 Datasheet, PDF (10/25 Pages) Texas Instruments – Brushed DC Motor Driver

DRV8870
SLVSCY8A – AUGUST 2015 – REVISED JANUARY 2016
7.3.5 Protection Circuits
The DRV8870 is fully protected against VM undervoltage, overcurrent, and overtemperature events.
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7.3.5.1 VM Undervoltage Lockout (UVLO)
If at any time the voltage on the VM pin falls below the undervoltage lockout threshold voltage, all FETs in the H-
bridge will be disabled. Operation will resume when VM rises above the UVLO threshold.
7.3.5.2 Overcurrent Protection (OCP)
If the output current exceeds the OCP threshold I_OCP for longer than t_OCP, all FETs in the H-bridge are disabled
for a duration of t_RETRY. After that, the H-bridge will be re-enabled according to the state of the INx pins. If the
overcurrent fault is still present, the cycle repeats; otherwise normal device operation resumes.
7.3.5.3 Thermal Shutdown (TSD)
If the die temperature exceeds safe limits, all FETs in the H-bridge will be disabled. After the die temperature has
fallen to a safe level, operation automatically resumes.
FAULT
VM undervoltage lockout (UVLO)
Overcurrent (OCP)
Thermal Shutdown (TSD)
Table 2. Protection Functionality
CONDITION
VM < V_UVLO
I_OUT > I_OCP
T_J > 150°C
H-BRIDGE BECOMES
Disabled
Disabled
Disabled
RECOVERY
VM > V_UVLO
t_RETRY
T_J < T_SD – T_HYS
7.4 Device Functional Modes
The DRV8870 can be used in multiple ways to drive a brushed DC motor.
7.4.1 PWM With Current Regulation
This scheme uses all of the device’s capabilities. I_TRIP is set above the normal operating current, and high
enough to achieve an adequate spin-up time, but low enough to constrain current to a desired level. Motor speed
is controlled by the duty cycle of one of the inputs, while the other input is static. Brake/slow decay is typically
used during the off-time.
7.4.2 PWM Without Current Regulation
If current regulation is not needed, pin ISEN should be directly connected to the PCB ground plane. VREF must
still be 0.3 to 5 V, and larger voltages provide greater noise margin. This mode provides the highest possible
peak current: up to 3.6 A for a few hundred milliseconds (depending on PCB characteristics and the ambient
temperature). If current exceeds 3.6 A, the device might reach overcurrent protection (OCP) or overtemperature
shutdown (TSD). If that happens, the device disables and protects itself for about 3 ms (t_RETRY) and then
resumes normal operation.
7.4.3 Static Inputs With Current Regulation
IN1 and IN2 can be set high and low for 100% duty cycle drive, and I_TRIP can be used to control the motor’s
current, speed, and torque capability.
7.4.4 VM Control
In some systems it is desirable to vary VM as a means of changing motor speed. See Motor Voltage for more
information.
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