Descripción

The DRV8870 device is a brushed-DC motor driver for printers, appliances, industrial equipment, and other small machines. Two logic inputs control the Hbridge driver, which consists of four N-channel MOSFETs that can control motors bidirectionally with up to 3.6-A peak current. The inputs can be pulsewidth modulated (PWM) to control motor speed, using a choice of current-decay modes. Setting both inputs low enters a low-power sleep mode.
The DRV8870 device features integrated current regulation, based on the analog input VREF and the voltage on the ISEN pin, which is proportional to motor current through an external sense resistor. The ability to limit current to a known level can significantly reduce the system power requirements and bulk capacitance needed to maintain stable voltage, especially for motor startup and stall conditions.
The device is fully protected from faults and short circuits, including undervoltage (UVLO), overcurrent (OCP), and overtemperature (TSD). When the fault condition is removed, the device automatically resumes normal operation.

 

Características

• H-Bridge Motor Driver
– Drives One DC Motor, One Winding of a Stepper Motor, or Other Loads
• Wide6.5-V to 45-V Operating Voltage
• 565-mΩ Typical RDS(on) (HS + LS)
• 3.6-A Peak Current Drive
• PWMControl Interface
• Integrated Current Regulation
• Low-Power Sleep Mode
• Small Package and Footprint
– 8-Pin HSOP With PowerPAD™
– 4.9 × 6.0 mm
• Integrated Protection Features
– VMUndervoltage Lockout (UVLO)
– Overcurrent Protection (OCP)
– Thermal Shutdown (TSD)
– Automatic Fault Recovery

 

Aplicaciones

• Printers
- Electrodomésticos
• Industrial Equipment
• Other Mechatronic Applications

 

Visión general

The DRV8870 device is an optimized 8-pin device for driving brushed DC motors with 6.5 to 45 V and up to 3.6.A peak current. The integrated current regulation restricts motor current to a predefined maximum. Two logic inputs control the H-bridge driver, which consists of four N-channel MOSFETs that have a typical Rds(on) of 565 mΩ (including one high-side and one low-side FET). A single-power input, VM, serves as both device power and the motor winding bias voltage. The integrated charge pump of the device boosts VM internally and fully enhances the high-side FETs. Motor speed can be controlled with pulse-width modulation, at frequencies between 0 to 100 kHz. The device has an integrated sleep mode that is entered by bringing both inputs low. An assortment of protection features prevent the device from being damaged if a system fault occurs.

 

Bridge Control

The inputs can be set to static voltages for 100% duty cycle drive, or they can be pulse-width modulated (PWM) for variable motor speed. When using PWM, switching between driving and braking typically works best. For example, to drive a motor forward with 50% of the maximum RPM, IN1 = 1 and IN2 = 0 during the driving period, and IN1 = 1 and IN2 = 1 during the other period. Alternatively, the coast mode (IN1 = 0, IN2 = 0) for fast current decay is also available. The input pins can be powered before VM is applied.

 

Dead Time

When an output changes from driving high to driving low, or driving low to driving high, dead time is automatically inserted to prevent shoot-through. The tDEAD time is the time in the middle when the output is High-Z. If the output pin is measured during tDEAD, the voltage depends on the direction of current. If the current is leaving the pin, the voltage is a diode drop below ground. If the current is entering the pin, the voltage is a diode drop above VM. This diode is the body diode of the high-side or low-side FET.

 

Sense Resistor

The power dissipated by the sense resistor equals IRMS2 × R. For example, if peak motor current is 3 A, RMS motor current is 1.5 A, and a 0.2-Ω sense resistor is used, the resistor dissipates 1.5 A2 × 0.2 Ω = 0.45 W. The power quickly increases with higher current levels.
Resistors typically have a rated power within some ambient temperature range, along with a derated power curve for high ambient temperatures. When a PCB is shared with other components generating heat, the system designer should add margin. Measuring the actual sense resistor temperature in a final system is always best.
Because power resistors are larger and more expensive than standard resistors, using multiple standard resistors in parallel, between the sense node and ground, is common and distributes the current and heat dissipation.