# What is meant constant voltage control of h-bridge

I am using LV8075LP as the h-bridge to drive small 3V, 90mA coin vibration motor. I came across a few terms that I need to understand.

1. Constant voltage control
2. Output full drive

Also, can I use this particular h bridge to drive motors using PWM or is it just used for switching ON and OFF the motor at full speed?

• You could drive it with PWM without an issue. What is the context of those terms? – sherrellbc Jun 25 '14 at 5:59
• @sherrellbc, For some reason I am extremely confused. I was looking to make this IC work with PWM but now I have my doubts that it would work because of the words the datasheet uses 'constant voltage control' and 'output full drive'. Did you go through the datasheet? – David Norman Jun 25 '14 at 6:04

## 1 Answer

The LV8075LP has internal analog buffers that drive the motor with a voltage that is 2x the voltage on the VC pin. This is the the reason it is called a constant voltage driver. The Vref pin provides a 1.5 volt reference that can be used as a voltage reference to connect directly to the VC pin or connect to the VC pin through a voltage divider. To drive the motor with the full supply voltage (full output drive), connect VC to VCC.

A PWM control scheme can be implemented in two ways: The first is it to drive the IN1 or IN2 pin with a PWM signal depending on which direction the motor should turn. The second is to used a filtered PWM signal to provide a DC voltage to the VC pin and use the constant voltage driver in the chip to drive the motor. Keeping in mind that the motor voltage is 2x the VC voltage.

• Thanks for your answer Waltx. See that is what I am confused about. I want to use PWM and not 'full drive'. So what if I connect VC directly to VCC, would that just drive the motor as full speed regardless of what comes into the IN1 and IN2 inputs? – David Norman Jun 25 '14 at 6:41
• By connecting the VC pin to the VCC supply pin the motor will be driven by the VCC voltage. The IN1 and IN2 pins are digital inputs and will control the motor direction and brake condition. If speed control is required the IN1 or IN2 pin can be driven by a PWM signal. – waltx Jun 25 '14 at 21:31
• To drive the motor VCC is connected to VM (motor voltage). But VC is an analog voltage – David Norman Jun 26 '14 at 1:34
• Please read the data sheet, study the block diagram and read the answer I posted previously. Yes, the VC pin is an analog pin. The VC pin is used as an input to an internal analog buffer that supplies the voltage to the motor through the H bridge. – waltx Jun 26 '14 at 4:22