Hello,
This is the first time we touch H-Bridge motor driver so there is a number of questions:
How to isolate MCU and other IC from the motor control part, such that the sudden on and off of motor doesn't cause
1. Noise
2. Instability
in other parts of the circuit?
We have an application powered by a 3.7V 1000mAh Lithium-ion battery. Other parts of the board in total, as we currently estimated, uses less than 500mA current at its maximum usage. However, there is also a stepper motor we are going to put on the board, and the current for driving each step of the motor could be as large as 800mA.
1C current | 1000mA |
Motor current | 800mA = 500mA × 160% |
Total current | 800mA + 500mA = 130% × 1C |
Motor speed | < 30 steps/sec |
Motor (H-Bridge) supply voltage | 3.7V |
We noticed that: (1) The sudden switch of motor cause current as large as 160% of all other microelectronic components together. (2) There sum exceeds "1C"rate, in which "1C" means the discharging rate as found on the battery label (here 1000mA).
So would this abrupt rise of current cause severe disruption to other part of the circuit? I guess that there are at least the following factors to consider:
1. Response time of battery.
2. Response time of power management IC (s)
Assume, as an extreme case, that the battery's response time is pretty poor: would the sudden rise of motor current depletes MCU and lowers MCU voltage? If it happens, this could cause MCU itself to reset, or voltage supervisory IC would reset the MCU. So how could disasters like this be prevented, given the above conditions (parameters)?
Aside from using another separate battery to power the motor, another tentative method I thought of is to use a capacitor to store the energy when the motor is off, and powers the motor using current discharged from the capacitor when H-Bridge is on. For capacitor discharging time, we have a basic constant -1/RC in the e-t/RC, and theoretically some parameters can be calculated. But since I have no practical experience in designing a discharging capacitor at all, I have little confidence in calculating out the accurate parameter of R and C's. I am also not sure if an inductor would be required.
And since this is the motor drive forum where many motor experts are viewing, and I believe such a problem of isolating MCU part from motor part is a very typical scenario in motor application, could anyone help me to find a solution?
Garry Hodges