voice coil driver circuit

Hi, I have a few question about the block diagram:

1. How does the feedback generate the sink current required to drive the voice coil?

2. The data sheet states:
"Resistors R and RSENSE are interleaved and matched on-chip. Their temperature coefficients and any nonlinearities over temperature are therefore matched, minimizing the output drift over temperature." Why is that?

3. How does the diode D1 offer output protection?

Any ideas are greatly appreciated.

Could you please let all of us know the background and describe the purpose of your circuit?

The diode is for free wheeling.

The output from DAC drives a current thru R and generates a voltage.

Another voltage is generated across the 3.3 ohms Rsense by the current (Isink) passing thru the voice coil.

The OP Amp generates a difference voltage (error voltage) based on these two voltages, and amplifies it (I guess, many other components are involved, including some energy storage elements, to provide optimal settling time for the difference), which, in turn, drives the MOSFET.

If R and Rsense change their values, the two voltages across them will change. This will generate an error voltage even though the current passing thru these resistors may be same.

However, if both change values by almost same amount, the differenece between two voltages will remain almost same.


Thats the reason these two restors are created like this to ensure that if their values change, both change in same direction, leading to ultimately same value resistors.

I hope this clarifies.

This IC is meant to drive a voice coil to move the lens of a digital still camera or mobile phone camera.
It is controlled by a µcontroller through an I²C bus.
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What does it mean by: "The diode is for free wheeling. "
and how does it work?

Freewheeling :

when you pass current through an inductor (voice coil), the inductor stores the current (this is the reason for phase change caused by inductance).

how ever, when the charging current stops, the current stored in the inductor starts collapsing. This generates a voltage across the inductor ends, but this voltage is of opposite polarity (-L * di/dt). The freewheeling diode completes the circuit for this voltage to discharge, there by preventing damage to the driving element (mosfet/BJT).

Check texts on internet and look at some basic electronics books : Art of Electronics, ARRL handbook, RSGB handbook etc.

https://en.wikipedia.org/wiki/Flyback_diode