MCU Controlled Buck Converter IC

Question

I am designing for an application where I need a buck converter that takes the voltage from a 2S Li-ion battery (6-8.4 V) and the load I need to drive is 0-6 V and will take 1.2 A max. I need to control the buck converter's output voltage (0-6 V) from my microcontroller.

In my particular application, I can not use bigger inductor or capacitor values so I need a higher switching frequency (greater than 1 MHz. 2 MHz is preferred).

I need a buck converter IC that is able to set the output voltage based on the signal from my microcontroller. The signal can be analog or digital. Maybe an IC that does not use its internal reference voltage but the reference voltage from my microcontroller's DAC.

I can not use a digital potentiometer like X9C104 because I will not be able to output a voltage less than the buck converter chip's internal reference voltage. I also tried a "hack" where I put a voltage on the soft start pin of the buck converter IC to control the output voltage but I am not able to make it work reliably.

Answer 1

Buck converter IC's almost invariably have a "FB" pin or equivalent that is driven high when Vout exceeds Vrequired and low when Vout is below Vrequired.
This can (usually very easily) be used to provide a uC controlled output by providing a comparator that is driven by Vout divided to some useful value and a reference voltage from the uC - either analog or filtered PWM.
When Vout divided is below Vref_microcontroller the FB pin is driven high.
When Vout_divided rises above Vref_microcontroller FB is driven low.

This is a very common method of control.
The divider ratio can be anything wanted (within reason).
If this arrangement does not meet your needs please advise why in adequate detail.

Diagrammatic only:

Original of hacked about image from here

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Applying the above method with this regulator, to your application appears to meet your need.
I've copied the first page of the datasheet below to show the specs that it meets and simplicity of operation. It does not have synchronous rectification so is not quite as efficient as the best in class. It achieves over 90% efficiency across some portions of its Vin/Vout/Iload map). (If desired, synchronous rectification which could be added with a FET across D1 and minimal control logic.)
The AP3211 costs $US1.02 in 1 quantity from Digikey and under $0.40/1000. (OR 15c and 11c from LCSC!.

Many maybes here

Answer 2

Many microcontrollers have timer peripherals that can be used to drive a power converter directly. These are the same peripherals that are used to perform PWM generation. One option would be to build buck converter out of a microcontroller, a gate driver IC, like the TI LM2101 or similar, and two MOSFETs.

However, this may be more work than using an off-the-shelf buck, either with a digital control interface, or an analog control scheme, like a digital potentiometer.

Answer 3

ST have chips with peripherals which can be used to control switch mode converters. There is even a dev board for one with demo apps that control some (very bright!) LEDs. I think you could start from this, you just need to play with the converter design for your target voltages and currents. Should save you a lot of time.