Single chip buck with programmable voltage and current like LT8613 - Page 1
Forum section: electronics / projects

author: prasimix
author_rank: Unknown
timestamp: November 11, 2016, 10:42:02 am
content: I'm searching for buck regulator (could be controller too) that has programmable voltage and current. The first one shouldn't be a problem but for current it should have something like Imon and Iset/Ictrl pins. In that way I can use MCU's DAC/PWM output to set both voltage and current, and also ADC inputs to monitor them.Input voltage is 12 VDC, and output should be variable e.g. 1-5 V and up to 4-5 A (max. power 25-30 W). So far I found only one candidateLT8613. It looks fine but its tiny QFN package is not so DIY-friendly or it is? Another possibility is regulator/controller with I2C or SPI bus that can be used for programming and monitoring output voltage and current in above mentioned range.

author: Paul Price
author_rank: Super Contributor
timestamp: November 11, 2016, 08:19:30 pm
content: It is easy enough to control the output voltage over the range you desire using a MCU delivering PWM control to set comparator levels controlling current and voltage of a chip buck converter.Depending on the load, I eliminate the buck converter entirely and use PWM to control a MOSFET switch to make my own PWM buck converter and use analog to digital converters to monitor the output current an voltage to close the control loop.A PIC chip running at 64MHz clock can do quite a good job of this depending on the rate of change of the output voltage required to feed a load connected to the output of this improvised buck converter.If a quite fast regulated response time is required, then I would use the MCU PWM and then integrate the PWM output to generate the control voltages of comparators that are inserted into the feedback loop of a single chip buck converter.The limitation of using a MCU to control an external chip buck converter would be the minimal output voltage of most buck chips which is usually set to match the chip's internal reference voltage, most usually around 1.21V.

author: prasimix
author_rank: Unknown
timestamp: November 11, 2016, 08:44:59 pm
content: Thanks for your reply. I already have a MCU, actually it's Arduino Due board that is pretty busy with many other things. I'd like to avoid introduction of another MCU and another "family" like (ds)PIC, etc.If buck regulator/controller don't have current control than I'll need a current monitor IC that further complicate design. Again I'd like to avoid that if possible.

author: Paul Price
author_rank: Super Contributor
timestamp: November 11, 2016, 09:16:44 pm
content: T.I. makes several models of single-chip synchronous buck converter managers(18-24 pin chips) but of course you will also need power MOSFETs and sense resistors and electrolytic caps and anyway you will still need some control interface, some improvised or chip D-->A converters for your Arduino MCU to set the output voltage and current limit control input voltages on the manager chip.On the other hand, a single additional MCU controller using a PIC chip or say an AVR uno chip would only require a small footprint (SOIC) and you could communicate to it easily using I2C or a single UART serial output of your Arduino to set output voltage and current.

author: prasimix
author_rank: Unknown
timestamp: November 11, 2016, 10:58:32 pm
content: External mosfet and accompanying passives is not an issue. Arduino Due has two DAC outputs, therefore no need for conditioning PWM outputs. Please let me know what TI ICs you have on mind.

author: prasimix
author_rank: Unknown
timestamp: November 18, 2016, 08:27:07 am
content: Small update here: people from LTC told me that LT8613 is not a good candidate because:QuoteTheLT3741has current control inputs (actually two of themCTRL1andCTRL2) but lacks current monitor output. Therefore I'll need to deploy an external current monitor and has to back into quest for a solution that works with low output voltage (down to 1V).I also asked TI people if they have something similar to LT8613. There I gotLM(2)5117where situation is opposite: it has current monitor output (CMpin) but without possibility to limit output current. It's advertised with "Programmable Current Limit" but it's actually fixed withRsense. On top of that if max. current is reached for more then 256 cycles it will enters so-called hiccup mode.

author: prasimix
author_rank: Unknown
timestamp: November 30, 2016, 07:22:18 am
content: Another update to close this topic: LTC hasLT3763that is advertised as LED driver controller. It has all what is needed to control/limit and monitor current, and come in convenient TSSOP28 package.