Convoy XHP35 Driver Analysis / Testing / Schematic

Here is direct link to circuit of first version of Tamagochi driver on another thread over fonarevka
There are also links to hex file for attiny85 Кастомим Skilhunt H03. | Мастерская: Tamagotchi и Rime for another version of that driver.
Very interesting how he generate such 300kHz high PMW frequency from attiny85. Also I readed that he implement the PID control algorithm for SMPS regulation.
Yes you right the output power is limited because of use of such low PWM frequency. I readed that driver have 18W output power at 6V, so 3A output current is very good from attiny control circuit.

Sorry to interrupt a bit this long boost converter design and optimization off-topic people. I made a question a couple days ago in #26, could you please comment about it? Auto-quoting myself:

I think it must will work. We just recalculate voltage divider for higher cutoff voltage. Direct connection to Vcc battery voltage is the best. Also if we want to protect LDO we can increase R1 value for higher voltage drop of it or install parralel of it 5Vzener for overvoltage protection but best will be to just use higher voltage LDO.

agnelucio or anyone who has this driver. Is it safe to reduce the diameter to 21mm?

Thanks. I wonder a little what is the point of R1, because the VLDO regulator feeds the MCU and the Current Control Feedback Comparator -CCFC- stages. The MCU theoretically drains less than 1mA (46µA / MHz according to Renesas RL78/GU10 datasheet), and don't know about the CCFC but pretty sure quite low power too (< 10mA). When ≈0.01A go across a 4.7Ω resistor the voltage drop is ≈47mV, so what is the point I wonder.

You mean a 5.1V zener reverse polarized in parallel with pins 3 and 1 from the VLDO regulator. In this case, R1 would probably need to be recalculated (never done this zener stuff in my life LoL). Would be nice to know, we need to figure out the regulator's power consumption (current to MCU and CCFC), doesn't it? Or is it easier to find a higher input voltage VLDO regulator? No hurry for now, though.

I think it would be impossible for MCU to do the MP3431's job. The MCU could use ADC and PWM to make a switching converter, but performance and efficiency would be very limited.

Companies like Monolithic, TI, LT have all spent millions over the last 20+ years to make dedicated DC/DC ICs so highly optimised for power and efficiency.

And with the op-amp, you are right, the small-signal performance is far better than 10/12bit ADC as you mentioned.

The Attiny1634 has a built-in comparator, but it's not good enough for this feedback loop.

But that IS the topic :D . We need to understand the driver design positives and flaws if we want to improve it!

I'd say no. It depends on what you're mounting it in, but the top side ground ring is already very narrow.

I think I found a suitable SOT-23 linear regulator supporting higher than 6V input voltages, the Zetex ZMR330FTA.

But still not a word I've heard about the onboard stock one, can someone tell me which device it is? So we can know its pinout, maximum input voltage and etc.

The point of R1 is cloned from classic DEL and TA drivers. The R1C1 form RC filter which clean input voltage. Because we have heavy load with high input currents there is pulsating voltage from battery. Also 4.7 ohm is exactly the same used in TA drivers. Also C1 is decoupling capacitor for MCU.
This Zetex LDO is very good indeed. The max input voltage is 22V and also have very low self consumption like 40uA max. Just you need to compare if pinouts are the same as installed on PCB LDO for direct replacement.
Yes you can use any zener diode larger from 3.8V-5.1V. Is good to have enough voltage room for LDO to stabilize to 3.3V Also another tip if you want to lower output current is just low power supply voltage of MCU :smiley: So in that case max reference voltage on inverting pin of opamp will be lower.

By the way Microchip have dedicated enhancement 8-bit micros with analog peripherals for power supply control like high resolution and fast PWM and ramp generator. Just see this AN from them for SEPIC led driver

After taking a peek at the newer AA/14500/16340 driver from Convoy, I think I have identified the SOT-23 LDO regulator in there and here. Marking in this (XHP35) driver's 3-pin SOT-23 is V1SE. Found it is a MicrOne ME6209A-33 regulator, check here (datasheet). Up to 18V of input, this means there's no need to replace it for 2S battery operation.

Nice find :+1:
From real photo from listed product here for 3.3V LDO LCSC and I also search over and find there are variants of that marking V1JE,V1SF, V1SE, V1QH. Seems the first two characters are voltage code and last two are code for year and month of production maybe.

If I would like to use this driver as single mode by removing the MCU what connections I should provide? Many thanks in advance.

If you remove R9 from schematic you will remove any control from MCU also you need to EN pin to positive terminal. But in that case you will lose any current control of circuit. It will work as ordinary DC DC power supply with fixed output voltage. Another better option is to recalculate the voltage divider which come from output of MCU to input of opamp.

Many thanks for your suggestion and help :slight_smile:

Damn this looks like a solid driver design.

Yes it is, hope it still is as good as it was in this review.

I recently made a comment about it here, comparing it with the not very sensical GT-FC40 driver; and now when I open the GT-FC40 driver store link I get a “Sorry, this item is no longer available!” message. Curious.

Tue, 03/15/2022 - 23:42

Simon’s shop is closed because of Covid restrictions.

What an awesome thread. Thanks for doing this agnelucio!

I would like to use this driver in a 3s configuration. I’m wondering what would be the result if I just hook the driver up as is with the factory 4s config? Is it necessary to change the R16 resistor for this? If so I could use a little help on the math. I’ve read your post about how you calculated the values twice now and I still don’t grasp it. I would also like to adjust the drive current down to about 1900-2000ma (by changing the value of R10 if I understand correctly). At 2000ma my VF would be 11.9v.

Rtop=Rbot×(Vfavg-VFB)VFB = 47×(9-1)/1=376k
360k will do

NewRsense = Rsense×I/Inew = 30x2.3/2 = 34.5mR
36mR is a common value and will give you Rsense×I/newRsense = 1.92A

Edit : nearly 4V at 2A ? Are those UV LEDs ? The default value (set for 11Vavg) will probably work. ”not working” means min mode higher than it should be. A too low value means lower current than it should be on the highest mode.

1 Thank

Has anyone make open source or aftermarket firmware that will work for this driver? I’d love to have it in a single mode…

No Attiny no custom UI