I am currently using a board with an LTC1760 to charge smart batteries. I'm having a problem with the buck fonctionnality. The schematic of my board is exactly the same as the schematic given on the datasheet (typycal application) :
Communication with smart batteries works. By visualizing the registers I see that by inserting a battery the system is ready to charge. The LTC1760 starts Buck operation but something goes wrong. If I visualize the voltage at the output of Rsens that's what I have :
Vin = 19V
It looks like the LTC1760 try every 250ms to restart buck. It force the QTG to stay open.....
If I look on the Vset pin the voltage is on the limit of the 0,8V reference voltage:
Any Idea ? thank you in advance
Can you tell me the requested ChargingVoltage() and ChargingCurrent() of your battery at the moment?
Can you also send me your layout? If you would like to do that privately, my email is [removed].
It seems that I meet the same problem as Jemson.
Could you please help to give some advices?
If you are indeed experiencing a layout issue, here are 3 resources I typically give:
1. Read this document: https://www.analog.com/media/en/technical-documentation/application-notes/an136f.pdf
It is a really good general guide for switcher layout and shows you which component placements are critical.
2. Follow all PCB Layout Considerations given in the datasheet. We give these for most of our products.
3. Use the demo board as a reference and copy it wherever possible.
A few general guidelines:
- Grounding matters. If you are charging with more than ~2A, it can sometimes be difficult to preserve a good GND reference to the IC on boards with less than 4 layers. It is best to have at least layer 2 on a 4-layer board as a designated GND plane.
- High-impedance traces (like measurement/feedback signals) should be routed away from power, possibly shielded by the GND plane.
- The input capacitance to a buck regulator should be directly across the top FET and the bottom FET.
- Ensure any logic rail caps are close to the IC and have short routing (including GND routing).
- Use Kelvin connections for all sense resistors.
Thanks for your advices.
I had done some check, and made some try in the past few days, but the problem is still there.
I have no the LTC1760 EVM by my hands.
Could you help to make sure that if the battery can be charged normally when it is not a smart one? In another word, if a battery has no SMBus interface to LTC1760, can it be charged as well?
The second thing is that I want to borrow one LTC1760 EVM from ADI for comparison test, could you help on this?
In standalone operation, the LTC1760 will only charge a smart battery. The LTC1760 is exclusively meant to be a smart battery charger.
You can try to fool the charger into thinking smart batteries are present by replying with their command responses through your own controller, but that is extra work. If you are not using smart batteries you would be better off using a different charger.
You can order our eval boards online or get in touch with support through the ADI website link to request a board sample.