TP5100 pros/cons Schottky diode  - Page 1
Forum section: electronics / projects

author: okw
author_rank: Frequent Contributor
timestamp: May 12, 2023, 09:51:34 am
content: I'm experimenting with the TP5100 li-ion charger. In the google translated datasheet, it says "anti-intrusion protection Schottky diode" not needed. Although all circuits features this diode.What are the pros and cons of adding or omitting the Schottky diode?And how do I size it properly? Datasheet says: "4. Selection Schottky diode voltage drop greater than or equal 2A small current capability of the Schottky diode." Something is obviously lost in translation.

author: Peabody
author_rank: Super Contributor
timestamp: May 12, 2023, 01:49:28 pm
content: I think there are two different diodes. The diode on the right side of the circuit drawings is part of the buck circuit. You will find that in any buck regulator unless it has been replaced by a mosfet, and it needs to be there for the buck process to work. I suspect the "anti-intrusion" diode is something you would find on the left side that would prevent current from flowing back into the input when its voltage is below the battery voltage. The TP4056 datasheet refers to this as a "blocking diode".If you are working with a TP5100 module, the diode is already on the module. In one closeup picture I found, it's an SS34, which is a 3-amp schottky.

author: David Hess
author_rank: Super Contributor
timestamp: May 12, 2023, 03:47:27 pm
content: It is referring to the diode which would normally be in series with the input or output to prevent reverse current flow through the body diode of the power MOSFET when the supply voltage is lower than the battery voltage. It is not required because the body diode of the integrated power MOSFET is not connected.When the input voltage or input voltage down below the battery voltage, the charger enters a low power shutdown mode, no external anti-intrusion diode chip drain from the battery approaches 1uA.

author: okw
author_rank: Frequent Contributor
timestamp: May 12, 2023, 06:22:57 pm
content: Thanks for your help.I'm having problems with starting the TP5100. I made a PCB to test with specific components (with known part numbers) so I can re-order the exact same components when the project is ready.But.... Sometimes it charges with the 500mA output I've set (Rsense 200mR), but most times it just idles (~2.15mA). Both LEDs (charging / done) are lit for some strange reason.I can't see from my schematic why it doesn't start. The battery I have connected shows 3.804V and should charge (TP5100 typical cut-off is 4.2V).If I disconnect the battery, the floating charge pin 9 shows 4.085V.R6 (trickle charge) is 27k (should trickle at 15% of the full 500mA), also tried to tie it to GND ("charging" 6mA, should be 10% (50mA)) and to float it ("charging" 24mA, should charge full 500mA). Anyway, trickle should only apply if battery is <2.9V.Input is 12V. If I increase to >13.25V, "charge done" LED goes dark. Strange. Output goes from 2.15mA to 3.6mA but still "dead".If I touch the CS pin with an unconnected test lead, "charge done" LED goes dark, and output rises to 4.8-4.9V. This pin should float for single cell (4.2V), or pulled down to shut down. The CS pin is traced across the board (~7 cm) to a pin header. Could this trace be so sensitive that it picks up something and shuts down?Sadly I forgot to order 22uH inductors, I just have 10, 47, 68 and 100uH. So I use 10uH (which I figured should be OK anyway with low current). Datasheet says at Vin=5V and 500mA, 10uH is ok. I also tried Vin=5V, nothing changed.I also thought the power supply (RD6006, non-linear 115kHz) could interfere with the buck, so I tried with a 12V battery pack instead. Same result.Then I tried replacing this Schottky:https://datasheet.lcsc.com/lcsc/2204281430_Guangdong-Hottech-1N5819WS_C191023.pdfwith a beefier one:https://datasheet.lcsc.com/lcsc/2210131730_HXY-MOSFET-K24_C5199107.pdfSlight drop in the 2.15mA to 2.10mA but still nothingI'm out of ideas...

author: okw
author_rank: Frequent Contributor
timestamp: May 12, 2023, 06:38:09 pm
content: Forgot to add my schematics.R1/R2 is there as pullups so I can read the signals with an MCU. Besides that, nothing special.EDIT: I see there are plenty of datasheets for this module and some of them lists VIN max 18V, others as 10V... I think I might have received one with max 10V. That could explain it...

author: thm_w
author_rank: Super Contributor
timestamp: May 12, 2023, 10:17:27 pm
content: It might be useful to have some modules on hand as they are only $1:https://www.aliexpress.us/item/2251832709023568.htmlTP5100 is rated for a Vin of 18V max. Can you link to anywhere claiming less?The schematic looks fine, other than pins 1 and 2 are not labeled so I have no idea what pins they actually connect to. I assume its the right ones, but not sure.CS pin says it has 200k divider resistors, so I wouldnt expect it to be super sensitive. You could always measure the voltage on it though.Could be a soldering issue.

author: okw
author_rank: Frequent Contributor
timestamp: May 12, 2023, 10:28:34 pm
content: yes, pin 1 is four pins and 2 are two pins (hence the multiplier *4 and *2), but they are routed correctly in the package (VIN 1/4/5/16 and LX 2/2).I bought it here, and sadly the attached datasheet says max 10V:https://datasheet.lcsc.com/lcsc/2210181000_TOPPOWER-Nanjing-Extension-Microelectronics-TP5100_C379389.pdfIf I remember correctly CS was 2.0-2.1V, which would be right with that divider at VREG=4.2V.I bought 10 assembled boards from JLCPCB, and so far I've tried 3. Only 1 worked, managed to fully charge one battery (perhaps 3-4 hours) but now that doesn't work either.I lean more to the 10V max.

author: thm_w
author_rank: Super Contributor
timestamp: May 12, 2023, 11:32:21 pm
content: Huh, it does say 10V absolute max in the datasheet, odd. We did have this before were someone bought a "1N4148" from LCSC and it wasn't up to regular spec for a 1N4148. So you have to read the datasheet to check, if its not a major supplier.But.. I have a TOPPOWER branded TP5100 aliexpress module right in front of me, and it can handle 12V fine.In the LCSC datasheet it still shows Vcc being tested to 12V, even when 10V is abs max.In the english translateddatasheet, its tested to 16V.I wonder if they went back and downrated the part (Rev 2.1 notes in datasheet says "2021.5.13 Modify input parameters").Maybe post some photos of your board?