TP5400 - Output to low: 4V instead of 5V?! - Page 1
Forum section: electronics / projects

author: HeinzA1
author_rank: Newbie
timestamp: January 25, 2022, 10:49:19 pm
content: Hi there!I am recently working on ansmall project and I'm using an TP5400 for power-regulation and battery charging.According to the datasheet I should have an 5V output, but I only get 4V.The input of the circuit is 5V via an USB-Connecter. The coil (sadly shown as an resistor in the my attached diagram...) has 10uH.The second picture shows the "typical usage" from the datasheet.I can not see a difference to my circuit so what could went bad?Can anyone tell me what I'm doing wrong?Thank you a lot for your help!

author: moffy
author_rank: Super Contributor
timestamp: January 25, 2022, 11:12:15 pm
content: Try putting the 0.3R resistor into the circuit, I doubt it is for decoration.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 26, 2022, 01:00:25 am
content: Making sense of the datasheet is pretty tough for many of us, since it's all in chinese.But to begin with, you might want to measure Vin when Vout is loaded, tell us if Vout is ~4V when it is loaded (if so, what kind of current), or just left open? You might also want to have a look at Vout with a scope. Etc.

author: Whales
author_rank: Super Contributor
timestamp: January 26, 2022, 01:28:55 am
content: Daft question: what are you using as the coil? Can you provide a photo or a part number?

author: moffy
author_rank: Super Contributor
timestamp: January 26, 2022, 05:09:53 am
content: Working from his drawing I suspect the coil is: Coilcraft 2929SQ-431E, an aircored RF inductor @ 4.2A rms.Woops! But I managed to match so many numbers.

author: HeinzA1
author_rank: Newbie
timestamp: January 26, 2022, 09:09:33 am
content: Quote from: moffy on January 25, 2022, 11:12:15 pmWhups you are right, thank you!Yes, could have been foolish to think that 0.3R doesn't matter... I'll order some and try it out.

author: HeinzA1
author_rank: Newbie
timestamp: January 26, 2022, 09:22:33 am
content: Thank you for your reply!Quote from: SiliconWizard on January 26, 2022, 01:00:25 amYes! I had to use an PDF-Translator to get any sense out of it.Vin is stable at 5V, even when it's loaded. Same thing if I power the circuit over an battery with ~3.7V. The voltage is the same, mo matter if open or loaded (which is ~80mA at the moment. Should have a peak of ~500mA since it is powering an ESP8266 and a servo, but since the voltage is under 5V, the ESP doesn't even start).Sadly, I don't have a scope...

author: HeinzA1
author_rank: Newbie
timestamp: January 26, 2022, 09:25:41 am
content: Quote from: Whales on January 26, 2022, 01:28:55 amI can give you the link to the part at LCSC:https://lcsc.com/product-detail/Inductors-SMD_SHOU-HAN-CY54-10UH_C2929431.html

author: HeinzA1
author_rank: Newbie
timestamp: January 26, 2022, 02:12:35 pm
content: Quote from: moffy on January 26, 2022, 05:09:53 amNot quite, it is the part number from LCSC. ^_^"So this coil is a Shou Han (whoever this is) with 1.42A metal core indcutor with 10uH.But yes, coilcraft would have been possible due to the part number. I should have declared that one.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 26, 2022, 05:54:00 pm
content: Quote from: HeinzA1 on January 26, 2022, 09:22:33 amAnd what is Vout? Is it exactly 4V? Is it closer to 4.2V?

author: RoGeorge
author_rank: Super Contributor
timestamp: January 26, 2022, 06:26:03 pm
content: Quote from: HeinzA1 on January 25, 2022, 10:49:19 pmThe datasheet looks misleading, or rather incorrect.That integrated circuit, TP5400, is meant to charge a single cell of Lithium based rechargeable battery. That is not a constant 5V output voltage stabilizer.A typical Li-Ion battery must be recharged with constant current (not constant voltage) at the beginning, then with constant voltage (typically 4.2V ... 4.3V at most) in the last charging phase, until the battery itself will reach its full charge voltage of about 4.2V.If you try to charge the battery up to 5V, the battery will get permanent damage or even worst, it may start a fire if overcharged.Your circuit measures OK, it doesn't has to have 5V.To test it, measure the short circuit current, and see if the current (not the voltage) stays limited at the value specified in the datasheet, then when the output is left open, it should show at most 4.3V or so, not 5V.I don't know why is there a 5V in the datasheet at the output, by the purpose of the circuit the 5V output looks like a typo to me. Also, note how the output is marked as Iout, and not Vout.----------------You don't need the 0.3 ohms resistor, that resistor is there instead of a fusible. You have the F1 fusible in your schematic, so you don't need the 0.3 ohms any more.

author: HeinzA1
author_rank: Newbie
timestamp: January 26, 2022, 07:51:10 pm
content: Thank you for this huge answer @RoGeorge!Im not sure if the datasheet in incorrect - the TP5400 is used in different products for delivering 5V from an Li-Ion (and also charge it). Like here:https://www.az-delivery.de/products/tp5400-usb-powerbank-modulThe Battery-connector of the TP5400 also delivers only ~4.2V.The Vout and Iout also confuses me...Thanks a lot for clearing the "0.3R-mistery". It now makes a lot of sense!

author: tunk
author_rank: Super Contributor
timestamp: January 26, 2022, 08:48:07 pm
content: No expert on this:If you have an oscilloscope, check if there's any signal across the inductor.Maybe also check the diode.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 26, 2022, 09:03:10 pm
content: Quote from: HeinzA1 on January 26, 2022, 07:51:10 pmMy bad, sorry, you were talking about Vout (pin 1), and I was thinking the measured problem is on Vbatt (pin 6).

author: moffy
author_rank: Super Contributor
timestamp: January 26, 2022, 11:44:46 pm
content: It is possible that the 0.3R resistor helps limit the surge current out of the USB port, which can trip fairly easily. Perhaps it helps the switching current be drawn from the 10u bypass capacitor rather than directly from the USB port. Since there is so little info I wouldn't dismiss its significance or not without trying it.By the way, what is the switching frequency of the TP5400?

author: thinkfat
author_rank: Unknown
timestamp: January 27, 2022, 12:30:32 am
content: I have used the TP5400 in two applications like yours and I confirm that your interpretation of the datasheet is correct: It's both a 1S charger and also boost converter. Also your schematic is largely OK, BUT: You're missing a power path.The TP5400 has two operation modes, it's either a charger OR a DC/DC converter, not both at the same time. As soon as you connect a 5V supply, the TP5400 goes into charger mode. In this mode, Vout will not reach 5V. As soon as you disconnect the 5V supply, the DC/DC converter acts as a boost converter and Vout will stabilize close to 5V.So, you need to provide a power path from the 5V supply to the output, like D1 in the attached schematic. There's likely a more sophisticated way with a Mosfet that doesn't have the voltage drop. Also, note that R1 is important: D1 will have a leakage current and will slowly charge C1 when the 5V supply is disconnected. This would periodically start the charger and you'd see a drop in output voltage whenever that happens.

author: thinkfat
author_rank: Unknown
timestamp: January 27, 2022, 12:53:40 am
content: There is (was?) a functionally equivalent TP5410 from the same manufacturer. I've attached its datasheet here. It is slightly more detailed, in particular it has two additional application circuits which detail the power path management you will want to add. The only difference I could find between the two chips is the programming resistor for the charge current.

author: HeinzA1
author_rank: Newbie
timestamp: January 27, 2022, 09:20:56 am
content: First of all, thankallof you for your answers!In the end, thinkfat nailed the problem:Quote from: thinkfat on January 27, 2022, 12:30:32 amI measured the voltage on Vout with only the battery connected and I've got ~4.9V.I will add a power path to my circuit and hope, that it will thank work properly.

author: HeinzA1
author_rank: Newbie
timestamp: January 27, 2022, 09:23:05 am
content: Quote from: thinkfat on January 27, 2022, 12:53:40 amYes, you're right. But since it seems to be way more expensive, it would be better for me to just use the TP5400 ;-)

author: thinkfat
author_rank: Unknown
timestamp: January 27, 2022, 10:49:08 am
content: Quote from: HeinzA1 on January 27, 2022, 09:23:05 amI've actually tried to source the TP5410 for a project, it is not available from LCSC and I found no other sources. But since the TP5400 seems to be essentially the same chip (and does what I needed), I stopped trying.