ULQ2003A driver issues - Page 1
Forum section: electronics / projects

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 06:48:32 pm
content: Hello,The 3.3v outputs of a microcontroller goes directly into an ULQ2003 chip. COM pin is at 5v. The outputs of the ULQ goes into a terminal block. All lines have a SMAJ5.0CA transient diode protection.With the MCU outputting LOW on input pins of the ULQ, the issue is the current measured at the output, it is around 0.160mA. Connecting a buzzer circuit at those outputs, it's a high pitch noise which goes up and down, not constant. Moving fingers across the pins of terminal block on the pcb side, the buzzer noise fades out or even completely disappear.The same circuit on a not very different PCB layout does not reproduce the problem, the measured current is 0.020mA in this case. Grounding issues, bad lot of chips, any other idea?Thanks.

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 07:07:36 pm
content: Post actual schematic. Does pulling inputs high work as expected? Did you measure actual voltage on the inputs? Where did you get those ICs?

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 07:16:57 pm
content: It's just a bunch of a 3.3v MCU pings going into 1-7 pins of the ULQ, 8 to GND, 9 to +5v, 10 to 16 are outputs. All outputs via a SMA diode to ground. 2 caps, 220uF and 0.1uF between COM and GND, pin 9 and 8.Yes, asserting HIGH on any line triggers the right output. Voltage at pin is 3.3v, I think is correct, it's 5v minus 1.6v voltage drop across darlingtons.Asserting LOW, still have that residual current, if I can call it like that.Can't say where the chips are coming from.The other PCB seems to be done with same chips, but really can't tell.What's strange to me, moving fingers across terminal block pins, especially having one finger on v+ and other on the output pin, it does cure the issue.

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 07:27:35 pm
content: Quote from: cio74 on May 13, 2015, 07:16:57 pmYou didn't say if you measured the actual LOW voltage on the MCU pins. Is this some kind of finished device you try to repair or not?What I can imagine is setting the MCU pins as inputs with pull ups enabled instead of output LOW. Otherwise I would suspect ULQ2003 or MCU dead (output low voltage unknown so far).

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 07:36:54 pm
content: It is not dead, it is works, it's just that in the OFF state, LOW level at the input pins, the output current is too high instead of 0 or very low.The MCU pins that control the ULQ are never set as inputs, they are always outputs and set either LOW or HIGH, not 3 state. The voltage is 3.3v when driven HIGH and 0.430v when driven LOW. I can measure it again.Input pins of the ULQ while OFF (input pins driven LOW), 0.430v. The ULQ output voltage while in OFF state is 0.0054v. The current is 0.160mA on the PCB with issues and it is 0.020mA on the one without.

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 07:45:07 pm
content: Quote from: cio74 on May 13, 2015, 07:36:54 pm0.43V is too high. It should be almost zero if set as LOW. Probably MCU is partially dead. It also could be issue with ground connection between ULQ2003 and MCU. But as you didn't post any photos, hard to say.

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 07:54:04 pm
content: True, I have just redone the measurements, when measured 0.430v I was using a ground chassis pin which affected the value.With ground probe on pin 8, input and output on OFF state are 0.0001v. ON state, 3.29v on inputs, 3.5v on outputs.

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 08:03:24 pm
content: Quote from: cio74 on May 13, 2015, 07:54:04 pmThis is not right. Definitely should be less than 1.4V on the output in the on state. Likely ULQ2003 is dead if you measure this right.

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 08:20:44 pm
content: That was with a led at the output, since ULQ is grounding the output I don't expect to have any voltage when pins are left unconnected to anything. Unless I have to measure with respect to the COM pin?

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 08:29:02 pm
content: Quote from: cio74 on May 13, 2015, 08:20:44 pmNow I don't understand what you are measuring across what. Either measure from the ground (com) or write what referenced to what. According to the datasheet, voltage drop between the output andCOM (wrote wrong pin name)GNDmust be less than 1.1V if output current is below 100mA, and I guess it is below 100mA if led is used. But better to just use some resistor for tests, like 1k.

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 09:01:31 pm
content: With a led and a resistor, 20mA for led at 5v, the voltage between COM (again connected at 5v) and output pin connected to led, it is 0v in OFF state and 4.40v in ON state.Unconnected output, voltage measured between COM and output pin (COM connected to +5v) it is 2.76v in OFF state and 4.43v in ON state. This is one output that is causing issues. Input voltage at that pin, with respect to GND this time is 0v OFF and 3.29v ON.Current on that output pin with a 1k resistor to +5v is 0.48mA in OFF state and 4.38mA in ON state.On the other PCB, the same 1k to the same output pin, the OFF current is 0.073mA.

author: mikerj
author_rank: Super Contributor
timestamp: May 13, 2015, 09:08:52 pm
content: Quote from: cio74 on May 13, 2015, 09:01:31 pmThis makes no sense. The 2003 has open collector outputs so when one channel is switched on, the output pin should be close to ground i.e. 0v in ON state and 4.4v in OFF state.

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 09:12:18 pm
content: It is measured with respect to the COM pin at +5v, not board GND.

author: mikerj
author_rank: Super Contributor
timestamp: May 13, 2015, 09:17:03 pm
content: Ok I understand. In your original circuit, is the COM pin and the supply to the buzzer from the same supply, and at the same voltage? Does the leakage current change if you ground the input pin directly to pin 8 (i.e. with a bit of wire)?

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 09:34:31 pm
content: Board is powered by external 12v power supply, then converted to 5v via SMPS and then to 3.3v via LDO. The buzzer is powered from the original 12v, pcb trace on the board and uses open collector output of the ULQ to generate sound.Shorting input pin to ground (pin 8 ) does not fix the problem.Touching the buzzer pins have a big influence, the tonality changes and eventually noise completely disappear.

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 09:40:19 pm
content: Quote from: cio74 on May 13, 2015, 09:01:31 pmI made a typo on previous post about COM pin but whatever. You didn't say that his happens only on one output. Anyway, either ULQ2003 have one output blown or SMAJ5.0CA is leaky, however your trick with moving fingers suggest more against blown ULQ. You could temporarily remove the transil diode to be 100% sure.However this design of those boards flawed (or you try to use them at lighter load than they are made for).According to the datasheet Max. Reverse Leakage current of the SMAJ5.0CA @ 5V Vrwm and 25oC = 800uA. Therefore if the leak happens through the transil, technically it is still within spec. Likely that's why you get noticeable leakage on the other board too.

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 09:44:53 pm
content: Quote from: cio74 on May 13, 2015, 09:34:31 pmYou cannot attach the load between 12V and output of of ULQ2003 because standoff voltage of SMAJ5.0CA is only 5V and breakdown voltage is 6.40 - 7.25V.You are indeed strange to not provide such an important fact from the beginning.

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 09:49:56 pm
content: The device connected at the terminal block requires 5-12v and has all input and output lines 5v compliant, regardless of its power voltage, its not just a buzzer with one wire at 12v and the other at ULQ output, apologize for not proving a full picture.The issue is happening on all outputs not only one but only on one PCB, not on the other, witch uses the same components. As a matter of fact, it somehow does happen on the other as well, but the current is so small the noise is more inaudible but definitely is not 0.The PCBs are not the same on both boards, small variation.Interesting thought about the transil diode, I shall remove one and see what's happening on that output.

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 09:57:56 pm
content: You cannot use this board at 12V output because everything will be clamped to 5V (com pin) through the internal diodes of ULQ2003. BTW to what second pin of SMAJ5.0CA is connected? To GND or to COM (+5V). If to GND, output will be definitely clamped to about 7V. or to about 5V more if connected to COM.If you want to use this board with 12V, you definitely need to connect the COM pin to 12V and change all transil diodes to higher voltage versions.That's why I asked for schematic on the first place, because you are obviously doing stupid thing. And that would be obvious from the schematic right away.

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 10:02:12 pm
content: The issue stays with the COM pin left unconnected, as a matter of fact unless driving inductive loads it can be left floating.The diode is connected to ground.I don't follow your logic on everything will be clamped at 5v, if I lower the board input voltage to 5v it is still the same issue.The diodes manufacturer are different on each PCB while the rest of the comps seems the same, could that really be an issue?

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 10:05:04 pm
content: Quote from: cio74 on May 13, 2015, 10:02:12 pmThen output will be clamped to about 7V through the transils if they really are SMAJ5.0CA. Maybe higher voltage version is used on another board?

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 10:07:08 pm
content: Quote from: cio74 on May 13, 2015, 10:02:12 pmYou describe the things quiet vaguely. First you say that COM is at 5V. Then you say it's left floating. If the COM would be connected to 5V of course outputs would be clamped. Therefore schematic of what you are doing would be the best of course.

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 10:09:10 pm
content: The output it is not supposed to be 12v anyway, the lines are all 5v.For simplicity lets forget about connecting anything to it, just the 1k resistor test I did, between 5v and output produced a different current reading on each board.On both boards, the COM is 5v, measured. The current via the 1k resistor is different, With nothing connected to the terminal block, just a single resistor between COM and output.

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 10:11:11 pm
content: There are only two things to cause the leakage. ULQ2003 and transil. That's all. Decide which is used wrong or being faulty.

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 10:14:23 pm
content: Diodes are not the same manufacturer, the rest seems to be. I'll do a test tomorrow and remove one, see if any changes.Thanks for your help, appreciate the time and effort have you put into this.

author: calexanian
author_rank: Super Contributor
timestamp: May 13, 2015, 10:28:42 pm
content: Your common freewheeling diode pin should be tied to the supply voltage of the load. In this case 12 volt supply of your buzzer or whatever you have. Also with these make sure your MUC output is actually pulled low and not just tristate high. You may need to add pull down resistors.

author: wraper
author_rank: Unknown
timestamp: May 13, 2015, 10:59:14 pm
content: Quote from: calexanian on May 13, 2015, 10:28:42 pmThere are pull downs inside of the ULQ2003A.

author: cio74
author_rank: Regular Contributor
timestamp: May 13, 2015, 11:27:19 pm
content: Found the problem, one PCB has LittleFuse TVS and the other AVX brand. Removing the AVX diode cured the issues.Not all TVS are made the same...

author: calexanian
author_rank: Super Contributor
timestamp: May 14, 2015, 06:05:58 pm
content: Quote from: wraper on May 13, 2015, 10:59:14 pmSorry. Cobwebs in the brain. My brain went to VQ1000 chips for some reason. Another until recently discontinued driver chip. I should have been more on top of it because we use ULN2803's here in mass quantities and it is a similar driver chip. I think as my beard turns grey its pulling the smarts out of my brain, and i did not have much to start with!

author: jeff.remus
author_rank: Contributor
timestamp: May 16, 2015, 10:48:49 am
content: Flux under the IC?