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  • TI Thinks Resolved

LM43601: +15V to -15V converter doesn't work properly

Prodigy 90 points

Replies: 17

Views: 401

Part Number: LM43601

I followed the Ti web design and created LM43601PWPR as follows, I built 2 pcb those can get -2.7V output only. My -15V load is about 0.3A.

Here is my original bom:

Bill Of Materials           May 6,2019     17:32:43

Item     Quantity             Value   Pcb Footprint     ManufPN           Manuf DgkPN Description         Price_1K               Reference

1             2             4.7uF_50V           C0805   C2012X5R1H475K125AB                 TDK Co. 445-5980-1-ND Cap MLCC 0805 4.7uF 10% 50V X5R     0.2346   C38,C40

2             1             2.2uF_16V           C0603   EMK107BB7225KA-T       Taiyo Yuden       587-5835-1-ND Cap Cer 2.2uF 16V X7R 0603             0.08898                 C39

3            1             .47uF_50V           C0603   UMK107B7474KA-TR     Taiyo Yuden       587-3170-1-ND Cap Ceramic 0603 0.47uF 10% 50V X7R       0.04413                 C41

4             1             220pF_50V         C0805   C0805C221J5GACTU        KEMET 399-1127-1-ND Cap 220pF/50V0805 C0G 5% Ceramic               0.02718                 C42

5             2             22uF_25V           C1206   CL31A226KAHNNNE       Samsung EM     1276-3047-1-ND               CAP CER 22uF 25V 10% X5R 1206           0.19685                 C43,C45

6             1             100uF_50V         CD83X105           EEE-FP1H101AP Panasonic EC     P19726TR-ND     Cap Aluminum Electrolytic 100uF 20% 50V SMD 180MOhm         0.27968                 C44

7              1             47uH_1.8A         DO3316P             DO3316P-473MLD           Coilcraft               |MPN_994-DO3316P-473MLB               DO3316P SMT Pwr Ind 47uH 20 % 1.8 A 0.914     L5

8             1             0603_1.00M       R0603   RT0603FRE071ML             Yageo   YAG5944CT-ND Res 1.00M 0603 1% 1/10W               0.0122   R41

9             1             73.2K     R0805   CR0805-8W-7322FT         Panasonic EC     ERJ-6ENF7322V Res 0805 73.2K Thick Chip 1% 1/8W 150V          0.01367                 R42

10           1             0603_105K         R0603   RC0603FR-07105KL         Yageo   311-105KHRCT-ND           Res 0603 105K 1/10W 1%         0.00476                 R43

11           1             LM43601PWPR HTSSOP16           LM43601PWPR Ti             296-40221-1-ND               IC REG BUCK ADJ 1A SYNC 16SSOP     2.03034                 U12

 

According to the chip AN SNVA722B, After I changed the C26 to 0.1uF, R24 to 140K, R26 to 10K, tried grounding the pin6. I found the LM43601 convertor works after apply external -15V to the LM43601 output (use Cn1). Once it start working, if I remove the external -15V, it keeps working. But it stop working if I only apply the +15V to my board (use J3) from beginning.(Note: the CN1 trick doesn’t work for the PCB without above changes)

My board needs designed use 15V as input J3. Before LM43601PWPR works, I have to use CN1 with +/-15V for the power input.

  • Hello,

    Would you be able to share the schematic? This will make it easier for us to help evaluate your problem.

    Thank you,
    Katelyn
  • In reply to Katelyn Wiggenhorn:

  • In reply to Katelyn Wiggenhorn:

    Yes, I did with MS word paste with schematic but those pictures lost. Anyway I just replied with two schematics.
    Update: today after I add a 50K from RT pin to GND (not -15V), one board work with light load now. But the 2nd board with heavy (0.3A) load still need external -15V make it work.
  • In reply to Nelson Niu:

    Hello,

    I am unable to open this file. Can attach this file as an attachment? I apologize for the inconvenience.

    Thank you,
    Katelyn
  • In reply to Katelyn Wiggenhorn:

    Hello,

    I received your schematic images via e-mail. Thank you for sharing.

    When your device is not working as expected, can you measure the VCC voltage? This will signify if the device has started up as expected. Second, if the VCC voltage is expected, can you measure the voltage from SW to GND? This will give us an idea of the operation of the device.

    Also, as you mentioned I would expect that decreasing the resistance of R24 and R26 could help. This will increase the current through the FB resistor divider and in turn make it less sensitive to noise.

    Thank you,
    Katelyn
  • In reply to Katelyn Wiggenhorn:

    Hello,

    I want to follow up with you. Were you able to measure the VCC and SW voltages?

    Thank you,
    Katelyn
  • In reply to Katelyn Wiggenhorn:

    Hello,

    Due to inactivity, I am going to close this thread. Please feel free to respond if you have any additional questions.

    Best Regards,
    Katelyn
  • In reply to Katelyn Wiggenhorn:

    Sorry I didn't get to this thread days ago. Here is my answers:
    1> I still have the startup problem.
    2>My VCC is good, variable power supply, I varied it from 12~16V no help for the start up. At same time, my other circuit works ok with this same power supply.
    3>When -15v fail to start up, I got ~2.7V voltage with slow ramp up/down.
    4>If I apply a -13~-15.5V power to my board, the LM43601 start working, then if I remove the -15V supply, the LM43601 can keep the output. I checked the switch waveform is around 500KHz with 50-50 duty.
  • In reply to Nelson Niu:

    Hello,

    Thank you for measuring the VCC. This means the internal device is on. Can you share the oscilloscope waveform of the Switch signal and output voltage?

    Thank you,
    Katelyn
  • In reply to Katelyn Wiggenhorn:

    I can't paste picture to this post. How can I send the waveform to you?

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