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LM5175: LM5175驱动紊乱

Part Number: LM5175
Other Parts Discussed in Thread: LM5176
谢谢:
    我遇到的问题分两种电路来描述
一:TI推荐电路,参考webbench。输入电压16V~40V,输出21V/7A电路。
      1:输入16V,输出21V,输出电流加大到6.4A时,LM5175会损坏。如附件图16V输入,21V6.4A输出的各位置波形。
      2:输出21V/3.5A,输入电压从16V加大到19V时,LM5175会损坏。如附件图19V输入,21V3.5A输出的各位置波形。
由于在第一种状态内发现,在6.4A负载时,左边上管和下官驱动有变化。为了排除问题,故先看boost状态是否正常。所以有了第二种情况:
二:(TI推荐电路,参考webbench输入电压16V~40V,输出21V/7A电路)这个电路的基础上,并把左上管DS短接、左下管取掉。图形见对应附件
     1:输入16V,输出21V,空载,左下管和左上管互补导通,左下管和右下管某些时候同时导通。(不符合我们对BOOST的理解:认为左下管不应该导通,左上管应该长通)。
     2:输入16V,输出21V,1A负载,左下管关闭,左上管长通,右下管脉冲导通关闭。(符合我们对BOOST的理解:认为左下管不应该导通,左上管应该长通)。
     3:输入19V,输出21V,1A负载,左下管和左上管互补导通,左下管和右下管某些时候同时导通。(不符合我们对BOOST的理解:认为左下管不应该导通,左上管应该长通)。情况跟空载相近。
损坏之前伴随着啸叫,没有发热现象,经常坏LM5175和左上管和左下管。
顶层:
中间层:
底层:
底层-镜像:
采集的波形:
第二电路:输入16V输出21V1A负载黄色(20倍衰减)为HDRV1蓝色为LDRV1:
第二电路:输入16V输出21V1A负载黄色为LDRV1蓝色为LDRV2
第二电路:输入16V输出21V空载黄色(20倍衰减)为HDRV1蓝色为LDRV1
第二电路:输入16V输出21V空载黄色为LDRV1蓝色为LDRV2
第二电路:输入19V输出21V1A负载黄色(20倍衰减)为HDRV1蓝色为LDRV1
第二电路:输入19V输出21V1A负载黄色为LDRV1蓝色为LDRV2
第一电路:16Vin-21Vout6.4A-Vboot1_sw1
第一电路:16Vin-21Vout6.4A-蓝色为Vboot2_sw2黄色为右上管Vgs
第一电路:16Vin-21Vout6.4A-蓝色为左上管Vgs-黄色为坐下管Vgs
第一电路:19Vin-21Vout3.5A-Vboot1_sw1
第一电路:19Vin-21Vout3.5A-蓝色为Vboot2_sw2黄色为右上管Vgs
第一电路:19Vin-21Vout3.5A-蓝色为左上管Vgs-黄色为坐下管Vgs
  • I am currently traveling.  Will review and get back to you tomorrow.

  • Sorry for the delay. I reviewed your schematic and the layout, and found you did not follow our layout guidelines presented in the datasheet. For instance, the gate drive trace for the right high side FET and the return trace are not placed closely side by side but they are separated widely over the switch node. This will affect the drive performance .

    The LDRV1 and LDRV2 should never give driving pulse at the same time. It is really weird to see it on your circuit, and it seems the IC is damaged somehow. Did you replace the IC and see it if still showing the overlapping drive signals?

    At 19Vin and 21Vout, the IC may be in the Buck-Boost Transition mode, namely both buck and boost leg will be switched alternatively. But it should not look like what you show here.

    As you may know, we recently released the LM5176, which is almost pin-to-pin compatible with the LM5175: you just need to change the RT resistor to keep the same switching frequency. The LM5176 can be seen as an improved version of the Lm5175, with greater noise immunity. Replacing the LM5175 with the LM5176 on your existing board may resolve many issues you are currently seeing.

    Thanks
  • 很高兴看见你的回复
    1:目前HDRV2驱动走线虽然不理想,但是波形暂时没有出现错误。
    2:更换IC,并查看过,还是有问题。
    3:你的建议是换成LM5176对吧。
    谢谢。
  • 你好

    1:我换了LM5176,在输入电压超过Vout电压时,还是会出现紊乱。

    2:能否详细讲解下这个IC的工作方式,详细到各个MOS的开关和电感中的电流方向。因为我发现,在升压进入降压时,电感电流方向会反相或者180°相移。

    3:请求比LM5175datasheet更详细的讲解。

    4:请问还有谁成功的使用过LM5175或者LM5176。能否给个联系方式咨询下。因为这个IC周围器件很少,不需要调试太多。我觉得是否是IC本身有问题。

    谢谢

  • 你好

       我调试了下,LM5176效果好很多了。没有了LM5175哪些问题了。

    但是我还是有一点问题:

    输入超过28V时,输出电流最大到4.9A能稳定工作,但是超过5A,就会出现不稳定。

    波形如下:

    黄色为SW2对GND波形,蓝色为SW1对GND波形。

    输入超过28V后,都有这个状况。

    请帮我分析一下,谢谢。

  • 我们也出现类似问题,是换成LM5176直接有改善吗?需要什么配置吗?
  • Again, sorry for the delay owing to being out of office during the Thanksgiving holidays.

    The SW1 should continue to switch in the buck mode. However, your waveform shows it intermittently stops switching.  

    There are a few possibilities to cause such abnormal switching behavior.  Have you monitored SW2?  And the input voltage and see if it fluctuates when such abnormal behavior occurs? Could you take a scope picture showing Vin, Vout, SW1 and SW2?

    Best Regards,

    Youhao Xi,  System and Applications Engineering, APP-BMC-BCS, TI 

  • 哦,好的,我再观察下,谢谢

    非常感谢