[Help needed] This is a slightly complicated schematic diagram, about the TI processor and USB power supply part. There are some things I don't understand and I would like to ask everyone for help.

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[Help needed] This is a slightly complicated schematic diagram, about the TI processor and USB power supply part. There are some things I don't understand and I would like to ask everyone for help. [Copy link]

 

 

Please help me look at this diagram. I have been looking at it for two or three days, but I still can't fully understand it. This schematic diagram is only a part of it. The whole diagram is quite large. If you need to see it, I can send it. The main problem is: According to my inference, the functions that the diagram itself should implement do not correspond to the functions shown in the schematic diagram. In the figure, VCC_5VD_IN is the external DC power input, and VCC_5VD is the 5V power supply on the board obtained by conversion. The functions that the diagram itself should implement, combined with the entire schematic diagram, I infer that: 1. Supply +5V power to the chip on the board; 2. When the chip on the board sends a USB power supply signal, supply 5V power to the power supply part of the USB interface of the board; However, combined with the chip manual, I can't deduce these two functions. There is a key point that EN2 and EN3 of TPS2087D are low-level enabled, but they are connected to the DC power supply VCC_5VD_IN, which causes channels 2 and 3 to be in a closed state all the time. I am stuck here. If you have any questions, please ask me. I hope I can provide some help. Attached is the information I found about TPS2087D, TPS2068DGNR and SN74AHC1G04DBVR. TPS2087D is a four-channel power distribution switch, EN low level enable. TPS2068DGNR is a single-channel power distribution switch, EN low level enable. SN74AHC1G04DBVR is an inverter. USB_DRVVBUSn outputs a high level to start USB power supply, and the inverter outputs a low level to enable TPS2087D.

qwqwqw2088

Take a good look at the TPS2087D manual

qwqwqw2088

The original poster's picture shows EN2 and EN3, but the one that is not used is EN4, corresponding to OUT4

qwqwqw2088

The control signal USB_DRVVBUSn pulls down EN4 through the 74 chip NOT gate of U2 to achieve the output of OUT4

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qwqwqw2088 posted on 2019-5-18 23:24 The control signal USB_DRVVBUSn pulls down EN4 through the 74 chip NOT gate of U2 to achieve the output of OUT4

Thank you for your answer! I have read the chip manual many times, and I have also pushed the function you mentioned, and there are still some minor problems. The input power voltage of this board is VCC_5VD_IN, which should be converted to VCC_5VD by TPS2068 and then output. In this way, IN4 of TPS2087D has input voltage. But the low level enable of TPS2068 is connected to the OUT3 pin of TPS2087D, while EN3 is de-enabled by VCC_5VD_IN, and IN3 is connected to OUT4, which is strange... Does TPS2087D directly output low level after being de-enabled? In this case, does the schematic mean: if USB is not connected, TPS2068 is used for power supply, and if USB is connected, TPS2068 fails and USB is used for power supply? Can you help me take a look...

qwqwqw2088

Liushixingkong published on 2019-5-20 10:12 Thank you for your answer! I have read the chip manual many times. I have also pushed the function you mentioned, and there are still some minor problems. The power input of this board...

Please read the manual circuit of 2068 carefully. The figure on the first floor uses ou4 and en4. This group is controlled by USB_DRVVBUSn through U2. OUT3's VCC-USB0-IN-K is U5 chip TPS2068 current limiting power distribution switch 4 pin control

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qwqwqw2088 posted on 2019-5-20 17:07 Please read the manual circuit of 2068 carefully. The figure on the first floor uses ou4 and en4. This group is controlled by USB_DRVVBUSn through U2 to control OUT3's VCC-USB0-IN...

I roughly understand it. Please check if this is correct. 1. When the voltage of VCC_USB0_IN is 0 and the voltage of VCC_5VD_IN is 5V, since OUT3 of TPS2087 fails, TPS2068 works and generates VCC_5VD voltage to power the board; at this time, EN2 and 3 fail because they are pulled up to 5V. If the USB_DRVVBUSn signal arrives at this time, OUT4 outputs 5V power supply to USB. 2. When the VCC_USB0_IN voltage is 5V and the VCC_5VD_IN voltage is 0, since the OUT2 and OUT3 of TPS2087 enable the pull-down resistors and enable the low level to be effective, OUT3 outputs 5V voltage, which in turn makes TPS2068 invalid, and drives OUT2 to output 5V voltage. At this time, the chip of the board generates EN4 enable signal, driving OUT4 to output 5V voltage, thereby realizing the voltage regulation function of the USB input voltage VCC_USB0_IN. Ah, thank you so much. I am the best!

qwqwqw2088

Liushixingkong published on 2019-5-20 21:01 I roughly understand it. Please check if this is correct. 1. When the voltage of VCC_USB0_IN is 0 and the voltage of VCC_5VD_IN is 5V, due to the O of TPS2087...

The understanding is basically correct. EN2 and EN3 do not need to be pulled up, so they cannot be said to be invalid. The 4 enables are only enabled by low level.

alan000345

Watching the conversation between experts, I learned a lot.

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qwqwqw2088 posted on 2019-5-21 07:57 The basic understanding is correct. EN2 and EN3 do not need to be pulled up, so they cannot be said to be invalid. The 4 enables are only enabled with low level.

Thank you for your help! I will keep working on it!

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alan000345 posted on 2019-5-21 08:06 Read the conversation between experts and learn more.

This is part of the OMAPL138 schematic diagram on TI's official website. If you are studying this chip, I can send you some related information.

alan000345

Liushixingkong published on 2019-5-21 12:10 This is part of the OMAPL138 schematic diagram on TI's official website. If you are studying this chip, I can send you some relevant information.

OK, thank you.

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alan000345 posted on 2019-5-22 08:47 OK, thank you.

Huihui

alan000345

Liushixingkong posted on 2019-5-22 14:45 Huihui

Thank you so much.

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alan000345 posted on 2019-5-24 09:04 Thank you so much.

It's just the way it should be.