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      Today, we are going to discuss how to improve eye diagram with TPS25840-Q1 using long USB cable. We will divide the topic in five sections, automotive USB port data transmission background, eye diagram in long cable challenge, TPS25840-Q1 single USB port controllers, how to improve eye diagram with TPS25840-Q1, and summary.

      In the car internal, there are lots of USB ports located in different places, such as head unit, below head unit, glove compartment, armrests, and rear seat. This USB port may have data communication and charging function. Data communication is a very important function in the automotive USB port. Some applications like CarPlay, Android Auto, and CarLife Function is required in some USB port. These functions need high-integrity cording in the USB port.

      Some USB ports may need a long data cable to do the communication with the front and head unit, such as [INAUDIBLE] below the armrest. However, the long cable will create an equivalent capacitance and resistance, which will make the USB port bandwidth become narrow and impede the signal integrity. In here, we can see the original signal source, after-- at the long cable, 1.8 meter, and 3 meter cable. The USB port's eye diagram rising and falling edge becomes lower, and the eye becomes closed. Finally, the long cable makes the data communication fail.

      TPS25840-Q1 single USB port controller. TPS25840-Q1 is a USB type-A BC1.2 charging controller. It integrates a 4.5 to 36 volt input, 3.5 amp buck with spread-spectrum features; support USB type A BC1.2 CDP and SDP mode; user programmable USB current limit; cable drop compensations can-- up to 1.5 volts; high bandwidth data switch on DP and DM; client mode for system upgrade; DP_IN and DM_IN short-to-battery and short-to-VBUS protection; DP_IN and DM_IN support IEC 610042.

      Hot to improve eye diagram with TPS25840-Q1. We have three methods. First, PCB layout. Second, add LC network in DP and DM. Third, add the signal redriver. In the PCB layout, first, the DP and DM signal should travel the same distance. Second, keep the DP and the DM trace difference impedance to 90 ohms in the PCB board. Third, keep the DP and DM trace away from the noisy power signal.

      We can also add the LC network in the DP and DM to boost the eye diagram. Without the LC network, the TPS25840-Q1 eye diagram will fail with the 1.8 meter data cable. After adding the 10 nanohenry and 4.7 picofarads, the eye diagram will open up again, and the test result is pass.

      We can also add the signal redriver in the DP and DM to boost the signal. PMP40544 is TI automotive USB type A charger reference design. It used the TPS25840-Q1 for a USB type A port BC1.2 control and TPS217Q1 for signal boost.

      This is the PMP40544EVM board top view and bottom view. The PCB size is 50 millimeters by 42 millimeters. This is the efficiency curve at different VIN. The peak efficiencies in 14.5 volt input is up to 93%. This is the eye diagram test resolved using 1.8 meters and 3 meters data cable. We can find the source eye diagram with 1.8 meter cable is good. When add the TPS25840-Q1EVM, the eye diagram becomes closed. But add the TSP217Q1 signal redriver-- then the eye diagram opens up again. The source eye diagram with 3 meter cable is not good. When add the TPS25840-Q1EVM, the eye diagram test is fail. But add the TPS217Q1 signal redriver, the eye diagram will open up and results finally pass the combined test.

      After [INAUDIBLE] introduction, we can know that signal integrity quality is critical in automotive USB port, and we can improve it by careful PCB layout; use LC network in the DP and DM; add signal redriver. More information on TPS25840-Q1-- just go to the Product folder on ti.com. Thanks for your time to watch this video. Bye.