USB Multi-Channel Power Debug Summary

Figure: General block Diagram (right-click on the New tab to open the picture for a larger view)

Figure: Circuit board layout

Test point

1. Add the test point to the 4055 to the back level R1

2. Set the test points R8 and R7 in the 34,712-way output respectively

Commissioning Process

1. Get the PCB template, test the short circuit and the circuit breaker with a Multimeter control plan

2. Welding components

1. First think about the welding sequence of components, need to consider the size, welding methods, and the impact of each other. Generally first welding low, first welding in the middle, but the actual need to be welded to other parts of the welding effect of the degree of order.

2. Welding: The welding process should pay attention to a lot of problems, not specifically said.

3. Check: Check the naked eye to see if there is a false welding, short-circuit and so on. Then use the multimeter to test the uncertainty of the place.

Figure: Welding Completion diagram

3. Stepwise Commissioning

1. Plug in the USB port first, the power led D20 on, indicating that the power is plugged in. Multimeter measurement 4055 Output 4.19V, normal, battery interface 5.15V, normal. The chip does not overheat, normal.

2. Turn on test point R1, led D1 and D2 lit, normal, multimeter measurement j3,1, 2-hole voltage 3.30v,3, 4-hole voltage 1.20V, normal.

3. Test R8 point voltage 5.05V, not normal, is due to improper resistance selection, but there is no suitable resistance at hand, temporarily regardless of

4. Test point R17 voltage -6.70v, a slight deviation, but also the resistance to select a slight deviation, but the latter stage has an ldo, this effect can also be ignored.

5. But there is a problem, 3471 is very hot, find a reason to find is because the welding is not the belly of the pad, because the chip only pad is GND foot. Immediately blow down to re-weld good, test OK, also not hot.

6. Turn on test point R17, light D5 on, normal, test voltage -5.02v, normal.

7. Later test 3.3V 1.2v-5v output is normal, but LT3471 7V output voltage is wrong, I pick 15K and 100K (instead of 90.0K), the output is 33v,100k 82K output is 28V, the 15K output is 8.7V. Obviously there is a problem, but -7v that road normal, observation pin no virtual welding, circuit no short circuit, then turn to the manual comparison schematic, only to find fb1p and Vref short and then capacitance grounding, I only put the capacitor to fb1p, finally found the problem, immediately hands, will be done. Measurement output OK. Connect to the rear stage and test all output voltages OK.

Figure: LT3471 SCH

4. Ripple & Load capacity

5. Deficiencies

1. The patch pin is too close to the bottom pad's clearance.

2.USB mouth does not have a silk screen printing layer.

3. Inductance should be in a test to leave the welding spare.

4. Each power supply outlet and LED is not specifically labeled.

5. The transistor package uses the official library, but the pin position is not correct.

6. The test point uses 0 ohm resistor, the advantage is that it can be debugged step by step

7. The battery interface has been forgotten by the standard positive and negative polarity.

8. The principle design does not have the device parameters for the specific node value clearly marked

9. Not careful, after drawing the schematic must carefully contrast check, the schematic correct, the electrical connection will not be wrong

　　

USB Multi-Channel Power Debug Summary