Design key points of MAX1576 white LED charge pump PCB
1. The ground end of any reference by-pass capacitance (MAX1576 does not have this pin) or the ground end with resistance (RM and RF of MAX1576) shall be connected to the ground pin (as opposed to the power ground).This helps reduce the coupled noise of the analog circuit.
2. The input, output and fly capacitance are best using electrolyte X5R or ceramic capacitors with better performance.Low ESR is critical for high current output, low input/output ripple and stability.
3. In order to avoid the switching noise of chip bias circuit, input capacitance (CIN and CINP) should be placed as close as possible to the input and ground pins, and the capacitance and chip are preferably not through holes.
4. To ensure the stable operation of charge pump, the output capacitance, COUT, should be placed as close as possible to the OUT pin.The ground end of the COUT is connected to the nearest power ground or ground pin, or bare solder pad (EP).
5. If there are independent ground and power ground and/or IN and PIN pins, the chip contains independent power and offset inputs.If the pins are not close together, two input capacitors are required: the CINP from PIN to power and the CIN from IN to ground, with each capacitor placed as close as possible to the chip.IN this case, the PIN and the power should be connected to the system power source and the strata respectively, while the IN and the ground should be connected to the nearest.The PCB power cord first enters CINP and INP, and then connects to CIN and IN through some overpasses, providing certain input noise filtering at IN end.The power ground and ground shall be connected together by a bare pad.
6. To ensure the ground output impedance of the charge pump, the flying capacitance (C1 and C2) should be installed as close as possible to the chip.If it is impossible to avoid the use of through-holes, it is best to make them series with C1 and/or C2, rather than CIN or CINP, as the flight capacitance has no effect on device stability.
7. The logic input can be wired as required to connect with LED.The holes in these leads do not cause any problems because the current at these output ends is stable.It is important to note, however, that if these leads are close to sensitive RF circuits, ripples on the leads may affect RF circuits.
8. Large holes can be selected for bare soldering pad, which is conducive to inspection of welding points, and it is convenient to remove the chip from PCB with soldering iron when repairing, so as to reduce damage to the chip.