Built 10 prototypes, and 2 of 10 provide 'garbage' during RS-232 communication at 155200 bps. Charge pump capacitors are 220 nF 25V X5R at 3.3 V supply voltage. Can it be the problem? What are requirements and tolerance for those capacitors? What else may cause such failure? There are also 33 Ohms 250 mA thermistors in series with TX and RX pins 7 and 8 and TVS and 1 nF 50 V X7R capacitors and TVS 5V diodes from those pins to ground. Can 5V TVS cause such problems. It seems that it work fine with few characters, like OK, but does not provide correct characters with longer streams of data.
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