Capacitor in Max 232 circuit

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Capacitor in Max 232 circuit

Postby nicholaswsw » Tue Mar 15, 2011 6:59 am

According to datasheet, it states that the charge pump capacitor of max232 circuit are 1uF. Just wondering does the capacitance affect the performance of the IC i.e capacitance would give a voltage level of +-10V instead of +-12V, or affects the baud rate (gives problem at high baud rate), or problems at high frequency?

just a noob question
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Re: Capacitor in Max 232 circuit

Postby ABSF » Tue Mar 15, 2011 4:51 pm

Does this question has any connection with your "ZigBee communication" problems?

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Re: Capacitor in Max 232 circuit

Postby nicholaswsw » Tue Mar 15, 2011 9:03 pm

I have Zigbee in my project but this is for the barcode scanner. And this is more to understand the operation and performance of the max232. So does is affect? Because bigger capacitance will take a longer time to charge.
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Re: Capacitor in Max 232 circuit

Postby shahrul » Wed Mar 16, 2011 12:51 am

In the datasheet, it's shows 1uF. I'm use 10uF, since now no problem yet. I have tried to high baudrate also, it's still ok. I'm not testing for the performance, since it's working.
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Re: Capacitor in Max 232 circuit

Postby FloatingMachine » Wed Mar 16, 2011 10:55 am

I tried using 0.1uF C-Cap as well and got no problem :)
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Re: Capacitor in Max 232 circuit

Postby ABSF » Thu Mar 17, 2011 3:41 pm

nicholaswsw WROTE:I have Zigbee in my project but this is for the barcode scanner. And this is more to understand the operation and performance of the max232. So does is affect? Because bigger capacitance will take a longer time to charge.


MAX232 was designed to replace the older 74188 & 74189 chips. If using 74188/189 pair, the +/-12V is supplied by the circuit designer which complicates the power supply design. MAX232 came out to simplify RS232 (V24I) for the MCU user. So performance wise, I would guess it is a compromise of the older design.

All the RS232 interface cards in my office equipments uses 74188/189 pairs because our terminals (PC) and the RS232 servers racks are very far apart. If I remembered correctly, I have connected a RS232 terminal 50M away from the RS232 server card and still worked.

I am not sure how far can a MAX232 serial interface work at 9600 bauds.

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