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Saltan,

I have tried to get the MAX232 to overheat but I was not successful. Can you return a couple devices to your distributor as defective for failure analysis. It would be good to return samples that have the overheat issue but still work after cooling off. Also return some that are permanently damaged (don't work when cool).

The C3 capacitor can be placed in either location for either device. It does not affect the charge pump action.

Hi,

I've connected the C8 negative pin to VCC and measured the VCC, V+, V- for damaged and not damaged IC at run time. Please see below 

NOT DAMAGED MAX232 ON BOARD 

VCC: 5.09V 

V+ : 9.3V 

V- : -8.71V 

Some Pins of MAX232: Squarewave signals 

Heating: NO 

DAMAGED MAX232 ON BOARD 

VCC: 5.09V 

V+ : 4.3V 

V- : 1.2V 

Some Pins of MAX232: NO Squarewave signals 

Heating: LIKE HELL 

I'm pretty sure that the VCC is stable

Dear All,

Do you think that the below switching freqencies are normal   

MAXIM MAX232CWE+  : nearly 600KHz at pin 3

TI MAX232 : nearly 45KHz at pin 3

I read to many things on the net about charge pump capacitors. In short;

- if you use fast switching you need lower capacitance

- if you need low switching you need higher capacitance

From this point of view, capacitors suggestions for  "600KHz and 45 Khz" are same and 1uF. for both TI and MAXIM ICs ???

Do you have any comments for switching frequencies and capacitor selection

Saltan,

45kHz is too low. I do not have data on hand for the nominal frequency of the charge pump. I will check some samples this week.
It takes a lot of current to pull the V- pin positive. There is a Schottky diode to ground on the V- pin.

On devices that overheat but are not destroyed, is the V- pin also positive? It seems that the MAX232 is latching up.
Other users who added a VCC resistor may have prevented latch up by limiting the (SCR) hold current so the latch is unsustainable.

I do not know where the trigger for the latch originates, but the trigger is certainly external to the device.

Have you considered upgrading to the MAX202? It is the same cost and is a drop in alternative to the MAX232. Both device have the same function, but the internal schematics are very different.

Dear Ron,

Thanks for your answer. Please see below for my answers;

45kHz is too low.

I see nearly 45kHz with an oscilloscope. 

I do not have data on hand for the nominal frequency of the charge pump. I will check some samples this week.

It takes a lot of current to pull the V- pin positive. There is a Schottky diode to ground on the V- pin.

On devices that overheat but are not destroyed, is the V- pin also positive?

Yes V- pin also positive for both TI, or MAXIM ICs. I tried them on the same PCB.

It seems that the MAX232 is latching up. 
Other users who added a VCC resistor may have prevented latch up by limiting the (SCR) hold current so the latch is unsustainable.

I do not know where the trigger for the latch originates, but the trigger is certainly external to the device.

Have you considered upgrading to the MAX202? It is the same cost and is a drop in alternative to the MAX232. Both device have the same function, but the internal schematics are very different.

I do not use MAX202 But I can. Pins are ok but footprints are a little different. I may use it.

Saltan,

You are correct, the MAX232 does run near 45kHz. It is the MAX202 and entire MAX/TRS32xx series that runs over 100kHz.

The V- should always be negative in operation. I tried forcing V- positive (up to 1Amp), but it ran normally once, I stopped the abuse.

I have not been able to get any MAX232 to latch-up (overheat) in the several times I have tried. Please try the MAX202 and let me know the result.

Dear Ertan Bey,

When you design the circuit you didn't consider ESD considerations.  am sure that the shield of DB9 its connected direct to GND or not connected. I always use 100 ohm serial,100nF to GND  for each pin from DB9 to IC. 1 uF capacitors use as multilayer ceramic low ESD type instead Tantalum. Less space, lower price better performance.

When you do this please share the results with us.

BTW - There in mounting hole on trace to Pin# 8 of DB9 I hope its not plated hole and you have short to GND

Sevgiler,

Haim Rodrik - CEO/CTO

jTrack M2M Tellocation Systems LLC

Note: Between the DB9 shield to board's GND connect via Ferrite bead parallel 1000pF/2kV 0805 capacitor.

  if you need more assistance feel free to use rodrik5000

I have reached this forum in search for a solution for the same latch-up situation.

In my case I think I have found the scenario that causes the latch-up - every time the analog side RS232 pins of the chip are connected to a powered serial port (e.g. connecting a board with the MAX232 to a running PC's serial port) without power applied to it's power pins (i.e. the board not powered), once I apply +5V to the chip it immediately enters the latch-up condition. I have narrowed this to the TxD input - because it's driven with a negative voltage (negative idle voltage on RS232 line), the combination of rising VCC and negative input on TxD causes in my opinion the latch-up condition. This seems like a bug of these chips related to the silicon implementation.

Can TI tech support check this analysis and try t simulate it too?

I.T.,

The TxD input is the R1IN or R2IN pin on the MAX232, correct?
I can try this this week.

 If you don't use the second  port T2  , the pin 10  must be fixed with a pull up .   Not every component have the internal pull up .

Yes, it's R1IN.

Hi Ron, any luck simulating the scenario I described? It's been over a week...

I.T,

I tried biasing the RS232 inputs one at a time and both at same time before applying VCC. I also tried floating TIN inputs. I tried slow and fast VCC ramps. However, I did not see an increase in supply current.