VOH and VOL min and max levels for LTC6995-1 chip

Hi Siddharth,

There is no measurement for 5V supply, and IOH = 4mA.  

These spec table measurements are done during ATE process. 

You can refer to the Output resistance vs Supply graph for estimation for 5V. 

Thanks,
Emrecan

ok. This part is used for 120s watchdog timer. Kindly review.

Hi,

I couldn't follow the schematic.

Where SET resistor is connected?  
Is there a voltage divider on the output? 
RSET value seems incorrect for the 120s watchdog timer.

You can use the following tool to calculate the required resistor values.

LTC6995 One Shot

Thanks,

Emrecan

Kindly revert.

HI, 

1. Set is connected to OUT pin6.

2. yes, voltage divider is added to meet 3.3V input IO level of a logic gate(inverter). Output of this timer is an input to an inverter logic gate.

3. RSET is calculated using the formula for our specs of 120 second timer (tout/2). 

Ndiv=32768

Tout=240s

Tout/2=120s

Rset=240*50k/(32768*1.024m) = 357k Ohms

4. What is the current output on Pin6 of the timer IC? 

Kindly revert.

Thanks and Regards,

Vidhya

Hi Vidhya,

Thanks for the clarification. I couldn't see a problem with the schematic. 

The output current depends on the load resistance. The maximum source/sink current is 20mA. The OUT pin swings from GND to V+ with an output resistance of approximately 30Ω. When driving an LED or other low-impedance load a series output resistor should be used to limit source/ sink current to 20mA

Thanks,
Emrecan

Hi Emrecan,

R685 and R118 are used as divider at Output.

R685 is 5.1K ohms and it Limits the current to 333uA. 

Kindly share your feedback on these resistors.

Thanks,

Vidhya

Hi Emrecan, 

R685 and R118 are used as divider at Output - can be removed and add a 1bit level translator to convert 3.3V to 5V?

Also, Vout (pin6) is 5V. but set pin maximum input voltage is 1.03V

Out pin is connected to set pin via 357K resistor. Does it have to be higher package?

Kindly revert.

Thanks and Regards,

Vidhya

Hi Vidhya,

Yes, a one-bit-level transistor can be used at the LTC6995's output. A resistive divider is also a viable option, though. 

By the way, LTC6995 can be run with a 3.3V supply. If the customer uses a 3.3V supply, output swings between 0 - 3.3V. 

No, the Set resistor doesn't need to be a higher-value resistor or a bigger package. The value of the Set resistor determines the period of the internal oscillator. Therefore, it should be calculated using the formula given in the datasheet. 

Normally, the set pin voltage is around 1V. When OUTPUT goes to 5V, the SET pin current is reversed. 

When there is no set pin current to GND, the internal oscillator is powered down. This is the basis of the power-on reset timer functionality. 

Thanks,

Emrecan

Hi Emrecan,

Sorry for the delay, I didn't get any notification about your response.

Happy New year!

Out pin is at 5V and is connected to SET pin at 1V via Rset=357K Ohms in my design.

The resistor sees drop of almost 4V? No need to worry about the package of Rset as resistance is higher?

Kindly revert.

Thanks,

Vidhya