iddq.dc concern

[user_4077216]

Hi everybody,

Sync SRAM (CY7C1370KV33 for instance) datasheets do not show the Iddq dc current vs. frequency and temperature.

Cypress calculator (see Junction Temperature for Sync SRAM: Maximum Junction Temperature and Power Consumption Calculator - KBA204198 ) do not apprehend this parameter that could add extra power consumption and show a higher junction temperature of the SRAM die as expected.

Other manufacturers indicate these iddq.dc (with open ouptuts) characterictics in their datasheets and comparing power management between memories is not easy as Cypress does not mention this feature...

Many thanks.

Pascal G.

[PradiptaB_11]

Hi Pascal,

Thanks for the update !

IDDQ does vary with the operating temperature, load capacitance and frequency which is why we have the following section in the tool. The tool will take care of the concern.

You are correct,that we do not provide IDDQ in datasheet but junction temp calculator has a section where IDDQ power can be calculated and junction temperature will incorporate this power in calculation.

Thanks and Regards,

Pradipta.

[user_4077216]

Hi Pradipta,

I am not sure we are on the same path…

I did expect Iddq was indeed affected by the switching power of the I/Os that addresses the discharge of the capacitors between leads and therefore this iddq (I called it iddq.ac) is a function driven by the SRAM clock frequency, the number of switching IOs as shown in the iddq section of the Cypress calculator (and also by other manufacturers calculators).

But the iddq.dc is never taken into account here!

This iddq is addressed when the outputs are open and therefore the capacitors between leads are not discharged as the IOs do not switch ON/OFF. This iddq.dc is the current of the output stages that drives current from Vddq when the outputs are in the open state.

This current value is also a affected by the SRAM clock frequency and a little by the die temperature.

As an example, I copied the Iddq features of a GSI sync SRAM (GS8160ZxxDGT) hereunder:

1. Iddq (open outputs) vs frequency and commercial/industrial operating temperature ranges

2. Iddq (open outputs) @200MHz with Military operating temperature range

In my examples above in the pipeline mode (x36), the iddq.dc @200MHz is increasing from 30mA @commercial/industrial range to 40mA in the military temperature range (temperature effect) and is increasing from 20mA to 65mA @150MHz to 400MHz in the commercial & industrial temperature ranges (frequency effect).

If we consider now that the outputs are switching, you need to add the outputs capacitors discharges in the vddq power calculation as follows (indicated in the iddq section of the Cypress calculator): iddq.ac:

Finally, the Vddq power is addressed by both iddq.dc and iddq.ac:

Vddq_power = vddq (iddq.dc + iddq.ac).

I hope my explanation makes sense this time.

Best regards,

Pascal-Louis GEYRE

FADEC Technical Leader

Safran Electronics & Defense

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[nileshbadodekar]

Hi Pascal,

Historically we haven't provided this data through datasheet as it is a very small percentage of total current. And we misunderstood your query as one for thermal performance of the device.

I need to check with the product engineers internally if this characterization can be performed. It Has to be a custom char as the spec was not defined explicitly for our testers to validate.

Regards,

Nilesh