SN74AVCBH164245: Power consumption estimation

MINKYUNG KIM

Part Number: SN74AVCBH164245
Other Parts Discussed in Thread: SN74AVC4T245

Hi team,

I need to provide guidance on calculating power consumption of SN74AVCBH164245. I found a thread below.

https://e2e.ti.com/support/logic/f/151/t/875721

It doesn't look suitable for this device, as this device is dual-rail bus transceiver. Plus, the thread is saying about Nsw, fi, fon, CLn, and Dn. Could you let me know more general/simple method to calculate power consumption, when such detailed operation conditions are not given? Thank you.

And I tried to calculate as below. Can you correct my understanding?

Can it be modeling simply as below load cirsuit, S1 = 2xVcco when High level transmission, S1 = Open when disable, and S1 = GND when Low level transmission? If then the calculation would be :

Supposed VCCA = VI = 3V, VCCB = VO = 3.3V and high/low level transmission at half rate.

Ptotal.dynamic = P(highIN-highOUT) + P(lowIN-lowOUT) = [(Vcca / RL) + (Vccb / RL)] / 2 + [(Vcca / RL / 2) + (Vccb / RL /2)] / 2 = [(3V * 3V / 500ohm + 3.3V * 3.3V / 500ohm)]/2 + [(3V * 3V / 250ohm + 3.3V * 3.3V / 250ohm)]/2 = 19.89mW + 39.78mW = 59.67 mW

Pstatic = VCCA * ICCA + VCCB * ICCB = 3V *40uA + 3.3V *40uA = 252uW

(There is no condition for VCCA = 3V, VCCB = 3.3V, so I choose case of VCCA = 3.6V, VCCB = 3.6V from table below.)

Thank you for your prompt response.

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 257000 points

You can model it as two devices, connected to V_CCA and V_CCB.

The resistors shown above are used in certain tests. If you do not actually connect those resistors, you cannot use them for your calculations.

How have you configured the DIR pins? What is the frequency of your signals? What are the actual loads in your circuit?

0 MINKYUNG KIM over 3 years ago in reply to Clemens Ladisch

Expert 1250 points

Hi Clemens,

Would you let me know your email? I cannot find you from the system.

0 MINKYUNG KIM over 3 years ago in reply to MINKYUNG KIM

Expert 1250 points

Clemens,

Customer is using all 16 Channel with bi-dir to transmit 10MHz signal. Can you let me know the approximately worst case max. power consumption in general design?

Plus, is there any guidance to calculate the power consumption? They are not providing their schematic but requesting how to calculate the power consumption.

Thanks!

0 Dylan Hubbard over 3 years ago in reply to MINKYUNG KIM

TI__Mastermind 43420 points

Hi Minkyung,

This FAQ should help: https://e2e.ti.com/support/logic/f/151/t/875721?tisearch=e2e-sitesearch&keymatch=faq%2525253Atrue. For the dynamic calculations, you would just use VCCO.

0 MINKYUNG KIM over 3 years ago in reply to Dylan Hubbard

Expert 1250 points

Hi Dylan,

Thank you for reply. Actually I already checked the FAQ you attached.

The FAQ is presenting CMOS buffer, so total power consumption of this level translator device is Ptotal in the FAQ multiplied by 2? (Clemens said "You can model it as two devices, connected to VCCA and VCCB." in previous thread.)

0 Clemens Ladisch over 3 years ago in reply to MINKYUNG KIM

Guru 257000 points

The datasheet gives V_CCA and V_CCB, and C_pdA and C_pdB. You can compute the static and transient power consumption from that. Assuming both sides are 3.3 V and all channels go from A to B, the worst-case consumption would be:

3.3 V × 40 µA + 3.3 V × 40 µA + 14 pF × (3.3 V)² × 10 MHz × 16 + 20 pF × (3.3 V)² × 10 MHz × 16 = 62 mW

The load power consumption depends on the load on the outputs. If you do not have the schematic, ignore it.

0 MINKYUNG KIM over 3 years ago in reply to Clemens Ladisch

Expert 1250 points

Clemens, Dylan,

Many thanks to your fast response and kind support.

0 MINKYUNG KIM over 3 years ago in reply to Clemens Ladisch

Expert 1250 points

Hi,

I have additional question.

When using all 16 channels with Vcca = Vccb = 3V, is the equation below okay to get power consumption in worst case?

P = 3V * (12mA * 16) = 576 W

I checked that method to calculate worst case power consumption was given to customer when they calculated the power consumption of SN74AVC4T245. If this method is valid also for SN74AVCBH164245, which method is more appropriate for being provided to customer? The one you said in previous thread, or this method?

0 Clemens Ladisch over 3 years ago in reply to MINKYUNG KIM

Guru 257000 points

If you connect a load (such as a LED) to each output, and if a current of 12 mA flows through each LED, and if the voltage drop over each LED and its current-limiting resistor is 3 V, then the total power consumption of all LEDs is 0.576 W.

The power consumption of the SN74AVCBH164245 itself would be much smaller, because the voltage drop over each output transistor is much smaller (see V_OL).

0 MINKYUNG KIM over 3 years ago in reply to Clemens Ladisch

Expert 1250 points

Thank you for reply.

Then when we simply model the output transistor as below,

Ptotal = P(HIGH in 8 channel) + P(LOW in 8 channel)

= ((3V - 2.3V x 12mA x 8) + ((3V - 0.7V) x 12mA x 8) = 288mW

Is it correct?

Plus, should it be multiplied by 2 when considering Input side?

0 Clemens Ladisch over 3 years ago in reply to MINKYUNG KIM

Guru 257000 points

Yes, that would be the worst-case power consumption.

CMOS input work differently; no current flows (except for leakage current, which is usually ignored).

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SN74AVCBH164245: Power consumption estimation