NVT4858 Power Consumption

[5Martin]

Hi 

We want to use NVT4858 in our design. I am referring to the user manual of NVT4858-4557-EVB evaluation board, UM11582.

I'm wondering why such powerful load switches (1.5A/2A) are used for the 1.8V/3.3V VCCB Power selection.

What is the current consumption on the VCCB pin?

Referring to the datasheet of the NVT4558 the power dissipation is max. 1W. How is this 1W split to VCCA and VCCB supply pins?

Note, I already checked this post regarding the load switch selection and why two different ones were used.
https://community.nxp.com/t5/Other-NXP-Products/NVT4858-VCCB-Power-Selection/m-p/1409540 

Thanks and best regards, 
Martin

[5Martin]

Hi Jozef, 
thanks for your reply. Let me rephrase my question.

What is the drive current of each driver? Those drive currents need to be supplied by VCCA and VCCB, refer to figure 10 in the datasheet:

Or reformulated even more, what is the requirement on the PMU or DC/DC shown in Figure 10?

The current consumption of the NVT4858 in table 11 only refers to the static current consumption which is not really of interest for me.


Best, 
Martin

[JozefKozon · Accepted solution]

Hi Martin,

for the worst case current consumption scenario, it will be VCCA+VCCB<15uA.

Then adding the worst case current consumption of the I/O pins, +/-100mA*8I/O pins=800mA. 

So the worst case current consumption will be 800.015mA, most of the time lower current consumption. You can design your DC/DC or MPU for this value (800.015mA).

With Best Regards,

Jozef

[JozefKozon]

Hi Martin,

for the NVT4858 current supply consumption please refer to the Table 11. in the NVT4858 datasheet. There is no separate current consumption only for VCCB, but for both VCCA and VCCB. 

The 1W total power dissipation seems low, but if I calculate the maximum junction temperature, it looks to be sufficient. Please check below. 

Ptot=1W

Tamax=85°C

Rthjc=51.4°C/W

Tjmax=Tamax+Ptot*Rthjc

Tjmax=85°C+1W*51.4°C/W

Tjmax=136.4°C.

Although I haven't found the Tjmax for the NVT4858, from my experience our components have can survive such junction temperature or even higher. 

In another document attached I have found, that the NVT4858 was tested for Tjmax=+150°C. 

With Best Regards,

Jozef