Hello ,
I have few queries on my SPI interface application.
Specifications:
Sensor: LDC1000. Controller: F28M35H52C
Data Out: Over SPI bus, f = 4MHz. SPI Bus Length = 2 meters.
Raising edge= Data out, Falling edge= Data In.
I want to use Differential drivers to have noise immunity.
Dual differential Driver P/N: **SN65C1168N** link: www.ti.com/.../sn75c1167.pdf
After going through the online documents on extended SPI communication, i have done below calculation.
f=4MHz => T=250ns. After Falling edge of SCLK, available time to get data from slave is
250ns/2 = 125ns. Otherwise it will be a transmit error (correct me if i am wrong ).
Propagation delay calculation:
1. Delay due to 2meter SPI bus = 10ns (signal velocity= 1m in 5ns)
2. Differential driver delay = 12ns. Differential receiver delay=27ns.
3. Sensor response time = 20ns
So total propagation delay between SCLK and SOMI is
2*(10ns+12ns+27ns)+ 20ns = 118ns.
available Extra time = 125ns - 118ns = 7ns.
Queries :
1. Is this calculation correct/accurate??
2. If yes, are there any risks in practical implementation??
3. What are the other better techniques ??
Note:
1. I have to use SPI interface only as per system requirements.
2. I am trying to avoid extra SPI interface as suggested in TI APN:
Link: www.ti.com/.../slyt441.pdf
Please share your valuable answers.
Regards,
Govind.