Answers Database

XC9500: Device Slew Rates (Rise/Fall times) with capacitive loads


Record #1490

Product Family:  Hardware

Product Line:  9500

Problem Title:
XC9500: Device Slew Rates (Rise/Fall times) with capacitive loads


Problem Description:
Keywords: 9500, slew rate, rise time, fall time, capacitive load

Urgency: Standard

What slew rates can be expected on 9500 outputs as the capacitive
load increases?


Solution 1:

	XC9500 Output rise/fall time with capacitive load

Note:	The numbers indicated below are based upon a single
	data point and are given solely as a service for our
	customers to estimate the effects of additional
	Capacitive loading. Xilinx does not guarantee these
	numbers.

Method:

	Capacitance of the test fixture was measured on the
	HP 4284A Precision LCR meter.  The capacitance of one I/O
	path in the speed board was approximately 35pF at 1MHz.

	Two XC95108 PC84 units were programmed to 16 bit counter
	pattern, one with SLOW slew rate and the other with FAST
	slew rate.  The parts then were exercised at the clock
	rate of 5MHz to determine additional output delays with
	additional capacitive loads.
	
	Output rise/fall time was observed on the HP 54720D
	oscilloscope with HP 54701A Active Probe.

Measurement Result:
	
SLOW SLEW MODE: Low to High  (rise time from 10 % to 90% of Vout)

Added Load     RISE TIME
-0-		 5.2ns
35pF		 5.2ns
57pF		 5.5ns
90pF		 5.8ns
157pF		 6.4ns
212pF		 7.0nS

FAST SLEW MODE: Low to High  (rise time from 10 % to 90% of Vout)

Added Load     RISE TIME
-0-		 570ps
35pF		 2.0ns
57pF		 2.5ns
90pF		 2.8ns
157pF		 3.0ns
212pF		 3.4ns

SLOW SLEW MODE: High to Low  (Fall time from 90 % to 10% of Vout)

Added Load     FALL TIME
-0-		 1.1ns
35pF		 1.8ns
57pF		 2.1ns
90pF		 2.3ns
157pF		 2.5ns
212pF		 2.5ns


FAST SLEW MODE: High to Low  (Fall time from 90 % to 10% of Vout)

Added Load     FALL TIME
-0-		 640ps
35pF		 1.6ns
57pF		 1.8ns
90pF		 1.9ns
157pF		 2.0ns
212pF		 2.0ns


Note 1.  Two units came from the assembly lot #A67562A PC84ASJ9641.
	 (Note: FAST and SLOW SLEW rates are spec'd the same for the
	 various speed grades of a given part.)
     2.  Measurement was done at Room temperature and Vcc = 5.0V.
     3.  HP 54720D oscilloscope bandwidth:  2.0GHz.
     4.  HP 54701A Active Probe bandwidth:  2.5GHz.
     5.  HP 54701A Active Probe Input impedance:   100k



End of Record #1490