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AR# 1490

CPLD XC9500 - Device Slew Rates (Rise/Fall/Switching times) with capacitive loads

Description

What slew rates can be expected on XC9500 outputs as the capacitive load increases?

Solution

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. Estimations for specific board/component interaction should use IBIS simulation.

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 1 MHz.

Two XC95108 PC84 units were programmed to 16 bit counter patterns, one with a SLOW slew rate and the other with a FAST slew rate. The parts were then exercised at the clock rate of 5 MHz 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 RESULTS:

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

NOTES:

1. Two units came from the assembly lot #A67562A PC84ASJ9641.

(FAST and SLOW SLEW rates are specified the same for the various speed grades of a given part.)

2. Measurement was performed at room temperature and Vcc = 5.0V.

3. HP 54720D oscilloscope bandwidth: 2.0 GHz.

4. HP 54701A Active Probe bandwidth: 2.5 GHz.

5. HP 54701A Active Probe Input impedance: 100k

AR# 1490
Date Created 08/21/2007
Last Updated 12/15/2012
Status Active
Type General Article