UG445 Datasheet, PDF (16/24 Pages) –

Thresholds
R
Tjmax > (ThetaJC * Pd) + Ta
- Where Tjmax = Tamax of 70°C
- ThetaJC is available in the Device Package User Guide (UG112)
- Pd is the power dissipated (use XPower, or measure the design power)
- Ta is the ambient temperature at which the device will run
For example, if you want to know how many output loads you could drive that each
require 40 mA with one device, the selected device is XCR3064XL-PC44:
- Tjmax is 70°C for a plastic package
- ThetaJC is 12.4°C/Watt for PC44 package
- Ta will not exceed 50°C
70 = (12.4*Pd) + 50
Pd = 1.613W
You need to expand Pd to take into account Pd of the design and the I/O:
(Pddesign + PdIO) = 1.613W
Pddesign is 66 mW from measurement; doubled to 132 mW for safety cushion.
When sourcing 40 mA, the voltage at the output of the CPLD is 2.3V (information obtained
from the I/V curve).
X * (3.3V – 2.3V) = 1.613W – 0.132W
X = 1.48W/(1)V
X = 1.48A
You will have 1480 mA to use to drive the I/O pins.
1480 mA/40 mA = 37 output loads can be driven by this device before you exceed the
acceptable temperature range.
How many 40 mA output loads can the device sink?
When sinking 40 mA, the voltage at the output of the CPLD is 0.7V.
(X*0.7V) = 1.613W - 0.132W
X = 1.481W/0.7V
X = 2.12A
You should have 2116 mA to use to drive the I/O pins.
2116 mA/40 mA = 53 LEDs can be driven by this device before before you exceed the
acceptable temperature range.
Drive Strength
You cannot select the drive strength for CPLDs. The drive strength must be read from the
I/V curve.
16
www.xilinx.com
CPLD I/O User Guide
UG445 (v1.2) January 14, 2014