EX128-TQG100A Datasheet, PDF (18/44 Pages) Actel Corporation – eX Automotive Family FPGAs

eX Automotive Family FPGAs
5 V Tolerance of 3.3 V LVTTL I/Os Using a Tristate Buffer
Input: 3.3 V LVTTL I/Os are 5-V-input tolerant only if the non-PCI mode is used (no clamp diode).
Output: To configure an Actel eX device to drive 5 V with V_CCI = 3.3 V, users can utilize an Open Drain configuration of
the I/O cell with an array inverter cell and an external pull-up resistor to 5 V. The recommended configuration is
illustrated in Figure 1-14. The I/O configuration must be set to LVTTL to disable the PCI clamp diode. For the
recommended resistor value in a specific application, please contact Actel Technical Support. For more details, refer to
the Design Tips section of the Actel eX, SX-A and RT54SX-S I/Os application note.
Actel Open Drain Configuration
5V
User Internal Signal
E
PAD
TRIBUFF
Figure 1-14 • Open-Drain Configuration for eX
Power Dissipation
Power consumption for eX devices can be divided into
two components: static and dynamic.
Static Power Component
The power due to standby current is typically a small
component of the overall power. Typical standby current
for eX devices is listed in Table 1-10 on page 1-12. For
example, the typical static power for eX128 at 3.3 V V_CCI
is:
I_CC * V_CCA = 795 µA x 2.5 V = 1.99 mW
Dynamic Power Component
Power dissipation in CMOS devices is usually dominated
by the dynamic power dissipation. This component is
frequency-dependent and a function of the logic and the
external I/O. Dynamic power dissipation results from
charging internal chip capacitance. An additional
component of the dynamic power dissipation is the
totem pole current in the CMOS transistor pairs. The net
effect can be associated with an equivalent capacitance
that can be combined with frequency and voltage to
represent dynamic power dissipation.
Dynamic power dissipation = CEQ * V_CCA2 x F
CEQ = Equivalent capacitance
F = switching frequency
Equivalent capacitance is calculated by measuring I_CCA at
a specified frequency and voltage for each circuit
component of interest. Measurements have been made
over a range of frequencies at a fixed value of V_CCA.
Equivalent capacitance is frequency-independent, so the
results can be used over a wide range of operating
conditions. Equivalent capacitance values are shown
below.
CEQ Values for eX Devices
Combinatorial modules (Ceqcm) 1.70 pF
Sequential modules (Ceqsm) 1.70 pF
Input buffers (Ceqi)
1.30 pF
Output buffers (Ceqo)
7.40 pF
Routed array clocks (Ceqcr)
1.05 pF
The variable and fixed capacitance of other device
components must also be taken into account when
estimating the dynamic power dissipation.
1-14
v3.2