A3P015 datasheet(9/212 Pages) MICROSEMI

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ProASIC3 Flash Family FPGAs

Re vi s i on 14

2 - 3

I/O Power-Up and Supply Voltage Thresholds for Power-On Reset

(Commercial and Industrial)

Sophisticated power-up management circuitry is designed into every ProASIC®3 device. These circuits

ensure easy transition from the powered-off state to the powered-up state of the device. The many

different supplies can power up in any sequence with minimized current spikes or surges. In addition, the

I/O will be in a known state through the power-up sequence. The basic principle is shown in Figure 2-1

on page 2-4.

There are five regions to consider during power-up.

ProASIC3 I/Os are activated only if ALL of the following three conditions are met:

1. VCC and VCCI are above the minimum specified trip points (Figure 2-1 on page 2-4).

2. VCCI > VCC – 0.75 V (typical)

3. Chip is in the operating mode.

VCCI Trip Point:

Ramping up: 0.6 V < trip_point_up < 1.2 V

Ramping down: 0.5 V < trip_point_down < 1.1 V

VCC Trip Point:

Ramping up: 0.6 V < trip_point_up < 1.1 V

Ramping down: 0.5 V < trip_point_down < 1 V

VCC and VCCI ramp-up trip points are about 100 mV higher than ramp-down trip points. This specifically

built-in hysteresis prevents undesirable power-up oscillations and current surges. Note the following:

•

During programming, I/Os become tristated and weakly pulled up to VCCI.

•

JTAG supply, PLL power supplies, and charge pump VPUMP supply have no influence on I/O

behavior.

PLL Behavior at Brownout Condition

Microsemi recommends using monotonic power supplies or voltage regulators to ensure proper power-

up behavior. Power ramp-up should be monotonic at least until VCC and VCCPLLX exceed brownout

activation levels. The VCC activation level is specified as 1.1 V worst-case (see Figure 2-1 on page 2-4

for more details).

When PLL power supply voltage and/or VCC levels drop below the VCC brownout levels (0.75 V ± 0.25

V), the PLL output lock signal goes low and/or the output clock is lost. Refer to the "Power-Up/-Down

Behavior of Low Power Flash Devices" chapter of the ProASIC3 FPGA Fabric User’s Guide for

information on clock and lock recovery.

Table 2-4 •

Overshoot and Undershoot Limits 1

VCCI and VMV

Average VCCI–GND Overshoot or Undershoot

Duration as a Percentage of Clock Cycle2

Maximum Overshoot/

Undershoot2

2.7 V or less

10%

1.4 V

1.49 V

3 V

10%

1.1 V

1.19 V

3.3 V

10%

0.79 V

0.88 V

3.6 V

10%

0.45 V

0.54 V

Notes:

1. Based on reliability requirements at 85°C.

2. The duration is allowed at one out of six clock cycles. If the overshoot/undershoot occurs at one out of two cycles, the

maximum overshoot/undershoot has to be reduced by 0.15 V.

3. This table does not provide PCI overshoot/undershoot limits.

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