Rainbow Electronics AT45DB021D - Manual (Page 28)

28
3638K–DFLASH–11/2012
AT45DB021D
14. Power-on/Reset State
When power is first applied to the device, or when recovering from a reset condition, the device will default to Mode
3. In addition, the output pin (SO) will be in a high impedance state, and a high-to-low transition on the CS pin will
be required to start a valid instruction. The mode (Mode 3 or Mode 0) will be automatically selected on every falling
edge of CS by sampling the inactive clock state.
14.1 Initial Power-up/Reset Timing Restrictions
At power up, the device must not be selected until the supply voltage reaches the V
CC
(min.) and further delay of
t
VCSL
. During power-up, the internal Power-on Reset circuitry keeps the device in reset mode until the V
CC
rises
above the Power-on Reset threshold value (V
POR
). At this time, all operations are disabled and the device does not
respond to any commands. After power up is applied and the V
CC
is at the minimum operating voltage V
CC
(min.),
the t
VCSL
delay is required before the device can be selected in order to perform a read operation.
Similarly, the t
PUW
delay is required after the V
CC
rises above the Power-on Reset threshold value (V
POR
) before the
device can perform a write (Program or Erase) operation. After initial power-up, the device will default in Standby
mode.
Table 14-1. Initial Power-up/Reset Timing Restrictions
15. System Considerations
The serial interface is controlled by the clock SCK, serial input SI and chip select CS pins. These signals must rise
and fall monotonically and be free from noise. Excessive noise or ringing on these pins can be misinterpreted as
multiple edges and cause improper operation of the device. The PC board traces must be kept to a minimum
distance or appropriately terminated to ensure proper operation. If necessary, decoupling capacitors can be added
on these pins to provide filtering against noise glitches.
As system complexity continues to increase, voltage regulation is becoming more important. A key element of any
voltage regulation scheme is its current sourcing capability. Like all Flash memories, the peak current for
DataFlash occur during the programming and erase operation. The regulator needs to supply this peak current
requirement. An under specified regulator can cause current starvation. Besides increasing system noise, current
starvation during programming or erase can lead to improper operation and possible data corruption.
In an effort to continue our goal of maintaining world-class quality leadership, Adesto has been performing
extensive testing on the AT45DB021D that would not normally be done with a Serial Flash device. The testing that
has been performed on the AT45DB021D involved extensive, non-stop reading of the memory array on pre-
conditioned devices. The pre-conditioning of the devices, which entailed erasing and programming the entire
memory array 10,000 times, was done to simulate a customer environment and to exercise the memory cells to a
certain degree. The non-stop reading of the devices was done in three levels of granularity, with the first level
involving a continuous, looped read of 256-bytes (a single page) of memory, the second level involving a
continuous, looped-read of a 4-Kbyte (16-pages) portion of memory, and the third level entailing non-stop reading
of the entire memory array. Read operations were performed at both +25°C and +125°C and with a supply voltage
of 3.7V, which exceeds the specified datasheet operating voltage range. The results of all of the extensive tests
indicate that the contents of a portion of memory being read continuously could be altered after 800,000,000 read
operations only if that portion of the memory was not erased or reprogrammed at all during the 800,000,000 read
operations. If that portion of memory was reprogrammed at some point, then it would take another 800,000,000
Symbol Parameter Min Typ Max Units
t
VCSL
V
CC
(min.) to Chip Select low 1 ms
t
PUW
Power-Up Device Delay before Write Allowed 20 ms
V
POR
Power-On Reset Voltage 1.5 2.5 V