128Mb, 64Mb, 32Mb
Q-FLASH MEMORY
09005aef80b5a323 Micron Technology, Inc., reserves the right to change products or specifications without notice.
MT28F640J3.fm – Rev. N 3/05 EN 39 ©2000 Micron Technology. Inc.
Design Considerations
Five-Line Output Control
Micron provides five control inputs (CE0, CE1, CE2,
OE#, and RP#) to accommodate multiple memory
connections in large memory arrays. This control pro-
vides the lowest possible memory power dissipation
and ensures that data bus contention does not occur.
To efficiently use these control inputs, an address
decoder should enable the device (see Table 2 on
page 11) while OE# is connected to all memory devices
and the system’s READ# control line. This ensures that
only selected memory devices have active outputs
while deselected memory devices are in standby
mode. During system power transitions, RP# should
be connected to the system POWERGOOD signal to
prevent unintended writes. POWERGOOD should also
toggle during system reset.
STS and Block Erase, Program, and Lock
Bit Configuration
Polling
As an open drain output, STS should be connected
to VCCQ by a pull-up resistor to provide a hardware
method of detecting block erase, program, and lock bit
configuration completion. It is recommended that a
2.5K resistor be used between STS# and VCCQ. In
default mode, it transitions low after block erase, pro-
gram, or lock bit configuration commands and returns
to High-Z when the ISM has finished executing the
internal algorithm. See the CONFIGURATION com-
mand for alternate configurations of the STS pin. STS
can be connected to an interrupt input of the system
CPU or controller. STS is active at all times. In default
mode, it is also High-Z when the device is in block
erase suspend (with programming inactive), program
suspend, or reset/power-down mode.
Power Supply Decoupling
Device decoupling is required for Flash memory
power switching characteristics. There are three sup-
ply current issues to consider: standby current levels,
active current levels, and transient peaks produced by
falling and rising edges of CEx and OE#. Transient cur-
rent magnitudes depend on the device outputs’ capac-
itive and inductive loading. Two-line control and
proper decoupling capacitor selection suppresses
transient voltage peaks. Because Micron Q-Flash
memory devices draw their power from three VCC pins
(these devices do not include a VPP pin), it is recom-
mended that systems without separate power and
ground planes attach a 0.1µF ceramic capacitor
between each of the device’s three VCC pins (this
includes VCCQ) and GND. These high-frequency, low-
inductance capacitors should be placed as close as
possible to package leads on each Micron Q-Flash
memory device. Additionally, for every eight devices, a
4.7µF electrolytic capacitor should be placed between
VCC and GND at the array’s power supply connection.
Reducing Overshoots and Undershoots
When Using Buffers or Transceivers
Overshoots and undershoots can sometimes cause
input signals to exceed Flash memory specifications as
faster, high-drive devices such as transceivers or buff-
ers drive input signals to Flash memory devices. Many
buffer/transceiver vendors now carry bus-interface
devices with internal output-damping resistors or
reduced-drive outputs. Internal output-damping
resistors diminish the nominal output drive currents,
while still leaving sufficient drive capability for most
applications. These internal output-damping resistors
help reduce unnecessary overshoots and undershoots
by diminishing output-drive currents. When consider-
ing a buffer/transceiver interface design to Flash,
devices with internal output-damping resistors or
reduced-drive outputs should be used to minimize
overshoots and undershoots.
VCC, VPEN, and RP# Transitions
If VPEN or VCC falls outside of the specified operat-
ing ranges, or RP# is not set to VIH, block erase, pro-
gram, and lock bit configuration are not guaranteed. If
RP# transitions to VIL during block erase, program, or
lock bit configuration, STS (in default mode) will
remain LOW for a maximum time of tPLPH + tPHRH,
until the RESET operation is complete and the device
enters reset/power-down mode. The aborted opera-
tion may leave data partially corrupted after program-
ming, or partially altered after an erase or lock bit
configuration. Therefore, block erase and lock bit con-
figuration commands must be repeated after normal
operation is restored. Device power-off or RP# = VIL
clears the status register. The CEL latches commands
issued by system software and is not altered by VPEN or
CEx transitions, or ISM actions. Its state is read array
mode upon power-up, upon exiting reset/power-
down mode, or after VCC transitions below VLKO. VCC
must be kept at or above VPEN during VCC transitions.