
W27C257
Publication Release Date: September 1998
- 3 -
Revision A2
Standby Mode
The standby mode significantly reduces VCC current. This mode is entered when CE = VIH. In
standby mode, all outputs are in a high impedance state, independent of OE .
Two-line Output Control
Since EPROMs are often used in large memory arrays, the W27C257 provides two control inputs for
multiple memory connections. Two-line control provides for lowest possible memory power
dissipation and ensures that data bus contention will not occur.
System Considerations
EPROM power switching characteristics require careful device decoupling. System designers are
interested in three supply current issues: standby current levels (ISB), active current levels (ICC), and
transient current peaks produced by the falling and rising edges of CE. Transient current magnitudes
depend on the device output's capacitive and inductive loading. Two-line control and proper
decoupling capacitor selection will suppress transient voltage peaks. Each device should have a 0.1
F ceramic capacitor connected between its VCC and GND. This high frequency, low inherent-
inductance capacitor should be placed as close as possible to the device. Additionally, for every eight
devices, a 4.7
F electrolytic capacitor should be placed at the array's power supply connection
between VCC and GND. The bulk capacitor will overcome voltage slumps caused by PC board trace
inductances.
TABLE OF OPERATING MODES
(VPP = 12V, VPE = 14V, VHH = 12V, VCP = 5V, X = VIH or VIL)
MODE
PINS
CE
OE
A0
A9
VCC
VPP
OUTPUTS
Read
VIL
X
VCC
DOUT
Output Disable
VIL
VIH
X
VCC
High Z
Standby (TTL)
VIH
X
VCC
High Z
Standby (CMOS)
VCC
±0.3V
X
VCC
High Z
Program
VIL
VIH
X
VCP
VPP
DIN
Program Verify
VIH
VIL
X
VCP
VPP
DOUT
Program Inhibit
VIH
X
VCP
VPP
High Z
Erase
VIL
VIH
VIL
VPE
VCC
VPE
DIH
Erase Verify
VIH
VIL
X
VCC
VPE
DOUT
Erase Inhibit
VIH
X
VCP
VPP
High Z
Product Identifier-manufacturer
VIL
VHH
VCC
DA (Hex)
Product Identifier-device
VIL
VIH
VHH
VCC
02 (Hex)