HT27C512 datasheet(7/10 Pages) HOLTEK

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stable for at least tACC-tOE.

Standby mode

The HT27C512 has CMOS standby mode which

reduces the maximum VCC current to 10

µA. It

is placed in CMOS standby when CE is at

VCC

±0.3V. The HT27C512 also has a TTL-

standby mode which reduces the maximum

VCC current to 1.0mA. It is placed in TTL-

standby when CE is at VIH. When in standby

mode, the outputs are in a high-impedance

state, independent of the OE input.

Two-line output control function

To accommodate multiple memory connections,

a two-line control function is provided to allow

for:

• Low memory power consumption

• Assurance that output bus contention will not

occur.

It is recommended that CE be decoded and used

as the primary device-selection function, while

OE be made a common connection to all devices

in the array and connected to the READ line

from the system control bus. This assures that

all deselected memory devices are in their low-

power standby mode and that the output pins

are only active when data is desired from a

particular memory device.

System considerations

During the switch between active and standby

conditions, transient current peaks are pro-

duced on the rising and falling edges of Chip

Enable. The magnitude of these transient cur-

rent peaks is dependent on the output capaci-

tance loading of the device. At a minimum, a

0.1

µF ceramic capacitor (high frequency, low

inherent inductance) should be used on each

device between VCC and VPP to minimize tran-

sient effects. In addition, to overcome the volt-

age drop caused by the inductive effects of the

printed circuit board traces on EPROM arrays,

a 4.7

µF bulk electrolytic capacitor should be

used between VCC and VPP for each eight de-

vices. The location of the capacitor should be

close to where the power supply is connected to

the array.

Operation mode truth table

All the operation modes are shown in the table following.

Mode

OE/VPP

Output

Read

VIL

X (2)

Dout

Output Disable

VIL

VIH

High Z

Standby (TTL)

VIH

High Z

Standby (CMOS)

VCC

± 0.3V

High Z

Program

VIL

VPP

DIN

Program Verify

VIL

DOUT

Product Inhibit

VIH

VPP

High Z

Manufacturer Code (3)

VIL

VH (1)

Device Type Code (3)

VIL

VIH

VH (1)

Notes: (1) VH = 12.0V

± 0.5V

(2) X=Either VIH or VIL

(3) For Manufacturer Code and Device Code, A1=VIH, When A1=VIL, both codes will read 7F

HT27C512

6th May ’99

HT27C512 Datasheet(PDF) 7 Page - Holtek Semiconductor Inc

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