12-131

IH6108 Application Information

ENABLE Input Strobing Levels

The ENABLE input on the IH6108 requires a minimum of

+4.5V to trigger to the “1” state and a maximum of +0.8V to

trigger to the “0” state. If the ENABLE input is being driven

from TTL logic, a pull-up resistor of 1k to 3k

Ω is required

from the gate output to +5V supply. (See Figure 4.)

When the EN input is driven from CMOS logic, no pullup is

necessary, see Figure 5.

The supply voltage of the CD4009 affects the switching

speed of the IH6108; the same is true for TTL supply voltage

supply varying from +4.5V to +5.5V.

The throughput rate can therefore be maximized by using a

+5V to +5.5V supply for the ENABLE Strobe Logic.

The examples shown in Figures 4 and 5 deal with ENABLE

strobing when expansion to more than eight channels is

required. In these cases the EN terminal acts as a fourth

address input. If eight channels or less are being multi-

plexed, the EN terminal can be directly connected to +5V

logic supply to enable the IH6108 at all times.

Using the IH6108 with Supplies Other Than

±15V

The IH6108 can be used with power supplies ranging from

voltages decrease, however, the multiplexer error term (the

constant since leakage decreases as the supply voltages

are reduced.

Caution must be taken to ensure that the enable (EN)

voltage is at least 0.7V below V+ at all times. If this is not

done, the Address input strobing levels will not function

properly. This may be achieved quite simply by connecting

EN (pin 2) to V+ (pin 13) via a silicon diode as shown in

Figure 6. When using this type of configuration, a further

requirement must be met: the strobe levels of A0 and A1

must be within 2.5V of the EN voltage in order to define a

binary “1” state. For the case shown in Figure 6 the EN volt-

age is 11.3V which means that logic high at A0 and A1 is

+8.8V (logic low continues to be 0.8V). In this configuration

the IH6108 cannot be driven by TTL (+5V) or CMOS (+5V)

logic. It can be driven by TTL open collector logic or CMOS

logic with +12V supplies.

If the logic and the IH6108 have common supplies, the EN

pin should again be connected to the supply through a

silicon diode. In this case, tying EN to the logic supply

directly will not work since it violates the 0.7V differential

voltage required between V+ and EN, (See Figure 7). A 1

µF

capacitor can be placed across the diode to minimize

switching glitches.

-2V

THRU

+15V

-15V

D

IH6108

EN

35pF

V-

GND

200

Ω

+5V

3V

0.8V

0.8V

S1 ON

S8 ON

50%

50%

THRU

+15V

-15V

IH6108

EN

35pF

GND

1k

Ω

OUT

5V

0.8V

0V

50%

90%

10%

CMOS OR TTL

SUPPLY VOLTAGE

+4.5V

400ns

+4.75V

300ns

+5.00V

250ns

+5.25V

200ns

+5.50V

175ns

IH6108