IH6208
Switching Information
S
1b
S
2b
THRU
S
3b
IH6208
S
4b
D
2
200Ω
GND
-15V
(Continued)
+15V
-2V
SWITCH
OUTPUT
V
OUT
(SEE PINOUT)
V
OUT
35pF
V
A
+0.8V
+3V
50%
t
OPEN
t
OPEN
A
1
A
0
V
A
+5V
EN
0
0.9V
O
V
O
V
S
FIGURE 2. t
OPEN
(BREAK-BEFORE-MAKE) SWITCHING TEST CIRCUIT AND WAVEFORMS
+15V
S
1b
ALL
OTHERS
IH6208
EN
V
EN
GND
S
4b
D
2
200Ω
-15V
V
OUT
35pF
-5V
V
EN
t
r
and t
f
≤
100ns +0.8V
0V
0.1V
O
SWITCH
OUTPUT
V
OUT
(SEE FIGURE 1)
0.9V
O
V
O
-5V
+5V
50%
t
EN(ON)
t
EN(OFF)
A
1
A
0
FIGURE 3. t
ON
AND t
OFF
SWITCHING TEST CIRCUIT AND WAVEFORMS
IH6208 Application Information
ENABLE Input Strobing Levels
The ENABLE input on the IH6208 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 1kΩ to 3kΩ is required
from the gate output to +5V supply. (See Figure 4)
When the EN in put is driven from CMOS logic, no pullup is
necessary, see Figure 5.
The supply voltage of the CD4009 affects the switching
speed of the IH6208; the same is true for TTL supply voltage
levels. The following chart shows the effect, on t
trans
for a
supply varying from +4.5V to +5.5V.
CMOS OR TTL
SUPPLY VOLTAGE
TYPICAL T
TRANS
AT 25
o
C
Using the IH6208 with Supplies Other Than
±15V
The IH6208 can be used with power supplies ranging from
±6V
to
±16V.
The switch r
DS(ON)
will increase as the supply
voltages decrease, however, the multiplexer error term (the
product of leakage times r
DS(ON)
) will remain approximately
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 14) 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
voltage 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 IH6208 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 IH6208 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 1µF
capacitor can be placed across the diode to minimize
switching glitches.
+4.5V
+4.75V
+5.00V
+5.25V
+5.50V
400ns
300ns
250ns
200ns
175ns
The throughput rate can therefore be maximized by using a
+5V to +5.5V supply for the ENABLE Strobe Logic.
The examples shown in Figure 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
multiplexed, the EN terminal can be directly connected to
+5V logic supply to enable the IH6208 at all times.
12-132
HARRIS [ HARRIS CORPORATION ]
