MAX378-MAX379 Maxim, MAX378-MAX379 Datasheet - Page 9

• Manufacturer Part Number: MAX378-MAX379
• Description: High-Voltage / Fault-Protected Analog Multiplexers
• Manufacturer: Maxim

The typical digital threshold of both the address lines
and the EN pin is 1.6V, with a temperature coefficient of
about -3mV/°C. This ensures compatibility with 0.8V to
2.4V TTL-logic swings over the entire temperature
range. The digital threshold is relatively independent of
the supply voltages, moving from 1.6V typical to 1.5V
typical as the power supplies are reduced from ±15V to
±5V. In all cases, the digital threshold is referenced to
GND.
The digital inputs can also be driven with CMOS-logic
levels swinging from either V+ to V- or from V+ to GND.
The digital input current is just a few nanoamps of leak-
age at all input voltage levels, with a guaranteed maxi-
mum of 1µA. The digital inputs are protected from ESD
by a 30V zener diode between the input and V+, and
can be driven ±4V beyond the supplies without drawing
excessive current.
The MAX378/MAX379 will function as a demultiplexer,
where the input is applied to the OUT pin, and the input
pins are used as outputs. The MAX378/MAX379 pro-
vide both break-before-make action and full fault protec-
tion when operated as a demultiplexer, unlike earlier
generations of fault-protected multiplexers.
At DC and low frequencies, channel-to-channel
crosstalk is caused by variations in output leakage cur-
Table 1b. MAX379 Charge Injection
Test Conditions: C
ed analog input level is applied to inputs 1A and 1B; channels
2 through 4 are open circuited. EN = +5V, A1 = 0V, A0 is tog-
gled from 0V to 3V at a 2kHz rate.
Voltage
Supply
±10V
±15V
±5V
Off Isolation, and Digital Feedthrough
Input Level
Analog
+1.7V
+10V
-1.7V
-10V
+5V
-5V
0V
0V
0V
L
Channel-to-Channel Crosstalk,
Operation as a Demultiplexer
= 1000pF on Out A and Out B; the tabulat-
_______________________________________________________________________________________
+105pC
+215pC
+135pC
+525pC
+180pC
+73pC
+48pC
+62pC
+55pC
Out A
Digital Interface Levels
Injected Charge
+107pC
+220pC
+139pC
+530pC
+185pC
+74pC
+50pC
+63pC
+55pC
Out B
Differential
High-Voltage, Fault-Protected
-2pC
-1pC
-2pC
-5pC
-4pC
-1pC
-5pC
-5pC
A-B
0pC
rents as the off-channel input voltages are varied. The
MAX378 output leakage varies only a few picoamps as
all seven off inputs are toggled from -10V to +10V. The
output voltage change depends on the impedance level
at the MAX378 output, which is R
signal source resistance in most cases, since the load
driven by the MAX378 is usually a high impedance. For
a signal source impedance of 10kΩ or lower, the DC
crosstalk exceeds 120dB.
Table 2 shows typical AC crosstalk and off-isolation per-
formance. Digital feedthrough is masked by the analog
charge injection when the output is enabled. When the
output is disabled, the digital feedthrough is virtually
unmeasurable, since the digital pins are physically iso-
lated from the analog section by the GND and V- pins.
The ground plane formed by these lines is continued
onto the MAX378/MAX379 die to provide over 100dB
isolation between the digital and analog sections.
Table 2a. Typical Off-Isolation
Rejection Ratio
Test Conditions: V
R
Table 2b. Typical Crosstalk
Rejection Ratio
Test Conditions: Specified R
EN = +5V, A0 = A1 = A2 = +5V (Channel 1 selected). 20V
at the tabulated frequency is applied to Channel 2. All other
channels are open circuited. Similar crosstalk rejection can be
observed between any two channels.
One Channel Driven
All Channels Driven
L
= 1.5kΩ between OUT and GND, EN = 0V.
Frequency
Frequency
Analog Multiplexers
F
R
L
L
= 1.5k
= 10k
OIRR = 20 Log ____________
IN
= 20V
100kHz
100kHz
74dB
64dB
70dB
62dB
P-P
L
connected from OUT to GND,
at the tabulated frequency,
V
20V
OUT (P-P)
DS(ON)
P-P
500kHz
500kHz
72dB
48dB
68dB
46dB
plus the input
1MHz
66dB
44dB
1MHz
64dB
42dB
P-P
9