_______________General Description
The MAX378 8-channel single-ended (1-of-8) multiplexer
and the MAX379 4-channel differential (2-of-8) multiplexer
use a series N-channel/P-channel/N-channel structure to
provide significant fault protection. If the power supplies to
the MAX378/MAX379 are inadvertently turned off while
input voltages are still applied,
all
channels in the muxes
are turned off, and only a few nanoamperes of leakage current will flow into the inputs. This protects not only the
MAX378/MAX379 and the circuitry they drive, but also the
sensors or signal sources that drive the muxes.
The series N-channel/P-channel/N-channel protection
structure has two significant advantages over the simple
current-limiting protection scheme of the industry’s firstgeneration fault-protected muxes. First, the Maxim protection scheme limits fault currents to nanoamp leakage
values rather than many milliamperes. This prevents damage to sensors or other sensitive signal sources. Second,
the MAX378/MAX379 fault-protected muxes can withstand
a
continuous
±60V input, unlike the first generation, which
had a continuous ±35V input limitation imposed by power
dissipation considerations.
All digital inputs have logic thresholds of 0.8V and 2.4V,
ensuring both TTL and CMOS compatibility without requiring pull-up resistors. Break-before-make operation is
guaranteed. Power dissipation is less than 2mW.
________________________Applications
Data Acquisition Systems
Industrial and Process Control Systems
Avionics Test Equipment
Signal Routing Between Systems
____________________________Features
♦ Fault Input Voltage ±75V with Power Supplies Off
♦ Fault Input Voltage ±60V with ±15V Power Supplies
♦ All Switches Off with Power Supplies Off
♦ On Channel Turns OFF if Overvoltage Occurs on
Input or Output
♦ Only Nanoamperes of Input Current Under All
Fault Conditions
♦ No Increase in Supply Currents Due to Fault
Conditions
♦ Latchup-Proof Construction
♦ Operates from ±4.5V to ±18V Supplies
♦ All Digital Inputs are TTL and CMOS Compatible
♦ Low-Power Monolithic CMOS Design
______________Ordering Information
Ordering Information continued at end of data sheet.
* Contact factory for availability.
**The substrate may be allowed to float or be tied to V+ (JI CMOS).
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
________________________________________________________________
Maxim Integrated Products
1
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
A1
A2
GND
V+
IN1
V-
EN
A0
TOP VIEW
MAX378
IN5
IN6
IN7
IN8
OUT
IN4
IN3
IN2
DIP
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
A1
GND
V+
IN1B
IN1A
V-
EN
A0
MAX379
IN2B
IN3B
IN4B
OUTB
OUTA
IN4A
IN3A
IN2A
DIP
__________________________________________________________Pin Configurations
Call toll free 1-800-998-8800 for free samples or literature.
19-1902; Rev 1; 8/94
PART
MAX378CPE
MAX378CWG
MAX378CJE 0°C to +70°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
16 Plastic DIP
24 Wide SO
16 CERDIP
MAX378EPE
MAX378EWG -40°C to +85°C
-40°C to +85°C 16 Plastic DIP
24 Wide SO
MAX378EJE
MAX378MJE -55°C to +125°C
-40°C to +85°C 16 CERDIP
16 CERDIP
MAX378MLP -55°C to +125°C 20 LCC*
Pin Configurations continued at end of data sheet.
MAX378C/D 0°C to +70°C Dice**
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V+ = +15V, V- = -15V; VAH(Logic Level High) = +2.4V, VAL(Logic Level Low) = +0.8V, unless otherwise noted.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage between Supply Pins..............................................+44V
V+ to Ground...................................................................+22V
V- to Ground......................................................................-22V
Digital Input Overvoltage:
V+......................................................................+4V
V-........................................................................-4V
Analog Input with Multiplexer Power On..............................±65V
Recommended V+.....................................+15V
Power Supplies V-.......................................-15V
Analog Input with Multiplexer Power Off..............................±80V
Continuous Current, IN or OUT...........................................20mA
Peak Current, IN or OUT
(Pulsed at 1ms, 10% duty cycle max) ............................40mA
Power Dissipation (Note 1) (CERDIP)................................1.28W
Operating Temperature Range:
MAX378/379C.....................................................0°C to +70°C
MAX378/379E..................................................-40°C to +85°C
MAX378/379M ...............................................-55°C to +125°C
Storage Temperature Range.............................-65°C to +150°C
(Note 4)
VIN= ±60V, V
OUT
= ±10V
(Notes 3, 4)
(Note 2)
MAX379 only
(Note 6)
VA= 5V or 0V (Note 5)
V
OUT
= 0V, VIN= ±60V
(Notes 3, 4)
(Note 4)
µA-1.0 1.0I
A
Input Leakage Current
(High or Low)
V2.4V
AH
Input High Threshold
-100 100
kΩ
3.0 4.0
V0.8V
AL
Input Low Threshold
µA25I
IN(OFF)
Input Leakage Current
(with Overvoltage)
µA10
V-15 +15V
AN
Analog Signal Range
nA-50 50I
DIFF
Differential OFF Output
Leakage Current
nA20
I
OUT(OFF)
Output Leakage Current
(with Input Overvoltage)
VEN, V
A
{
{}
Note 1: Derate 12.8mW/°C above TA= +75°C
V
OUT
= ±10V, IIN= 100µA
VAL= 0.8V, VAH= 2.4V
2.0 3.0
r
DS(ON)
ON Resistance
Full
+25°C
Full
Full
Full
+25°C
Full
+25°C
-1.0 1.0
2.4
-100 100
3.0 4.0
0.8
40
20
-15 +15
-50 50
20
2.0 3.5
nA
-50 50
VIN= ±10V, V
OUT
= 10V
V
EN
= 0.8V (Note 6)
-0.5 0.03 0.5
I
IN(OFF)
OFF Input Leakage Current
+25°C
-50 50
-1.0 0.03 1.0
nA-200 200
V
OUT
= ±10V, VIN= 10V
VEN= 0.8V MAX378
(Note 6) MAX379
-1.0 0.1 1.0
I
OUT(OFF)
OFF Output Leakage Current
+25°C
-200 200
-2.0 0.1 2.0
nA-600 600
V
IN(ALL)
= V
OUT
= ±10V
VAH= VEN= 2.4V MAX378
VAL= 0.8V (Note 5) MAX379
-10 0.1 10
I
OUT(ON)
ON Channel Leakage Current
+25°C
-600 600
-20 0.1 20
-300 300 -300 300
VIN= ±75V, VEN= V
OUT
= 0V
A0= A1= A2= 0V or 5V
µA10I
IN(OFF)
Input Leakage Current
(with Power Supplies Off)
+25°C 20
MIN TYP MAX MIN TYP MAX
CONDITIONS UNITS
-55°C to +125°C
SYMBOLPARAMETER TEMP
0°C to +70°C
and
-40°C to +85°C
STATIC
FAULT
CONTROL
±
±
Full
Full
Full
Full
Full
Full
Full
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
_______________________________________________________________________________________ 3
Note 2: When the analog signal exceeds +13.5V or -12V, the blocking action of Maxim’s gate structure goes into operation. Only
leakage currents flow and the channel ON resistance rises to infinity.
Note 3: The value shown is the steady-state value. The transient leakage is typically 50µA. See
Detailed Description
.
Note 4: Guaranteed by other static parameters.
Note 5: Digital input leakage is primarily due to the clamp diodes. Typical leakage is less than 1nA at +25°C.
Note 6: Leakage currents not tested at T
A
= cold temp.
Note 7: Electrical characteristics, such as ON Resistance, will change when power supplies other than ±15V are used.
ELECTRICAL CHARACTERISTICS (continued)
(V+ = +15V, V- = -15V; VAH(Logic Level High) = +2.4V, VAL(Logic Level Low) = +0.8V, unless otherwise noted.)
pF0.1C
DS(OFF)
Input to Output Capacitance
VEN= 0.8V or 2.4V
All VA= 0V or 5V
+25°C
VEN= 0.8V, RL= 1kΩ, CL= 15pF
V = 7V
RMS
, f = 100kHz
(Note 7)
MAX378
MAX379
CONDITIONS
0.1
V±4.5 ±18V
OP
Power-Supply Range for
Continuous Operation
0.3 0.7
ns
1000
mA
0.1 0.6
I+Positive Supply Current
pF5C
A
Digital Input Capacitance
12
dB50 68OFF
(ISO)
“OFF Isolation”
pF5C
IN(OFF)
Channel Input Capacitance
pF
25
C
OUT(OFF)
Channel Output Capacitance
UNITS
-55°C to +125°C
SYMBOLPARAMETER
Figure 3
400 750
t
ON(EN)
Enable Delay (ON)
+25°C
+25°C
+25°C
+25°C
+25°C
+25°C
TEMP
+25°C
±4.5 ±18
0.5 1.0
1500
0.2 1.0
5
12
50 68
5
25
0°C to +70°C
and
-40°C to +85°C
400 1000
µs
3.5
1.2
t
SETT
Settling Time (0.1%)
(0.01%)
+25°C
3.5
1.2
Figure 1 µs0.5 1.0t
A
Access Time +25°C 0.5 1.0
VEN= +5V, VIN= ±10V
A0, A1, A2strobed
ns25 200tON-t
OFF
Break-Before-Make Delay
(Figure 2)
+25°C 25 200
ns
1000
Figure 3
300 500
t
OFF(EN)
Enable Delay (OFF)
+25°C
1000
300
VEN= 0.8V or 2.4V
All VA= 0V or 5V
0.02 0.2
mA
0.01 0.1
I-Negative Supply Current
+25°C
0.02 0.1
0.01 0.1
MIN TYP MAX MIN TYP MAX
SUPPLY
DYNAMIC
Full
Full
Full
Full
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
4 _______________________________________________________________________________________
1m
10p
-100 -50 50 100
INPUT LEAKAGE vs.
INPUT VOLTAGE WITH V+ = V- = 0V
1n
10µ
MAX378-1
V
IN
(V)
INPUT CURRENT (A)
0
100n
100p
10n
100µ
1µ
-80V
+80V
OPERATING
RANGE
100µ
1p
-120 -60 60 120
OFF CHANNEL LEAKAGE CURRENT vs.
INPUT VOLTAGE WITH ±15V SUPPLIES
100p
1µ
MAX378-2
V
IN
(V)
I
IN(OFF)
(A)
0
10n
10p
1n
10µ
100n
OPERATING
RANGE
-60V
+60V
10n
1p
-120 -60 60 120
OUTPUT LEAKAGE CURRENT vs. OFF CHANNEL
OVERVOLTAGE WITH ±15V SUPPLIES
100p
MAX378-3
V
IN(OFF)
(V)
I
OUT(OFF)
(A)
0
10p
1n
OPERATING
RANGE
-60V
+60V
0
-10 -5 5 15-15 0 20
DRAIN-SOURCE ON-RESISTANCE vs.
ANALOG INPUT VOLTAGE
MAX3784
ANALOG INPUT (V)
R
DS(ON)
(kΩ)
10
1
3
2
4
5
6
7
±5V
SUPPLIES
±15V
SUPPLIES
+13V
+13V
+3.5V +4V
__________________________________________Typical Operating Characteristics
NOTE: Typical R
DS(ON)
match @ +10V
Analog in (±15V supplies) = 2%
for lowest to highest R
DS(ON)
channel; @ -10V Analog in,
match = 3%.
MAX378
GND
14pF
PROBE
OUT
+V
AH
IN8
IN2-IN7
IN1
IN2
A2
A1
V
A
MAX378: VAH = 3.0V
0V
-10V
OUTPUT A
90%
+10V
50%
t
A
A0
10V
±
EN
10M
50Ω
±10V
ADDRESS
DRIVE (V
A
)
Figure 1. Access Time vs. Logic Level (High)
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
_______________________________________________________________________________________ 5
MAX378*
GND
V
OUT
OUT
2.4V
IN8
IN2-IN7
IN1
IN2
A2
A1
V
A
MAX358: VAH = 3.0V
ADDRESS
DRIVE (V
A
)
OUTPUT
50%50%
0V
t
OPEN
A0
EN
*SIMILAR CONNECTION FOR MAX379
12.5pF
1k
50Ω
+5V
Figure 2. Break-Before-Make Delay (t
OPEN
)
MAX378*
GND
OUT
IN2-IN7
IN1
A2
A1
V
A
A0
EN
*SIMILAR CONNECTION FOR MAX379
12.5pF
1k
50Ω
+10V
MAX378: V
AH
= 3.0V
0V
ENABLE DRIVE
OUTPUT
90%
50%
t
ON(EN)
t
OFF(EN)
90%
Figure 3. Enable Delay (t
ON(EN)
, t
OFF(EN)
)
MAX378
V-
±60V
V-
GND
OUT
A0
A1
A2
EN
IN1
IN8
10k
+15V+5V
-15V
I
V
±10V
ANALOG
SIGNAL
Figure 4. Input Leakage Current (Overvoltage)
MAX378
V-
±75V
V-
GND
OUT
A0
A1
A2
EN
IN1
10k
0V
+5V
or
0V
0V
I
Figure 5. Input Leakage Current (with Power Supplies OFF)
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
6 _______________________________________________________________________________________
_______________Typical Applications
Figure 6 shows a typical data acquisition system
using the MAX378 multiplexer. Since the multiplexer
is driving a high-impedance input, its error is a function of its own resistance (R
DS(ON)
) times the multi-
plexer leakage current (I
OUT(ON)
) and the amplifier
bias current (I
BIAS
):
V
ERR
= R
DS(ON)
x (I
OUT(ON)
+ I
BIAS
(MAX420))
= 2.0kΩ x (2nA + 30pA)
= 18.0µV maximum error
In most cases, this error is low enough that preamplification of input signals is not needed, even with very
low-level signals such as 40µV/°C from type J thermocouples.
In systems with fewer than eight inputs, an unused channel can be connected to the system ground reference
point for software zero correction. A second channel
connected to the system voltage reference allows gain
correction of the entire data acquisition system as well.
A MAX420 precision op amp is connected as a programmable-gain amplifier, with gains ranging from 1 to
10,000. The guaranteed 5µV unadjusted offset of the
MAX420 maintains high signal accuracy, while programmable gain allows the output signal level to be scaled to
the optimum range for the remainder of the data acquisition system, normally a Sample/Hold and A/D. Since
the gain-changing multiplexer is not connected to the
external sensors, it can be either a DG508A multiplexer
or the fault-protected MAX358 or MAX378.
Truth Table—MAX378
A2 A1 A0 EN
ON
SWITCH
X
0
0
0
0
1
1
1
1
X
0
0
1
1
0
0
1
1
X
0
1
0
1
0
1
0
1
0
1
1
1
1
1
1
1
1
NONE
1
2
3
4
5
6
7
8
Truth Table—MAX379
A1 A0 EN
ON
SWITCH
X
0
0
1
1
X
0
1
0
1
0
1
1
1
1
NONE
1
2
3
4
Note: Logic “0” = VAL≤ 0.8V, Logic “1” = VAH≥ 2.4V
MAX420
+15V
-15V
V+
+15V
1M
100k
10k
OUT
OUT
1k
111Ω
IN1
IN1
IN2
IN3
IN4
IN5
V+
THERMOCOUPLE
+15V
-15V
V- GND
DG508A
MAX358
OR
MAX378
MAX378
IN2
STRAIN GUAGE
IN7
+10V
GAIN REFERENCE
IN8
ZERO REFERENCE
IN3
4-20mA LOOP
TRANSMITTER
IN4
IN5
IN6
-15V
V- GND
Figure 6. Typical Data Acquisition Front End
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
_______________________________________________________________________________________ 7
Input switching, however, must be done with a faultprotected MAX378 multiplexer, to provide the level of
protection and isolation required with most data acquisition inputs. Since external signal sources may continue to supply voltage when the multiplexer and system
power are turned off, non-fault-protected multiplexers,
or even first-generation fault-protected devices, will
allow many milliamps of fault current to flow from outside sources into the multiplexer. This could result in
damage to either the sensors or the multiplexer. A nonfault-protected multiplexer will also allow input overvoltages to appear at its output, perhaps damaging
Sample/Holds or A/Ds. Such input overdrives may also
cause input-to-input shorts, allowing the high current
output of one sensor to possibly damage another.
The MAX378 eliminates all of the above problems. It
not only limits its output voltage to safe levels, with or
without power applied (V+ and V-), but also turns all
channels off when power is removed. This allows it to
draw only sub-microamp fault currents from the inputs,
and maintain isolation between inputs for continuous
input levels up to ±75V with power supplies off.
_______________Detailed Description
Fault Protection Circuitry
The MAX378/MAX379 are fully fault protected for continuous input voltages up to ±60V, whether or not the V+
and V- power supplies are present. These devices use
a “series FET” switching scheme which not only protects the multiplexer output from overvoltage, but also
limits the input current to sub-microamp levels.
Figures 7 and 8 show how the series FET circuit protects against overvoltage conditions. When power is
off, the gates of all three FETs are at ground. With a -60V
input, N-channel FET Q1 is turned on by the +60V gate-
G
D
Q
1
S
-60V
-60V
OVERVOLTAGE
N-CHANNEL MOSFET
IS TURNED ON
BECAUSE V
GS
= +60V
P-CHANNEL
MOSFET IS OFF
G
D
Q
2
S
G
D
Q
3
S
Figure 7. -60V Overvoltage with Multiplexer Power OFF
Q
1
V
TN = +1.5V
-15V +15V -15V
+13.5V
+60V
OVERVOLTAGE
N-CHANNEL MOSFET
IS TURNED ON
BECAUSE V
GS
= -45V
Q
2
Q
3
N-CHANNEL
MOSFET IS ON
+13.5V
OUTPUT
+15V FROM
DRIVERS
-15V FROM
DRIVERS
Figure 10. +60V Overvoltage Input to the ON Channel
Q
1
-15V +15V -15V
-60V
-60V
OVERVOLTAGE
N-CHANNEL MOSFET
IS TURNED OFF
BECAUSE V
GS
= +45V
Q
2
Q
3
P-CHANNEL
MOSFET IS OFF
N-CHANNEL
MOSFET IS OFF
+60V FORCED
ON COMMON
OUTPUT
LINE BY
EXTERNAL
CIRCUITRY
-15V FROM
DRIVERS
+15V FROM
DRIVERS
Figure 9. -60V Overvoltage on an OFF Channel with
Multiplexer Power Supply ON
G
D
Q
1
S
+60V
OVERVOLTAGE
N-CHANNEL MOSFET
IS TURNED OFF
BECAUSE V
GS
= -60V
G
D
Q
2
S
G
D
Q
3
S
Figure 8. +60V Overvoltage with Multiplexer Power OFF
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
8 _______________________________________________________________________________________
to-source voltage. The P-channel device (Q2), however, has +60V VGSand is turned off, thereby preventing
the input signal from reaching the output. If the input
voltage is +60V, Q1 has a negative VGS, which turns it
off. Similarly, only sub-microamp leakage currents can
flow from the output back to the input, since any voltage will turn off either Q1 or Q2.
Figure 9 shows the condition of an OFF channel with
V+ and V- present. As with Figures 7 and 8, either an
N-channel or a P-channel device will be off for any
input voltage from -60V to +60V. The leakage current
with negative overvoltages will immediately drop to a
few nanoamps at +25°C. For positive overvoltages,
that fault current will initially be 40µA or 50µA, decaying
over a few seconds to the nanoamp level. The time
constant of this decay is caused by the discharge of
stored charge from internal nodes, and does not compromise the fault-protection scheme.
Figure 10 shows the condition of the ON channel with
V+ and V- present. With input voltages less than ±10V,
all three FETs are on and the input signal appears at the
output. If the input voltage exceeds V+ minus the Nchannel threshold voltage (VTN), then the N-channel
FET will turn off. For voltages more negative than Vminus the P-channel threshold (VTP), the P-channel
device will turn off. Since VTNis typically 1.5V and V
TP
is typically 3V, the multiplexer’s output swing is limited
to about -12V to +13.5V with ±15V supplies.
The
Typical Operating Characteristics
graphs show typical leakage vs. input voltage curves. Although the maximum rated input of these devices is ±65V, the
MAX378/MAX379 typically have excellent performance
up to ±75V, providing additional margin for the unknown
transients that exist in the real world. In summary, the
MAX378/MAX379 provide superior protection from all
fault conditions while using a standard, readily produced junction-isolated CMOS process.
Switching Characteristics
and Charge Injection
Table 1 shows typical charge-injection levels vs.
power-supply voltages and analog input voltage. Note
that since the channels are well matched, the differential charge injection for the MAX379 is typically less
than 5pC. The charge injection that occurs during
switching creates a voltage transient whose magnitude
is inversely proportional to the capacitance on the multiplexer output.
The channel-to-channel switching time is typically 600ns,
with about 200ns of break-before-make delay. This 200ns
break-before-make delay prevents the input-to-input short
that would occur if two input channels were simultaneous-
ly connected to the output. In a typical data acquisition
system, such as in Figure 6, the dominant delay is not the
switching time of the MAX378 multiplexer, but is the settling time of the following amplifiers and S/H. Another limiting factor is the RC time constant of the multiplexer
R
DS(ON)
plus the signal source impedance multiplied by
the load capacitance on the output of the multiplexer.
Even with low signal source impedances, 100pF of capacitance on the multiplexer output will approximately double
the settling time to 0.01% accuracy.
Operation with Supply Voltage
Other than ±15V
The main effect of supply voltages other than ±15V is
the reduction in output signal range. The MAX378 limits
the output voltage to about 1.5V below V+ and about 3V
above V-. In other words, the output swing is limited to
+3.5V to -2V when operating from ±5V. The
Typical
Operating Characteristics
graphs show typical R
DS(ON)
,
for ±15V, ±10V, and ±5V power supplies. Maxim tests
and guarantees the MAX378/MAX379 for operation from
±4.5V to ±18V supplies. The switching delays are
increased by about a factor of 2 at ±5V, but breakbefore-make action is preserved.
The MAX378/MAX379 can be operated with a single +9V
to +22V supply, as well as asymmetrical power supplies
such as +15V and -5V. The digital threshold will remain
approximately 1.6V above GND and the analog characteristics such as R
DS(ON)
are determined by the total voltage
difference between V+ and V-. Connect V- to 0V when
operating with a +9V to +22V single supply.
This means that the MAX378/MAX379 will operate with
standard TTL-logic levels, even with ±5V power supplies. In all cases, the threshold of the EN pin is the
same as the other logic inputs.
Table 1a. MAX378 Charge Injection
Test Conditions: CL= 1000pF on multiplexer output; the tabulated analog input level is applied to channel 1; channels 2
through 8 are open circuited. EN = +5V, A1 = A2 = 0V, A0 is
toggled at 2kHz rate between 0V and 3V. +100pC of charge
creates a +100mV step when injected into a 1000pF load
capacitance.
Supply Voltage Analog Input Level Injected Charge
±5V
+1.7V
0V
-1.7V
+100pC
+70pC
+45pC
±10V
+5V
0V
-5V
+200pC
+130pC
+60pC
±15V
+10V
0V
-10V
+500pC
+180pC
+50pC
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
_______________________________________________________________________________________ 9
Digital Interface Levels
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 leakage at all input voltage levels, with a guaranteed maximum 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.
Operation as a Demultiplexer
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 provide both break-before-make action and full fault protection when operated as a demultiplexer, unlike earlier
generations of fault-protected multiplexers.
Channel-to-Channel Crosstalk,
Off Isolation, and Digital Feedthrough
At DC and low frequencies, channel-to-channel
crosstalk is caused by variations in output leakage cur-
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
DS(ON)
plus the input
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 performance. 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 isolated 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 1b. MAX379 Charge Injection
+1.7V
0V
-1.7V
+105pC
+73pC
+48pC
±10V
+5V
0V
-5V
+215pC
+135pC
+62pC
±15V
+10V
0V
-10V
+525pC
+180pC
+55pC
±5V
Test Conditions: CL= 1000pF on Out A and Out B; the tabulated analog input level is applied to inputs 1A and 1B; channels
2 through 4 are open circuited. EN = +5V, A1 = 0V, A0 is toggled from 0V to 3V at a 2kHz rate.
+107pC
+74pC
+50pC
+220pC
+139pC
+63pC
+530pC
+185pC
+55pC
Out A Out B
Injected Charge
-2pC
-1pC
-2pC
-5pC
-4pC
-1pC
-5pC
-5pC
0pC
Differential
A-B
Supply
Voltage
Analog
Input Level
Table 2a. Typical Off-Isolation
Rejection Ratio
Test Conditions: VIN= 20V
P-P
at the tabulated frequency,
R
L
= 1.5kΩ between OUT and GND, EN = 0V.
20V
P-P
OIRR = 20 Log ____________
V
OUT (P-P)
Frequency 100kHz 500kHz 1MHz
One Channel Driven
74dB 72dB 66dB
All Channels Driven
64dB 48dB 44dB
Table 2b. Typical Crosstalk
Rejection Ratio
Test Conditions: Specified RLconnected from OUT to GND,
EN = +5V, A0 = A1 = A2 = +5V (Channel 1 selected). 20V
P-P
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.
Frequency
100kHz 500kHz 1MHz
FL= 1.5k
70dB 68dB 64dB
RL= 10k
62dB 46dB 42dB
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
10 ______________________________________________________________________________________
_____________________________________________Pin Configurations (continued)
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
A1
A2
GND
N.C.
N.C.
N.C.
EN
A0
TOP VIEW
V+
IN5
IN6
N.C.
IN3
IN2
IN1
V-
16
15
14
13
9
10
11
12
IN7
N.C.
N.C.
IN8
OUT
N.C.
N.C.
IN4
SO
MAX378
24
23
22
21
20
19
18
17
1
2
3
4
5
6
7
8
A1
N.C.
GND
N.C.
N.C.
N.C.
EN
A0
V+
IN1B
IN2B
IN3B
IN3A
IN2A
IN1A
V-
16
15
14
13
9
10
11
12
IN4B
N.C.
N.C.
OUTB
OUTA
N.C.
N.C.
IN4A
SO
LCC
LCC
MAX379
14
15
16
17
184
5
6
7
8
3
2
1
20
19
9
101112
13
MAX378
V-
IN1
N.C.
IN2
IN3
GND
V+
N.C.
IN5
IN6
EN
A0
N.C.
A1
A2
IN4
OUT
N.C.
IN8
IN7
14
15
16
17
184
5
6
7
8
3
2
1
20
19
9
101112
13
MAX379
VIN1A
N.C.
IN2A
IN3A
V+
IN1B
N.C.
IN2B
IN3B
EN
A0
N.C.
A1
GND
IN4A
OUTA
N.C.
OUTB
IN4B
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
______________________________________________________________________________________ 11
_Ordering Information (continued)
* Contact factory for availability.
**The substrate may be allowed to float or be tied to V+ (JI CMOS).
_________________Chip Topographies
GND
V+
IN5
IN6
IN7
IN7
IN8 OUT
MAX378
IN4
A0
0.229"
(5.816mm)
0.151"
(3.835mm)
A2 A1 EN
V-
NOTE: Connect substrate to V+ or leave it floating.
NOTE: Connect substrate to V+ or leave it floating.
IN1
IN2
IN3
GND
V+
IN1B
IN2B
IN3B
IN4B
OUTB OUTA
MAX379
IN4A
A0
0.229"
(5.816mm)
0.151"
(3.835mm)
A1 EN
V-
IN1A
IN2A
IN3A
PART
MAX379CPE
MAX379CWG
MAX379CJE 0°C to +70°C
0°C to +70°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
16 Plastic DIP
24 Wide SO
16 CERDIP
MAX379EPE
MAX379EWG -40°C to +85°C
-40°C to +85°C 16 Plastic DIP
24 Wide SO
MAX379EJE
MAX379MJE -55°C to +125°C
-40°C to +85°C 16 CERDIP
16 CERDIP
MAX379MLP -55°C to +125°C 20 LCC*
MAX379C/D 0°C to +70°C Dice**
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12
__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1994 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
MAX378/MAX379
High-Voltage, Fault-Protected
Analog Multiplexers
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12
__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1994 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
________________________________________________________Package Information
DIM
A
A1
B
C
E
e
H
L
MIN
0.093
0.004
0.014
0.009
0.291
0.394
0.016
MAX
0.104
0.012
0.019
0.013
0.299
0.419
0.050
MIN
2.35
0.10
0.35
0.23
7.40
10.00
0.40
MAX
2.65
0.30
0.49
0.32
7.60
10.65
1.27
INCHES MILLIMETERS
21-0042A
Wide SO
SMALL-OUTLINE
PACKAGE
(0.300 in.)
DIM
D
D
D
D
D
MIN
0.398
0.447
0.496
0.598
0.697
MAX
0.413
0.463
0.512
0.614
0.713
MIN
10.10
11.35
12.60
15.20
17.70
MAX
10.50
11.75
13.00
15.60
18.10
INCHES MILLIMETERS
PINS
16
18
20
24
28
1.27
0.050
L
HE
D
e
A
A1
C
0°- 8°
0.101mm
0.004in.
B
C
A
A2
E1
D
E
e
A
e
B
A3
B1
B
DIM
A
A1
A2
A3
B
B1
C
D
D1
E
E1
e
e
A
e
B
L
α
MIN
–
0.015
0.125
0.055
0.016
0.050
0.008
0.745
0.005
0.300
0.240
–
0.115
0˚
MAX
0.200
–
0.150
0.080
0.022
0.065
0.012
0.765
0.030
0.325
0.280
0.400
0.150
15˚
MIN
–
0.38
3.18
1.40
0.41
1.27
0.20
18.92
0.13
7.62
6.10
–
2.92
0˚
MAX
5.08
–
3.81
2.03
0.56
1.65
0.30
19.43
0.76
8.26
7.11
10.16
3.81
15˚
INCHES MILLIMETERS
2.54 BSC
7.62 BSC
0.100 BSC
0.300 BSC
A1
L
D1
e
21-587A
α
16-PIN PLASTIC
DUAL-IN-LINE
PACKAGE
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