MAX355 Maxim, MAX355 Datasheet - Page 9

• Manufacturer Part Number: MAX355
• Description: The MAX354/MAX355 fault-protected multiplexers (muxes) use a series N-channel, P-channel, N-channel structure that protects the devices from overvoltage up to 40V beyond the supply rails during power-up, power-down, and fault conditions
• Manufacturer: Maxim

Figure 10 shows the condition of an off channel with V+
and V- present. As with Figures 8 and 9, either an N-
channel or a P-channel device will be off for any input
voltage from -40V to +40V. 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 10µA or 20µA, 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 com-
promise the fault-protection scheme.
Figure 11 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
N-channel threshold voltage (V
will turn off. For voltages more negative than V- minus
the P-channel threshold (V
turn off. Since V
3V, the multiplexer’s output swing is limited to about -12V
to +13.5V with ±15V supplies.
Figure 8. -25V Overvoltage with Multiplexer Power Off
Figure 10. -25V Overvoltage on an Off Channel with
Multiplexer Power Supply On
N-CHANNEL MOSFET
BECAUSE V
IS TURNED ON
N-CHANNEL MOSFET
BECAUSE V
OVERVOLTAGE
IS TURNED ON
GS
OVERVOLTAGE
-25V
= +10V
-25V
GS
= +25V
-15V FROM
TN
DRIVERS
MOSFET IS OFF
-15V
_______________________________________________________________________________________
S
P-CHANNEL
is typically 1.5V and V
Q1
MOSFET IS OFF
P-CHANNEL
Q1
G
D
+15V FROM
DRIVERS
TP
+15V
-25V
S
Fault-Protected Analog Multiplexers
), the P-channel device will
Q2
TN
Q2
G
), the N-channel FET
D
-15V
S
Q3
EXTERNAL CIRCUITRY
TP
Q3
G
OUTPUT LINE BY
+25V FORCED
ON COMMON
MOSFET IS OFF
D
N-CHANNEL
is typically
Table 1 shows typical charge injection levels versus
power-supply voltages and analog input voltage. The
charge injection that occurs during switching creates a
voltage transient whose magnitude is inversely propor-
tional to the capacitance on the multiplexer output.
Table 1. MAX354 Charge Injection
Test Conditions: C
analog input level is applied to channel 1; channels 2–8 inputs
are open circuited. EN = +5V, V
a 2kHz rate between 0V and 3V. +100pC of charge creates a
+100mV step when injected into a 1000pF load capacitance.
Figure 9. +25V Overvoltage with Multiplexer Power Off
Figure 11. +25V Overvoltage Input to the On Channel
Supply Voltage
N-CHANNEL MOSFET
BECAUSE V
IS TURNED OFF
N-CHANNEL MOSFET
BECAUSE V
IS TURNED OFF
±10V
±15V
OVERVOLTAGE
±5V
OVERVOLTAGE
GS
+25V
+25V
= -10V
GS
= -25V
L
+15V FROM
, = 1000pF on mux output; the tabulated
DRIVERS
S
Analog Input Level
-15V
Q1
Switching Characteristics
V
Q1
G
TN
D
= 1.5V
+10V
-10V
+2V
+5V
13.5V
-2V
-5V
0V
0V
0V
-15V FROM
DRIVERS
A1
S
and Charge Injection
+15V
= V
Q2
Q2
G
A2
D
= 0V, V
S
-15V
Injected Charge
Q3
Q3
G
MOSFET IS ON
O
N-CHANNEL
105pC
180pC
52pC
35pC
16pC
65pC
25pC
80pC
15pC
D
OUTPUT
is toggled at
13.5V
9