MAX320/MAX321/MAX322
Precision, Dual-Supply, SPST
Analog Switches
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__________Applications Information
Logic Levels
Calculate the logic thresholds typically as follows: V
IH
=
(V+ - 1.5V) and V
IL
= (V+ - 2.5V).
Power-supply consumption is minimized when IN1 and
IN2 are driven with logic-high levels equal to V+ and logic-
low levels well below the calculated V
IL
of (V+ - 2.5V). IN1
and IN2 can be driven to V- without damage.
Analog Signal Levels
Analog signals that range over the entire supply voltage
(V- to V+) can be switched, with very little change in on-
resistance over the entire voltage range (see
Typical
Operating Characteristics
). All switches are bidirec-
tional, so NO_, NC_, and COM_ pins can be used as
either inputs or outputs.
Power-Supply Sequencing
and Overvoltage Protection
Do not exceed the absolute maximum ratings, because
stresses beyond the listed ratings may cause perma-
nent damage to the devices.
Proper power-supply sequencing is recommended for
all CMOS devices. Always apply V+, followed by V-,
before applying analog signals or logic inputs, especial-
ly if the analog or logic signals are not current-limited. If
this sequencing is not possible, and if the analog or
logic inputs are not current-limited to <30mA, add two
small signal diodes (D1, D2) as shown in Figure 1.
Adding protection diodes reduces the analog signal
range to a diode drop (about 0.7V) below V+ for D1,
and a diode drop above V- for D2. Leakage is not
affected by adding the diodes. On-resistance increas-
es by a small amount at low supply voltages. Maximum
supply voltage (V- to V+) must not exceed 17V.
Adding protection diode D1 causes the logic thresh-
olds to be shifted relative to the positive power-supply
rail. This can be significant when low positive supply
voltages (+5V or less) are used. Driving IN1 and IN2 all
the way to the supply rails (i.e., to a diode drop higher
than the V+ pin or a diode drop lower than the V- pin) is
always acceptable.
The protection diodes D1 and D2 also protect against
some overvoltage situations. With the circuit of Figure 1,
if the supply voltage is below the absolute maximum
rating and if a fault voltage up to the absolute maximum
rating is applied to an analog signal pin, no damage
will result. For example, with ±5V supplies, analog sig-
nals up to ±8.5V will not damage the circuit of Figure 1.
If only a single fault signal is present, the fault voltage
can rise to +12V or to -12V without damage.
_____________________Pin Description
POSITIVE SUPPLY
COM
D1
D2
NO
V-
V
g
V+
NEGATIVE SUPPLY
MAX320
MAX321
MAX322
Figure 1. Overvoltage Protection Using Two External Blocking
Diodes
5
Normally Closed Analog
Switch Terminal
NC2
(MAX321/MAX322)
Normally Open Analog
Switch Terminal
NO2
(MAX320)
Negative SupplyV-4
Logic InputsIN2, IN13, 7
PIN
Analog Switch Common
Terminals
COM1, COM22, 6
Normally Closed Analog
Switch Terminal
NC1
(MAX321)
Normally Open Analog
Switch Terminal
NO1
(MAX320/MAX322)
1
FUNCTIONNAME
Positive SupplyV+8
