__________Applications Information
Power-Supply Considerations
The MAX4503/MAX4504’s construction is typical of
most CMOS analog switches, except they have only
two supply pins: V+ and V-. These voltages set the
analog voltage limits of the switch. Reverse ESD-pro-
tection diodes are internally connected between IN and
each analog signal pin and both V+ and V-. If any ana-
log signal exceeds V+ or V-, one of these diodes will
conduct. During normal operation, these (and other)
reverse-biased ESD diodes leak, forming the only cur-
rent drawn from V-. Additional current flows through V+
from the logic-level translator.
Virtually all the analog leakage current is provided
through the ESD diodes. Although the ESD diodes on a
given signal pin are identical and therefore fairly well
balanced, they are reverse biased differently. Each is
biased by either V+ or V- and the analog signal. This
means their leakages will vary as the signal varies. The
difference in the two diode leakages to the V+ and V-
pins constitutes the analog-signal-path leakage current.
All analog leakage current flows between each pin and
one of the supply terminals, not to the other switch ter-
minal. This is why both sides of a given switch can
show leakage currents of either the same or opposite
polarity.
There is no connection between the analog signal
paths and V+ or V-.
V+ and V- also power the internal logic and logic-level
translators. Since there is no ground pin, the logic input
has a low-current pull-up to V+ and the logic limit is set
by an internal comparator referenced to V+. The logic-
level translators convert the logic levels to switched V+
and V- signals, to drive the gates of the analog signals.
This drive signal is the only connection between the
logic supplies (and signals) and the analog supplies.
COM, NO, and NC pins have ESD-protection diodes to
V+ and V-.
The logic is CMOS compatible when V+ is +5V. CMOS
compatibility is maintained with all V+ values, assuming
that the CMOS logic is operated from the same V+ sup-
ply. Since the MAX4503/MAX4504 have no ground
pins, the logic levels are internally referenced to V+.
Do not connect the MAX4503/MAX4504 V+ to +3V
and connect the logic-level pins to TTL-logic-level
signals. TTL levels can exceed +3V and violate the
absolute maximum ratings, damaging the part
and/or external circuits.
High-Frequency Performance
In 50Ω systems, signal response is reasonably flat up
to 50MHz. (see Typical Operating Characteristics).
Above 20MHz the on-response has several minor
peaks which are highly layout dependent. The problem
is not in turning the switch on, but in turning it off. The
off-state switch acts like a capacitor, and passes higher
frequencies with less attenuation. At 10MHz, off isola-
tion is about -65dB in 50Ω systems, becoming worse
(approximately 20dB per decade) as frequency
increases. Higher circuit impedances also make off iso-
lation worse.
MAX4503/MAX4504
Low-Voltage, Dual-Supply, SPST,
CMOS Analog Switches
6 _______________________________________________________________________________________
______________________________________________________________Pin Description
MAX4503
DIP/SO SOT23-5
FUNCTION
1 1 Analog Switch Common Terminal
2, 3, 5
—
No Connect (not internally connected)
8 2 Analog Switch Normally Open Terminal
7 3 Negative (analog) Supply Voltage Input
6 4 Digital Control Input
4 5 Positive (analog and digital) Supply Voltage Input
— —
Analog Switch Normally Closed Terminal
MAX4504
DIP/SO SOT23-5
PIN
1 1
2, 3, 5
—
— —
7 3
6 4
4 5
8 2
NAME
COM
N.C.
NO
V-
IN
V+
NC
Note: NO, NC, and COM pins are identical and interchangeable. Either may be considered as an input or output; signals pass
equally well in both directions.
