Index DW9937S, Service Manual

Page: 44 / 112

MAX4051/A, MAX4052/A, MAX4053/A
V+ and GND power the internal logic and logic-level
translators, and set both the input and output logic lim-
its. The logic-level translators convert the logic levels
into switched V+ and V- signals to drive the gates of
the analog signals. This drive signal is the only connec-
tion between the logic supplies (and signals) and the
analog supplies. V+ and V- have ESD-protection
diodes to GND.
The logic-level thresholds are TTL/CMOS compatible
when V+ is +5V. As V+ rises, the threshold increases
slightly, so when V+ r12V, the threshold is
about 3.1V; above the TTL-guaranteed high-level mini-
mum of 2.8V, but still compatible with CMOS outputs.
Bipolar Supplies
These devices operate with bipolar supplies between
±3.0V and ±8V. The V+ and V- supplies need not be
symmetrical, but their sum cannot exceed the absolute
maximum rating of +17V.
Single Supply
These devices operate from a single supply between
+3V and +16V when V- is connected to GND. All of the
bipolar precautions must be observed. At room temper-
ature, they actually “work” with a single supply at near
or below +1.7V, although as supply voltage decreases,
switch on-resistance and switching times become very
high.
Overvoltage Protection
Proper power-supply sequencing is recommended for
all CMOS devices. Do not exceed the absolute maxi-
mum ratings, because stresses beyond the listed rat-
ings can cause permanent damage to the devices.
Always sequence V+ on first, then V-, followed by the
logic inputs (NO) and by COM. If power-supply
sequencing is not possible, add two small signal diodes
(D1, D2) in series with the supply pins for overvoltage
protection (Figure 1).
Adding diodes reduces the analog signal range to one
diode drop below V+ and one diode drop above V-, but
does not affect the devices’ low switch resistance and
low leakage characteristics. Device operation is
unchanged, and the difference between V+ and V-
should not exceed 17V. These protection diodes are
not recommended when using a single supply if signal
levels must extend to ground.
High-Frequency Performance
In 50
Ω
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 turning the switch on, but 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 -45dB in 50
Ω
systems, becoming worse
(approximately 20dB per decade) as frequency
increases. Higher circuit impedances also make off iso-
lation worse. Adjacent channel attenuation is about 3dB
above that of a bare IC socket, and is entirely due to
capacitive coupling.
Low-Voltage, CMOS Analog
Multiplexers/Switches
COM NO
V-
V+
* INTERNAL PROTECTION DIODES
D2
D1 EXTERNAL BLOCKING DIODE
EXTERNAL BLOCKING DIODE
V-
V+
MAX4051/A
MAX4052/A
MAX4053/A
*
* *
*
Figure 1. Overvoltage Protection Using External Blocking
Diodes
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