MAX395EWG+ Datasheet MAX395EWG+, MAX395CWG+, MAX395CAG+ | P13-P15

MAX395

Serially Controlled, Low-Voltage,

8-Channel SPST Switch

______________________________________________________________________________________ 13

8x1 Multiplexer

To use the MAX395 as an 8x1 multiplexer, connect all

common pins together (COM0–COM7) to form the mux

output; the mux inputs are NO0–NO7.

The mux can be programmed normally, with only one

channel selected for every eight clock pulses, or it can

be programmed in a fast mode, where channel chang-

ing occurs on each clock pulse. In this mode, the chan-

nels are selected by sending a single high pulse

(corresponding to the selected channel) at DIN, and a

corresponding CS low pulse for every eight clock puls-

es. As this is clocked through the register by SCLK,

each switch sequences one channel at a time, starting

with Channel 7.

Dual, Differential 4-Channel Multiplexer

To use the MAX395 as a dual (4x2) mux, connect

COM0–COM3 together and connect COM4–COM7

together, forming the two outputs. The mux input pairs

become NO0/NO4, NO1/NO5, NO2/NO6, and NO3/NO7.

The mux can be programmed normally, with only one

differential channel selected for every eight clock puls-

es, or it can be programmed in a fast mode, where

channel changing occurs on each clock pulse.

In fast mode, the channels are selected by sending two

high pulses spaced four clock pulses apart (corre-

sponding to the two selected channels) at DIN, and a

corresponding CS low pulse for each of the first eight

clock pulses. As this is clocked through the register by

SCLK

DIN

DOUT



I/O

MICROWIRE

PORT

MAX395



THE DOUT-SI CONNECTION IS NOT REQUIRED FOR WRITING TO THE

MAX395, BUT MAY BE USED FOR DATA-ECHO PURPOSES.

Figure 3. Connections for Microwire

DOUT

DIN

SCLK

MISO

MOSI

SCK

I/O

SPI

PORT

MAX395

THE DOUT-MISO CONNECTION IS NOT REQUIRED FOR WRITING TO THE

MAX395, BUT MAY BE USED FOR DATA-ECHO PURPOSES.

CPOL = 0, CPHA = 0

Figure 4. Connections for SPI and QSPI

SCLK

DIN

MAX395

SCLK

DIN

MAX395

SCLK

DIN

MAX395

DOUT DOUT DOUT

SCLK

DIN

TO OTHER

SERIAL DEVICES

Figure 5. Daisy-Chained Connection

MAX395

Serially Controlled, Low-Voltage,

8-Channel SPST Switch

14 ______________________________________________________________________________________

SCLK, each switch sequences one differential channel

at a time, starting with channel 7/0. After the first eight

bits have been sent, subsequent channel sequencing

can occur by repeating this sequence or, even faster,

by sending only one DIN high pulse and one CS low

pulse for each four clock pulses.

SPDT Switches

To use the MAX395 as a quad, single-pole/double-

throw (SPDT) switch, connect COM0 to NO1, COM2 to

NO3, COM4 to NO5, and COM6 to NO7, forming the

four “common” pins. Program these four switches with

pairs of instructions, as shown in Table 2.

Reset Function

RESET is the internal reset pin. It is usually connected

to a logic signal or V+. Drive RESET low to open all

switches and set the contents of the internal shift regis-

ter to zero simultaneously. When RESET is high, the

part functions normally and DOUT is sourced from V+.

RESET must not be driven beyond V+ or GND.

Power-Supply Considerations

Overview

The MAX395 construction is typical of most CMOS ana-

log switches. It has three supply pins: V+, V-, and

GND. V+ and V- are used to drive the internal CMOS

switches and to set the limits of the analog voltage on

any switch. Reverse ESD-protection diodes are inter-

nally connected between each analog signal pin and

both V+ and V-. If any analog signal exceeds V+ or V-,

one of these diodes will conduct. During normal opera-

tion, these (and other) reverse-biased ESD diodes leak,

forming the only current drawn from V+ or V-.

Virtually all the analog leakage current is through the

ESD diodes. Although the ESD diodes on a given sig-

nal 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 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 leak-

FOUR CLOCK

PULSES



DIN

SCLK

SW4

SW0

Figure 7. Differential Multiplexer Input Control

SCLK

DIN

MAX395

SCLK

DIN

MAX395

SCLK

DIN

MAX395

TO OTHER

SERIAL

DEVICES

DIN

SCLK

CS1

CS2

CS3

Figure 6. Addressable Serial Interface

MAX395

Serially Controlled, Low-Voltage,

8-Channel SPST Switch

______________________________________________________________________________________ 15

age current flows to the supply terminals, not to the

other switch terminal. 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 GND.

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 to

switched V+ and V- signals to drive the analog signal

gates. This drive signal is the only connection between

the logic supplies (and signals) and the analog sup-

plies. V+, and V- have ESD-protection diodes to GND.

The logic-level inputs and output have ESD protection

to V+ and to GND.

The logic-level thresholds are CMOS and TTL compati-

ble when V+ is +5V. As V+ is raised, the threshold

increases slightly. So when V+ reaches +12V, the

threshold is about 3.1V; slightly above the TTL guaran-

teed high-level minimum of 2.8V, but still compatible

with CMOS outputs.

Bipolar Supplies

The MAX395 operates 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. Do not connect the MAX395

V+ to +3V and connect the logic-level pins to TTL

logic-level signals. This exceeds the absolute maxi-

mum ratings and can damage the part and/or exter-

nal circuits.

Single Supply

The MAX395 operates from a single supply between

+3V and +16V when V- is connected to GND. All of the

bipolar precautions must be observed.

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 that 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 frequen-

cies with less attenuation. At 10MHz, off isolation is

about -45dB in 50Ω systems, becoming worse (approx-

imately 20dB per decade) as frequency increases.

Higher circuit impedances also make off isolation

worse. Adjacent channel attenuation is about 3dB

above that of a bare IC socket, and is due entirely to

capacitive coupling.

RESET

FUNCTION

DATA BITS

All switches open, D7–D0 = 0

Switch 6 off and 7 on

Switch 7 off and 6 on

Switch 4 off and 5 on

Switch 2 off and 3 on

Switch 3 off and 2 on

Switch 5 off and 4 on

X XX XX1 10 Switch 1 off and 0 onX

Table 2. SPDT Switch Programming

X XX XX1 01 Switch 0 off and 1 onX

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P16

MAX395EWG+

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Manufacturer:

Maxim Integrated

Description:

Analog Switch ICs Serially Controlled 8Ch SPST Switch

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MAX395EWG+

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