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Applications Information

Serial Bus Configurations

The MAX14724 was designed to support a wide variety of

multiplexing applications. Multiple devices can be used in

a system to expand the number of ports being multiplexed.

With the address-select pin provided in I2C mode, two devices

can be attached to the same I2C bus simultaneously. There

are also several options for addressing multiple devices

when using the SPI interface. Using only three pins on the

microcontroller, as many devices as desired can be loaded

by connecting all CS and SCK pins in parallel and chaining

the DO pin from one device to the DI pin on the next. It

is also acceptable to provide a separate CS pin for each

device so they can be individually addressed and loaded.

Alternatively, a separate data line can be used for each

device to reduce the time required to load all the devices.

Some of the options and tradeoffs are listed in Table 5,

as well as example application diagrams in the typical

application circuit.

Extended ESD

ESD-protection structures are incorporated on all pins

to protect against electrostatic discharges up to ±2kV

(Human Body Model) encountered during handling and

assembly. NO_ and COM_ are further protected against

ESD up to ±30kV (Human Body Model), ±15kV (Air

Gap Discharge method described in IEC 61000-4-2),

and ±10kV (Contact Discharge method described in

IEC 61000-4-2) without damage.

The ESD structures withstand high ESD both in normal

operation and when the device is powered down. After

an ESD event, the device continues to function without

latchup.

ESD Test Condition

ESD performance depends on a variety of conditions.

Contact Maxim for a reliability report that documents test

setup, test methodology, and test results.

Human Body Model

Figure 16 shows the Human Body Model. Figure 17 shows

the current waveform it generates when discharged into a

low impedance. This model consists of a 100pF capacitor

charged to the ESD voltage of interest that is then discharged

into the device through a 1.5kΩ resistor.

Table 5. Benefits and Limitations of Different Serial-Bus Configurations

SERIAL BUS

PINS

BENEFITS

LIMITATIONS

I2C (Figure 20)

Fewest pins

Maximum two devices per bus, slow protocol,

no simultaneous updates across all devices

SPI Daisy-Chain

(Figure 21)

Faster than I2C with only one additional pin,

simultaneous updates across all devices in chain

n x 32 clocks required to load all devices

SPI Separate CS

(Figure 22)

n+2

Common SPI implementation, quick for single

device updates

n x 32 clocks required to load all devices,

requires an additional pin per device, no

simultaneous updates across all devices

SPI Separate

Data (Figure 23)

n+2

Fastest loading for multiple devices,

simultaneous updates across all devices

Requires an additional pin per device, may not

be supported by the SPI controller

Figure 16. Human Body ESD Test Model

Figure 17. Human Body Current Waveform

CHARGE-CURRENT-

LIMIT RESISTOR

DISCHARGE

RESISTANCE

STORAGE

CAPACITOR

100pF

1MΩ

1.5kΩ

HIGH-

VOLTAGE

SOURCE

DEVICE

UNDER

TEST

IP 100%

90%

36.8%

tRL

TIME

tDL

CURRENT WAVEFORM

PEAK-TO-PEAK RINGING

(NOT DRAWN TO SCALE)

10%

AMPERES

MAX14724

Serial-Controlled 8:4 Matrix Switch Multiplexer

www.maximintegrated.com

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