internal biasing. Use a resistor value of 39k

Ω.

Applications Information

Low-Voltage Operation

The MAX7301 operates down to 2V supply voltage

(although the sourcing and sinking currents are not

guaranteed), providing that the MAX7301 is powered

up initially to at least 2.5V to trigger the device’s internal

reset, and also that the serial interface is constrained to

10Mbps.

SPI Routing Considerations

The MAX7301’s SPI interface is guaranteed to operate

at 26Mbps on a 2.5V supply, and on a 5V supply typi-

cally operates at 50Mbps. This means that transmission

line issues should be considered when the interface

connections are longer than 100mm, particularly with

higher supply voltages. Ringing manifests itself as

communication issues, often intermittent, typically due

to double clocking due to ringing at the SCLK input. Fit

a 1k

Ω to 10kΩ parallel termination resistor to either

GND or V+ at the DIN, SCLK, and

CS input to damp

ringing for moderately long interface runs. Use line-

impedance matching terminations when making con-

nections between boards.

PC Board Layout Considerations

For the TQFN version, connect the underside exposed

pad to GND. Ensure that all the MAX7301 GND connec-

tions are used. A ground plane is not necessary, but

may be useful to reduce supply impedance if the

MAX7301 outputs are to be heavily loaded. Keep the

short as possible, and take the GND end of the resistor

either to the ground plane or directly to the ground pins.

Power-Supply Considerations

The MAX7301 operates with power-supply voltages of

2.5V to 5.5V. Bypass the power supply to GND with a

0.047µF capacitor as close to the device as possible.

Add a 1µF capacitor if the MAX7301 is far away from

the board’s input bulk decoupling capacitor.

Chip Information

TRANSISTOR COUNT: 30,316

PROCESS: CMOS

4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and

28-Port I/O Expander

_______________________________________________________________________________________

9

MICROCONTROLLER

SERIAL-DATA OUTPUT

SERIAL CS OUTPUT

SERIA-CLOCK OUTPUT

SERIAL-DATA INPUT

DIN

SCLK

CS

DOUT

DIN

SCLK

CS

DOUT

DIN

SCLK

CS

DOUT

MAX7301

MAX7301

MAX7301

Figure 3. Daisy-Chain Arrangement for Controlling Multiple MAX7301s

D15

= 0

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

D15 = 0

CS

SCLK

DIN

DOUT

Figure 4. Transmission of a16-Bit Write to the MAX7301