Datasheet

External Component R
ISET
The MAX7301 uses an external resistor, R
ISET
, to set
internal biasing. Use a resistor value of 39kW.
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 com-
munication issues, often intermittent, typically due to
double clocking due to ringing at the SCLK input. Fit
a 1kW to 10kW 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 con-
nections 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
track length from the ISET pin to the R
ISET
resistor as
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
PROCESS: CMOS
Figure 4. Transmission of a16-Bit Write to the 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
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
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MAX7301 4-Wire-Interfaced, 2.5V to 5.5V,
20-Port and 28-Port I/O Expander