General Description

The MAX4820/MAX4821 8-channel relay drivers offer built-in kickback protection and drive +3.3V/+5V nonlatching or dual-coil-latching relays. These devices are especially useful when driving +3V relays. Each independent open-drain output features a 2Ω on-resistance and is guaranteed to sink 70mA (min) of load current. Both devices consume less than 50µA (max) quiescent current and have 1µA output off-leakage current.
The MAX4820 features an SPI™-/QSPI™-/MICROWIRE™compatible serial interface. Input data is shifted into an 8bit shift register and latched to the outputs when CS transitions from low to high. Each data bit in the shift register corresponds to a specific output, allowing independent control of all outputs.
The MAX4821 features a 4-bit (A0, A1, A2, LVL) parallel-input interface. The first three bits (A0, A1, A2) determine the output address, and the fourth bit (LVL) determines whether the selected output is switched on or off. Data is latched to the outputs when CS transitions from low to high.
Both devices feature separate set and reset functions that allow the user to turn on or turn off all outputs simultaneously with a single control line. Built-in hysteresis (Schmidt trigger) on all digital inputs allows this device to be used with slow rising and falling signals, such as those from optocouplers or RC power-up initialization circuits. The MAX4820/MAX4821 are available in 20-pin TSSOP and space-saving 20-pin Thin QFN packages.

 

Applications

Central Office
ATE
DSL, ADSL Line Cards
Industrial Equipment
E1/T1 Redundancy

 

Features

♦ 8 Independent Output Channels
♦ Built-In Inductive Kickback Protection
♦ Drive +3V and +5V Relays
♦ Guaranteed 70mA (min) Coil Drive Current
♦ SETFunction to Turn On All Outputs Simultaneously
♦ RESETFunction to Turn Off All Outputs Simultaneously
♦ SPI-/QSPI-/MICROWIRE-Compatible Serial Interface (MAX4820)
♦ Serial Digital Output for Daisy Chaining (MAX4820)
♦ Parallel Interface (MAX4821)
♦ Low 50µA (max) Quiescent Supply Current
♦ Space-Saving 20-Pin Thin QFN Package

 

Detailed Description

The MAX4820/MAX4821 8-channel relay drivers offer built-in kickback protection and drive +3.3V/+5V nonlatching or dual-coil-latching relays. These devices are especially useful when driving +3V relays. Each independent open-drain output features a 2Ωon-resistance and is guaranteed to sink 70mA (min) load current. Both devices consume less than 50µA (max) quiescent current and feature 1µA (min) output off-leakage current.
The MAX4820 features an SPI/QSPI/MICROWIRE compatible serial interface. Input data is shifted into an 8-bit shift register and latched to the outputs when CS transitions from low to high. Each data bit in the shift register corresponds to a specific output, allowing independent control of all outputs.
The MAX4821 features a 4-bit (A0, A1, A2, LVL) parallel input interface. The three bits (A0, A1, A2) determine the output address, and LVL determines whether the selected output is switched on or off. Data is latched to the outputs when CS transitions from low to high.
Both devices feature separate set and reset functions that allow the user to turn on or turn off all outputs simultaneously with a single control line. Built-in hysteresis (Schmidt trigger) on all digital inputs allows this device to be used with slow rising and falling signals, such as those from optocouplers or RC power-up initialization circuits. The MAX4820/MAX4821 are available in 20-pin TSSOP and space-saving 20-pin Thin QFN packages.

 

Applications Information

The MAX4820 features a digital output, DOUT, that provides a simple way to daisy chain multiple devices. This feature allows the user to drive large banks of relays using only a single serial interface. To daisy chain multiple devices, connect all CS pins together, and connect the DOUT of one device to the DIN of another device. During operation, a stream of serial data is shifted through all the MAX4820s in series. When CS goes high, all outputs update simultaneously.
The MAX4820 can also be used in a slave configuration that allows the user to address individual devices. Connect all the DIN pins together, and use the CS input to address one device at a time. Drive CS low to select a slave and input the data into the shift register. Drive CS high to latch the data and turn on the appropriate outputs. Typically, in this configuration only one slave is addressed at a time.