13

LTC1482

The supply current does not drop below 20

µA immedi-

ately. DE and DI/SHDN must be low for a least 600ns

ping to the 20

µA level. Taking either DE or DI/SHDN high

will wake the LTC1482 within 5

µs.

GND through external resistors to force the line to a high

or low state when all connected drivers are disabled. In

shutdown, the supply current will be higher than 10

µA due

to the additional current drawn through the external pull-

up and the 22k input resistance of the LTC1482.

ESD Protection

The ESD performance of the LTC1482 A and B pins is

characterized to meet

±15kV using the Human Body

Model (100pF, 1.5k

Ω), IEC-1000-4-2 Level 4 (±8kV)

contact mode and IEC-1000-4-2 Level 3 (

±8kV) air dis-

charge mode. This means that external voltage suppres-

sors are not required in many applications, when com-

pared with parts that are only protected to

±2kV. Pins

other than the A and B pins are protected to

±3kV typical

per the Human Body Model.

When powered up, the LTC1482 does not latch up or

sustain damage when the A and B pins are tested using any

of the three conditions listed. The data during the ESD

event may be corrupted, but after the event the LTC1482

continues to operate normally. The additional ESD protec-

tion at the A and B pins is important in applications where

these pins are exposed to the external world via connec-

tions to sockets.

Fault Protection

When shorted to – 7V or 10V at room temperature, the

short-circuit current in the driver pins is limited by internal

protection circuitry to 250mA. Over the industrial tem-

perature range, the absolute maximum positive voltage at

any driver pin should be limited to 10V to avoid damage to

the part. At higher ambient temperatures, the rise in die

temperature, due to the short-circuit current, may trip the

thermal shutdown circuit. This circuit protects the part

against prolonged shorts at the driver outputs. If a driver

will be limited to 250mA. If the die temperature rises above

150

°C, the thermal shutdown circuit three-states the

driver outputs to open the current path. When the die cools

down to about 130

°C, the driver outputs are taken out of

three-state. If the short persists, the part will heat again

and the cycle will repeat. This thermal oscillation occurs at

about 10Hz and protects the part from excessive power

dissipation. The average fault current drops as the driver

cycles between active and three-state. When the short is

removed, the part will return to normal operation.

When the driver is disabled, the receiver inputs can

withstand the entire – 7V to 12V RS485 common mode

range without damage.