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MAX14821

IO-Link Device Transceiver

Maxim Integrated 

MAX14821

IO-Link Device Transceiver

DO Fault Detection

The device registers a DoFault event when a short circuit

is present at the DO output for 440Fs. A short condition

exists when the load current on the DO driver exceeds

the 135mA (typ) DO current limit. When a short-circuit

condition is detected, the DO driver enters autoretry

mode. In autoretry mode the device periodically checks

whether the error is still present. Autoretry attempts last

for 440µs (typ) and occur every 26ms (typ). When a

DoFault error is detected, the DoFault and DoFaultInt bits

are set, IRQ asserts, and the driver is turned off 440µs

(typ) after the start of the DO faults.

Reverse-Polarity Protection

The device is protected against reverse-polarity connec-

tions on VCC, C/Q, DO, DI, and GND. Any combination

of these pins can be connected to DC voltages up to

40V (max). A short to 40V results in a current flow of less

than 500FA.

Ensure that the maximum voltage between any of these

pins does not exceed 40V.

5V and 3.3V Linear Regulators

The device includes two internal regulators to generate 5V

(V5) and 3.3V (LDO33). LDO5 is specified for 10mA total

external load current (i.e., LDO33 + V5) when bypassed

with a 0.1µF capacitor to ground. Add the compensation

network shown in Figure 7 to draw up to 30mA of total

external load current from the 5V LDO. LDO33 is speci-

fied at 20mA. The input of V5, LDOIN, can be powered

from VP, the protected 24V supply output, or to another

voltage in the 7V to 36V range.

If the external circuits that are powered by the linear regulators

require an input bypass capacitance larger than 100nF

for 5V or 1µF for 3.3V, a compensation network must be

added on V5 and/or LDO33. The compensation network

consists of a 10W series resistor and a capacitor equal

to the value required by the external circuit, as shown

in Figure 8. The capacitors C33* and C5* in Figure 8

represent the capacitance required by the external

circuits. Figure 8 does not show any protection diodes

for simplicity.

When the internal 5V LDO is not used, V5 becomes the

supply input for the internal analog and digital functions and

thus has to be supplied externally so that the MAX14820

operates normally. The 5V LDO can be disabled by

connecting LDOIN to V5. Apply an external voltage of

4.75V to 5.25V to V5 when the LDO is disabled.

V5

MAX14821

LDO33

VL

0.1µF

5V

10Ω

1µF

3.3V

1µF

Figure 7. V5 Compensation Network

V5

MAX14821

LDO33

10W

0.1µF

10W

1µF

5V

C5

3.3V

C33

Figure 8. Larger Bypass Capacitance for Powering External

Circuits

Use the LDO33Dis bit in the Mode register to disable

LDO33. See the Mode Register [R1, R0] = [1,1] section

for more information. V5 and LDO33 are not protected

against short circuits.

Power-Up

The C/Q and DO driver outputs and the UV output are

high impedance when VCC, V5, VL, and/or LDO33 voltages

are below their respective undervoltage thresholds during

power-up. UV goes low and the drivers are enabled when

all these voltages exceed their respective undervoltage-

lockout thresholds.

The drivers are automatically disabled if VCC, V5, or VL

falls below its UVLO threshold.

Undervoltage Detection

The device monitors VCC, V5, VL, and optionally LDO33

for undervoltage conditions. UV is high impedance when

any monitored voltage falls below its UVLO threshold.

VCC, V5, and VL undervoltage detection cannot be disabled.

When VCC falls below the VCCUVLO threshold, the UV24 and

UV24Int bits are set, UV asserts high, and IRQ asserts low.

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