Datasheet

MAX14820
IO-Link Device Transceiver
27Maxim Integrated
Applications Information
UART Interfacing
The logic levels of the microcontroller interface I/Os
(TXC, TXQ, TXEN, and RX) are defined by V
L
.
The device can be interfaced to microcontrollers where the
on-board UART TX output cannot be programmed as a logic
output (GPO). In this case, connect the TX output of the UART
to the TXC input for IO-Link communication and connect a
separate GPO output on the microcontroller to TXQ for stan-
dard IO (SIO) mode operation (Figure 12). As the TXQ and
TXC inputs are internally logically ANDed, the unused input
(TXC or TXQ) must be held high while the other is in operation.
Transient Protection
Inductive load switching, surges, and bursts create high
transient voltages. C/Q, DO, and DI should be protect-
ed against high overvoltage and undervoltage transients.
Positive voltage transients on C/Q, DO, and DI must be lim-
ited to +55V relative to GND and negative voltage transients
must be limited to -55V (relative to V
CC
) on DO and C/Q and
to -55V (relative to GND) on DI. Figure 12 shows suitable
protection using TVS diodes to meet both the IEC 61000-
4-2 ESD and IEC 61000-4-5 surge testing. Other protection
schemes may also be suitable.
The device has to be protected against transients that
occur during hot-plugging of the L+ sensor supply (VCC
input). This is achieved by placing a 10W resistor with
1µF capacitor before LDOIN and connecting an RC
between the sensor supply input and the VCC pin, as
shown in Figure 13. The RC time constant of the filter on
VCC should be larger or equal to 0.8µs. In case that VL is
supplied by V5 and the bypass capacitor on V5 is 100nF,
the 10W resistor in series with LDOIN is not needed.
External Powering
The MAX14820 is powered by V
CC
and V
5
. V
L
is a reference
voltage input to set the logic levels of the microcontroller
interface. The logic and SPI interface are operational when
V
5
and V
L
are present even if V
CC
is not present.
The V
P
output provides a reverse-polarity-protected voltage
one diode drop below V
CC
and can be used for supplying
external circuitry, like power supplies. The current drawn from
V
P
cannot exceed 50mA. Be aware that capacitance on V
P
can cause transient currents at power-up equal to C x dV
CC
/
dt. In order to reduce power dissipated in the device, an
reverse protection diode can be used to power the external
circuitry, instead of using VP, as shown in Figure 15.
V
5
is typically powered by the internal 5V regulator, but
can alternatively be powered by an external 5V regula-
tor. When powering V
5
externally, connect LDOIN to V
5
.
(Figure 15). This configuration disables operation of the
internal 5V regulator and reduces power consumption.
When an external 5V regulator is used to power V5, the
V5 bypass capacitance is determined by that regulator,
and is not limited to 100nF.
Figure 12. UART Interface
Figure 13. MAX14820 Operating Circuit with TVS Protection
MICROCONTROLLER
TXQGPO
TXCTX
TXENRTS
RXRX
MAX14820
MAX14820
0.8Ω
1μF
1μF
V
CC
LDOIN
DO
1/2
SDC36C
1/2
SDC36C
GND
C/Q
1/2
SDC36C
SDC36C
DI
V
P
10Ω