LT3669 View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LT3669

IO-Link Transceiver with Integrated Step-Down Regulator and LDO

Linear Technology 

LT3669/LT3669-2

OPERATION

The LT3669/LT3669-2 is a complete industrial slave in-

terface, including a switching voltage regulator, an LDO,

a data transceiver with wake-up detect, a second driver

and a power-on reset circuit. This set of features allows a

typical industrial slave device to be built with just a sensor

or actuator, the LT3669 and a microcontroller to provide

the digital conversion and signal processing.

The line transceiver circuitry includes a receiver that

monitors the CQ1 line for data and sets the output RXD1

accordingly, and a driver that drives the CQ1 line controlled

by inputs TXEN1 and TXD1. Additionally, a second driver

controlled by inputs TXEN2 and TXD2 drives the Q2 line.

Both drivers share a common user-adjustable sink/source

current limit (up to ±330mA, typical) by connecting a

resistor to AGND at the ILIM pin. The drivers feature four

modes of operation: push-pull, pull-up only, pull-down

only, as well as a high impedance mode.

The CQ1 driver also includes a built-in wake-up pulse detect

circuitry that senses when the output CQ1 is forced oppo-

site of its driven value for a minimum of 75µs. When this

wake-up signal is detected, the WAKE output pulls low to

alert the host system that a data transmission is expected.

The WAKE output returns to high impedance again when

the host acknowledges the wake-up request by executing

the handshake sequence of setting the TXEN1 input low

(receive mode) and toggling the TXD1 input, or under an

internal reset event. Both drivers support COM1 (4.8kb/s),

COM2 (38.4kb/s) and COM3 (230.4kb/s) communication

modes. The receiver supports logic swings on the CQ1 pin

in accordance with the IO-Link communication standard.

Tying CQ1 and Q2 pins together, as well as pins TXD1

and TXD2 and TXEN1 and TXEN2, increases the overall

current capability.

The drivers are equipped with a pulsing scheme that

allows them to safely drive heavy capacitive loads and

incandescent bulbs. Outputs SC1 and SC2 will flag if CQ1

or Q2 outputs are forced within 2.95V of the opposite rail

they are trying to reach. A blanking time prevents false

alarms during normal output transitions.

The switching regulator of the LT3669 integrates the catch

diode and provides a typical conversion efficiency greater

than 60% at its maximum load current of 100mA with a

standard industrial supply voltage of 24V at the L+ pin and

5V output. The LT3669-2 requires an external catch diode

and provides a typical efficiency greater than 75% at its

maximum load current of 300mA. Compared to a linear

regulator, this drastically minimizes power dissipation in

the slave device, and minimizes current draw on the in-

dustrial 24V line. The regulator features an on-chip power

switch and built-in compensation, soft-start, current limit,

and other support circuits required to maintain a robust,

well regulated output voltage. The switching frequency is

adjustable with a resistor to AGND at the RT pin to allow

the circuit to be optimized either for space or efficiency,

and the frequency can be synchronized to an external clock

to minimize interference with signal processing circuits.

A precision UVLO circuit allows the system to shut down

at a user-selectable voltage.

An on-chip LDO linear regulator provides a second out-

put voltage at up to 150mA. The LDO has current limit

with foldback for robust performance in fault conditions.

The reset output (RST) goes low at start-up and remains

low until each regulated output is within 7.3% of its final

value and the user-adjustable reset timer has expired. This

ensures that the supply voltages are in regulation and

stable before the signal processing circuitry is allowed

to start. The reset timer is programmed with an external

capacitor to AGND at the CPOR pin.

The LT3669 tolerates transient swings to +60V from

GND and –60V from L+ on the CQ1 and Q2 pins without

damage.

Logic inputs TXD1, TXD2, TXEN1, TXEN2 and SR feature

900mV thresholds and logic input SYNC a 1.5V threshold

to interface easily with low voltage logic. All logic outputs

(RXD1, RST, SC1, SC2 and WAKE) are open collector.

3669fa

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For more information www.linear.com/LT3669

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