LT3669EUFD 데이터 시트보기 (PDF) - Linear Technology

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LT3669EUFD

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

Linear Technology 

LT3669/LT3669-2

APPLICATIONS INFORMATION

b) if TXEN1 is low, WAKE will pull low if CQ1 is forced to

a voltage higher than VL+ – 2.95V for more than 75µs

regardless of the TXD1 level. This relies on the fact

that the external device has a current sink or pull-down

resistor, meaning that the default level for CQ1 when

TXEN1 is low will also be low.

Once WAKE pulls low, it will stay low until a defined

handshaking sequence is applied to pin TXD1 and TXEN1.

This sequence is as follows: TXEN1 must be set low and

TXD1 toggled at least once. Figures 16a and 16b show the

handshaking mechanism after WAKE pulls low for TXEN1

high and low, respectively. The WAKE output returns to

high impedance also after an internal reset event.

Note that driving heavy loads or placing an external pull-

up load to L+ (in case CQ1 is configured in pull-down

mode) may cause WAKE to pull low as well, even if there

is no external device driving the outputs. This could lead

to false wake-up events which need to be handled by the

microcontroller. Real wake-up events are normally fol-

lowed by an exchange of information between the slave

and the external device driving the outputs (master). A

microcontroller can be programmed to react to a limited

number of wake-up events. If no successful communication

is established, then most likely there is no external driving

device, but a heavy load or a pull-up load attached to the

CQ1 output and the microcontroller’s reaction to wake up

events may be adjusted accordingly. For example, driving

a 10µF capacitive load high (TXD1 set low) will force the

CQ1 output below VL+ – 2.95V for more than 75µs (as

shown in Figure 17), thus generating a false wake-up event.

Similarly, configuring CQ1 in pull-down mode (TXD1 high)

with an external 1k pull-up resistor to L+ will generate a

false wake-up event as soon as TXEN1 is set low and the

CQ1 output is pulled high by the external pull-up resistor

for more than 75µs.

VTXEN1

5V/DIV

VTXD1

5V/DIV

VWAKE

5V/DIV

ICQ1

0.2A/DIV

0A

VTXEN1

5V/DIV

VTXD1

5V/DIV

VWAKE

5V/DIV

VILIM = 0V

20µs/DIV

(a)

36692 F16a

VCQ1

10V/DIV

0V

20µs/DIV

(b)

36692 F16b

Figure 16. WAKE Handshaking Sequence When TXEN1 Is (a) High and (b) Low for VL+ = 24V

VTXEN1

5V/DIV

VWAKE

5V/DIV

VCQ1

10V/DIV

0V

VTXD1 = 0V

100µs/DIV

36692 F17

Figure 17. False Wake-Up Event When Driving a 10µF Capacitor

For more information www.linear.com/LT3669

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