For information on ESD protection please see: HERE

TTL Output Components

Each TTL output includes the following components:

	Protection Diode (Large) – Leshan Radio – LBAS21HT1G
	Protection Diode (Small / TVS) – NXP – PESD5Z5.0
	Screw Terminal Output

TTL Output Testing

TTL Output Protection Overview

Each TTL output on MASSO is protected by two diodes:

• The diodes are installed as a pair for each output.

• In most cases, the diode pair is located directly above the screw terminal.

• In some cases, the diodes may be slightly offset to one side.

• The diode order may vary between outputs.

Observing the repeating layout pattern on the board will help identify the correct diode pair for each output.

	Each output on MASSO is made up of 2 protection diodes - Leshan Radio - LBAS21HT1G
	This is the larger of the 2 diodes on the output.
	The output for the relevant diode.
	This is the smaller of the diode pair - NXP - PESD5Z5.0

This diode can be tested using the Diode Test function on a standard digital multimeter as follows:

1. Turn MASSO OFF and leave it off for all testing.

2. Disconnect all wiring from the output under test.

3. Set the multimeter to Diode Test mode.

4. Connect the black meter lead to the output under test (Point C in the diagram above).

5. Connect the red meter lead to the far side of the diode (Point B in the diagram above).

    • Expected reading: ~0.6 V nominal

6. Reverse the meter leads:

    • Connect the red meter lead to the output under test (Point C).

    • Connect the black meter lead to the far side of the diode (Point B).

    • Expected result: Open circuit.

Some meters may display OL, 1, or -1 to indicate an open circuit. This is the same reading shown when the meter probes are not connected while in Diode Test mode.

NXP – PESD5Z5.0

This is the smaller diode in the protection pair. It can be tested using the Diode Test function on a digital multimeter as follows:

1. Turn MASSO OFF and leave it off for all testing.

2. Disconnect all wiring from the output under test.

3. Set the multimeter to Diode Test mode.

Test 1

• Connect the black meter lead to MASSO GND.

• Connect the red meter lead to the output under test.

• Expected result: Open circuit.

Some meters may display OL, 1, or ?1 to indicate an open circuit. This is the same reading shown when the meter probes are not connected while in Diode Test mode.

Test 2

• Connect the red meter lead to MASSO GND.

• Connect the black meter lead to the output under test.

• Expected reading: ~0.77 V nominal.

Fault Condition

If this diode is found to be short circuit, it can be removed from the board.
If this is the only fault, the output should resume normal operation.

The diode is not required for normal operation and may be replaced or left out.
Leaving it out will remove ESD protection for that output.