Overtemperature Protection

Overview

The overtemperature protection is designed to protect the laser diode from overheating. This feature provides automatic thermal shutdown when the temperature exceeds safe limits.

Configuration Characteristics

Coupled Temperature Settings

The overtemperature shutdown is bound to the operating temperature and cannot be set independently.

Changing the operating temperature will change the shutdown temperature as well.

Temperature Thresholds

The system uses two temperature points:

1. Threshold Temperature - When this temperature is exceeded, the laser is disabled
2. Hysteresis Temperature - The temperature must drop below this value before the laser can be re-enabled

Temperature Relationship

Normal Operation
      ↓
Temperature Rising
      ↓
Threshold Reached ──→ Laser DISABLED
      ↓
Temperature Falling
      ↓
Hysteresis Reached ──→ Laser can be ENABLED

Temperature Tables (NTCAFLEX05103HH)

Temperature Threshold Examples

Operating Temp (°C)	Threshold Temp (°C)	Hysteresis Temp (°C)	RPOT (kΩ)
10	15	6	41.5492
15	20	12	32.9716
20	25	18	26.3520
25	30	23	21.2049
30	35	29	17.1752
35	40	34	13.9995
40	45	39	11.4805
45	50	44	9.4699
50	55	49	7.8555
55	60	54	6.5516
60	65	58	5.4925
65	70	63	4.6279
70	75	67	3.9183
75	80	71	3.3327
80	85	75	2.8476
85	90	79	2.4434
90	95	83	2.1054
95	100	87	1.8213

NTC-Specific Values

The resistor values shown in the table are only valid for the included 10k foil NTC (NTCAFLEX05103HH).

If you want to use another 10k NTC, you need to adapt the values following the instructions in “Settings with Other NTCs”.

Understanding the Temperature Spread

Example: 25°C Operating Temperature

• Operating Temperature: 25°C (target for TEC control)
• Threshold Temperature: 30°C (+5°C above operating)
• Hysteresis Temperature: 23°C (-2°C below operating)

23°C ─────────── Hysteresis (Re-enable point)
                     ↕ 2°C
25°C ─────────── Operating Temperature (Target)
                     ↕ 5°C
30°C ─────────── Threshold (Shutdown)

Temperature Zones

  0°C ═══════════════════════════════════════
       Safe Operation Zone
       (Temperature well below threshold)
  ↓
 23°C ───────────────────────────────────────
       Hysteresis Point
       (Can re-enable laser)
  ↕
 25°C ═══════════════════════════════════════
       Operating Temperature
       (TEC target temperature)
  ↕
 30°C ───────────────────────────────────────
       Threshold Temperature
       (SHUTDOWN - Temp exceeded)
  ↓
 50°C ═══════════════════════════════════════
       Overtemperature State
       (Laser disabled, TEMP LED flashing)

Shutdown Behavior

When Temperature Exceeds Threshold:

1. ⚠️ Temperature reaches threshold
2. ❌ Laser disabled within microseconds
3. 🔴 TEMP LED starts flashing
4. Driver enters failure mode

Recovery Process:

1. 🌡️ Temperature must drop below hysteresis threshold
2. ⏱️ Operating mode determines recovery:
   • ARM Mode: Automatic re-enable after 5-second delay
   • Standard Mode: Manual start signal reset required
3. ✅ Laser can be enabled again

Practical Considerations

Temperature Margin

Design Recommendation

Set the operating temperature at least 5-10°C below the laser diode’s maximum rated temperature to provide adequate safety margin.

Thermal Time Constants

• The NTC responds quickly to temperature changes
• Thermal shutdown occurs within microseconds
• Allow sufficient cooling time before restart
• Consider thermal mass of laser mount

Placement Importance

Critical Placement

The distance between the laser diode, the NTC, and the TEC needs to be chosen as short as possible.

Otherwise, the driver will not be able to keep the temperature stable at the needed value and may oscillate.

Common Operating Temperatures

Application	Typical Operating Temp	Threshold Temp
Room Temperature	25°C	30°C
Cooled Operation	15-20°C	20-25°C
High Power	30-35°C	35-40°C
Precision Wavelength	25°C	30°C

Testing Overtemperature Protection

Functional Test Procedure

1. Set a low threshold temperature (e.g., 25°C)
2. Enable laser operation
3. Allow laser to heat naturally or apply gentle heat
4. Verify shutdown when threshold is reached
5. Verify TEMP LED flashing
6. Allow cooling below hysteresis
7. Verify recovery behavior

Test Safely

Do not allow the laser diode to reach its absolute maximum temperature during testing.

Troubleshooting

Frequent Thermal Shutdowns

Causes:

• Insufficient cooling
• TEC not functioning properly
• Ambient temperature too high
• Thermal contact issues

Solutions:

• Improve heat sinking
• Verify TEC operation
• Reduce ambient temperature
• Check NTC placement and contact

Temperature Oscillation

Causes:

• NTC too far from laser diode
• Poor thermal contact
• Inadequate thermal mass

Solutions:

• Reposition NTC closer to laser
• Improve thermal coupling
• Add thermal mass if needed