Inductor

Curent

1A/

50ms/div

Short triggered

Output

Voltage

2V/div

Inductor

Curent

2A/

50ms/div

Short Released

LIMIT

SC

OUT max

I

I

I

2

13

LM60440, LM60430

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SNVSBN5A – FEBRUARY 2020 – REVISED JUNE 2020

Product Folder Links: LM60440 LM60430

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Copyright © 2020, Texas Instruments Incorporated

Feature Description (continued)

Characteristics table) before the next clock cycle. When this occurs, the valley current limit control skips that

cycle, causing the switching frequency to drop. Further overload causes the switching frequency to continue to

drop, and the inductor ripple current to increase. When the peak of the inductor current reaches the high-side

falls out of regulation. This represents the maximum output current from the converter and is given approximately

by Equation 1.

(1)

If, during current limit, the voltage on the FB input falls below about 0.4 V due to a short circuit, the device enters

ms and then goes through a normal re-start with soft start. If the short-circuit condition remains, the device runs

in current limit for about 20 ms (typical) and then shuts down again. This cycle repeats, as shown in as long as

the short-circuit-condition persists. This mode of operation helps reduce the temperature rise of the device during

a hard short on the output. The output current is greatly reduced during hiccup mode. Once the output short is

removed and the hiccup delay is passed, the output voltage recovers normally as shown in Figure 6.

Figure 5. LM60440 Inductor Current Burst in Short-Circuit

Mode

Figure 6. LM60440 Short-Circuit Transient and Recovery

8.3.4 Undervoltage Lockout and Thermal Shutdown

The LM604x0 incorporates an undervoltage-lockout feature on the output of the internal LDO (at the VCC pin).

When VCC reaches about 3.7 V, the device is ready to receive an EN signal and start up. When VCC falls below

about 3 V, the device shuts down, regardless of EN status. Because the LDO is in dropout during these

transitions, the above values roughly represent the input voltage levels during the transitions.

Thermal shutdown is provided to protect the regulator from excessive junction temperature. When the junction

temperature reaches about 165°C, the device shuts down; re-start occurs when the temperature falls to about

148°C.