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7.3.12 Thermal Shutdown

Thermal shutdown limits total power dissipation by turning off the internal switches when the device junction

temperature exceeds 150°C (typical). After thermal shutdown occurs, hysteresis prevents the device from

switching until the junction temperature drops to approximately 135°C. When the junction temperature falls

below 135°C, the LM76005 attempts to soft start.

7.4 Device Functional Modes

7.4.1 Shutdown Mode

The EN pin provides electrical on/off control for the LM76005. When the EN pin voltage is below 0.3 V (typical),

both the regulator and the internal LDO have no output voltages, and the device is in shutdown mode. In

shutdown mode the quiescent current drops to typically 1.2 µA. The LM76005 also employs UVLO protection. If

VCC voltage is below the UVLO level, the output of the regulator is turned off.

7.4.2 Standby Mode

The internal LDO has a lower EN threshold than the regulator. When the EN pin voltage is above 1.2 V

(maximum) and below the precision enable threshold for the output voltage, the internal LDO regulates the VCC

voltage at 3.29 V typically. The precision enable circuitry is ON once VCC is above the UVLO. The internal

MOSFETs remain in tri-state unless the voltage on EN pin goes above the precision enable threshold. The

LM76005 also employs UVLO protection. If VCC voltage is below the UVLO level, the output of the regulator is

turned off.

7.4.3 Active Mode

The LM76005 is in active mode when the EN pin and UVLO high threshold levels are satisfied. The simplest way

to enable the operation of the LM76005 is to connect the EN pin to VIN, which allows self start-up of the

LM76005 when the input voltage is in the operation range: 3.5 V to 60 V. See Section 7.3.4 for details on setting

these operating levels.

In active mode, depending on the load current, the LM76005 will be in one of five sub modes:

1. CCM with fixed switching frequency with load between half of IMINPK to full load

2. DCM when the load current is lower than half of the inductor current ripple

3. Light load mode where the device uses pulse frequency modulation (PFM) and lowers the switching

frequency at load under half of IPEAK_MIN to improve efficiency

4. Foldback mode when switching frequency is reduced to maintain output regulation with supply voltages that

cause the minimum tON or tOFF to be exceeded

5. Forced-pulse-width modulation (FPWM) is similar to CCM with fixed switching frequency, but extends the

fixed frequency range of operation from full to no load.

7.4.4 CCM Mode

CCM operation is employed in the LM76005 when the load current is higher than ½ of the peak-to-peak inductor

current. If the load current is decreased, the device enters DCM mode. In CCM operation, the frequency of

operation is constant and fixed unless the minimum tON or tOFF are exceeded which causes the part to enter

foldback mode (refer to Section 7.3.5 for details). In these cases, PWM is still maintained, but the frequency of

operation is folded back (reduced) to maintain proper regulation.

7.4.5 DCM Mode

DCM operation is employed in the LM76005 when the load current is lower than ½ of the peak-to-peak inductor

current. In DCM operation (also known as diode emulation mode), the LS FET is turned off when the inductor

current drops below 0 A to keep operation as efficient as possible by reducing switching losses and preventing

negative current conduction. In PWM operation, the frequency of operation is constant and fixed unless the load

current is reduced below IPEAK_MIN, which causes the part to enter light load mode, or if the minimum tON or tOFF

are exceeded, which cause the device to enter foldback mode.

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LM76005

SNVSBK5A – FEBRUARY 2020 – REVISED JULY 2020

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