Output voltage setting and protections

L6739

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DocID026384 Rev 1

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Overtemperature protection (OT)

To avoid any damage to the device when reaching high temperature, when the junction

temperature reaches 140 °C, the device turns off both MOSFETs. If the junction

temperature drops below 100 °C, the device restarts with a new soft-start sequence.

Protections are active also during soft-start (See Section 5).

For proper operations, VCC needs to be at least 1.5 V higher than the programmed output

voltage.

Table 7. L6739 Protection at a glance

Overcurrent

The overcurrent function protects the converter from a shorted output or overload, by

sensing the output current information across the inductor DCR. This method reduces cost

and enhances converter efficiency by avoiding the use of expensive and space consuming

sense resistors.

The inductor DCR current sense is implemented by comparing and monitoring the

difference between the CSP and CSN pins. If the monitored voltage is bigger than the

internal thresholds, an overcurrent event is detected.

DCR current sensing requires time constant matching between the inductor and the reading

network:

Equation 3

The L6739 device monitors the voltage between CSP and CSN, when this voltage exceeds

the OC threshold, an overcurrent is detected. The IC works in constant current mode,

turning on the low-side MOSFET immediately while the OC persists and, in any case, until

the next clock cycle. After seven consecutive OC events, overcurrent protection is triggered

and the IC latches.

L6739

Comments

Overvoltage (OV)

VSEN = +15% above reference.

Action: IC latch; LS = ON until VSEN = 50% of Vref; PGOOD = GND.

Action (EN = 0): IC latch; LS = ON; reset by EN rising edge (PreOVP).

Undervoltage (UV)

VSEN = -25% below reference.

Action: IC latch; HiZ; PGOOD = GND.

Action (SS): SS reset (VIN detection).

PGOOD

PGOOD is set to zero whenever VSEN falls outside the +15% / -25% of Vref.

Action: PGOOD transition coincides with OV/UV protection set.

Overcurrent (OC)

Current monitor across inductor DCR.

Overtemperature (OT)

drops to 100 °C.

L

DCR

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RC

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