L6738 datasheet(16/32 Pages) STMICROELECTRONICS

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Output voltage setting and protections

L6738

16/32

Doc ID 18133 Rev 1

Table 6.

L6738 Protection at a glance.

6.1

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:

The L6738 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.

When overcurrent protection is triggered, the device turns off both LS and HS MOSFETs in

a latched condition.

To recover from an overcurrent protection triggered condition, VCC power supply or EN

must be cycled.

For proper current reading, the CSN pin must be filtered by 100 nF (Typ.) MLCC to GND.

L6738

Comments

Overvoltage

(OV)

VSEN = +25 % 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 +/-25 % of Vref.

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

Overcurrent (OC)

Current Monitor across Inductor DCR.

Action: 1st Threshold (20 mV): IC latch after 7 consecutive constant current

events.

DCR

-------------

CSP-CSN

DCR

OUT

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