L6728A datasheet(13/32 Pages) STMICROELECTRONICS

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L6728A

Output voltage setting and protections

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Output voltage setting and protections

L6728A is capable to precisely regulate an output voltage as low as 0.8 V. In fact, the device

comes with a fixed 0.8 V internal reference that guarantee the output regulated voltage to be

within ±1% tolerance over line and temperature variations (excluding output resistor divider

tolerance, when present).

Output voltage higher than 0.8 V can be easily achieved by adding a resistor ROS between

FB pin and ground. Referring to Figure 1, the steady state DC output voltage will be:

where VREF is 0.8 V.

L6728A monitors the voltage at VSEN pin and compares it to internal reference voltage in

order to provide under voltage and overvoltage protections as well as PGOOD signal.

According to the level of VSEN, different actions are performed from the controller:

●

PGOOD

If the voltage monitored through VSEN exits from the PGOOD window limits, the device

de-asserts the PGOOD signal still continuing switching and regulating. PGOOD is

asserted at the end of the soft-start phase.

●

Under voltage protection

If the voltage at VSEN pin drops below UV threshold, the device turns off both HS and

LS MOSFETs, latching the condition. Cycle VCC to recover.

●

Overvoltage protection

If the voltage at VSEN pin rises over OV threshold (1 V typ), overvoltage protection

turns off HS MOSFET and turns on LS MOSFET. The LS MOSFET will be turned off as

soon as VSEN goes below VREF/2 (0.4 V). The condition is latched, cycle VCC to

recover. Notice that, even if the device is latched, the device still controls the LS

MOSFET and can switch it on whenever VSEN rises above 0.4V.

●

Feedback disconnection protection

In order to provide load protection even if VSEN pin is not connected, a 100 nA bias

current is always sourced from this pin. If VSEN pin is not connected, this current will

permanently pull it up causing the device to detect an OV: thus LS will be latched on

preventing output voltage from rising out of control.

OUT

REF

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