Device description

ALED6001

20/26

DocID026965 Rev 2

7.4

Device protections

7.4.1

Linear regulators undervoltage lockout

Both the 5 V and 3.3 V linear regulators of the ALED6001 are equipped with an

undervoltage lockout (UVLO) protection. The UVLO protections avoid improper device

operation in case at least one of the two outputs (VDR and LDO3) is below the allowed

level. In particular, the ALED6001 performs the soft-start sequence only after both VDR and

LDO3 cross their respective upper UVLO threshold.

7.4.2

Power switch overcurrent

The current flowing through the external Power MOSFET is monitored, cycle-by-cycle, by

sensing the voltage across the shunt resistor in series with its source. If the voltage drop

exceeds the overcurrent protection (OCP) level, the ongoing switching cycle is suddenly

terminated (cycle-by-cycle Power MOSFET OCP). Normal operation is automatically

resumed once the root cause has been removed. The XFAULT pin is not affected by OCP.

As explained in Section 7.2 on page 12 the slope compensation is added by injecting

a sawtooth current at the CSNS pin. As a consequence, the OCP threshold depends on

both the slope compensation amount and the boost converter's operating point:

Equation 6

7.4.3

Output overvoltage and OVFB pin disconnection

The output overvoltage fault detection is achieved by comparing the voltage at the OVFB

pin with an internal threshold. Because of this fault can potentially damage both the device

and the external components, a latched turn off condition is triggered once this event has

been detected. A resistor divider connected to the output of the boost converter sets the

desired OVP threshold.

The OVFB is internally pulled-up in order to protect the device against an OVFB pin

disconnection fault: if the pin is left floating, the OVP is suddenly triggered regardless of the

designing an OVP output divider involving high resistance values. Equation 7 allows setting

whose central tap is connected to the OVFB pin of the ALED6001):

Equation 7

Once the OVP faulty condition is detected, the ALED6001 device suddenly stops switching.

Both GATE and PWMO are forced low and the XFAULT pin is lowered. The condition is

latched and normal operation is resumed by toggling the PWMI pin (PWMI has to be low for

more than 10 ms) after the root cause has been removed.

I

MOS OCP

,

V

CSNS OCP

,

DI

SL

R

SLOPE

•

•

–

R

SNS

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

=

V

OUT OVP

,

R

OVPH

R

OVPL

+

R

OVPL

,

R

OVPL

I

OVFB PU

,

•

–

=