L6732_08 datasheet(18/37 Pages) STMICROELECTRONICS

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Device description

L6732

18/37

Equation 4

During soft-start the OC acts in constant current mode: a current control loop limits the value

of the error amplifier output (comp), in order to avoid its saturation and thus recover faster

when the output returns in regulation. Figure 12. shows the behavior of the device during an

over current condition that persists also in the soft-start phase.

L6732 provides under voltage (UV) protection: when the voltage on FB pin falls below 80 %

of the reference, the IC will enter HICCUP mode.

Feedback disconnection is also provided by sourcing a 100 nA current from FB pin. if FB

results being floating, the IC will detect and OV so latching its condition with Low Side

MOSFET firmly ON

5.9

Thermal shutdown

When the junction temperature reaches 150 °C ±10 °C the device enters in thermal

shutdown. Both MOSFETs are turned off and the soft-start capacitor is rapidly discharged

with an internal switch. The device doesn't restart until the junction temperature goes down

to 120 °C and, in any case, until the voltage at the soft-start pin reaches 500 mV.

5.10

Synchronization

The presence of many converters on the same board can generate beating frequency noise.

To avoid this it is important to make them operate at the same switching frequency.

Moreover, a phase shift between different modules helps to minimize the RMS current on

the common input capacitors. Figure 13 and Figure 14 shows the results of two modules in

synchronization. Two or more devices can be synchronized simply connecting together the

SYNCH pins. The device with the higher switching frequency will be the Master while the

Figure 12.

Constant current and hiccup mode during an OCP

MIN

VALLEY

MAX

Vout

Vin

⋅

−

VSS

VCOMP

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