L5963DN-EHT datasheet(27/49 Pages) STMICROELECTRONICS

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L5963

Functional Description

Pulse-by-pulse current limiting (OCP)

The current in the upper MOSFET is monitored and if it exceeds the pulse-by-pulse over-

current threshold (ILIM) then the upper MOSFET is turned off. Normal PWM operation

resumes on the next oscillator clock pulse. DC/DCs’ embed leading edge blanking to

prevent falsely triggering the pulse-by-pulse current limit when the upper MOSFET is turned

on. The blanking time is about 100 ns, so the minimum switching on time should be bigger

than 100 ns:

Equation 1

From the above equation, when the input and output voltage are already known, the

switching frequency should be within the range of the above equation, otherwise the OCP

function is not guaranteed. Pulse-by-pulse current limiting is always active. The threshold of

OCP is about 3.5 A for dc-dc1 and 4A for dc-dc2.

Low-Side Over Current Protection (LS OCP)

LS OCP protects DC/DCs by limiting inductor current, when either the load is too high at

high frequency or when the output of the converter is shorted to ground.

The current in the low-side MOSFET is monitored and, if it exceeds the pulse-by-pulse

overcurrent threshold (ILIM), it prevents the turning on of the high-side MOSFET in the

successive switching period.

In high frequency and high load conditions, the inductor current cannot decrease even if HS

OCP is triggered due to the blanking time, which results in the inductor current getting

higher and higher every switching period. If inductor current reaches LS OCP threshold, that

is set to a level higher than HS OCP one, PWM switching is stopped, waiting for the inductor

current to decrease to a lower value. PWM switching will recover as soon as LS OCP is

released.

If high load and high frequency conditions remain, for instance in case of a short circuit

being present on the regulator output, another LS OCP will occur. Upon removal of the short

circuit PWM switching will immediately recover, bringing the regulator back to normal

operation.

Discontinuous Mode Detection (DMD)

In order to save quiescent current when switching regulators are working in light load

condition, L5963 embeds a Discontinuous Mode Detection (DMD) circuit: DMD prevents

inductor current to continuously flow to ground during Toff by turning off LS MOSFET and

leaving PWM in tristate.

Over temperature protection (OTP)

Each DC/DC has its own OTP, which detects the local temperature and shuts down the

regulator when temperature reaches the specified threshold.

Dump protection

If the voltage on VBAT supply exceeds the over-voltage shut-down threshold, DC/DCs are

disabled. Once VBAT returns to working conditions, the output recovers to the normal state.

L5963DN-EHT Datasheet(PDF) 27 Page - STMicroelectronics

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