L6726A_07 STMICROELECTRONICS [STMicroelectronics], L6726A_07 Datasheet - Page 13

• Manufacturer Part Number: L6726A_07
• Description: Single phase PWM controller
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

L6726A
7
7.1
7.1.1
7.2
Protections
Over current protection
The over current feature protects the converter from a shorted output or overload, by
sensing the output current information across the Low Side MOSFET drain-source on-
resistance, R
the use of expensive and space-consuming sense resistors.
The low side R
node when LS MOSFET is turned on with the programmed OCP threshold voltage,
internally held. If the monitored voltage drop (GND to PHASE) exceeds this threshold, an
Over Current Event is detected. If two Over Current Events are detected in two consecutive
switching cycles, the protection will be triggered and the device will turn off both LS and HS
MOSFETs in a latched condition.
To recover from Over Current Protection triggered, VCC power supply must be cycled.
Over current threshold setting
L6726A allows to easily program an Over Current Threshold ranging from 50mV to 550mV,
simply by adding a resistor (R
During a short time following VCC rising over UVLO threshold, an internal 10µA current
(I
voltage drop will be sampled and internally held by the device as Over Current Threshold.
The OC setting procedure overall time length ranges from 5.5ms to 6.5ms, proportionally to
the threshold being set.
Connecting a R
R
If the voltage drop across R
inrush current and noise. This can result in undesired OCP triggering. In this case, consider
increasing R
In case R
value: an internal safety clamp on LGATE is triggered as soon as LGATE voltage reaches
700mV (typ), enabling the 400mV default threshold and suddenly ending OC setting phase.
See
waveforms.
Feedback disconnection protection
In order to provide load protection even if FB pin is not connected, a 100nA bias current is
always sourced from this pin. If FB pin is not connected, bias current will permanently pull
up FB: this forces COMP pin low, avoiding output voltage rising to dangerous levels.
OCSET
OCSET
Figure 6
) is sourced from LGATE pin, determining a voltage drop across R
I
values range from 5kΩ to 55kΩ.
OCth
OCSET
OCSET
dsON
for OC threshold setting procedure timings picture and oscilloscope sample
dsON
=
OCSET
is not connected, the device switches the OCP threshold to a 400mV default
. This method reduces cost and enhances converter efficiency by avoiding
I
------------------------------------------- -
OCSET
value.
current sense is implemented by comparing the voltage at the PHASE
resistor between LGATE and GND, the programmed threshold will be:
R
dsON
⋅
OCSET
R
OCSET
OCSET
is too low, the system will be very sensitive to start-up
) between LGATE and GND.
OCSET
Protections
. This
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