l6712a STMicroelectronics, l6712a Datasheet - Page 16

• Manufacturer Part Number: l6712a
• Description: Two-phase Interleaved Dc/dc Controller
• Manufacturer: STMicroelectronics

L6712A L6712
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Figure 9. UVP Protection & Hiccup Mode.
SOFT START AND INHIBIT
At start-up a ramp is generated increasing the loop reference from 0V to the final value programmed by
VID in 2048 clock periods as shown in figure 10.
Once the soft start begins, the reference is increased: upper and lower Mosfets begin to switch and the
output voltage starts to increase with closed loop regulation. At the end of the digital soft start, the Power
Good comparator is enabled and the PGOOD signal is then driven high (See fig. 10).
The Under Voltage comparator is enabled when the increasing reference voltage reaches 0.6V while OVP
comparator is always active with a threshold equal to the +15%_min of the final reference.
The Soft-Start will not take place, if both VCC and VCCDR pins are not above their own turn-on thresholds.
During normal operation, if any under-voltage is detected on one of the two supplies the device shuts
down. Forcing the OSC/INH pin to a voltage lower than 0.5V (Typ.) disables the device: all the power mos-
fets and protections are turned off until the condition is removed.
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is finished (2048 clock cycles after start-up). During Soft-Start this pin is forced low.
UVP. If the output voltage monitored by VSEN drops below the 60% of the reference voltage for more
than one clock period, the device turns off all mosfets and resets restarting operations with a new soft-
start phase (hiccup mode, see figure 9).
OVP. Enabled once VCC crosses the turn-ON threshold: when the voltage monitored by VSEN reaches
115% (min) of the programmed voltage (or the external reference) the controller permanently switches
on both the low-side mosfets and switches off both the high-side mosfets in order to protect the load.
The OSC/ FAULT pin is driven high (5V) and power supply (VCC) turn off and on is required to restart
operations.
Both Over Voltage and Under Voltage are active also during soft start (Under Voltage after than the
reference voltage reaches 0.6V). The reference used in this case to determine the UV thresholds is the
increasing voltage driven by the 2048 soft start digital counter while the reference used for the OV
threshold is the final reference programmed by the VID pins or available on the REF_IN/OUT pin.
CH1=PGOOD; CH2=Vout; CH3=REF_OUT; CH4=Iout