L6712A L6712
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usual way until another OCP event is detected.
This means that the average current delivered can slightly increase also in Over Current condition since
the current ripple increases. In fact, the ON time increases due to the OFF time rise because of the current
has to reach the IOCPx bottom. The worst-case condition is when the ON time reaches its maximum value.
When this happens, the device works in Constant Current and the output voltage decrease as the load
increase. Crossing the UVP threshold causes the device to reset.
It can be observed that the peak current (Ipeak) is greater than the IOCPx but it can be determined as follow:
Where VoutMIN is the minimum output voltage (VID-40% as follow).
The device works in Constant-Current, and the output voltage decreases as the load increase, until the
output voltage reaches the under-voltage threshold (VoutMIN).
The maximum average current during the Constant-Current behavior results:
In this particular situation, the switching frequency results reduced. The ON time is the maximum allowed
(TonMAX) while the OFF time depends on the application:
Figure 10. Constant Current operation
Over current is set anyway when IINFOx reaches 35A (IFB=70A). The full load value is only a convention
to work with convenient values for IFB. Since the OCP intervention threshold is fixed, to modify the per-
centage with respect to the load value, it can be simply considered that, for example, to have on OCP
threshold of 200%, this will correspond to IINFOx = 35A (IFB = 70A). The full load current will then corre-
spond to IINFOx = 17.5A (IFB = 35A).
Once the UVP threshold has been intercepted, the device resets with all power mosfets turned OFF. An-
other soft start is then performed allowing the device to recover from OCP once the over load cause has
been removed.
Crossing the UVP threshold causes the device to reset: all mosfets are turned off and a new soft start is
I
peak
I
OCPx
V
IN
Vout
min
–
L
-------------------------------------- Ton
MAX
I
OCPx
V
IN
Vout
MIN
–
L
--------------------------------------- 0.40 T
+
=
+
=
I
MAX,TOT
2I
MAX
2I
OCPx
Ipeak
I
OCPx
–
2
--------------------------------------
+
=
=
T
OFF
L
Ipeak
I
OCPx
–
V
OUt
--------------------------------------
f
1
T
ONmax
T
OFF
+
------------------------------------------
=
=
a) Maximum current for each phase
b) Output Characteristic
TonMAX
IOCPx
Ipeak
IMAX
Vout
Iout
(IDROOP=50A)
2IOCPx (IDROOP=70A)
IMAX,TOT
UVP
Droop effect