L6714 STMicroelectronics, L6714 Datasheet - Page 51

• Manufacturer Part Number: L6714
• Description: IC CTRLR 4PH W/DRIVERS 64-TQFP
• Manufacturer: STMicroelectronics

Specifications of L6714

• Applications: Controller, Intel VR10, VR11, AMD CPU
• Voltage - Input: 12V
• Number Of Outputs: 4
• Voltage - Output: 0.3 ~ 1.6 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 64-TQFP Exposed Pad, 64-eTQFP, 64-HTQFP, 64-VQFP
• Mounting Style: SMD/SMT
• Case: QFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

L6714
18.1
Low side MOSFET sense over current
The device detects an Over Current condition for each phase when the current information
I
keeps the relative LS MOSFET on, also skipping clock cycles, until the threshold is crossed
back and I
the LS MOSFET is turned off and the HS is turned on with a duty cycle driven by the PWM
comparator.
Keeping the LS on, skipping clock cycles, causes the on-time subsequent to the exit from
the OC condition, driven by the control loop, to increase. Considering now that the device
has a maximum on-time dependence with the delivered current given by the following
relationship:
Where I
(T
current of 0.40·T
When the current information I
device enters in Quasi-Constant-Current operation: the low-side MOSFET stays ON until
the current read becomes lower than I
side MOSFET can be then turned ON with a T
turn-off and the device works in the usual way until another OCP event is detected.
This means that the average current delivered can slightly increase in Quasi-Constant-
Current operation 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 I
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 latch
shows this working condition).
It can be observed that the peak current (I
determined as follow:
Where V
threshold is crossed, all MOSFET are turned OFF and the device stops working. Cycle the
power supply or the OUTEN pin to restart operation.
The maximum average current during the Constant-Current behavior results:
INFOx
SW
=1/F
I
overcomes the fixed threshold of I
PEAK
OUT
outMIN
SW
INFOx
is the output current (
). This linear dependence has a value at zero load of 0.80·T
=
I
OCPx
is the UVP threshold, (inductor saturation must be considered). When that
results being lower than the I
SW
typical.
+
I
V
----------------------------------------- -
MAX tot
IN
–
V
T
OUT min
L
ON max
=
INFOx
N
I
OUT
overcomes the fixed threshold of I
I
=
MAX
OCPx
T
OCTH
0.80
0.40
ON max
=
=
PEAK
(I
N
I
INFOx
OCTH
PHASEx
(35 A Typ,). When this happens, the device
ON
T
T
) is greater than I
SW
SW
=
I
OCPx
imposed by the control loop after the LS
< I
threshold. After exiting the OC condition,
I
OCPx
) and T
OCTH
I
I
+
DROOP
DROOP
+
I
------------------------------------
PEAK
) skipping clock cycles. The high
V
----------------------------------------- -
OCPx
SW
IN
–
=
=
2
–
is the switching period
V
I
0 A
140 A
OCPx
bottom. The worst-case
OCPx
OUT min
L
Over current protection
but it can be
OCTH
SW
and at maximum
0.40
(35 A Typ), the
(Figure 20
T
SW
51/70