L6722TR STMicroelectronics, L6722TR Datasheet - Page 24

• Manufacturer Part Number: L6722TR
• Description: IC BUCK ADJ 2A TRPL 36VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L6722TR

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 3
• Voltage - Output: Adj to 0.8V
• Current - Output: 2A
• Frequency - Switching: 100kHz
• Voltage - Input: 12V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 36-VFQFN, 36-VFQFPN
• Power - Output: 3.5W
• Operating Temperature Range: - 40 C to + 125 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-5904-2

9 Output voltage monitor and protections
9.5
9.6
24/34
PGOOD
It is an open-drain signal set free after the soft-start sequence has finished. It is pulled low
when the output voltage drops below -150mV of the programmed voltage.
Over-current protection
The Over Current threshold has to be programmed, by designing the R
value, in order to be sure that the device doesn't enter OCP during normal operations. This
value must take into consideration also the process spread and temperature variations of the
sensing elements as well as the minimum value I
where I
Quasi-Constant-Current.
Since the device reads the current across Low Side mosfets, it limits the bottom of the inductor
current entering in constant current until setting UVP as below explained. I
calculated starting from the corresponding output current value I
device holds the valley current information:
where I
Current, and I
limits the valley of the inductor current, the ripple entity, when not negligible, impacts on the real
OC threshold value and must be considered.
The device detects an Over Current condition for each phase when the current information
I
relative LS mosfet on, also skipping clock cycles, until the threshold is crossed back and I
results being lower than the I
each inductor current ripple). After exiting the OC condition, 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. The device enters in Quasi-Constant-
Current operation: the low-side mosfets stays ON until the current read becomes lower than
I
a T
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
the ON time reaches its maximum value.
When this happens, the device works in Real Constant Current and the output voltage
decrease as the load increase. Crossing the UVP threshold causes the device to latch driving
high the OSC pin.
It can be observed that the peak current (I
as follow:
ISENx
OCPx
ON
(I
overcomes the fixed threshold of I
imposed by the control loop after the LS turn-off and the device works in the usual way
OCPx
OUT(OCP)
INFOx
is the current measured by the current reading circuitry when the device enters
< I
PP
OCTH
is the inductor current ripple in each phase. In particular, since the device
is still the output current value at which the device enters Quasi-Constant-
) skipping clock cycles. The high side mosfet can be then turned ON with
OCTH
Rg
I
OCPx
threshold (this implies that the device limits the bottom of
=
I
-------------------------------------------------------------------- -
OCPx max
OCTH
=
PEAK
I
--------------------------- -
(
OUT OCP
I
OCPx
. When this happens, the device keeps the
OCTH min
) is greater than I
3
(
)
OCTH(min)
⋅
bottom. The worst-case condition is when
(
R
dsON max
)
–
)
∆I
----------- -
2
PP
(
of the threshold as follow:
)
OCPx
OUT(OCP)
but it can be determined
ISENx
as follow since the
OCPx
resistors, to a safe
must be
L6722
ISENx