L6712QTR STMicroelectronics, L6712QTR Datasheet - Page 14

• Manufacturer Part Number: L6712QTR
• Description: IC CTRLR DC/DC 2PH SYNC 36VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L6712QTR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.9 ~ 3.3 V
• Current - Output: 2A
• Frequency - Switching: 150kHz
• 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: 497-4219-2

L6712A L6712
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 I
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.
Figure 10 shows this working condition.
It can be observed that the peak current (I
Where V
The device works in Constant-Current, and the output voltage decreases as the load increase, until the
output voltage reaches the under-voltage threshold (Vout
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
(T
Figure 10. Constant Current operation
Over current is set anyway when I
to work with convenient values for I
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 I
spond to I
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
14/29
onMAX
) while the OFF time depends on the application:
outMIN
INFOx
TonMAX
I
peak
is the minimum output voltage (VID-40% as follow).
a) Maximum current for each phase
= 17.5µA (IFB = 35µA).
OCPx
=
T
bottom. The worst-case condition is when the ON time reaches its maximum value.
I
OCPx
OFF
I
MAX,TOT
=
+
V
------------------------------------- - Ton
L
TonMAX
IN
⋅
INFOx
Ipeak I
------------------------------------- -
–
FB
Vout
=
L
. Since the OCP intervention threshold is fixed, to modify the per-
V
2 I
reaches 35µA (I
OUt
–
⋅
peak
min
INFOx
MAX
OCPx
) is greater than the I
⋅
= 35µA (I
=
2
MAX
⋅
⎛
⎝
I
OCPx
FB
=
MIN
FB
Ipeak
I
I
=70µA). The full load value is only a convention
MAX
OCPx
I
OCPx
= 70µA). The full load current will then corre-
).
+
Ipeak I
------------------------------------- -
f
=
+
OCPx
----------------------------------------- -
T
V
-------------------------------------- - 0.40 T
ONmax
Vout
UVP
(I
IN
DROOP
2
–
but it can be determined as follow:
–
OCPx
Vout
=50µA)
b) Output Characteristic
L
1
+
T
⎞
⎠
MIN
OFF
2·I
⋅
OCPx
Droop effect
(I
DROOP
⋅
I
MAX,TOT
=70µA)
Iout