L6710 STMicroelectronics, L6710 Datasheet - Page 12

• Manufacturer Part Number: L6710
• Description: IC CTRLR 6BIT 2PH PROGR 44-TQFP
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L6710

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.84 ~ 1.6 V
• Current - Output: 2A
• Frequency - Switching: 150kHz
• Voltage - Input: 12V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 44-TQFP, 44-VQFP
• Power - Output: 2.5W
• Product: Half-Bridge Drivers
• Supply Current: 12.5 mA
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

L6710
Since the current is read in differential mode, also negative current information is kept; this allow the de-
vice to check for dangerous returning current between the two phases assuring the complete equalization
between the phase's currents. From the current information of each phase, information about the total cur-
rent delivered (I
is taken. I
current carried by the two phases.
The transconductance resistor Rg can be designed in order to have current information of 25µA per phase
at full nominal load; the over current intervention threshold is set at 140% of the nominal (I
According to the above relationship, the over current threshold (I
placed at 1/2 of the total delivered maximum current, results:
Since the device senses the output current across the low-side mosfets (or across a sense resistors in
series with them) the device limits the bottom of the inductor current triangular waveform: an over current
is detected when the current flowing into the sense element is greater than I
Introducing now the maximum ON time dependence with the delivered current (where T is the switching
period T=1/F
Where I
This linear dependence has a value at zero load of 0.80·T and at maximum current of 0.40·T typical and
results in two different behaviors of the device:
Figure 3. Current reading timing (left) and circuit (right)
12/34
T
OUT
ON,MAX
CURRENT
INFO (I
INFOX
TOTAL
I
I
INFO2
INFO1
is the output current.
I
I
SW
LS2
LS1
FB
)
is then compared to I
):
FB
=
(
=I
0.80 I
INFO1
–
FB
+ I
I
⋅
OC Px
5.73k
INFO2
Track & Hold
=
) T
) and the average current for each phase (I
⋅
35µA Rg
-------------------------- -
AVG
R
SENS E
=


0.80
to give the correction to the PWM output in order to equalize the
⋅
–
R
--------------------- - I
SENS E
Rg
⋅
Rg
OUT
=
⋅
I
----------------------------------------- -
OC Px
5.73k
100 µ A
LGATE1
PGNDS
35µA
OCPx
ISEN1
⋅
ISEN2
 T =

R
⋅
SENSE
) for each phase, which has to be





T
T
OCPx
=
=
0.80 T I
0.40 T I
AVG
50 µ A
50 µ A
I
I
ISEN1
ISEN2
(I
Rg
Rg
Rg
Rg
⋅
⋅
INFOx
= (I
INFO1
FB
FB
>35µA).
=
=
INFOx
0µA
70µA
+ I
INFO2
= 35µA).
)/2 )