LT3743IFE#PBF Linear Technology, LT3743IFE#PBF Datasheet - Page 20

• Manufacturer Part Number: LT3743IFE#PBF
• Description: IC LED DVR HP CONST CURR 28TSSOP
• Manufacturer: Linear Technology
• Type: High Power, Constant Currentr

Specifications of LT3743IFE#PBF

• Topology: High Side, Low Side, PWM, Step-Down (Buck)
• Number Of Outputs: 1
• Internal Driver: No
• Type - Primary: General Purpose
• Type - Secondary: RGB
• Frequency: 200kHz ~ 1MHz
• Voltage - Supply: 6 V ~ 36 V
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP Exposed Pad, 28-eTSSOP, 28-HTSSOP
• Operating Temperature: -40°C ~ 125°C
• Internal Switch(s): Yes
• Efficiency: 92%
• Led Driver Application: Lighting
• No. Of Outputs: 1
• Output Current: 20A
• Output Voltage: 40V
• Input Voltage: 6V To 36V
• Dimming Control Type: PWM
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Current - Output / Channel: -

LT3743
APPLICATIONS INFORMATION
Average Current Mode Control Compensation
The use of average current mode control allows for precise
regulation of the inductor and LED currents. Figure 16
shows the average current mode control loop used in the
LT3743, where the regulation current is programmed by
a current source and a 3k resistor.
To design the compensation network, the maximum com-
pensation resistor needs to be calculated. In current mode
controllers, the ratio of the sensed inductor current ramp
to the slope compensation ramp determines the stability
of the current regulation loop above 50% duty cycle. In
the same way, average current mode controllers require
the slope of the error voltage to not exceed the PWM ramp
slope during the switch off-time.
Since the closed-loop gain at the switching frequency
produces the error signal slope, the output impedance of
the error amplifi er will be the compensation resistor, R
Table 6. Recommended Compensation Values
20
Figure 16. LT3743 Average Current Mode Control Scheme
V
IN
12
12
12
24
24
(V)
R
C
C
C
MODULATOR
ERROR AMP
V
O
4
4
5
4
4
(V)
g
m
+
–
V
CTRL
• 11μA/V
L
I
L
10
20
20
5
2
(A)
3743 F16
R
3k
S
LOAD
f
SW
0.25
0.5
0.5
0.5
0.5
(MHz)
C
.
Use the following equations as a good starting point for
compensation component sizing:
where f
value, V
For most LED applications, a 4.7nF compensation capaci-
tor is adequate and provides excellent phase margin with
optimized bandwidth. Please refer to Table 6 for recom-
mended compensation values.
For applications where the load is not an LED, please call
the factory for additional compensation assistance.
Board Layout Considerations
Average current mode control is relatively immune to the
switching noise associated with other types of control
schemes. Placing the sense resistor as close as possible
to the SENSE
ensures the fastest LED current transition time. For currents
exceeding 5A, use 10Ω resistors in-series with SENSE
SENSE
to the SENSE
plane underneath the switching components will minimize
interplane noise coupling. To dissipate the heat from the
switching components, increase the area of the switching
node as much as possible without negatively affecting the
radiated noise. The interconnect inductance and resistance
between the output capacitors and the LED load directly
impacts the rise time of the load current. To reduce the
inductance and resistance, make the traces as wide as
physically possible and minimize the trace length.
R
L (μH)
1.5
1.5
1.8
1.0
1.0
C
=
–
S
IN
, with a 33nF capacitor placed as close as possible
f
S
is the switching frequency, L is the inductance
is the input voltage and R
•L • 1000V
V
O
+
+
•R
and SENSE
and SENSE
R
S
S
2.5
2.5
2.5
(mΩ)
5
5
[Ω], C
–
–
pins avoids noise issues and
pins. Utilizing a good ground
C
=
R
C
47.5
47.5
38.3
52.3
52.3
0.002
(kΩ)
S
f
S
is the sense resistor.
[F]
C
C
4.7
4.7
8.2
4.7
4.7
(nF)
+
3743fb
and