Datasheet

LT3741/LT3741-1
16
37411fe
For more information www.linear.com/LT3741
Output Current Regulation
To adjust the regulated load current, an analog voltage is
applied to the CTRL1 pin. Figure 5 shows the regulated
voltage across the sense resistor for control voltages
up to 2V. Figure 6 shows the CTRL1 voltage created by
a voltage divider from V
REF
to ground. When sizing the
resistor divider, please be aware that the V
REF
pin is current
limited to 500µA. Above 1.5V, the control voltage has no
effect on the regulated inductor current.
applicaTions inFormaTion
LT3741
V
REF
R2
R1
3741 F06
CTRL1
Figure 5. Sense Voltage vs CTRL Voltage
Figure 6. Analog Control of Inductor Current
V
CTRL
(V)
0
0
V
SENSE
+
– V
SENSE
–
(mV)
10
20
30
40
50
60
0.5 1.0 1.5
3741 F05
2.0
not leave this pin open under any condition. The RT pin
is also current limited to 60µA. See Table 4 and Figure 8
for resistor values and the corresponding switching
frequencies.
Table 4. Switching Frequency
SWITCHING FREQUENCY (MHz) R
T
(kΩ)
1 40.2
0.750 53.6
0.5 82.5
0.3 143
0.2 200
Figure 7. Output Voltage Regulation and Overvoltage Protection
Feedback Connections
LT3741
R2
V
OUT
R1
3741 F07
FB
R
T
(kΩ)
0
FREQUENCY (MHz)
0.4
0.8
1.2
0.2
0.6
1.0
100 200 300 400
3743 F08
500
500 150 250 350 450
Figure 8. Frequency vs R
T
Resistance
Voltage Regulation and Overvoltage Protection
The LT3741 uses the FB pin to regulate the output voltage
and to provide a high speed overvoltage lockout to avoid
high voltage conditions. The regulated output voltage
is programmed using a resistor divider from the output
and ground (Figure 7). When the output voltage exceeds
125% of the regulated voltage level (1.5V at the FB pin),
the internal overvoltage flag is set, terminating switching.
The regulated output voltage must be greater than 1.5V
and is set by the equation:
V
OUT
= 1.21V 1+
R2
R1
⎛
⎝
⎜
⎞
⎠
⎟
Programming Switching Frequency
The LT3741 has an operational switching frequency range
between 200kHz and 1MHz. This frequency is programmed
with an external resistor from the RT pin to ground. Do