Datasheet

LT3763
18
3763fa
For more information www.linear.com/LT3763
applicaTions inForMaTion
Figure 6. Analog Control of Inductor Current
Figure 7. Input Current Monitoring Voltage
vs Input Current Sense Voltage
Figure 8. Output Current Monitoring Voltage
vs Output Current Sense Voltage
Figure 9. Output Voltage Regulation and Overvoltage
Protection Feedback Connections
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 should have a total load
current less than 0.5mA, and that above 1.5V, the control
voltage has no effect on the regulated inductor current.
Setting CTRL1 to 0V does not automatically stop switch
-
ing. To disable switching, set PWM pin voltage below 1.5V.
Input Current Monitoring
Users can
monitor the input current at the IVINMON pin,
which produces 0V to 1V as the voltage between IVINP and
IVINN varies from 0mV to 50mV, as shown in Figure 7. Due
to the switching of the high side FET, the input current is
noisy and monitoring the average input current requires an
external filter with 1k resistors connecting IVINP and IVINN
to the input current sense resistor R
SENSE_IN
. Choose the
capacitor for this filter according to the switching frequency
so that the noise is reduced by at least a factor of 100. If
the frequency is 500kHz, for example, 1µF is sufficient,
and higher switching frequencies will require a smaller
capacitor. A resistor and capacitor may be connected to
IVINMON to further filter the noise. With both input and
LT3763
V
REF
R2
R1
3763 F06
CTRL1
output current monitoring, the LT3763 enables users to
calculate the overall efficiency of the circuit including the
losses in the external components.
Output Current Monitoring
The LT3763 provides users the capability to monitor the
output current as a voltage provided at the ISMON pin.
The voltage will linearly increase from 0V to 1V as the
voltage between SENSE
+
and SENSE
–
increases from 0mV
to 50mV as shown in Figure 8. If, for example, a 2.5mΩ
resistor is chosen for R
S
, then a 1V output at ISMON will
indicate a 20A output current. A resistor and capacitor
may be connected to ISMON to filter noise.
Voltage Regulation and Overvoltage Protection
The LT3763 uses the FB pin to regulate the output volt
-
age and to provide an overvoltage lockout to avoid high
voltage conditions. The regulated output voltage is pro-
grammed using a resistor divider from the output to the
FB pin (Figure
9). When the output voltage approaches
V
IVINP
– V
IVINN
(mV)
0
0
V
IVINMON
(V)
0.5
1.0
1.5
2.0
25 50 75
3763 F07
100
V
SENSE
+
– V
SENSE
–
(mV)
0
0
V
ISMON
(V)
0.5
1.0
1.5
2.0
25 50 75
3763 F08
100
LT3763
R2
V
OUT
R1
3763 F09
FB