lt3743 Linear Technology Corporation, lt3743 Datasheet - Page 16

• Manufacturer Part Number: lt3743
• Description: High Current Synchronous Step-down Led Driver With Three-state Control
• Manufacturer: Linear Technology Corporation

LT3743
APPLICATIONS INFORMATION
V
The bypass capacitor for the V
than 5μF for stability and has no ESR requirement. It
is recommended that the ESR be lower than 50mΩ to
reduce noise within the LT3743. For driving MOSFETs
with gate charges larger than 10nC, use 0.5μF/nC of total
gate charge.
LED Current Dimming
The LT3743 provides the capability of traditional zero to full
current PWM dimming as well as PWM dimming between
two regulated LED current states. When the PWM signal
is low, no switching occurs and the output capacitors
are disconnected from ground. When PWM is high and
CTRL_SEL is low, the inductor current is regulated to the
low current state. In this state, the PWMGL signal is high,
connecting the output capacitor for the low regulated
current state. When PWM and CTRL_SEL are both high,
the inductor current is regulated to the high current state.
In this state, the PWMGH signal is high, connecting the
output capacitor for the high regulated current state. The
transition time between each of the regulated inductor
currents is determined by the inductor size, V
Due to the use of the switched output capacitors, the LED
current will begin to fl ow within 130ns of the transition on
the CTRL_SEL pin. Figure 8 shows the LED and inductor
current waveforms with the various states of the control
signals.
To adjust the regulated LED current for the two control
states, an analog voltage is applied to the CTRL_L and
CTRL_H pins. Figure 6 shows the regulated voltage across
the sense resistor for control voltages up to 2V. Figure 7
shows the CTRL_L voltage created by a voltage divider
from V
please be aware that the V
500μA. Above 1.5V, the control voltage has no effect on
the regulated LED current.
For the widest dimming range, use the highest switching
frequency possible and lowest PWM frequency. For con-
fi guration with the maximum PWM range, please contact
factory for optimized component selection.
16
CC_INT
REF
Capacitor Selection
to ground. When sizing the resistor divider,
REF
CC_INT
pin is current limited to
pin should be larger
IN
and V
O
.
INDUCTOR
CTRL_SEL
CURRENT
CURRENT
PWMGH
PWMGL
PWM
LED
60
50
40
30
20
10
Figure 7. Analog Control of LED Current
Figure 6. LED Current vs CTRL Voltage
Figure 8. LED Current vs CTRL Voltage
0
0
t
ON(PWM)
t
PWM
0.5
ICTRL_H
LT3743
CTRL_L
V
V
CTRL
REF
1.0
3743 F07
(V)
R2
R1
1.5
3743 F06
2.0
3743 F08
ICTRL_L
3743f