Datasheet

LT3760
9
3760fc
block DiagraM
operaTion
The operation of the LT3760 is best understood by referring
to the typical application circuit on the front page and the
Block Diagram in Figure 1. The LT3760 drives 8 strings
of LEDs by using a constant switching frequency, current
mode boost controller to generate a single output voltage
V
OUT
for the top (anode) of all LED strings. LED string
current is generated and controlled by connection of the
bottom LED in each string (cathode) to a current source
contained in each corresponding LED pin. Each LED pin
contains an accurate current sink to ground, program-
mable between 20mA to 100mA using a single resistor
at the I
SET
pin. LED channels can be paralleled to achieve
higher LED currents. For applications requiring less than
8 strings of LEDs, channels can be paralleled or disabled
(connect LED pin to V
OUT
before startup). For optimum
efficiency, V
OUT
regulates to the lowest possible voltage
allowable to maintain regulated current in each LED string.
Any OPEN LED fault is indicated by the FAULT pin driven
low without effecting the operation of the connected LED
strings.
The Block Diagram in Figure 1 illustrates the key functions
of the LT3760. It can be seen that
two external supplies,
V
REF
and INTV
CC
, are generated by the LT3760. The V
REF
pin provides a precision 1.485V output for use with external
resistors to program the CTRL, OVP
SET
and T
SET
input
pins. The INTV
CC
pin provides a regulated 7V output to
supply the gate driver for the boost controller GATE pin.
An accurate 1.476V threshold on the SHDN/UVLO pin
combined with a SHDN/UVLO pin current hysteresis allows
a programmable resistor divider from V
IN
to SHDN/UVLO
Figure 1. LT3760 Block Diagram
3760 BD
+
+
+
–
CHANNEL X
OVERVOLTAGE
AMP
LED AMP
6V
1.1V
+
–
+
–
+
–
+
–
LED
LOGIC
R
S
Q
+
–
INTV
CC_UV
V
IN_UV
V
IN
SHDN_UV
SHDN/UVLO
PWM
V
REF
CTRL
1V
SS
R
56R
600k
15
14
13
1.476V
1.485V
SLOPE
100mV
OVER
CURRENT
52mV
PEAK
CURRENT
HICCUP__MODE
V
C
EN
PWM
EN
EN
7V(REGULATED) UVLO(+) = 3.8V, UVLO(−) = 3.4V
4.2V(+)
3.7V(−)
+
–
REF
1.485V
27
1
2 4
26
24
V
PTAT
+
–
EN
GATE
SYNC
RT
SENSE
V
OUT
LEDx
6 TO 9, 20 TO 23
FAULT
SOFT
START
+
–
3
16
18
11
OSC
12
25
17
28
LED CURRENT
CONTROL
INTV
CC
OVP
SET
V
C
I
SET
T
SET
GND PGND (10, 19, EXPOSED PAD (29))
+
–
+
–