LT3478 Datasheet, PDF (8/24 Pages) Linear Technology – 4.5A Monolithic LED Drivers with True Color PWM Dimming

LT3478/LT3478-1
PI FU CTIO S
exceeds 6A or V_OUT exceeds OVP, an internal soft-start
latch is set, the power NPN is immediately turned off and
the SS pin is discharged. The soft-start latch is also set
if V_IN and/or ^⎯S^⎯H^⎯D^⎯N do not meet their turn on thresholds.
The SS pin only recharges when all faults are removed
and the pin has been discharged below 0.25V.
Exposed Pad (Pin 17): The ground for the IC and the con-
verter. The FE package has an Exposed Pad underneath the
IC which is the best path for heat out of the package. Pin 17
should be soldered to a continuous copper ground plane
under the device to reduce die temperature and increase
the power capability of the LT3478/LT3478-1.
BLOCK DIAGRA
SHDN
11
10µA
V_S
L
4
5
V_C
–
1.4V +
V_IN
3
REF
1.24V
UVLO
9.5mΩ
–
–+ ^57mV
+
INRUSH
CURRENT
PROTECTION
SS
16
SW
1, 2
OVERVOLTAGE
DETECT
SOFT-START
OVPSET
100Ω
V_REF
10
CTRL1
12
CTRL2
13
1.05V
+
+
+
–
PWM
DETECT
OSC
PWM
Q2
SLOPE
COMP
Σ
SQ
R
1000Ω
Q1
R_S
V_OUT
6
R_SENSE
0.1Ω
(INTERNAL FOR
LT3478-1)
R_SENSE
(EXTERNAL FOR
LT3478)
LED
7
LED
LED
LED
GM
LED
1V
PWM
14
TO OVERVOLTAGE
DETECT CIRCUIT
8
OVPSET
15
R_T
17
9
EXPOSED PAD
V_C
(GND)
3478 F01
Figure 1
34781f
8