DC1124A - Demo Manual

DC1124A
QUICK START GUIDE
LT3591
LED Driver with Integrated Schottky in
3mm×2mm DFN
DESCRIPTION
Demonstration circuit 1124 is an LED Driver w ith
Integrated Schottky in 3mmx2mm DFN featuring the
LT3591. The LT3591 is a fixed frequency step-up current
mode DC/DC converter to drive up to ten w hite LEDs in
series. The high sw itching frequency allow s using tiny
components for the circuit. External components are
minimized by integrating the schottky diode and the open
circuit protection into the package. The high side current
sensing feature of the LT3591 allow s “one w ire” current
source, i.e. the low side of the LED string can return to
ground anyw here. The input voltage range of the demo
board is from 3V to 9V. This driver can provide 20mA for
up to 10 LEDs. Different dimming controls can be
implemented on the demo board. Please refer to the
quick start procedure.
The LT3591 datasheet gives complete description of the
part, operation and application information. The
datasheet must be read in conjunction w ith this quick
start guide for w orking on or modifying the demo circuit
1124.
Design files for this circuit board are available. Call
the LTC factory.
,LTC and LT are registered trademarks ofLinear Technology Corporation. ThinSOT and
Pow erPath are trademarks ofLinear Technology Corporation.
PERFORMANCE SUMMARY
Specifications are at TA = 25°C
SYM BO L
VIN
IOUT
PAR AM ETER
Input Supply Range **
Output Current
η
VOPEN
IQ
IQSHDN
Fs
Efficiency
CAP pin Over voltage Protection
Quiescent Current
Quiescent Current W hile in Shutdow n
Sw itching Frequency
CO NDITION S
M IN
3
TYP
VIN = 3V, 10 LEDs
VIN = 3.6V, 10 LEDs
LED Open
VIN = 3V,VCTR L=3V
VIN = 3V,VCTR L=0V
40
78.2
42
0.75
1
M AX
9
20
UN ITS
V
mA
44
5
11
1.2
%
V
mA
µA
M Hz
** The Input Supply R ange of the demo circuit 1124 is limited by the input capacitors. The input voltage absolute
maximum rating ofthe LT3591 is 12V.
QUICK START PROCEDURE
Demonstration circuit 1124 is easy to set up to evaluate
the performance of the LT3591. R efer to Figure 1 for
proper measurement equipment setup and follow the
procedure below :
1
LT3591
NOTE. W hen measuring the input or output voltage ripple,care must be
taken to avoid a long ground lead on the oscilloscope probe. M easure the
input or output voltage ripple by touching the probe tip directly across the
Vin or Vout and GND terminals. See Figure 2 for proper scope probe
technique. Place jumper JP1 in the ON position.
1.
W ith pow er off,connect the input pow er supply to VIN
and G N D.
2.
Turn on the pow er at the input.
NOTE. M ake sure that the input voltage does not exceed 9V.
3.
4.
O nce proper operation is established, adjust the input
w ithin the operating range and observe the parameters
ofinterest.
5.
To test the filtered PW M dimming or the direct DC
dimming,apply the PW M or the DC signal to the CTR L
terminal and observe the brightness of the LED
output.
6.
To test the direct PW M dimming, remove C4 and R3.
Install Q1 and connect CTR L w ith PW M pin. Apply the
PW M signal to the PW M pin and observe the
brightness ofthe LED output.
Check for the proper voltage and current.
NOTE. Ifthe LEDs do not light up,check the jumper setting and LED
connection.
Figure 1.
Proper M easurem ent Equipm ent Setup
GND
VIN
Figure 2. M easuring Input or Output Ripple
2
LT3591
3
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