DC905A - Demo Manual

DEMO CIRCUIT 905
LT3491
QUICK START GUIDE
LT3491
LED Driver in SC70 With Built-in Schottky
WARNING!
DO NOT LOOK AT OPERATING LED.
This circuit produces light that can damage eyes.
DESCRIPTION
Demonstration circuit 905 is a LED Driver in SC70 W ith
Built-in Schottky featuring the LT3491. The LT3491 is a
fixed frequency step-up current mode DC/DC converter.
There are tw o circuits on demonstration board 905. The
“Small Size” circuit generates 15mA LED current at the
smallest possible solution size. The “High Efficiency”
circuit generates 20mA LED current at higher efficiency.
The circuit outputs share 6 LEDs. At any given time, depending on the positions of jumpers, only one circuit is
in operation. Other features of the LT3491, such as the
internal schottky diode,the high sw itching frequency and
the internal open circuit protection, allow tiny components for both circuits. The input range of the demo
board is from 3V to 5V. Different dimming controls can
be implemented on the demo board. Please refer to the
quick start procedure. The high side current sensing feature of the LT3491 allow s “one w ire” current source, i.e.
the low side of the LED string can return to ground anyw here.
The LT3491 datasheet gives a 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 demo circuit 905.
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
VOUT
Output Voltage
η
Efficiency
VOPEN
IQ
IQSHDN
Fs
CAP pin Over-voltage Protection
Quiescent Current
Quiescent Current W hile in Shutdow n
Sw itching Frequency
CO NDITION S
Small Size circuit
High Efficiency circuit
Small Size circuit
High Efficiency circuit
VIN = 4.2V,Small Size circuit
VIN = 4.2V,High Efficiency circuit
LED Open
VIN = 4.2V,CTRL = ON
VIN = 4.2V,CTRL = OFF
M IN
3
14.25
19
TYP
26
15
20
20.3
20.6
73.6
75.5
27
1.8
2.3
M AX
5
15.75
21
UN ITS
V
mA
V
%
28
4
10
2.8
V
mA
µA
M Hz
** The Input Supply R ange ofdemo circuit 905 is limited by the input capacitors. The input voltage absolute maximum
rating ofthe LT3491 is 12V.
1
LT3491
QUICK START PROCEDURE
Demonstration circuit 905 is easy to set up to evaluate
the performance of the LT3491. R efer to Figure 1 for
proper measurement equipment setup and follow the
procedure below :
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.
1.
Place jumpers in the follow ing positions to test the
“SM ALL SIZE” circuit:
ON
JP1
O FF
JP2
SIZE
JP3
SIZE
JP4
2. Place jumpers in the follow ing positions to test the
“H IG H EFFICIEN CY” circuit:
JP1
JP2
JP3
JP4
2
O FF
ON
EFFICIEN CY
EFFICIEN CY
3.
Prior to connection, preset the input pow er supply to
the desired voltage (3V to 5V). W ith pow er off, connect the input pow er supply to VIN and G N D.
4.
Turn on the pow er at the input.
NOTE. M ake sure that the input voltage does not exceed 5V.
5.
Check for the proper voltages and currents.
NOTE. Ifthe LEDs do not light up,check all the jumper settings.
6.
O nce proper operation is established, adjust the input
w ithin the operating range and observe the parameters
ofinterest.
7.
To test the filtered PW M dimming or the direct DC
dimming, remove the jumper JP1 or JP2, apply the
PW M or the DC signal to the CTRL1 or CTR L2 and
observe the brightness ofthe LED output.
8.
To test the direct PW M dimming, follow the Direct
PW M Dimming section in the datasheet.
LT3491
Figure 1. Proper M easurem entEquipm entSetup
GND
VIN
Figure 2. M easuring Inputor OutputRipple
3
LT3491
4
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