DC1285A - Demo Manual

DEMO CIRCUIT 1285
LT3598
QUICK START GUIDE
LT3598
6-String 30mA LED Driver with 1.5%
Current Matching
DESCRIPTION
WARNING!
Do not look directly at operating LED.
This circuit produces light that can damage eyes.
Demonstration circuit 1285 is a 6-String 30mA LED
Driver with 1.5% Current Matching featuring the
LT3598. The LT3598 is a step-up DC/DC converter
designed to drive up to 6-strings of LEDs at an
output voltage up to 44V. The LED strings are
connected to internal current sources where the
current level is set with an external resist.
The demonstration circuit drives 20mA through
each LED string. Each string can have up to 10
white LEDs. The circuit operation frequency is set
to 1MHz. Parameters such as the LED current; the
switching frequency, etc can be modified easily
based on the demo circuit. When a string is not
used, tie its LED pin to VOUT. Any unused string is
no longer in the regulation loop. Direct paralleling
multiple strings together to achieve higher per
string current is allowed. To paralleling strings, tie
the respective LEDn pins together. OPENLED indicator flags should any string be left open. To improve efficiency, it is recommended that VIN is between 3.2V and 5.5V. The VIN bias capacitor of the
demo circuit is rated at 6.3V. PWM dimming ratio
can be as high as 3000:1.
The LT3598 datasheet gives complete descriptions
of the part, operation and application information.
The datasheet must be read in conjunction with
this quick start guide for working on or modifying
the demo circuit 1285.
Design files for this circuit board are available.
Call the LTC factory.
L, LTC, LTM, LT are trademarks of Linear Technology Corporation. Other product
names may be trademarks of the companies that manufacture the products.
PERFORMANCE SUMMARY Specifications are at TA = 25°C
SYMBOL
VIN
PVIN
IQ
FSW
ILED
IM
Eff
DPWM
PARAMETER
Input Supply Range
Power Input Supply Range**
Quiescent Current
Switching Frequency
LED String Current
LED String Current Matching***
Efficiency
PWM dimming ratio
CONDITIONS
MIN
3.2
3
PWM=0V, Not switching
0.9
19.5
VIN = 3.3V; PVIN = 12V; ILED = 20mA
PVIN = 12V
TYP
3.5
1
20
0.5
90
3000:1
MAX
5.5*
40
5
1.1
20.7
1.5
UNITS
V
V
mA
MHz
mA
%
%
*: Limited by the voltage rating of the bias capacitor, C2, on the demo circuit. The IC rating is 30V.
**: MIN PVIN depends on LED string voltages and the Maximum Switch Duty Cycle (specified on page 3
of the datasheet). PVIN greater than MAX LED string voltage is permitted but power dissipation needs to
be taken into considerations.
***: Specifications apply over the full operating temperature range.
1
LT3598
QUICK START PROCEDURE
Demonstration circuit 1285 is easy to set up to
evaluate the performance of the LT3598. Refer to
Figure 1 for proper measurement equipment setup
and follow the procedure below:
1. With power off, connect the input power supply
to VIN and GND.
2. Connect the power input power supply to PVIN
and GND.
3. Tie PWM to VIN or a PWM signal.
2
4. Connect LED strings to LEDn+ and LEDn-. If
any string is not used, tie LEDn- to LEDn+,
where n is the string number (between 1 and 6).
5. Turn on power supplies for VIN and PVIN.
NOTE. Make sure that VIN does not exceed 5.5V and PVIN
does not exceed 40V.
6. Check for the proper LED voltage and current.
LT3598
Figure 1. Proper Measurement Equipment Setup
3
LT3598
L1
E6
C1
2.2uF
50V
E5
C7
10uF
50CE10BJ
OPT
VISHAY IHLP-2525BD-01
E9
E11
E13
E15
E17
E19
LED1+ LED2+ LED3+ LED4+ LED5+ LED6+
VIN
U1
7
VIN
20
2
15
14
R7
100K 1%
16
18
23
LED1
RT
LED2
LED3
VREF
LED4
R6
10K
1%
LED5
R2
2.4M
1%
178K
1%
C10
47pF
1
2
3
4
5
6
CTRL
12
R9
13
R8
14.7K
1%
VC
9
LED6
11
10
E20
R12
107K
1%
4
NC
SY NC
SS
CTRL
100K 1%
PWM
C8 0.1uF
R5
51.1K
1%
R11
FB
17
E7
SHDN
TSET
E4
24
OPENLED
GND
100K 1%
SY NC
VO_SW
R4 76.8K 1%
1
JP1
PWM
LED1LED2LED3LED4LED5LED6E8
E10
E12
E14
E16
E18
ON
3
R3
VIN
25
OFF
LT3598EUF
VOUT
22
E3
ISET
E2
R1
100K
1%
SW
C2
1uF
6.3V
21
OPENLED
VOUT
1
40V 1A
E1
3.2V - 5.5V
GND
+
19
VIN
D1
2
3V - 40V
GND
10uH
8
PVIN
R10
C4
C9
0.1uF
100pF
3K
1%
C5
10nF
C6
4.7uF
50V
C3
4.7uF
50V
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