DC1327B - Demo Manual

DEMO CIRCUIT 1327B
QUICK START LT3599
GUIDE
LT3599
4-Channel 120mA LED Driver with
+/-1.5% Current Matching
DESCRIPTION
WARNING!
Do not look directly at operating LEDs.
This circuit produces light that can damage eyes.
NOTE: This document is for Demo Circuit 1327B.
Demonstration circuit 1327B is a 4-Channel 120mA LED
Driver with +/-1.5% Current Matching featuring the
LT3599. The LT3599 is a step-up DC/DC converter designed to drive up to 4-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 resistor.
The demonstration circuit drives 80mA 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
current per string is allowed. To paralleling strings, tie
the respective LEDn pins together. OPENLED indicator
flags if any string is left open. To improve efficiency, it is
recommended that VIN is between 3.1V 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 soft
start will not start until the 1st PWM pulse is presented.
The LT3599 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
1327B.
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
3.1
8
PWM=0V, Not switching
0.9
77.6
VIN = 3.3V; PVIN = 12V; ILED = 80mA
PVIN = 12V
TYP
3
1
80
+/-0.25
90
3000:1
MAX
5.5*
16
5
1.1
82.4
+/-1.5
UNITS
V
V
mA
MHz
mA
%
%
*: Limited by the voltage rating of the bypass capacitor, C3, on the demo circuit. The IC rating is 30V.
**: PVIN below 8V causes current derating but the circuit operates fine. PVIN between 16V and 40V may be acceptable
depending on the number of LEDs, desired LED current, etc. Power dissipation needs to be taken into considerations if
PVIN is greater than the Maximum LED string voltage.
***: Specifications apply over the full operating temperature range.
QUICK START PROCEDURE
1
LT3599
Demonstration circuit 1327B is easy to set up to evaluate
the performance of the LT3599. 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.
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 4).
5. Turn on power supplies for VIN and PVIN.
6. A PWM signal needs to be applied if PWM is not tied
to VIN.
7. If analog dimming is to be tested by varying the level
of CTRL pin voltage, remove R15 to prevent triggering
UVLO at low PVIN (<10V).
8. Removing R15 disables the programmed UVLO and
LED current derating. If those functions are required in
the test in 7, use two independent resistor dividers for
UVLO and CTRL.
9. Check for the proper LED voltage and current.
Figure 1. Proper Measurement Equipment Setup
2
LT3599
3
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