Datasheet AD8240 (Analog Devices) - 6
| Manufacturer | Analog Devices |
| Description | LED Driver/Monitor |
| Pages / Page | 12 / 6 — AD8240. USING/EVALUATING THE AD8240 LED DRIVER MONITOR. Shunt Resistor … |
| File Format / Size | PDF / 223 Kb |
| Document Language | English |
AD8240. USING/EVALUATING THE AD8240 LED DRIVER MONITOR. Shunt Resistor Selection. SETUP. Circuit Configuration. RSHUNT. VBATT
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AD8240 USING/EVALUATING THE AD8240 LED DRIVER MONITOR
Figure 3 shows a connection diagram for a typical application.
Shunt Resistor Selection
The shunt resistor is chosen by the equation
SETUP
R ≤ . 0 2 V I In order to set up and evaluate the AD8240, the following SHUNT LOAD components and equipment are needed: For example if the load is expected to be 500 mA, the shunt • A shunt resistor (typically 0.1 Ω to 0.5 Ω depending on the value should be equal to or less than 0.4 Ω. This keeps the load). See the Shunt Resistor Selection section. output of the current sense amplifier from being greater than • 4.8 V in normal operation to prevent noise from causing the A transistor (the type depends on the load) output to latch off. • Two capacitors •
Circuit Configuration
LED load Connect the pass transistor, capacitors, and LED load(s) as • 5 V reference voltage shown in Figure 3. It is important to note that the value of CM • 9 V to 27 V supply should be at least 22 nF to ensure circuit stability. • Oscilloscope The LED lamp should be configured to expect 12 V. This is • Digital voltmeter (DVM) the result of selecting the series/parallel combinations of LEDs and series resistors. The series resistors can be used to adjust for LED supplier brightness variations from lot to lot. Connect 5 V to Pin 2 (5 V reference) and at least 9 V to Pin 5 (VPLUS). It may be necessary to raise the VPLUS voltage to more than 13 V, depending on the drop across the pass transistor, for the output to be regulated at 12 V. This varies according to the application and the pass transistor type. .
RSHUNT VBATT CM CL 47nF VPLUS 22nF V SHUNT BASE O 5 6 7 8 RSENSE V 1 SENSE 10k
Ω
5V 2 REFERENCE R1 350k
Ω
LATCH-OFF PWM 3 DRIVER R2 250k
Ω
4 GND
04824-0-003 Figure 3. Connections for Typical Applications Rev. 0 | Page 6 of 12 Document Outline FEATURES GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM PRODUCT HIGHLIGHTS SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS PRODUCT DESCRIPTION LINEAR REGULATOR (BLOCK A) HIGH-SIDE CURRENT-SENSE AMPLIFIER WITH OPEN LED DETECTION (B COMPARATOR WITH LATCH-OFF OVERCURRENT PROTECTION (BLOCK C) INTELLIGENT DRIVER (BLOCK D) USING/EVALUATING THE AD8240 LED DRIVER MONITOR SETUP Shunt Resistor Selection Circuit Configuration CONTROLLING THE LED LAMP USING/EVALUATING THE VSENSE OUTPUT Using/Evaluating the Short-Circuit Protection Feature ADVANTAGES OF DRIVING LED LAMPS WITH CONSTANT VOLTAGE BACKGROUND MONITORING THE LEDS DRIVING AUTOMOTIVE LEDS Constant Current Constant Voltage OUTLINE DIMENSIONS ORDERING GUIDE
AD8240 USING/EVALUATING THE AD8240 LED DRIVER MONITOR
Figure 3 shows a connection diagram for a typical application.
Shunt Resistor Selection
The shunt resistor is chosen by the equation
SETUP
R ≤ . 0 2 V I In order to set up and evaluate the AD8240, the following SHUNT LOAD components and equipment are needed: For example if the load is expected to be 500 mA, the shunt • A shunt resistor (typically 0.1 Ω to 0.5 Ω depending on the value should be equal to or less than 0.4 Ω. This keeps the load). See the Shunt Resistor Selection section. output of the current sense amplifier from being greater than • 4.8 V in normal operation to prevent noise from causing the A transistor (the type depends on the load) output to latch off. • Two capacitors •
Circuit Configuration
LED load Connect the pass transistor, capacitors, and LED load(s) as • 5 V reference voltage shown in Figure 3. It is important to note that the value of CM • 9 V to 27 V supply should be at least 22 nF to ensure circuit stability. • Oscilloscope The LED lamp should be configured to expect 12 V. This is • Digital voltmeter (DVM) the result of selecting the series/parallel combinations of LEDs and series resistors. The series resistors can be used to adjust for LED supplier brightness variations from lot to lot. Connect 5 V to Pin 2 (5 V reference) and at least 9 V to Pin 5 (VPLUS). It may be necessary to raise the VPLUS voltage to more than 13 V, depending on the drop across the pass transistor, for the output to be regulated at 12 V. This varies according to the application and the pass transistor type. .
RSHUNT VBATT CM CL 47nF VPLUS 22nF V SHUNT BASE O 5 6 7 8 RSENSE V 1 SENSE 10k
Ω
5V 2 REFERENCE R1 350k
Ω
LATCH-OFF PWM 3 DRIVER R2 250k
Ω
4 GND
04824-0-003 Figure 3. Connections for Typical Applications Rev. 0 | Page 6 of 12 Document Outline FEATURES GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM PRODUCT HIGHLIGHTS SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS PRODUCT DESCRIPTION LINEAR REGULATOR (BLOCK A) HIGH-SIDE CURRENT-SENSE AMPLIFIER WITH OPEN LED DETECTION (B COMPARATOR WITH LATCH-OFF OVERCURRENT PROTECTION (BLOCK C) INTELLIGENT DRIVER (BLOCK D) USING/EVALUATING THE AD8240 LED DRIVER MONITOR SETUP Shunt Resistor Selection Circuit Configuration CONTROLLING THE LED LAMP USING/EVALUATING THE VSENSE OUTPUT Using/Evaluating the Short-Circuit Protection Feature ADVANTAGES OF DRIVING LED LAMPS WITH CONSTANT VOLTAGE BACKGROUND MONITORING THE LEDS DRIVING AUTOMOTIVE LEDS Constant Current Constant Voltage OUTLINE DIMENSIONS ORDERING GUIDE
