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AD8240 Arkusz danych(PDF) 5 Page - Analog Devices |
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AD8240 Arkusz danych(HTML) 5 Page - Analog Devices |
5 / 12 page AD8240 Rev. 0 | Page 5 of 12 PRODUCT DESCRIPTION The AD8240 consists of four functional blocks labeled A through D, as shown in Figure 2. B GND VO VSENSE 5V REFERENCE PWM VPLUS BASE SHUNT C AD8240 D A Figure 2. Simplified Functional Block Diagram Table 3 briefly describes the blocks, while the sections that follow provide more detailed information. Table 3. Block Description A Linear regulator B High-side current-sense amplifier C Comparator D Driver LINEAR REGULATOR (BLOCK A) The simplified architecture of the linear regulator block is an amplifier and resistor divider. One input to the amplifier is tied to the 5 V reference. The other input is tied to a resistor divider that sets the ratio of the 5 V reference to VO. As a result, the accuracy of the voltage output is proportional to the accuracy of the 5 V reference. For example, if the 5 V reference is 5% high (5.25 V), the output is 5% high (12.6 V). HIGH-SIDE CURRENT-SENSE AMPLIFIER WITH OPEN LED DETECTION (BLOCK B) This amplifier is used to measure the LED current by ampli- fying the voltage across a user-selected shunt resistor. It has a gain of 24 and an overall accuracy of 5%. The output of the amplifier is typically connected to a microcontroller A/D converter input so that the condition of the LED lamp can be determined. This output can also be tied to other devices such as a latching comparator or output buffer. It is important to note that the output of this amplifier has a relatively high impedance of approximately 10 kΩ. As a result, a buffer amplifier should be used if the load is less than 100 kΩ. COMPARATOR WITH LATCH-OFF OVERCURRENT PROTECTION (BLOCK C) This block is used to shut down the output in the case of a short circuit or an overcurrent condition. When the output of the high-side current-sense amplifier approaches 5 V, the comparator output switches, causing the driver to latch off the output voltage. INTELLIGENT DRIVER (BLOCK D) The intelligent driver provides multiple functions: • Level shifts and conditions the output of the regulator amplifier to drive an external user-selected power transistor. • Accepts PWM input so that LED brightness can be controlled by a user-supplied PWM signal. • The PWM input can also be used as a simple on/off control for applications that do not require variable brightness. • Latch-off input that latches the output off when the comparator trips during an overcurrent event. The latch is reset by cycling the PWM input. |
Podobny numer części - AD8240_15 |
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Podobny opis - AD8240_15 |
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