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PAM2810ENG 数据表(PDF) 6 Page - Power Analog Micoelectronics |
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PAM2810ENG 数据表(HTML) 6 Page - Power Analog Micoelectronics |
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6 / 10 page  Application Information , Power Analog Microelectronics Inc 6 www.poweranalog.com The PAM2810 is a 4-channel programmable white-LED driver. The matched current regulators each have a 100:1 ratio between the LEDx outputs and the ISET current. The PAM2810 is capable of supplying 40mA per channel with the proper selection of the external RSET resistor, with a total of 160mA output current available. LED brightness control of PAM2810 can be achieved with a PWM signal. The PAM2810 is capable of providing up to 40mA per LED under an input voltage of 2.7V to 5.5V. An external resistor is used to set the output current, as approximated with the following equation: R =100 *(1.22V / I ) In order that the output currents could be regulated properly, the LEDx pin voltage(V ) must be larger than the dropout voltage of the current sink(V ). To ensure the desired current is obtained, apply the following equation to determine the minimum input voltage: V- V = V V V is the diode forward voltage, and some typical value of V can be found from the following table. Table 1. I , R and V Brightness control can be realized by applying a PWM signal to the EN pin. The constant current is set by the external resistor selected using the RSET equation. The L ED brightness i s proportional to the duty cycle (D) of the PWM signal. The PWM frequency (f) should be limited to accommodate the start-up time (50 s) of the device. D * (1/f) > The maximum PWM frequency can be selected according to the table above. If the PWM frequency is much less than 100Hz, flickering may be seen in the LEDs. For the PAM2810, zero duty cycle will turn off the LEDs and a 50% duty cycle will result in an average ILED being half of the programmed LED current. For example, if RSET is set to program 20mA, a 50% duty cycle will result in an average ILED of 10mA. RSET should be chosen not to exceed the maximum current capability of the device. The PAM2810 equips over temperature protection. When the junction temperature (T ) exceeds +150°C, the current source turns off automatically. The device will turn on again after the IC’s Output Current Capability PWM Over Temperature Protection SET LEDX LEDX DROPOUT IN DIODE LEDX DROPOUT DIODE DROPOUT LED SET DROPOUT J ≥ Brightness Control Shutdown μ 50 s Table 2. PWM Frequency and Duty cycle When the EN pin is logic low, the PAM2810 will be in shutdown mode. While disabled, the PAM2810 typically draws 0.1 A current form the power supply. There is no internal pull-up or pull-down on the EN pin. T cools down under +125°C. Operating at absolute m aximum temperature i s not recommended. μ μ J ILED RSET VDROPOUT 10mA 12.7kΩ 40mV 20mA 6.2kΩ 80mV 30mA 4.3kΩ 120mV 40mA 3.2kΩ 150mV PAM2810 4-Channel Programmable LED Current Sink Frequency Cycle Duty-Cycle Request 100Hz 10ms > 0.5 100 1kHz 1ms > 5 100 2 kHz 500μs > 10 100 4 kHz 250μs > 20 100 8 kHz 125μs > 40 100 10 kHz 100μs > 50 100 07/2008 Rev 1.1 |
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