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NUD4301 Datasheet(数据表) 5 Page - ON Semiconductor

部件型号  NUD4301
说明  Dual Low Dropout Voltage LED Driver/Current Source
下载  6 Pages
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制造商  ONSEMI [ON Semiconductor]
网页  http://www.onsemi.com
标志 ONSEMI - ON Semiconductor

NUD4301 Datasheet(HTML) 5 Page - ON Semiconductor

  NUD4301 数据表 HTML 1Page - ON Semiconductor NUD4301 数据表 HTML 2Page - ON Semiconductor NUD4301 数据表 HTML 3Page - ON Semiconductor NUD4301 数据表 HTML 4Page - ON Semiconductor NUD4301 数据表 HTML 5Page - ON Semiconductor NUD4301 数据表 HTML 6Page - ON Semiconductor  
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NUD4301
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5
Figure 7. Dimming Operation Curves
(Graph obtained from SPICE simulations)
Analog
Operation
Digital
Operation
time
time
VDIM
3.3 V
ILimit
ILED
Iavg
Theory of Operation
This device contains two LED current sources. Each
channel is comprised of a lateral N−channel FET controlled
by a current limit circuit that senses the voltage drop across
the Rsense resistor and compares it with an internal voltage
reference to provide the current regulation. For dimming
applications,
the
current
limit
circuit
operates
in
combination with the PWM signal applied to the dim pin of
the device for control purposes.
Current Limit and PWM Circuits
With a DC voltage of 3.3 volts applied to the Dim pin of
the device, the internal reference voltage of the current limit
circuit is set to 93.5 mV. The Rsense resistor is then selected
through a very simple formula: Rsense = 93.5 mV / ILED. This
allows the user to set different LED currents (between 1 mA
and 30 mA).
For dimming control, a PWM signal may be applied to the
dim pin of the device. This PWM signal can be used to
perform digital dimming.
For digital dimming, the amplitude of the PWM signal
must be 3.3 V or higher. The LED current will be
proportional to the duty cycle of the PWM signal.
For analog dimming, the input signal to the Dim pin must
be between 0 and 3.3 volts. The resulting output current will
be given by the following formula:
ILED +
(Vdim 35.3)
Rsense
If a PWM signal is beyond the input frequency range for
the Dim pin, a RC filter may be used to convert it to an analog
signal.
The RC filter generates an analog voltage signal, which is
proportional to the duty cycle of the PWM signal applied.
This analog signal is then used as the new reference voltage
for the current limit circuit, which compares it with the
voltage signal generated across Rsense to provide the current
regulation.
Enable
The enable circuit turns the device on when a positive
signal is applied to the enable pin. The circuit is designed to
allow low current consumption (0.1
mA typical) when the
device is disabled.




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