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6276 Просмотр технического описания (PDF) - Allegro MicroSystems

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6276 16-BIT SERIAL-INPUT, CONSTANT CURRENT LATCHED LED DRIV ER Allegro
Allegro MicroSystems Allegro
6276 Datasheet PDF : 14 Pages
First Prev 11 12 13 14
6276
16-BIT SERIAL-INPUT,
CONSTANT-CURRENT
LATCHED LED DRIVER
Applications Information
The load current per bit (IO) is set by the external resistor
(REXT) as shown in the figure below.
Package Power Dissipation (PD). The maximum al-
lowable package power dissipation is determined as
PD(max) = (150 - TA)/RθJA.
The actual package power dissipation is
PD(act) = DC • (VCE • IO • 16) + (VDD • IDD) ,
where DC is the duty cycle.
When the load supply voltage is greater than 3 V to 5 V,
considering the package power dissipating limits of these
devices, or if PD(act) > PD(max), an external voltage re-
ducer (VDROP) should be used.
Load Supply Voltage (VLED). These devices are de-
signed to operate with driver voltage drops (VCE) of
0.4 V to 0.7 V with LED forward voltages (VF) of 1.2 V to
4.0 V. If higher voltages are dropped across the driver,
package power dissipation will be increased significantly.
To minimize package power dissipation, it is recom-
mended to use the lowest possible load supply voltage or
to set any series dropping voltage (VDROP) as
VDROP = VLED - VF - VCE
with VDROP = Io • RDROP for a single driver, or a Zener
diode (VZ), or a series string of diodes (approximately
0.7 V per diode) for a group of drivers. If the available
voltage source will cause unacceptable dissipation and
series resistors or diode(s) are undesirable, a regulator
such as the Sanken Series SAI or Series SI can be used to
provide supply voltages as low as 3.3 V.
For reference, typical LED forward voltages are:
White
3.5 – 4.0 V
Blue
3.0 – 4.0 V
Green
1.8 – 2.2 V
Yellow
2.0 – 2.1 V
Amber
1.9 – 2.65 V
Red
1.6 – 2.25 V
Infrared
1.2 – 1.5 V
Pattern Layout. This device has a common logic-
ground and power-ground terminal. If ground pattern lay-
out contains large common-mode resistance, and the volt-
age between the system ground and the LATCH ENABLE
or CLOCK terminals exceeds 2.5 V (because of switching
noise), these devices may not operate correctly.
115 Northeast Cutoff, Box 15036
11
Worcester, Massachusetts 01615-0036 (508) 853-5000
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