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PDF EUP2794 Data sheet ( Hoja de datos )
| Número de pieza | EUP2794 | |
| Descripción | White LED Driver | |
| Fabricantes | Eutech Microelectronics | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de EUP2794 (archivo pdf) en la parte inferior de esta página. Total 13 Páginas | ||
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EUP2794
White LED Driver with 1X /1.5X
High-Efficiency Charge Pump
DESCRIPTION
The EUP2794 is a low noise, constant frequency
charge pump that uses a dual mode load switch (1X)
and fractional (1.5X) conversion to maximize
efficiency for white LED applications. The EUP2794
delivers up to 80mA of load current and provides four
regulated current sources, each capable of driving up to
20mA through white LEDs. All LED pin currents are
regulated, constant and tightly matched to achieve
uniformity of brightness across the LCD backlight. The
switching frequency is 900kHz.(typ.) to keep the
www.DcaotanSdhuecette4dU.conmoise spectrum away from sensitive
frequencies within portable RF devices.
An external resistor (RSET) sets the current in each of
the LED outputs. In addition, brightness can be
controlled by both linear and PWM techniques. An
analog voltage between 0V and 3.0V may be applied to
the BRGT pin to linearly vary the LED current. By
adjusting current with BRGT pin , the brightness of the
LEDs can be smoothly varied. Alternatively, a PWM
digital signal can be applied to the SD pin to vary the
perceived brightness of the LED.
The EUP2794 is available in a 16-pin 3mm × 3mm
QFN package.
FEATURES
z Regulated Current Sources with 0.6%
Mis-matching between any Two Outputs
z High Efficiency 1.5X Charge Pump
z Drives One, Two, Three or Four White LEDs
z 2.7V to 5.5V Input Voltage
z Up to 80mA Output Current
z Analog or PWM Brightness Control
z Soft Start Function
z Low Shutdown Current
z 900kHz Switching Frequency (typ.)
z Tiny 3mm × 3mm QFN-16 Package
z RoHS Compliant and 100% Lead(Pb)-Free
APPLICATIONS
z White LED Backlighting
z 1-Cell Li-Ion battery-operated equipment
including PDAs, hand-held PCs, cellular
phones
Typical Application Circuit
DS2794 Ver0.5 Mar. 2006
Figure 1.
1
1 page  
Typical Operating Characteristics
www.DataSheet4U.com
EUP2794
DS2794 Ver0.5 Mar. 2006
5
5 Page 
Parallel Dx Outputs for Increased Current Drive
Outputs D1 through D4 may be connected together in
any combination to drive higher currents through
fewer LEDs. For example in Figure 5, outputs D1 and
D2 are connected together to drive one LED while D3
and D4 are connected together to drive a second LED.
EUP2794
Connecting outputs in parallel does not affect internal
operation of the EUP2794 and has no impact on the
Electrical Characteristics and limits previously
presented. The available diode output current,
maximum diode voltage, and all other specifications
provided in the Electrical Characteristics table apply
to parallel output configurations, just as they do to the
standard 4-LED application circuit.
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Thermal Protection
When the junction temperature exceeds 150°C (typ.),
the EUP2794 internal thermal protection circuitry
disables the part. This feature protects the device
from damage due to excessive power dissipation. The
device will recover and operate normally when the
junction temperature falls below 140°C (typ.). It is
important to have good thermal conduction with a
proper layout to reduce thermal resistance.
Figure 5. Two Parallel Connected LEDs
With this configuration, two parallel current sources
of equal value provide current to each LED. RSET and
VBRGT should therefore be chosen so that the current
through each output is programmed to 50% of the
desired current through the parallel connected LEDs.
For example, if 30mA is the desired drive current for
2 parallel connected LEDs , RSET and VBRGT should
be selected so that the current through each of the
outputs is 15mA. Other combinations of parallel
outputs may be implemented in similar fashions, such
as in Figure 6.
Figure 6. One Parallel Connected LED
Power Efficiency
Figure 7 shows the efficiency of the EUP2794. The
change in efficiency shown by the graph comes from
the transition from Pass Mode to a gain of 1.5.
Efficiency (E) of the EUP2794 is defined here as the
ratio of the power consumed by LEDs (PLED) to the
power drawn from the input source (PIN). In the
equations below, IQ is the quiescent current of the
EUP2794, ILED is the current flowing through one
LED, VLED is the forward voltage at that LED current,
and N is the number of LEDs connected to the
regulated current outputs. In the input power
calculation, the 1.5 represents the switched capacitor
gain configuration of the EUP2794.
PLED = N × VLED × ILED
PIN = VIN × IIN
( )PIN = VIN × 1.5 × N × ILED + IQ
E = (PLED ÷ PIN )
Efficiency, as defined here, is in part dependent on
LED voltage. Variation in LED voltage does not
affect power consumed by the circuit and typically
does not relate to the brightness of the LED. For an
advanced analysis, it is recommended that power
consumed by the circuit (VIN x IIN) be evaluated
rather than power efficiency. Figure 8 shows the
power consumption of the EUP2794 Typical
Application Circuit.
DS2794 Ver0.5 Mar. 2006
11
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| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet EUP2794.PDF ] | |
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