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PDF HY7700S8R Data sheet ( Hoja de datos )
| Número de pieza | HY7700S8R | |
| Descripción | High Brightness LED Driver | |
| Fabricantes | Oristreak | |
| Logotipo |  |
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Description
HY7700 is a PWM high-efficiency LED
driver controller IC. It allows efficient
operation of High Brightness （HB） LED(s)
from voltage sources ranging from 9VDC up
to 450VDC. HY7700 controls an external
MOSFET at variable switching frequency up
to 300 kHz. The constant off-time can be
programmed using a single resistor. The LED
string is driven at constant current rather than
constant voltage, thus providing constant
light output and enhanced reliability. The
output current can be programmed between
a few milliamps and up to more than 1.0A
.
Typical Applications Circuit
HY7700
High Brightness LED Driver
Features
n >90% efficiency.
n 9V to 450V input Range.
n Constant Current LED driver.
n More than 1.0A output applications.
n PWM Low-Frequency Dimming via
Enable pin.
n Input Voltage Surge ratings up to 450V.
Applications
n DC/DC LED Driver Application.
n RGB backlighting LED driver.
n Back lighting of flat panel displays.
n LED Lighting Application
n Automotive LED Lighting Application.
Copyright © 2009 Oristreak Ltd.,
HTTP://WWW.ORISTREAK.COM
-1-
HY7700 V1.0
1 page  
HY7700
High Brightness LED Driver
APPLICATION INFORMATION
The HY7700 is optimized to drive buck LED drivers using open-loop peak current mode control.
This method of control enables fairly accurate LED current control without the need for high side
current sensing or the design of any closed loop controllers. The IC uses very few external components
and enables both Linear and PWM dimming of the LED current.
A resistor connected to the RT pin programs the off-time of operation (or the frequency). The
oscillator produces pulses at regular intervals. These pulses set the SR flip-flop in the HY7700 which
causes the gate driver to turn on. The same pulses also start the blanking timer which inhibits the reset
input of the SR flip flop and prevent false turn-offs due to the turn-on spike. When the FET turns on, the
current through the inductor starts ramping up. This current flows through the external sense resistor
RSE and produces a ramp voltage at the CS pin. The comparators are constantly comparing the CS pin
voltage to both the voltage at the LD pin and the internal 250mV. Once the blanking timer is complete,
the output of these comparators is allowed to reset the flip flop. When the output of either one of the two
comparators goes high, the flip flop is reset and the gate output goes low. The gate goes low until the SR
flip flop is set by the oscillator. Assuming a 30% ripple in the inductor, the current sense resistor RSE
can be set using:
RSE = 0.25V (or LD)
1.15 × ILED (A)
Constant frequency peak current mode control has an inherent disadvantage - at duty cycles greater
than 0.5, the control scheme goes into sub harmonic oscillations. To prevent this, an artificial slope is
typically added to the current sense waveform. This slope compensation scheme will affect the accuracy
of the LED current in the present form. However, a constant off-time peak current control scheme does
not have this problem and can easily operate at duty cycles greater then and also gives inherent input
voltage rejection making the LED current almost insensitive to input voltage variations. But, it leads to
variable frequency operation and the frequency range depends greatly on the input and output voltage
variation HY7700 makes it easy to switch between the two modes of operation by changing one
connection (see oscillator section).
Input Voltage Regulator
The HY7700 can be powered directly from its VIN pin and can work from 9-450 VDC at its VIN pin.
When a voltage is applied at the VIN pin, the HY7700 maintains a constant 7.5V at the VDD pin. This
voltage is used to power the IC and any external resistor dividers needed to control the IC. The VDD pin
must be bypassed by a low ESR capacitor to provide a low impedance path for the high frequency
current of the output gate driver. The HY7700 can also be operated by supplying a voltage at the VDD
pin greater than the internally regulated voltage. This will turn off the internal linear regulator of the IC
Copyright © 2009 Oristreak Ltd.,
HTTP://WWW.ORISTREAK.COM
-5-
HY7700 V1.0
5 Page | ||
| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet HY7700S8R.PDF ] | |
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