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I NTEGRATED C IRCUITS D IVISION
2. Functional Description
Figure 1 Typical Application Circuit
8-450V
MXHV9910
V DD
6
1
V DD
V IN
Voltage
Regulator
Voltage
Reference
250mV
8
R T
OSC
7
LD
-
+
-
PWM
Control
GATE
4
+
5
PWMD
3
GND
CS
2
R SENSE
2.1 Overview
The MXHV9910 is a high-efficiency, low cost, off-line
LED driver designed using IXYS IC Division's state of
the art BCDMOS on SOI process. The driver can
operate from a DC supply voltage between 8 to
450V DC . The versatile input supply voltage range
enables this driver to be used in a broad range of
applications such as flat panel display RGB
backlighting, signage, decorative LED lighting, and
up the voltage across the current sense resistor
located at the CS pin. When the rising voltage at the
current sense, CS, pin exceeds V CS(high) , the internally
set threshold, the gate drive signal goes low and turns
off the external power MOSFET. Turning the power
MOSFET off causes the inductor current to decay until
the next rising edge of the clock, and the process
repeats.
incandescent lamp replacement.
The peak current threshold is set by comparing the
The MXHV9910 IC is configured in a buck converter
topology, which is a perfect choice for off-line and DC
applications driving multiple LEDs in series or parallel.
This method provides excellent efficiency and enables
a buck switcher design using a minimum number of
external components. An external current sense
resistor sets the peak current to the LED string. In
addition, LED dimming can be implemented by either
applying a DC control voltage to the LD pin, or by
applying a low frequency, pulse-width modulated
digital signal to the PWMD pin (typically 500 Hz).
voltage developed across the R SE N SE resistor to the
internal threshold, V CS(high) . This default threshold can
be overridden externally by applying a voltage less
than V CS(high) to the LD pin. The lower of these two
thresholds limits the peak current in the inductor
A soft-start function can be implemented by slowly
ramping up the DC voltage at the LD pin from 0mV to
a level greater than 250mV. Figure 2 shows a typical
recommended soft-start circuit design.
Figure 2 Soft-Start RC Network
2.2 LED Driver Theory of Operation
MXH V 9910
51k Ω
The gate driver pulse width mode (PWM) control
circuit is enabled by connecting the PWMD pin to the
V DD pin. When enabled, the rising edge of each
internal clock turns on the gate driver and the external
power MOSFET, causing the inductor current to ramp
www.ixysic.com
R03
V IN
CS
GND
GATE
R T
LD
V DD
P W MD
2k Ω
0.1 μ F
5
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