SQ9910/SQ9910A
Universal High Brightness LED Driver
FEATURES
●
>90% Efficiency
●
Universal rectified 85 to 265V
AC
input range
●
Constant-current LED driver
●
Applications from a few mA to more than
1A Output
●
LED string from one to hundreds of diodes
●
PWM Low-Frequency Dimming via
Enable pin
●
Input voltage surge ratings up to 500V
●
Internal Thermal Protection (OTP)
●
7.5V MOSFET drive – SQ9910
10V MOSFET drive – SQ9910A
PRODUCT DESCRIPTION
The SQ9910 is a PWM high-efficiency LED driver
control IC. It allows efficient operation of High
Brightness (HB) LEDs from voltage sources
ranging from 85V
AC
up to 265V
AC
. The SQ9910
controls an external MOSFET at fixed switching
frequency up to 300kHz. The frequency 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.
The SQ9910 uses a rugged high voltage junction
isolated process that can withstand an input
voltage surge of up to 500V. Output current to
an LED string can be programmed to any value
between zero and its maximum value by
applying an external control voltage at the linear
dimming control input of the SQ9910. The
SQ9910 provides a low-frequency PWM dimming
input that can accept an external control signal
with a duty ratio of 0-100% and a frequency of
up to a few kilohertz
TYPICAL APPLICATIONS
●
DC/DC or AC/DC LED Driver application
●
RGB Backlighting LED Driver
●
Back Lighting of Flat Panel Displays
●
General purpose constant current source
●
Signage and Decorative LED Lighting
APPLICATION CIRCUIT
SQ9910/SQ9910A
APPLICATION INFORMATION
AC/DC Off-Line Applications
The SQ9910 is a low-cost off-line buck or boost
converter control IC specifically designed for driving
multi-LED stings or arrays. It can be operated from
either universal AC line or any DC voltage between 8-
450V. Optionally, a passive power factor correction
circuit can be used in order to pass the AC harmonic
limits set by EN 61000-3-2 Class C for lighting
equipment having input power less than 25W. The
SQ9910 can drive up to hundreds of High-Brightness
(HB) LEDs or multiple strings of HB LEDs. The LED
arrays can be confi gured as a series or series/parallel
connection. The SQ9910 regulates constant current
that ensures controlled brightness and spectrum of the
LEDs, and extends their lifetime. The SQ9910 features
an enable pin (PWM_D) that allows PWM control of
brightness.
The SQ9910 can also control brightness of LEDs by
programming continuous output current of the LED
driver (so-called linear dimming) when a control
voltage is applied to the LD pin.
The SQ9910 is offered in a standard 8-pin SOIC
package. It is also available in a high voltage rated
SO-16 package for applications that require V
IN
greater than 250V.
The SQ9910 includes an internal high-voltage linear
regulator that powers all internal circuits and can also
serve as a bias supply for low voltage external
circuitry.
externally by applying voltage to the LD pin.
therefore, assuring that output current of the LED
ramps gradually. When soft start is required, a
capacitor can be connected to the LD pin to allow
this voltage to ramp at a desired rate. Additionally,
a simple passive power factor correction circuit,
consisting of 3 diodes and 2 capacitors, can be
added as shown in the typical application circuit
diagram of Figure 1
.
Supply Current
A current of 1mA is needed to start the SQ9910.
As shown in the block diagram on page 3, this
current is internally generated in the SQ9910
without using bulky startup resistors typically
required in the offl ine applications. Moreover, in
many applications the SQ9910 can be
continuously powered using its internal linear
regulator that provides a regulated voltage of 7.5V
for all internal circuits
.
Setting Light Output
When the buck converter topology of Figure 2 is
selected, the peak CS voltage is a good
representation of the average current in the LED.
However, there is a certain error associated with
this current sensing method that needs to be
accounted for. This error is introduced by the
difference between the peak and the average
current in the inductor. For example if the peak-to-
peak ripple current in the inductor is 150mA, to get
a 500mA LED current, the sense resistor should
be 250mV/(500mA+ 0.5*150mA) = 0.43Ω
.
LED Driver Operation
The SQ9910 can control all basic types of converters,
isolated or non-isolated, operating in continuous or
discontinuous conduction mode. When the gate signal
enhances the external power MOSFET, the LED driver
stores the input energy in an inductor or in the primary
inductance of a transformer and, depending on the
converter type, may partially deliver the energy directly
to LEDs The energy stored in the magnetic component
is further delivered to the output during the off-cycle of
the power MOSFET producing current through the
string of LEDs (Flyback mode of operation).
When the voltage at the V
DD
pin exceeds the UVLO
threshold the gate drive is enabled. The output current
is controlled by means of limiting peak current in the
external power MOSFET. A current sense resistor is
connected in series with the source terminal of the
MOSFET. The voltage from the sense resistor is
applied to the CS pin of the SQ9910. When the
voltage at CS pin exceeds a peak current sense
voltage threshold, the gate drive signal terminates, and
the power MOSFET turns off. The threshold is
internally set to 250mV, or it can be programmed
Dimming
Dimming can be accomplished in two ways,
separately or combined, depending on the
application. Light output of the LED can be
controlled either by linear change of its current, or
by switching the current on and off while
maintaining it constant. The second dimming
method (so-called PWM dimming) controls the
LED brightness by varying the duty ratio of the
output current.
The linear dimming can be implemented by
applying a control voltage from 0 to 250mV to the
LD pin. This control voltage overrides the
internally set 250mV threshold level of the CS pin
and programs the output current accordingly. For
example, a potentiometer connected between V
DD
and ground can program the control voltage at the
CS pin. Applying a control voltage higher than
250mV will not change the output current setting.
When higher current is desired, select a smaller
sense resistor.
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