LED 节能灯 电源驱动芯片 OS9910 资料

LED 节能灯 日光灯 电源驱动芯片 OS9910 资料

OS9910

Universal High Brightness LED Driver

Features

Switch mode controller for single switch LED driversEnhanced drop-in replacement to the OS9910Open loop peak current controllerInternal 8.0V to 450V linear regulator

Constant frequency or constant off-time operationLinear and PWM dimming capability

Requires few external components for operation

General Description

The OS9910 is an open loop current mode control LED driver IC. The OS9910 can be programmed to operate in either a constant frequency or constant off-time mode. It includes an 8 – 450V linear regulator which allows it to work from a wide range of input voltages without the need for an external low voltage supply. The 9910 includes a 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. It also includes a 0 – 250mV linear dimming input which can be used for linear dimming of the LED current.

The OS9910 is ideally suited for buck LED drivers. Since the OS9910 operates in open loop current mode control, the controller achieves good output current regulation without the need for any loop compensation. PWM dimming response is limited only by the rate of rise and fall of the inductor current, enabling very fast rise and fall times. The OS9910 requires only three external components (apart from the power stage) to produce a controlled LED current making it an ideal solution for low cost LED drivers.

Applications

DC/DC or AC/DC LED driver applicationsRGB backlighting LED driverBack lighting of at panel displays

General purpose constant current sourceSignage and decorative LED lightingChargers

Typical Application Circuit

LED 节能灯 日光灯 电源驱动芯片 OS9910 资料

Ordering Information

Pin Description

-G indicates package is RoHS compliant (‘Green’)

8-Lead SO

(top view)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the speci cations is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

(The * denotes speci cations which apply over the full operating ambient temperature range of -40°C<TA<125°C.

Otherwise speci cations are at T= 25°C. V= 12V, unless otherwise noted. All Typical Numbers are at T = 25°C )

Electrical Characteristics

Input

LED 节能灯 日光灯 电源驱动芯片 OS9910 资料

Internal Regulator (cont.)

1. Also limited by package power dissipation limit, whichever is lower. VDD load current external to the OS9910* Speci cations that apply over the full temperature range are guaranteed by design and characterization# Guaranteed by design

LED 节能灯 日光灯 电源驱动芯片 OS9910 资料

Block Diagram

VIN

VDD

LD

GATE

CS

LED 节能灯 日光灯 电源驱动芯片 OS9910 资料

Application Information

The OS9910 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 frequency of operation (or the off-time). The oscillator produces pulses at regular intervals. These pulses set the SR ip- op in the OS9910 which causes the gate driver to turn on. The same pulses also start the blanking timer which inhibits the reset input of the SR ip op 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 ows through the external sense resistor RCS 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 ip op. When the output of either one of the two comparators goes high, the ip op is reset and the gate output goes low. The gate goes low until the SR ip op is set by the oscillator. Assuming a 30% ripple in the inductor, the current sense resistor RCS can be set using:0.25V (or VLD)

RCS =

1.15 ILED

(A)

●

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 OS9910 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 and the OS9910 will operate directly off the voltage supplied at the VDD pin. Please note that this external voltage at the VDD pin should not exceed 12V.

Although the VIN pin of the OS9910 is rated up to 450V, the actual maximum voltage that can be applied is limited by the power dissipation in the IC. For example, if an 8-pin SOIC (junction to ambient thermal resistance Rθ,j-a = 128°C/W) OS9910 draws about IIN = 2mA from the VIN pin, and has a maximum allowable temperature rise of the junction temperature limited to about ΔT = 100°C, the maximum volt-age at the VIN pin would be:

In these cases, to operate the OS9910 from higher input

Constant frequency peak current mode control has an in-voltages, a Zener diode can be added in series with the VIN herent disadvantage – at duty cycles greater than 0.5, the pin to divert some of the power loss from the OS9910 to control scheme goes into subharmonic oscillations. To pre-the Zener diode. In the above example, using a 100V zener vent this, an arti cial slope is typically added to the current diode will allow the circuit to easily work up to 450V.sense waveform. This slope compensation scheme will af-fect the accuracy of the LED current in the present form. The input current drawn from the VIN pin is a sum of the However, a constant off-time peak current control scheme 1.0mA current drawn by the internal circuit and the current does not have this problem and can easily operate at duty drawn by the gate driver (which in turn depends on the switch-cycles greater then 0.5 and also gives inherent input volt-ing frequency and the gate charge of the external FET).age rejection making the LED current almost insensitive to

input voltage variations. But, it leads to variable frequency IIN ≈ 1.0mA + QG fS operation and the frequency range depends greatly on the input and output voltage variation.OS9910 makes it easy In the above equation, fS is the switching frequency and QG to switch between the two modes of operation by changing is the gate charge of the external FET (which can be ob-one connection (see oscillator section).tained from the datasheet of the FET).

Input Voltage Regulator

The OS9910 can be powered directly from its VIN pin and can work from 8-450VDC at its VIN pin. When a voltage is applied at the VIN pin, the OS9910 maintains a constant

LED 节能灯 日光灯 电源驱动芯片 OS9910 资料

Current Sense

Linear Dimming

The Linear Dimming pin is used to control the LED current.

The current sense input of the OS9910 goes to the non-inverting inputs of two comparators. The inverting terminal There are two cases when it may be necessary to use the

of one comparator is tied to an internal 250mV reference Linear Dimming pin.whereas the inverting terminal of the other comparator is

In some cases, it may not be possible to nd the exact connected to the LD pin. The outputs of both these compara-RCS value required to obtain the LED current when the tors are fed into an OR gate and the output of the OR gate

internal 250mV is used. In these cases, an external volt-is fed into the reset pin of the ip- op. Thus, the comparator

age divider from the VDD pin can be connected to the LD which has the lowest voltage at the inverting terminal deter-pin to obtain a voltage (less than 250mV) corresponding to mines when the GATE output is turned off.

the desired voltage across RCS.

The outputs of the comparators also include a 150-280ns

Linear dimming may be desired to adjust the current blanking time which prevents spurious turn-offs of the exter-level to reduce the intensity of the LEDs. In these cases, nal FET due to the turn-on spike normally present in peak

an external 0-250mV voltage can be connected to the LD current mode control. In rare cases, this internal blanking

pin to adjust the LED current during operation.might not be enough to lter out the turn-on spike. In these

cases, an external RC lter needs to be added between the

To use the internal 250mV, the LD pin can be connected to external sense resistor (RCS) and the CS pin.

VDD.

Please note that the comparators are fast (with a typical

80ns response time). Hence these comparators are more Note: Although the LD pin can be pulled to GND, the output susceptible to be triggered by noise than the comparators current will not go to zero. This is due to the presence of a of the OS9910. A proper layout minimizing external induc-minimum on-time (which is equal to the sum of the blanking

time and the delay to output time) which is about 450ns. tances will prevent false triggering of these comparators.

This will cause the FET to be on for a minimum of 450ns and thus the LED current when LD = GND will not be zero. This Oscillator

current is also dependent on the input voltage, inductance

The oscillator in the HV9910B is controlled by a single re-value, forward voltage of the LEDs and circuit parasitics. To sistor connected at the RT pin. The equation governing the get zero LED current, the PWMD pin has to be used.oscillator time period tOSC is given by:PWM Dimming

PWM Dimming can be achieved by driving the PWMD pin with a low frequency square wave signal. When the PWM

If the resistor is connected between RT and GND, HV9910B signal is zero, the gate driver is turned off and when the operates in a constant frequency mode and the above equa-PWMD signal if high, the gate driver is enabled. Since the tion determines the time-period. If the resistor is connected PWMD signal does not turn off the other parts of the IC, between RT and GATE, the HV9910B operates in a constant the response of the OS9910 to the PWMD signal is almost off-time mode and the above equation determines the off-instantaneous. The rate of rise and fall of the LED current is

thus determined solely by the rise and fall times of the induc-time.

tor current.

GATE Output

The gate output of the OS9910 is used to drive and external FET. It is recommended that the gate charge of the external FET be less than 25nC for switching frequencies ≤ 100kHz and less than 15nC for switching frequencies > 100kHz.

To disable PWM dimming and enable the OS9910 perma-nently, connect the PWMD pin to VDD.

LED 节能灯 日光灯 电源驱动芯片 OS9910 资料

8-Lead SOIC (Narrow Body) Package Outline (LG)

4.9x3.9mm body, 1.75mm height (max), 1.27mm pitch

Note 1:

This chamfer feature is optional. If it is not present, then a Pin 1 identi er must be located in the index area indicated.The Pin 1 identi er may be either a mold, or an embedded metal or marked feature.

JEDEC Registration MS-012, Variation AA, Issue E, Sept. 2005.Drawings not to scale.

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