HV9910B 查看數據表（PDF） - Microsemi Corporation

零件编号

产品描述 (功能)

生产厂家

HV9910B

Universal High-Brightness LED Driver

Microsemi Corporation 

HV9910B

3.0 APPLICATION INFORMATION

HV9910B 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 fre-

quency of operation (or the off-time). The oscillator pro-

duces pulses at regular intervals. These pulses set the

SR flip-flop in the HV9910B which causes the GATE

driver to turn on. The same pulses also start the blank-

ing 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 induc-

tor starts ramping up. This current flows through the

external sense resistor RCS and produces a ramp volt-

age 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 RCS

can be set using:

RCS = 0-1---..-2-1---5-5---V----I--Lo---E-r--DV-----LA--D----

Constant frequency peak current mode control has an

inherent disadvantage – at duty cycles greater than

0.5, the control scheme goes into subharmonic oscilla-

tions. To prevent this, an artificial slope is typically

added to the current sense waveform. This slope com-

pensation 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 0.5. This control scheme also gives inherent input

voltage rejection, making the LED current almost

insensitive to input voltage variations. However, this

scheme leads to variable frequency operation and the

frequency range depends greatly on the input and out-

put voltage variation. HV9910B makes it easy to switch

between the two modes of operation by changing one

connection (see Section 3.3 “Oscillator”).

3.1 Input Voltage Regulator

HV9910B can be powered directly from its VIN pin and

can work from 8.0 - 450VDC at its VIN pin. When a volt-

age is applied at the VIN pin, the HV9910B maintains a

constant 7.5V at the VDD pin. This voltage is used to

power the IC and any external resistor dividers needed

DS20005344A-page 6

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.

HV9910B 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 HV9910B 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 HV9910B is rated up to

450V, the actual maximum voltage that can be applied

is limited by the power dissipation in the IC. For exam-

ple, if an 8-pin SOIC (junction to ambient thermal resis-

tance Rθ,j-a = 128°C/W) HV9910B draws about IIN =

2.0mA from the VIN pin, and has a maximum allowable

temperature rise of the junction temperature limited to

about ∆T = 100°C, the maximum voltage at the VIN pin

would be:

VINMAX = R--------Tj--–---a-  I--1I--N- = 1----2-1--8--0---0--C----C----W----  2----m-1-----A--= 390V

In these cases, to operate the HV9910B from higher

input voltages, a Zener diode can be added in series

with the VIN pin to divert some of the power loss from

the HV9910B to the Zener diode. In the above exam-

ple, using a 100V Zener diode will allow the circuit to

easily work up to 450V.

The input current drawn from the VIN pin is a sum of the

1.0mA current drawn by the internal circuit and the cur-

rent drawn by the GATE driver.The GATE driver

depends on the switching frequency and the GATE

charge of the external FET).

IIN  1.0mA + Qg  fs

In the above equation, fS is the switching frequency and

QG is the GATE charge of the external FET (which can

be obtained from the data sheet of the FET).

3.2 Current Sense

The current sense input of the HV9910B goes to the

non-inverting inputs of two comparators. The inverting

terminal of one comparator is tied to an internal 250mV

reference, whereas the inverting terminal of the other

comparator is connected to the LD pin. The outputs of

both these comparators are fed into an OR GATE and

the output of the OR GATE is fed into the reset pin of

the flip-flop. Thus, the comparator which has the lowest

voltage at the inverting terminal determines when the

GATE output is turned off.

 2015 Microchip Technology Inc.

Share Link: