HV9989 datasheet(9/22 Pages) MICROCHIP

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 2014 Microchip Technology Inc.

DS20005296B-page 9

HV9989

3.0

FUNCTIONAL DESCRIPTION

3.1

Power Topology

HV9989 is a three-channel, switch-mode converter,

LED driver designed to control a continuous conduction

mode boost or SEPIC device in a constant frequency

mode. The IC includes an internal linear regulator,

which operates from 10 to 40V input voltages. This

device can also be powered directly using the VDD

pins and bypassing the internal linear regulator.

HV9989 includes features typically required in LED

drivers such as open LED protection, output short cir-

cuit protection, linear and PWM dimming, programma-

ble input current limiting and accurate control of the

LED current. A high current gate drive output enables

the controller to be used in high power converters.

HV9989 is ideally suited for back-light applications

using either RGB or multi-channel white LED

configurations.

3.2

Power Supply to the IC (VIN, VDD,

VDD1-3)

The HV9989 can be powered directly from its VIN pin

that takes a voltage up to 40V. When a voltage is

applied at the VIN pin, the HV9989 tries to maintain a

constant 7.75V (typ) at the VDD pin. The regulator also

has a built in under-voltage lockout which shuts off the

IC if the voltage at the VDD pin falls below the UVLO

threshold. By connecting this VDD pin to the individual

VDD pins of the three channels, the internal regulator

can be used to power all three channels in the IC.

In case the internal regulator is not utilized, an external

power supply (7-9V) can be used to power the IC. In

this case, the power supply is directly connected to the

VDD pins and the VIN pin is left unconnected.

All four VDD pins must be bypassed by a low ESR

capacitor (≥0.1 µF) to provide a low impedance path for

the high frequency current of the output gate driver.

These capacitors must be referenced to the individual

grounds for proper noise rejection. Also, in all cases,

the four VDD pins must be connected together

externally.

The input current drawn from the external power supply

(or VIN pin) is a sum of the 4 mA current drawn by the

all the internal circuitry (for all three channels) and the

current drawn by the gate drivers (which in turn

depends on the switching frequency and the gate

charge of the external FET).

In the preceding equation, fS is the switching frequency

of the converters and QG1-3 are the gate charges of the

external FETs (which can be obtained from the FET

data sheets).

The EN pin is a TTL-compatible input used to disable

the IC. Pulling the EN pin to GND will shut down the IC

and reduce the quiescent current drawn by the IC to be

lower than 500 μA. If the enable function is not

required, the EN pin can be connected to VDD.

3.3

Clock Input (CLK)

The switching frequency of the converters are set by

using a TTL-compatible square wave input at the CLK

pin. The switching frequencies of the three converters

will be 1/12th the frequency of the external clock.

3.4

Current Sense (CS1-3)

The current sense input is used to sense the source

current of the switching FET. The CS input of the

HV9989 includes a built-in 100 ns (minimum) blanking

time to prevent spurious turn off due to the initial current

spike when the FET turns on.

The IC includes an internal resistor divider network,

which steps down the voltage at the COMP pins by a

factor of 12 (including the internal diode drop). This

stepped-down voltage is given to one of the

comparators as the current reference.

It is recommended that the sense resistor RCS be cho-

sen so as to provide about 250 mV current sense signal.

3.5

Slope Compensation

For continuous conduction mode converters operating in

the Constant Frequency mode, slope compensation

becomes necessary to ensure stability of the peak cur-

rent mode controller, if the operating duty cycle is greater

than 0.5. Choosing a slope compensation which is one

half of the down slope of the inductor current ensures

that the converter will be stable for all duty cycles.

Slope compensation in the HV9989 can be pro-

grammed by a single resistor at SC input common for

all three channels. Assuming a down slope of DS (A/

ms) for the inductor current, the SC resistor can be

computed as:

where RCS is the current sense resistor at the CSX

inputs.

IIN 4mA Q

QG2 QG3 



+fs



RSC

2VDD



SC 

–





DS 10

RCSCSC EFF





--------------------------------------------------------------

V

DS RCSCSC EFF





-----------------------------------------------



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