MXHV9910

8

www.clare.com

R01

The inductor peak current rating is given by:

2.2.7 Gate Output Drive

The MXHV9910 uses an internal gate drive circuit to

turn on and off an external power MOSFET. The gate

driver can drive a variety of MOSFETs. For a typical

off-line application, the total MOSFET gate charge will

be less than 25nC.

2.2.8 Linear Dimming

A linear dimming function can be implemented by

applying a DC control voltage to the LD pin. By varying

this voltage, the user can adjust the current level in the

LEDs, which in turn will increase or decrease the light

intensity. The control voltage to the LD pin can be

generated from an external voltage divider network

LED current at a particular level and there is no exact

higher than the current sense threshold voltage at the

LD pin will not change the output current due to the

fixed threshold setting. When the LD pin is not used, it

Figure 5 Typical Linear Dimming Application Circuit

2.2.9 PWM Dimming

Pulse width modulation dimming can be implemented

by driving the PWMD pin with a low frequency square

wave signal in the range of a few hundred Hertz. The

PWMD signal controls the LED brightness by gating

the PWM gate driver output pin GATE.

The signal can be generated by a microcontroller or a

pulse generator with a duty cycle proportional to the

amount of desired light output. When PWMD is low,

gate drive is off; when PWMD is high, gate drive is

enabled.

Figure 6 Buck Driver for PWM Dimming Application Circuit

×

()

+

[]

×

=

HB LEDs

350mA

D1

BYV26B

C1

0.1

μF

400V

C1

22

μF

400V

R1

402k

Ω

L1

4.7mH

R4

0.56

Ω

R2

51k

Ω

RA1

5.0k

Ω

C1

2.2

μF

16V

C1

0.1

μF

25V

AC

AC

+

-

BR1

Fuse F2

2A

NTC1

MXHV9910

V

IN

CS

GND

GATE

R

T

LD

V

DD

PWMD

IXTA8N50P

LD

Monitor

AC Input

90 - 265V

rms

HB LEDs

900mA Max

ASMT-Mx00

D1 Schottky

40V

0.1

μF

50V

402k

Ω

220

μH

R1

0.27

Ω

10

μF

50V

MXHV9910

V

IN

CS

GND

GATE

R

T

LD

V

DD

PWMD

Q1

V

IN

12 - 30V

DC

PWM

CPC1001N*

*Optional Isolation