HV9918DB1 Supertex, HV9918DB1 Datasheet - Page 6

• Manufacturer Part Number: HV9918DB1
• Description: LED Lighting Development Kits HI CURR LED DRIVER DEMOBOARD
• Manufacturer: Supertex

Thermal Shutdown
The HV9918 thermal-shutdown feature turns off the SW driv-
er when the junction temperature exceeds +140°C. The SW
driver turns back on when the junction temperature drops
60°C below the shutdown temperature threshold.
Freewheeling Diode Selection
The forward voltage of the freewheeling diode should be
as low as possible for better efficiency. A Schottky diode
is a good choice as long as the breakdown voltage is high
enough to withstand the maximum operating voltage. The
forward current rating of the diode must be at least equal to
the maximum LED current.
LED Current Ripple
The LED current ripple is equal to the inductor current ripple.
In cases when a lower LED current ripple is needed, a ca-
pacitor can be placed across the LED terminals.
Pin Description
Pin #
TAB
1
2
3
4
5
6
7
8
Supertex inc.
RAMP
ADIM
GND
GND
VDD
DIM
VIN
Pin
SW
CS
Description
Current sense input. Senses LED string current.
Input voltage 4.5 to 40V DC.
Analog PWM dimming ramp output.
Analog 0 ~ 2.0V signal input for analog control of PWM dimming.
PWM signal input.
Internally regulated supply voltage. Connect a capacitor from VDD to ground.
Device ground.
Open Drain Output of an internal 40V 1.0Ω MOSFET.
Must be wired to pin 7 on PCB.
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1235 Bordeaux Drive, Sunnyvale, CA 94089
6
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching losses
and stable operation. Use a multilayer board whenever pos-
sible for better noise immunity. Minimize ground noise by
connecting high-current ground returns, the input bypass
capacitor ground lead, and the output filter ground lead to
a single point (star ground configuration). The fast di/dt loop
is formed by the input capacitor C
and the HV9918 switching MOSFET. To minimize noise inter-
action, this loop area should be as small as possible. Place
R
better noise immunity, a Kelvin connection is strongly recom-
mended between CS and R
of the IC to a large-area ground plane for improved power
dissipation.
SENSE
as close as possible to the input filter and VIN. For
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Tel: [phone]
SENSE
●
www.supertex.com
. Connect the exposed tab
IN
, the free-wheeling diode
HV9918