September 13, 2005
Dual Output LNB Supply and Control
Voltage Regulator with I2C Interface for
Advanced Satellite Set-Top Box Designs
The ISL6424 is a highly integrated voltage regulator and
interface IC, specifically designed for supplying power and
control signals from advanced satellite set-top box (STB)
modules to the low noise blocks (LNBs) of two antenna
ports. The device is comprised of two independent current-
mode boost PWMs and two low-noise linear regulators along
with the circuitry required for 22kHz tone generation,
modulation and I2C device interface. The device makes the
total LNB supply design simple, efficient and compact with
low external component count.
Two independent current-mode boost converters provide the
linear regulators with input voltages that are set to the final
output voltages, plus typically 1.2V to insure minimum power
dissipation across each linear regulator. This maintains
constant voltage drops across each linear pass element
while permitting adequate voltage range for tone injection.
The final regulated output voltages are available at two
output terminals to support simultaneous operation of two
antenna ports for dual tuners. The outputs for each PWM are
set to 13V or 18V by independent voltage select commands
(VSEL1, VSEL2) through the I2C bus. Additionally, to
compensate for the voltage drop in the coaxial cable, the
selected voltage may be increased by 1V with the line length
compensation (LLC) feature. All the functions on this IC are
controlled via the I2C bus by writing 8 bits on System
Register (SR, 8 bits). The same register can be read back,
and two bits will report the diagnostic status. Separate enable
commands sent on the I2C bus provide independent standby
mode control for each PWM and linear combination, disabling
the output into shutdown mode.
Each output channel is capable of providing 750mA of
continuous current. The overcurrent limit can be digitally
programmed. The SEL18V pin allows the 13V to 18V
transition with an external pin, overriding the I2C input.
The ISL6424 is offered in a 32 Ld 5x5 QFN.
• Single Chip Power Solution
- True Dual Operation for 2-Tuner/2-Dish Applications
- Both Outputs May be Enabled Simultaneously at
- Integrated DC-DC Converter and I2C Interface
• Switch-Mode Power Converter for Lowest Dissipation
- Boost PWMs with > 92% Efficiency
- Selectable 13V or 18V Outputs
- Digital Cable Length Compensation (1V)
• I2C Compatible Interface for Remote Device Control
- Registered Slave Address 0001 00XX
- Full 3.3V/5V Operation up to 400kHz
• External Pins to Select 13V/18V Option
• DSQIN1&2 and SEL18V1&2 pins 2.5V Logic Compatible
• Built-In Tone Oscillator Factory Trimmed to 22kHz
- Facilitates DiSEqC (EUTELSAT) Encoding
• Internal Over-Temperature Protection and Diagnostics
• Internal Overload and Overtemp Flags (Visible on I2C)
• LNB Short-Circuit Protection and Diagnostics
• QFN Package
- Compliant to JEDEC PUB95 MO-220 QFN - Quad Flat
No Leads - Product Outline
- Near Chip-Scale Package Footprint
• Pb-Free Plus Anneal Available (RoHS Compliant)
• LNB Power Supply and Control for Satellite Set-Top Box
• Tech Brief 389 (TB389) - “PCB Land Pattern Design and
Surface Mount Guidelines for QFN Packages”; Available
on the Intersil website, www.intersil.com
PART # *
MARKING (°C) PACKAGE DWG. #
ISL6424ER -20 to 85 32 Ld 5x5 QFN L32.5x5
ISL6424ERZ (Note) ISL6424ERZ -20 to 85 32 Ld 5x5 QFN L32.5x5
*Add “-T” suffix for tape and reel.
NOTE: Intersil Pb-free plus anneal products employ special Pb-free
material sets; molding compounds/die attach materials and 100%
matte tin plate termination finish, which are RoHS compliant and
compatible with both SnPb and Pb-free soldering operations. Intersil
Pb-free products are MSL classified at Pb-free peak reflow
temperatures that meet or exceed the Pb-free requirements of
IPC/JEDEC J STD-020.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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