The ISL6423B 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 singe antenna
ports. The device consists of a current-mode boost PWM
and a low-noise linear regulator 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.
The current-mode boost converters provides the linear
regulator with input voltage that is set to the final output
voltages, plus typically 0.8V to insure minimum power
dissipation across each linear regulator. This maintains
constant voltage drop across the linear pass element while
permitting adequate voltage range for tone injection.
The final regulated output voltage is available at output
terminals to support the operation of an antenna port for
single tuners. The outputs for each PWM can be controlled
in two ways, full control from I2C using the VTOP and VBOT
bits or set the I2C to the lower range i.e., 13V/14V, and
switch to higher range i.e., 18V/19V, with the SELVTOP pin.
All the functions on this IC are controlled via the I2C bus by
writing 8 bits words onto the System Registers (SR). The
same register can be read back, and five I2C bits will report
the diagnostic status. Separate enable command sent on the
I
2C bus provides for standby mode control for the PWM and
linear combination, disabling the output and forcing a shutdown
mode. The output channel is capable of providing 750mA of
continuous current. The overcurrent limit can be digitally
programmed to four levels.
The External modulation input EXTM can accept a
modulated Diseqc command and transfer it symmetrically to
the output. Alternatively the EXTM pin can be used to
modulate the continuos internal tone.
The FLT pin serves as an interrupt for the processor when
any condition turns OFF the LNB controller (Over
Temperature, Overcurrent, Disabled). The nature of the
Disable can be read of the I2C registers.

Features
• Single Chip Power solution
- Operation for 1-Tuner/1-Dish Applications
- Integrated DC/DC Converter and I2C Interface
• Switch-Mode Power Converter for Lowest Dissipation
- Boost PWMs with >92% Efficiency
- Selectable 13.3V or 18.3V Outputs
- Digital Cable Length Compensation (1V)
- I2C and Pin Controllable Output
• Output Back Bias Capability of 28V
• I2C Compatible Interface for Remote Device Control
• Registered Slave Address 0001 00XX
• 2.5V, 3.3V, 5V Logic Compatible
• External Pin to Toggle Between V and H Polarization
• Built-In Tone Oscillator Factory Trimmed to 22kHz
- Facilitates DiSEqC (EUTELSAT) Encoding
- External Modulation Input
• Internal Over-Temperature Protection and Diagnostics
• Internal OV, UV, Overload and Overtemp Flags
(Visible on I2C)
• FLT signal
• LNB Short-Circuit Protection and Diagnostics
• QFN, EPTSSOP Packages
• Pb-Free Available (RoHS Compliant)

Applications
• LNB Power Supply and Control for Satellite Set-Top Box