ISL6422
Dual Output LNB Supply and Control Voltage Regulator with I²C Interface for Advanced Satellite Set-Top Box Designs

Key Features

• Single Chip Power Solution
• True Dual Operation for 2-Tuner/2-Dish Applications
• Both Outputs May be Enabled Simultaneously at Maximum Power
• 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
• Four level Slave Address 0001 00XX
• 2.5V, 3.3V, 5V Logic Compatible
• External Pins to Toggle Between V and H Polarization.
• Supports DiSEqC 2.0 Protocol
• 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 Over-Temperature Flags (Visible on I²C)
• FLT Signal
• LNB Short-Circuit Protection and Diagnostics
• QFN, EPTSSOP Packages
• Pb-Free Plus Anneal Available (RoHS Compliant)

Description

The ISL6422 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 consists 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 0.8V 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 can be controlled in two ways:

• Full control from I²C using the VTOP1, VTOP2, VBOT1, and VBOT12 bits, or
• Set the I²C to the lower range (13V/14V) and switch to the higher range (18V/19V) with the SELVTOP1 or
  SELVTOP2 pin.

All the functions on this IC are controlled via the I²C bus by writing 8-bit words onto the System Registers (SR). The same register can be read back, and 4-bits per output 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 External modulation input EXTM1, EXTM2 can accept a modulated Diseqc command and transfer it symmetrically to the output. Alternatively, the EXTM1 or EXTM2 pin can be used to modulate the continuous internal tone.

The FLT pin serves as an interrupt for the processor when an over temperature, overcurrent or backwards overcurrent fault conditions is detected by the LNB controller or when both channels are disabled by the I²C EN bits set low. The nature of the fault can be read of the I²C registers.

Applications

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