ISL6421 Datasheet, PDF (6/10 Pages) Intersil Corporation – Single Output LNB Supply and Control Voltage Regulator with I2C Interface for Advanced Satellite Set-top Box Designs

ISL6421
Functional Pin Description
SDA
SCL
SYMBOL
Bidirectional data from/to I²C bus.
Clock from I²C bus.
FUNCTION
VSW
Input of the linear post-regulator.
PGND
Dedicated ground for the output gate driver of the PWM.
CS
Current sense input; connect Rsc at this pin for desired over current value for the PWM.
SGND
Small signal ground for the IC.
AGND
Analog ground for the IC.
TCAP
Capacitor for setting rise and fall time of the output of the LNB. Use a capacitor value of 1µF or higher.
BYPASS
Bypass capacitor for internal 5V.
DSQIN
When HIGH this pin enables the internal 22kHz modulation for the LNB, Use this pin for tone enable function for
the LNB.
VCC
Main power supply to the chip.
GATE
This is the device output of the PWM. This high current driver output is capable of driving the gate of a power FET.
This output is actively held low when Vcc is below the UVLO threshold.
VOUT
Output voltage for the LNB.
ADDR
Address pin to select two different addresses per voltage level at this pin.
COMP
Error amp output used for compensation.
FB
Feedback pin for the PWM.
CPVOUT, CPSWIN, CPSWOUT Charge pump connections.
SEL18V
When connected HIGH, this pin will change the output of the PWM to 18V.
Functional Description
The ISL6421 single output voltage regulator makes an ideal
choice for advanced satellite set-top box and personal video
recorder applications. Both supply and control voltage
outputs for a low noise block (LNB) are available
simultaneously in any output configuration. The device
utilizes a built-in DC/DC step-converter that, from a single
supply source ranging from 8V to 14V, generates the voltage
that enables the linear post-regulator to work with a
minimum of dissipated power. An under voltage lockout
circuit disables the circuit when V_CC drops below a fixed
threshold (7.5V typ).
DiSEqC Encoding
The internal oscillator is factory-trimmed to provide a tone of
22kHz in accordance with DISeqC standards. No further
adjustment is required. The 22kHz oscillator can be
controlled either by the I²C interface (ENT bit) or by a
dedicated pin (DSQIN) that allows immediate DiSEqC data
encoding for the LNB. All the functions of this IC are
controlled via the I²C bus by writing to the system registers
(SR). The same registers can be read back, and two bits will
report the diagnostic status. The internal oscillator operates
the converters at ten times the tone frequency. The device
offers full I²C compatible functionality, 3.3V or 5V, and up to
400kHz operation.
If the Tone Enable (ENT) bit is set LOW through I²C, then
the DSQIN terminal activates the internal tone signal,
modulating the dc output with a 0.3V, 22kHz, symmetrical
waveform. The presence of this signal usually gives the LNB
information about the band to be received.
Burst coding of the 22kHz tone can be accomplished due to
the fast response of the DSQIN input and rapid tone
response. This allows implementation of the DiSEqC
(EUTELSAT) protocols.
When the ENT bit is set HIGH, a continuous 22kHz tone is
generated regardless of the DSQIN pin logic status. The
ENT bit must be set LOW when the DSQIN pin is used for
DiSEqC encoding.
Linear Regulator
The output linear regulator will sink and source current. This
feature allows full modulation capability into capacitive loads
as high as 0.25µF. In order to minimize the power
dissipation, the output voltage of the internal step-up
converter is adjusted to allow the linear regulator to work at
minimum dropout.
When the device is put in the shutdown mode (EN = LOW),
the PWM power block is disabled. When the regulator block
is active (EN = HIGH), the output can be logic controlled to
be 13V or 18V (typical) by means of the VSEL bit (Voltage
Select) for remote controlling of non-DiSEqC LNBs.
Additionally, it is possible to increment by 1V (typical) the
selected voltage value to compensate for the excess voltage
drop along the coaxial cable (LLC bit HIGH).
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