MAX3580ETJ+T Maxim Integrated Products, MAX3580ETJ+T Datasheet - Page 18

• Manufacturer Part Number: MAX3580ETJ+T
• Description: IC TV TUNER DIRECT-CONV 32TQFN
• Manufacturer: Maxim Integrated Products
• Type: Direct Conversion TV Tunerr

Specifications of MAX3580ETJ+T

• Applications: Set-Top Boxes
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Direct-Conversion TV Tuner
The MAX3580 is designed to be suitable for operation
in the 170MHz to 230MHz VHF-III band and in the
470MHz to 878MHz UHF band.
A switch selects either RFIN or RFIN2 as the input to the
single-ended broadband matched LNA. This switch is
programmed through the RFS bit (bit 5) of register 0x05.
The LNA provides a continuous gain control range of
typically 50dB before the signal is downconverted.
For optimal matching above 600MHz, add a 5nH to
6nH inductor in series with a capacitor at either of the
RF input. Application Note: Front End Diplexer Filter for
MAX3580 is available, detailing the implementation of a
UHF and VHF simple diplexer. This simple diplexer
improves strong-signal-handling capabilities of the
MAX3580.
The MAX3580 features an on-chip fast-settling, DC-off-
set cancellation circuitry that requires no off-chip com-
ponents. Note that the offset correction circuit is not
enabled when the device is powered up. To enable the
offset correction circuit, program the DC-Offset Control
Register to the recommended default setting.
When active, the offset correction circuit creates a high-
pass characteristic in the signal path with a typical cor-
ner frequency of 200Hz, and the residual DC offset can
be as high as ±70mV.
The MAX3580 features two VGA circuits that can be
used to achieve the optimum SNR. The two circuits can
be driven independently by the baseband controller,
which allows balancing the gain based on SNR measure-
ments in the digital demodulator. If only one gain control
voltage can be provided by the digital demodulator, see
Figure 1. See the Baseband Power Detector section. In
this operation mode, the baseband gain is set by an
amplitude detector in the digital demodulator.
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Applications Information
DC-Offset Cancellation
Band Selection
Gain Control
RF Inputs
Maxim recommends disabling this feature. See expla-
nation in the Shutdown Control (Register Address 0x08)
section and Table 2 (address 0x08, bit D5). For single-
loop AGC control, see Figure 1.
A second-order lowpass loop filter is used to connect
the PLL to the RF local oscillator. A loop filter bandwidth
of 30kHz is optimal for fractional PLL spurs and integrat-
ed LO phase noise. Refer to the EV kit data sheet for the
recommended loop-filter component values.
The MAX3580 reference oscillator circuitry can be used
either as a high-impedance reference input driven by
an external source, or be configured as a crystal oscil-
lator. In the latter case, the resulting frequency can be
used to drive the digital demodulator chip through the
buffered reference output of the MAX3580. When using
an external reference oscillator, drive the XB input
through an AC-coupling capacitor with amplitude of
approximately 1.5V
Note that the phase noise of the external reference
needs to exceed -140dBc/Hz at offsets of 1kHz to
100kHz. When connecting directly to a crystal, see the
Typical Application Circuit for the required topology.
For particular capacitor values, possible changes to
accommodate for different crystal frequencies, crystal
load-capacitance requirements, and crystal power-dis-
sipation requirements, refer to the EV kit data sheet.
Crystal-Oscillator Interface
P-P
Baseband Power Detector
, and leave XE unconnected.
Synthesizer Loop Filters