MAX9546(2005) View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MAX9546 Datasheet PDF : 12 Pages
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Differential Video Interface Chipset
Common-Mode Balance
A driver is typically specified as having a property called
common-mode balance (CMB), longitudinal balance, or
simply line imbalance. Although balance is associated
with the source, it assumes a perfectly balanced, cor-
rectly terminated, differential load. Common-mode bal-
ance is a measure of the ratio between the differential to
the common-mode output in decibels as shown below.
⎛ (OUT+) − (OUT−) ⎞
CMB
=
20Log⎜
⎝
(OUT
+
)
+
(OUT
−
)
⎟
⎠
Common-mode balance is dominated by the gain-band-
width product at high frequencies and the output resis-
tance at low frequencies; therefore, it is important to
specify CMB over a frequency range. The receiver-side
balance is determined by the common-mode rejection
ratio (CMRR). The CMRR is usually quite large compared
to the CMB; therefore, the CMB is the limiting factor.
Fault Protection and Detection
The MAX9546 fault protection insures the driver outputs
survive a short to any voltage from -2V to +16V and are
ESD-protected to ±15kV HBM. Faults are indicated by
an open-drain fault output (FAULT) being asserted low
and requires a pullup resistor from FAULT to VCC.
MAX9547
Receiver
The MAX9547 receiver is a differential-to-single-ended
converter that removes any common-mode input. The
unique architecture allows the signal gain to be set by
a ratio of two impedances: the user-selected transcon-
ductance element or network (ZZT), and an output load
resistance, RL. The gain is set by a fixed internal cur-
rent gain (K) and the ratio of ZZT and RL. The ZT termi-
nals can be bridged with a complex impedance to
provide lead-lag compensation.
The output is essentially a voltage-controlled current
source as shown in Figure 1. The MAX9547 output is a
current proportional to the differential input voltage, and
inversely proportional to the impedance of the user-
selected transconductance network, ZZT. The current
output provides inherent short-circuit protection for the
output terminal. A differential input voltage applied to
the input terminals causes current to flow in the
transconductance element (ZZT), which is equal to VIN /
ZZT. This current in the transconductance element is
multiplied by the preset current gain (K) and appears
on the output terminal as a current equal to (K) x (VIN /
ZZT). This current flows through the load impedance to
produce an output voltage according to the following
equation:
IN+
1
+
VIN
IN-
-
4
7
IOUT
K
VIN ZZT
Figure 1. Operational Mode
VOUT
=
⎛
K⎝⎜
VIN
ZZT
⎞
⎠⎟RL
where K = current-gain ratio (K = 1 for MAX9547), RL =
output load impedance, ZZT = transconductance ele-
ment impedance, VIN = differential input voltage.
Loss-of-Signal
The receiver includes an LOS output to indicate a sig-
nal by detecting the presence of H-Sync. This allows
the MAX9547 to be used with monochrome or color
video. LOS is an open-drain output and requires a
pullup resistor from LOS to VCC.
Setting the Circuit Gain
The MAX9547 produces an output current by multiply-
ing the differential input voltage, VIN, by the transcon-
ductance ratio, K (RL / ZZT), where K = 1. The voltage
gain (AV) is set by the impedance of the transconduc-
tance network (ZZT) and the output load impedance
(RL) according to the following formula:
AV
=
⎛
K⎝⎜
RL
ZZT
⎞
⎠⎟
The factor ZZT is the impedance of the user-selected,
two-terminal transconductance element or network,
connected across the terminals labeled ZT+ and ZT-.
The network ZZT is selected, along with the output
impedance RL, to provide the desired circuit gain and
frequency shaping.
To maintain linearity, the transconductance network
should also be selected so that current flowing through
it, equal to VIN / ZZT, does not exceed 18mA under
worst-case conditions of maximum input voltage and
minimum transconductance element impedance (ZZT).
Output current should not exceed ±8.8mA except
under fault conditions.
8 _______________________________________________________________________________________
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