Rainbow Electronics MAX9532 - Manual (Page 8)

MAX9532
With the DirectDrive amplifier, the black level is held at
ground. The video signal is constrained between
-0.3V to +0.7V. Figure 2 shows the video signal from a
DirectDrive amplifier with the same input signal as the
AC-coupled system.
Video Reconstruction Filter
The MAX9532 features an internal five-pole, Butterworth
lowpass filter to condition the video signal. The recon-
struction filter smoothes the steps and reduces the
spikes created whenever the DAC output changes
value. In the frequency domain, the steps and spikes
cause images of the video signal to appear at multiples
of the sampling clock frequency. The reconstruction fil-
ter typically provides ±1dB passband flatness of
9.5MHz and 42dB attenuation at 27MHz.
Transparent Sync-Tip Clamp
The MAX9532 contains an integrated, transparent sync-
tip clamp. When using a DC-coupled input, the sync-tip
clamp does not affect the input signal as long as the
input signal remains above ground. When using an AC-
coupled input, the sync-tip clamp automatically clamps
the input signal to ground, preventing the input signal
from going lower. A low current of 2µA pulls down on
the input to prevent an AC-coupled signal from drifting
outside the input range of the device.
Short-Circuit
and Short-to-Battery Protection
The MAX9532 typical operating circuit includes a 50
Ω
or 75
Ω back-termination resistor that limits short-circuit
current when an external short is applied to the video
output. The MAX9532 also features an internal output
short-circuit protection to prevent device damage in
prototyping and applications where the amplifier output
can be directly shorted to ground.
To protect the device from output short circuits to volt-
ages higher than the supply voltage V
DD , the MAX9532
utilizes an internal switch in series with the amplifier out-
put. When the JACKSENSE input detects that the out-
put connector of the circuit is shorted to the battery
voltage (up to 18V) higher than the internal 8V thresh-
old, an internal comparator disables the switch in 10µs
(typ) preventing the MAX9532 from being damaged.
After the output is shorted to a battery, the output
immediately resumes normal operation when the short
is removed within 1ms. When the output is shorted to
the battery for longer than 1ms, the output resumes nor-
mal operation 10ms after the short is removed.
Applications
Power Consumption
Quiescent power consumption is defined when the
MAX9532 is operating without load. In this case, the
MAX9532 consumes about 47.355mW. Average power
consumption, when the MAX9532 drives a 100
Ω and
150
Ω load to ground with a 50% flat field, is about
51.596mW and 49.513mW, respectively. Table 1 shows
the power consumption with different video signals.
Notice that the two extremes in power consumption
occur with a video signal that is all black and a video
signal that is all white. The power consumption with
75% color bars and 50% flat field lies in between the
extremes.
DirectDrive Video Amplifier with
Short-to-Battery Protection
8 _______________________________________________________________________________________
INPUT
500mV/div
OUTPUT
500mV/div
2ms/div
Figure 1. AC-Coupled Output
INPUT
500mV/div
OUTPUT
1V/div
2ms/div
0V
0V
Figure 2. DirectDrive Output