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MAX9532

DirectDrive Video Amplifier with Short-to-Battery Protection

Maxim Integrated 

DirectDrive Video Amplifier with

Short-to-Battery Protection

INPUT

500mV/div

0V

INPUT

500mV/div

OUTPUT

0V

500mV/div

OUTPUT

1V/div

2ms/div

2ms/div

Figure 1. AC-Coupled Output

Figure 2. DirectDrive Output

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 50Ω

or 75Ω 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 VDD, 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 100Ω and

150Ω 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.

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