audio/videoZONE Products for the week of August 19, 2002
Linear Technology Says . . .
LT6550/51: 3.3-V Video Amplifiers Occupy 15mm²
while Eliminating Gain Setting Resistors
Linear Technology Corporation introduced the LT6550 and LT6551 triple and
quad, fixed gain of two video amplifiers. Eliminating the need for external
gain setting resistors, the LT6550 and LT6551 are the first to offer guaranteed
performance on a single 3.3V supply. Available in the space saving, 10-pin
MSOP package that occupies only 15mm² of board space, they are the
smallest triple and quad video buffers available on the market.
"Designers of low voltage video systems have, for the first time, at their disposal a compact solution that integrates gain setting resistors and guarantees performance on supply voltages as low as 3.3V; thus simplifying their power supply requirements and saving board space," according to applications manager, Tim Regan.
The LT6550 and LT6551 feature a -3dB bandwidth of 110MHz, a high slew
rate of 340V/µs and a fast settling time of 20ns to 3%, making them
ideal for RGB video processing providing 1024 x 768 resolution. Furthermore,
their ability to accept RGB video signals without the need for AC coupling
or level shifting of the incoming signals make them an ideal choice for
low voltage video applications while their internal gain of two makes them
ideal for driving double-terminated cables.
analogZone Says . . .
Low rail voltages and video amplifiers don't generally co-exist but here Linear has squeezed a gain of two into a single 3.3-V rail with room to spare. A signal on each channel up to 1.45 V linearly swings the outputs to within 400 mV of the rail with a terminated 75 ohm cable (150 ohms) load. The low output voltage is 60 mV sinking 5 mA and 90 mV sinking 10 mA. On the 3-channel LT6550 the internal gain resistor is taken to a separate ground pin so that the supplies can be split if it is required to have a mode including ground. Those split supplies can be run down to +/-3 V or up to +/-12.6 V (for more industrial systems) but the data sheet only provides the +/-5 V specifications for the 3-channel part, and single 3.3 V and 5.0 V rail specifications for both parts.
With the single 3.3-V rail the small-signal -3 dB bandwidth is 90 MHz and the 0.25-dB gain flatness runs out to 30 MHz. Gain matching between channels is within 0.15 dB while separation between channels is 60 dB at 10 MHz -- perfectly adequate for most professional systems as well as consumer. For high-bandwidth systems (video signals out to 25 - 30 MHz) there is insufficient data to judge performance from the initial release data sheet. There are no linearity numbers either, although I am quite sure they will be more than adequate for component signals out to 10 MHz.
The supply current per amplifier is a typical 8 mA and it should be remembered that includes the part of the load current flowing through the feedback and gain resistors that are on-chip. Typical slew rate (3.3 V rail) is a remarkable 250 V/µs. Back-to-back series diodes on the inputs limit the differential input voltage to +/-1.45 V. All the inputs and outputs have reverse-biased ESD-diode protection. The part can drive up to 50 mA (at 3.3 V) and the 3% settling time is a typical 20 ns
Exhibiting extremely good performance with the number of external components minimized by having the gain resistors on-chip, and with good pricing at about 60 cents a channel make these parts a shoe-in for high-volume video gain applications. The LT6550 triple will be used in GBR applications, while the LT6551 adds a sync -- or possibly an alpha -- channel. It should also be remembered that the LT6551 can also be used (with split rails) in Y, B-Y, R-Y applications -- which I have not seen addressed in any other monolithic video amplifier. Because the gain resistor is on a separate ground pin in the LT6551 it would also be possible to reduce the gain, if desired, or to get even more accurate channel matching beyond the already very good specifications.
The LT6550 and LT6551 are in production in MSOP-10 with pricing of the
3-channel part at $1.75 each in 1000-piece lots.