6207 데이터 시트보기 (PDF) - Linear Technology

부품명

상세내역

제조사

6207

Single/Dual/Quad Single Supply 3V, 100MHz Video Op Amps

Linear Technology 

LT6205/LT6206/LT6207

APPLICATIO S I FOR ATIO

Amplifier Characteristics

Figure 1 shows a simplified schematic of the LT6205/

LT6206/LT6207. The input stage consists of transistors

Q1 to Q8 and resistor R1. This topology allows for high

slew rates at low supply voltages. The input common

mode range extends from ground to typically 1.75V from

VCC, and is limited by 2 VBEs plus a saturation voltage of

a current source. There are back-to-back series diodes, D1

to D4, across the + and – inputs of each amplifier to limit

the differential voltage to ±1.4V. RIN limits the current

through these diodes if the input differential voltage ex-

ceeds ±1.4V. The input stage drives the degeneration

resistors of PNP and NPN current mirrors, Q9 to Q12,

which convert the differential signals into a single-ended

output. The complementary drive generator supplies cur-

rent to the output transistors that swing from rail-to-rail.

The current generated through R1, divided by the capaci-

tor CM, determines the slew rate. Note that this current,

and hence the slew rate, are proportional to the magnitude

of the input step. The input step equals the output step

divided by the closed loop gain. The highest slew rates are

therefore obtained in the lowest gain configurations. The

Typical Performance Characteristic Curve of Slew Rate vs

Closed Loop Gain shows the details.

ESD

The LT6205/LT6206/LT6207 have reverse-biased ESD

protection diodes on all inputs and outputs as shown in

Figure 1. If these pins are forced beyond either supply

unlimited current will flow through these diodes. If the

current is transient, and limited to 25mA or less, no

damage to the device will occur.

Layout and Passive Components

With a gain bandwidth product of 100MHz and a slew rate

of 450V/µs the LT6205/LT6206/LT6207 require special

attention to board layout and supply bypassing. Use a

ground plane, short lead lengths and RF-quality low ESR

supply bypass capacitors. The positive supply pin should

be bypassed with a small capacitor (typically 0.01µF to

0.1µF) within 0.25 inches of the pin. When driving heavy

loads, an additional 4.7µF electrolytic capacitor should be

used. When using split supplies, the same is true for the

10

negative supply pin. For optimum performance all feed-

back components and bypass capacitors should be con-

tained in a 0.5 inch by 0.5 inch area. This helps ensure

minimal stray capacitances.

The parallel combination of the feedback resistor and gain

setting resistor on the inverting input can combine with

the input capacitance to form a pole which can degrade

stability. In general, use feedback resistors of 1k or less.

Capacitive Load

The LT6205/LT6206/LT6207 are optimized for wide band-

width video applications. They can drive a capacitive load

of 20pF in a unity-gain configuration. When driving a

larger capacitive load, a resistor of 10Ω to 50Ω should be

connected between the output and the capacitive load to

avoid ringing or oscillation. The feedback should still be

taken from the output pin so that the resistor will isolate

the capacitive load and ensure stability. The Typical Per-

formance Curves show the output overshoot when driving

a capacitive load with different series resistors.

Video Signal Characteristics

Composite video is the most commonly used signal in

broadcast-grade products and includes Luma (or lumi-

nance, the intensity information), Chroma (the colorim-

etry information) and Sync (vertical and horizontal raster

timing) elements combined into a single signal, NTSC and

PAL being the common formats. Component video for

entertainment systems include separate signal(s) for the

Luma and Chroma (i.e. Y/C or YPbPr) with Sync generally

applied to the Luma channel (Y signal). In some instances,

native RGB signals (separate intensity information for

each primary color: red, green, blue) will have Sync

included as well. All the signal types that include Sync are

electrically similar from a voltage-swing standpoint, though

various timing and bandwidth relationships exist depend-

ing on the applicable standard.

The typical video waveforms that include Sync (including

full composite) are specified to have nominal 1VP-P ampli-

tude. The lower 0.3V is reserved for “sync tips” that carry

timing information, and by being at a lower potential than

all the other information, represents blacker-than-black

intensity, thereby causing scan retrace activity to be

620567f

Share Link: