Datasheet LT6559 (Analog Devices) - 8

LT6559
PIN FUNCTIONS GND (Pins 1, 4):
Ground. Not connected internally.
OUT G (Pin 10):
G Channel Output.
–IN G (Pin 2):
Inverting Input of G Channel Amplifi er. ⎯
E
⎯
N G (Pin 11):
G Channel Enable Pin. Logic low to enable.
+IN G (Pin 3):
Noninverting Input of G Channel Amplifi er.
V+ (Pin 12):
Positive Supply Voltage, Usually 5V.
+IN B (Pin 5):
Noninverting Input of B Channel Amplifi er.
OUT R (Pin 13):
R Channel Output.
–IN B (Pin 6):
Inverting Input of B Channel Amplifi er. ⎯
E
⎯
N R (Pin 14):
R Channel Enable Pin. Logic low to enable. ⎯
E
⎯
N B (Pin 7):
B Channel Enable Pin. Logic low to enable.
–IN R (Pin 15):
Inverting Input of R Channel Amplifi er.
OUT B (Pin 8):
B Channel Output.
+IN R (Pin 16):
Noninverting Input of R Channel Amplifi er.
V– (Pin 9):
Negative Supply Voltage, Usually Ground
Exposed Pad (Pin 17):
V–. Must Be Soldered to the PCB. or –5V.
APPLICATIONS INFORMATION Feedback Resistor Selection
fi er bandwidth is only reduced when the capacitive load is present. The disadvantage is that the gain is a function The small-signal bandwidth of the LT6559 is set by the of the load resistance. external feedback resistors and the internal junction capacitors. As a result, the bandwidth is a function of
Power Supplies
the supply voltage, the value of the feedback resistor, the closed-loop gain and the load resistor. Optimized for The LT6559 will operate from single or split supplies from ±5V and single-supply 5V operation, the LT6559 has a ±2V (4V total) to ±6V (12V total). It is not necessary to use –3dB bandwidth of 300MHz at gains of +1, –1, or +2. equal value split supplies, however the offset voltage and Refer to the resistor selection guide in the Typical AC inverting input bias current will change. The offset voltage Performance table. changes about 600µV per volt of supply mismatch. The inverting bias current will typically change about 2µA per
Capacitance on the Inverting Input
volt of supply mismatch. Current feedback amplifi ers require resistive feedback from
Slew Rate
the output to the inverting input for stable operation. Take care to minimize the stray capacitance between the output Unlike a traditional voltage feedback op amp, the slew and the inverting input. Capacitance on the inverting input rate of a current feedback amplifi er is dependent on the to ground will cause peaking in the frequency response amplifi er gain confi guration. In a current feedback ampli- and overshoot in the transient response. fi er, both the input stage and the output stage have slew rate limitations. In the inverting mode, and for gains of 2
Capacitive Loads
or more in the noninverting mode, the signal amplitude between the input pins is small and the overall slew rate The LT6559 can drive many capacitive loads directly when is that of the output stage. For gains less than 2 in the the proper value of feedback resistor is used. The required noninverting mode, the overall slew rate is limited by the value for the feedback resistor will increase as load ca- input stage. pacitance increases and as closed-loop gain decreases. Alternatively, a small resistor (5Ω to 35Ω) can be put in The input slew rate of the LT6559 is approximately 600V/µs series with the output to isolate the capacitive load from and is set by internal currents and capacitances. The output the amplifi er output. This has the advantage that the ampli- slew rate is set by the value of the feedback resistor and 6559f 8