LTC6256IKC#TRMPBF-ES Linear Technology, LTC6256IKC#TRMPBF-ES Datasheet - Page 16

• Manufacturer Part Number: LTC6256IKC#TRMPBF-ES
• Description: IC OPAMP DUAL 6.5MHZ 8-UTDFN
• Manufacturer: Linear Technology

Specifications of LTC6256IKC#TRMPBF-ES

• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Slew Rate: 1.8 V/µs
• Gain Bandwidth Product: 6.5MHz
• -3db Bandwidth: 4.5MHz
• Current - Input Bias: 5nA
• Voltage - Input Offset: 100µV
• Current - Supply: 65µA
• Current - Output / Channel: 35mA
• Voltage - Supply, Single/dual (±): 1.8 V ~ 5.25 V, ±0.9 V ~ 2.625 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-µTDFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC6255/LTC6256/LTC6257
TYPICAL APPLICATIONS
RC Component Equations
16
Maximum f
R2 =
R3 =
R1=
Maximum Gain =
Gain =
C1> 4 Q
V
IN
Gain
1−
4 π
R2
R2
R1
R1
2
2
(
⎛
⎝ ⎜
–3dB
Gain + 1
R2 C1 C2 f
1− 4 Q
4 π Q f
R2
1
C1
R3
= 100kHz and
V
100kHz
+
2
)
f
–3dB
[
C2
Gain + 1
O
Figure 5
10μF
100k
100k
C2
O
C2
2
4
3
]
–
+
C2
C1
LTC6255
V
+
2
6
⎞
⎠ ⎟
0.1μF
SHDN
625567 F05
5
1
V
OUT
Table 1.
f
2nd Order Lowpass
Butterworth
Bessel
4th Order Lowpass
Butterworth
Bessel
2μs Rise Time Analog 1A Pulsed LED Current Driver
Figure 6 shows the LTC6255 applied as a fast, effi cient
analog LED current driver. High power LEDs are used in
applications ranging from brake lights to video projectors.
Most LED applications pulse the LEDs for the best effi ciency,
and many applications take advantage of control of both
pulse width and analog current amplitude.
In order to extend the circuit’s input range to accommodate
5V output DACs, the input voltage is initially divided by
50 through the R1:R2 divider. The reduced step is applied
to the LTC6255 non inverting input, and LTC6255 output
rises until MOSFETs Q1 through Q3 begin to turn on,
increasing the current in their drains and therefore the
LED. The amount of current is sensed on R3, and fed back
to the LTC6255 inverting input through R5. The loop is
compensated by R5 and C1, with R4 distancing the gate
capacitance from the op amp output for the best time
domain response. 10% to 90% rise time was measured
at 2μs on a 10mA to 1A pulse. Starting at 0 current there
is an additional delay of 2.7μs.
It may seem strange to use a micropower op amp in a high
current LED application, but it can be justifi ed by the low
duty cycles encountered in LED drive applications. A one
amp LED is quite bright even when driven at 1% or even
0.1% duty cycles and these constitute 10mA and 1mA
average current levels respectively, in which case the supply
current of the op amp becomes noticeable. The LTC6255
combines 6.5MHz of gain-bandwidth product and 1.8V/μs
slew rate on a supply current budget of only 65μA.
O
AND Q VALUES
f
f
f
f
f
f
O
O
O
O
O
O
= f
= 1.274 • f
= f
= f
= 1.419 • f
= 1.591 • f
–3dB
–3dB
–3dB
–3dB
–3dB
–3dB
Q = 0.707
Q = 0.577
Q = 0.541
Q = 1.307
Q = 0.522
Q = 0.806
625567fa