LTC1404CS8 datasheet(13/24 Pages) LINER

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LTC1404

APPLICATIONS INFORMATION

LT1229/LT1230: Dual and quad 100MHz current feedback

amplifiers.

±2V to ±15V supplies, 6mA supply current

each amplifier. Low noise. Good AC specs.

LT1360: 37MHz voltage feedback amplifier.

±5V to ±15V

supplies. 3.8mA supply current. Good AC and DC specs.

70ns settling to 0.5LSB.

LT1363: 50MHz, 450V/

µsopamps.±5Vto ±15Vsupplies.

6.3mA supply current. Good AC and DC specs. 60ns

settling to 0.5LSB.

LT1364/LT1365: Dual and quad 50MHz, 450V/

µsopamps.

±5Vto±15Vsupplies,6.3mAsupplycurrentperamplifier.

60ns settling to 0.5LSB.

Internal Reference

The LTC1404 has an on-chip, temperature compensated,

curvature corrected, bandgap reference, which is factory

trimmed to 2.43V. It is internally connected to the DAC and

is available at Pin 3 to provide up to 1mA of current to an

external load. For minimum code transition noise, the

reference output should be decoupled with a capacitor to

filter wideband noise from the reference (10

µF tantalum in

parallel with a 0.1

µF ceramic). The VREF pin can be driven

with a DAC or other means to provide input span adjust-

ment in bipolar mode. The VREF pin must be driven to at

least 2.46V to prevent conflict with the internal reference.

The reference should not be driven to more than 5V.

Figure 6 shows an LT 1360 op amp driving the reference

pin. Figure 7 shows a typical reference, the LT1019A-5

connected to the LTC1404. This will provide an improved

Figure 6. Driving the VREF with the LT1360 Op Amp

Figure 7. Supplying a 5V Reference Voltage to the

LTC1404 with the LT1019A-5

drift (equal to the maximum 5ppm/

°C of the LT1019A-5)

and a

±4.215V full scale. If VREF is forced lower than

2.43V, the REFRDY bit in the serial data output will be

forced to low.

UNIPOLAR / BIPOLAR OPERATION AND ADJUSTMENT

Figure 8 shows the ideal input/output characteristics for

the LTC1404. The code transitions occur midway between

successive integer LSB values (i.e., 0.5LSB, 1.5LSB,

2.5LSB, … FS – 1.5LSB). The output code is natural binary

with 1LSB = 4.096/4096 = 1mV. Figure 9 shows the

input/output transfer characteristics for the bipolar mode

in two’s complement format.

Unipolar Offset and Full-Scale Error Adjustments

In applications where absolute accuracy is important,

offset and full-scale errors can be adjusted to zero. Figure

10a shows the extra components required for full-scale

error adjustment. Figure 10b shows offset and full-scale

adjustment. Offset error must be adjusted before full-

scale error. Zero offset is achieved by applying 0.5mV (i.e.,

0.5LSB) at the input and adjusting the offset trim until the

LTC1404 output code flickers between 0000 0000 0000

and 0000 0000 0001. For zero full-scale error, apply an

analog input of 4.0945V (FS – 1.5LSB or last code transi-

tion) at the input and adjust R5 until the LTC1404 output

code flickers between 1111 1111 1110 and 1111 1111

1111.

1404 F06

–

VREF(OUT) ≥ 2.46V

AIN

VREF

GND

µF

Ω

INPUT RANGE

±0.843 • VREF(OUT)

–5V

LTC1404

LT1360

VCC

VSS

1404 F07

µF

Ω

INPUT RANGE

±4.215V

±0.843 • VREF)

–5V

LT1019A-5

10V

VIN

VOUT

GND

AIN

VREF

GND

LTC1404

VCC

VSS

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