ISL71091SEH20

11

FN8632.2

March 17, 2016

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Device Operation

Bandgap Precision References

The ISL71091SEH20 uses a bandgap architecture and special

trimming circuitry to produce a temperature compensated,

precision voltage reference with high input voltage capability and

moderate output current drive.

Applications Information

Board Mounting Considerations

For applications requiring the highest accuracy, board mounting

location should be reviewed. The device uses a ceramic flatpack

package. Generally mild stresses to the die when the Printed

Circuit (PC) board is heated and cooled, can slightly change the

shape. Because of these die stresses, placing the device in areas

subject to slight twisting can cause degradation of reference

voltage accuracy. It is normally best to place the device near the

edge of a board, or on the shortest side, because the axis of

bending is most limited in that location. Mounting the device in a

cutout also minimizes flex. Obviously, mounting the device on

flexprint or extremely thin PC material will likewise cause loss of

reference accuracy.

Board Assembly Considerations

Some PC board assembly precautions are necessary. Normal

output voltage shifts of 100µV to 500µV can be expected with

Pb-free reflow profiles or wave solder on multilayer FR4 PC

boards. Precautions should be taken to avoid excessive heat or

extended exposure to high reflow or wave solder temperatures.

Noise Performance and Reduction

The output noise voltage in a 0.1Hz to 10Hz bandwidth is typically

bandpass filter. The filter is made of a 1-pole high-pass filter, with a

corner frequency at 0.1Hz, and a 2-pole low-pass filter, with a

corner frequency (3dB) at 9.9Hz, to create a filter with a 9.9Hz

bandwidth. Noise in the 10Hz to 1kHz bandwidth is approximately

This noise measurement is made with a 2 decade bandpass filter.

The filter is made of a 1-pole high-pass filter with a corner

frequency at 10Hz of the center frequency, and 1-pole low-pass

filter with a corner frequency at 1kHz. Load capacitance up to

10µF can be added but will result in only marginal improvements

in output noise and transient response.

Turn-On Time

Normal turn-on time is typically 344µs, as shown in Figure 20 on

page 9. The circuit designer must take this into account when

looking at power-up delays or sequencing.

Temperature Coefficient

The limits stated for temperature coefficient (Tempco) are governed

by the method of measurement. The overwhelming standard for

specifying the temperature drift of a reference is to measure the

reference voltage at two temperatures. Take the total variation,

ppm/°C. This is the “Box” method for specifying temperature

coefficient.

Output Voltage Adjustment

The output voltage can be adjusted above and below the

factory-calibrated value via the trim terminal. The trim terminal is

the negative feedback divider point of the output op amp. The

voltage at the trim pin is set at approximately 1.216V by the

internal bandgap and amplifier circuitry of the voltage reference.

The suggested method to adjust the output is to connect a very

high value external resistor directly to the trim terminal and

connect the other end to the wiper of a potentiometer that has a

much lower total resistance and whose outer terminals connect

on the trim terminal to preserve output amplifier stability. It is

also best to connect the series resistor directly to the trim

terminal, to minimize that capacitance and also to minimize

noise injection. Small trim adjustments, such as ±0.25%, will not

disturb the factory-set temperature coefficient of the reference,

but trimming by large amounts can.

Output Stage

The output stage of the device has a push-pull configuration with

a high-side PNP and a low-side NPN. This helps the device to act

as a source and sink. The device can source 10mA and sink

5mA.

Use of COMP Capacitors

by adding a capacitor from the COMP pin to GND. See Table 2 for

recommended values of the COMP capacitor.

Data from SEE testing suggests the best option to use is 1µF for

more details.

DNC Pins

These pins are for trimming purposes and for factory use only. Do

not connect these to the circuit in any way. It will adversely effect

the performance of the reference.

Simulation Model

A SPICE simulation model is available under the Documents tab

of the ISL71091SEH20 landing page on the Intersil website.

Figures 24 through 29 show a comparison of the characterized

part performance and the simulated part performance.

TABLE 2.

(µF)

(nF)

0.1

1

11

10

10