ISL71090SEH50

9

FN8588.3

March 15, 2016

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Device Operation

Bandgap Precision Reference

The ISL71090SEH50 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 typically 100µV 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 over the 0.1Hz to 10Hz bandwidth is

with a 9.9Hz bandpass filter. Noise in the 10Hz to 1kHz

the output. This noise measurement is made with a bandpass

filter of 990Hz. Load capacitance up to 10µF (with COMP

capacitor from Table 2) 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 250µs, 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, which

provide for the maximum voltage deviation and take the total

the nominal reference voltage (at T = +25°C) and multiplied by

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 1MΩ external

resistor directly to the trim terminal and connect the other end to the

wiper of a potentiometer that has a 100kΩ resistance and whose

connected to trim, the output adjust range will be ±6.3mV. The TRIM

pin should not have any capacitor tied to its output, also it is

important to minimize the capacitance on the trim terminal during

layout 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 will not disturb the factory-set temperature coefficient

of the reference, but trimming near the extreme values can.

Output Stage

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

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

as a source and sink. The device can source 20mA.

Use of COMP Capacitors

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

recommended values of the COMP capacitor.

SEE Testing

The SET result is based on the ISL71090SEH25. The

ISL71090SEH25 and ISL71090SEH50 share the same active

circuitry consisting of a precision bandgap ckt and a trimmable

amplifier to set the output reference with only a resistor change to

scale the output. The SET test was done under an ion beam having

to a VDD of 36V and at +125°C. Single Event transients were

observed and are summarized in the Table 3:

DNC Pins

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

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

the performance of the reference.

TABLE 2.

(µF)

(nF)

0.1

1

11

10

10

TABLE 3.

(V)

(mA)

(µF)

SET

45

1

-4.6

30

5

1

-4.4

30

5

10

-1.0