ISL71091SEH20 Datasheet, PDF (11/16 Pages) Intersil Corporation – 2.048V Radiation Hardened Ultra Low Noise

ISL71091SEH20
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
3.8µV_P-P (V_OUT = 2.048V). The noise measurement is made with a
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
3.4µV_RMS (V_OUT = 2.048V), with 0.1µF capacitance on the output.
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,
(V_HIGH – V_LOW), and divide by the temperature extremes of
measurement (T_HIGH – T_LOW). The result is divided by the nominal
reference voltage (at T = +25°C) and multiplied by 10⁶ to yield
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
to V_OUT and ground. It is important to minimize the capacitance
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
The reference can be compensated for the C_OUT capacitors used
by adding a capacitor from the COMP pin to GND. See Table 2 for
recommended values of the COMP capacitor.
C_OUT
(µF)
0.1
1
10
TABLE 2.
C_COMP
(nF)
1
1
10
Data from SEE testing suggests the best option to use is 1µF for
C_OUT and 1nF for C_COMP. Refer to the SEE report (AN1938) 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.
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FN8632.2
March 17, 2016