AD1580

Rev. F | Page 9 of 12

TRANSIENT RESPONSE

Many ADC and DAC converters present transient current

loads to the reference. Poor reference response can degrade

the converter’s performance.

Figure 22 displays both the coarse and fine settling characteristics

of the device to load transients of ±50 μA.

(a)

(b)

1µs/DIV

1mV/DIV

20mV/DIV

1mV/DIV

20mV/DIV

Figure 22. Transient Settling

Figure 22a shows the settling characteristics of the device for

an increased reverse current of 50 μA. Figure 22b shows the

response when the reverse current is decreased by 50 µA.

The transients settle to 1 mV in about 3 µs.

Attempts to drive a large capacitive load (in excess of 1000 pF) may

result in ringing, as shown in the step response (see Figure 23).

This is due to the additional poles formed by the load capacit-

ance and the output impedance of the reference. A recommended

method of driving capacitive loads of this magnitude is shown

in Figure 20. A resistor isolates the capacitive load from the

output stage, while the capacitor provides a single-pole low-pass

filter and lowers the output noise.

1.8V

2.0V

50µs/DIV

10mV/DIV

Figure 23. Transient Response with Capacitive Load

PRECISION MICROPOWER LOW DROPOUT

REFERENCE

The circuit in Figure 24 provides an ideal solution for making

a stable voltage reference with low standby power consumption,

low input/output dropout capability, and minimum noise output.

The amplifier both buffers and optionally scales up the AD1580

1 mA of load current. A one-pole filter connected between the

AD1580 and the OP193 input can be used to achieve low output

noise. The nominal quiescent power consumption is 200 µW.

3V

34.8k

Ω

AD1580

OP193

OR

R3

R2

4.7µF

205

Ω

Figure 24. Micropower Buffered Reference

USING THE AD1580 WITH 3 V DATA CONVERTERS

The AD1580 low output drift (50 ppm/°C) and compact submi-

niature SOT-23 package make it ideally suited for today’s high

performance converters in space critical applications.

One family of ADCs for which the AD1580 is well suited is the

AD7714-3 and AD7715-3. The AD7714/AD7715 are charge-

balancing ( ∑-∆) ADCs with on-chip digital filtering intended for

the measurement of wide dynamic range, low frequency signals

such as those representing chemical, physical, or biological

processes. Figure 25 shows the AD1580 connected to the

AD7714-3/AD7715-3 for 3 V operation.

AD7714-3 AND AD7715–3

AD1580

3V

34.8k

Ω

REFIN(+)

REFIN(–)

HIGH

IMPEDANCE

>1G

Ω

5k

Ω (TYP)

(3pF TO 8pF)

SWITCHING

FREQUENCY DEPENDS

ON

Figure 25. Reference Circuit for the AD7714-3 and AD7715-3