Internal and External Reference

The MAX115/MAX116 can be used with an internal or

external reference voltage. An external +2.5 reference

can be connected directly at REFIN. An internal buffer

with a gain of +1 provides +2.5V at REFOUT.

Internal Reference

The full-scale range with the internal reference is ±5V

for the MAX115 and ±2.5V for the MAX116. Bypass

REFIN with a 0.1µF capacitor to AGND, and bypass the

REFOUT pin with a 4.7µF (min) capacitor to AGND

(Figure 6). The maximum value to compensate the ref-

erence buffer is 22µF. Larger values are acceptable if

low-ESR capacitors are used.

External Reference

For operation over a wide temperature range, an exter-

nal +2.5V reference with tighter specifications improves

accuracy. The MAX6325 is an excellent choice

to match the MAX115/MAX116 accuracy over the

commercial and extended temperature ranges with a

1ppm/°C (max) temperature drift. Connect an external

reference at REFIN as shown in Figure 7. The minimum

impedance is 7k

Ω for DC currents in both normal oper-

ation and shutdown. Bypass REFOUT with a 4.7µF low-

ESR capacitor.

Power-On Reset

When power is first applied, the internal power-on reset

(POR) circuitry activates the MAX115/MAX116 with INT

= high, ready to convert. The default conversion mode

is Input Mux A/Single Channel Conversion. See the

Programming Modes section if other configurations are

desired.

After the power supplies have been stabilized, the reset

time is 5µs. No conversions should be performed

during this phase. At power-up, data-in memory is

undefined.

Software Power-Down

Software power-down is activated by setting bit A3 of

the control word high (Table 1). It is asserted after the

WR or CS rising edge, at which point the ADC immedi-

ately powers down to a low quiescent-current state.

drops to 13µA (typ). The ADC circuitry and reference

buffer are turned off, but the digital interface and the

reference remain active for fast power-up recovery.

Wake up the MAX115/MAX116 by writing a control

word (A0–A3, Table 1). The bidirectional interface inter-

prets a logic zero at A3 as the start signal, and powers

up in the mode selected by A0, A1, and A2. The refer-

ence buffer’s settling time and the bypass capacitor’s

value dominate the power-up delay. With the recom-

mended 4.7µF at REFOUT, the power-up delay is typi-

cally 20ms.

Transfer Function

The MAX115/MAX116 have bipolar input ranges. Figure

8 shows the bipolar/output transfer function. Code tran-

sitions occur at successive-integer least significant bit

2x4-Channel, Simultaneous-Sampling

12-Bit ADCs

______________________________________________________________________________________

11

TO DAC

REFIN

10k

4.7

µF

2.5V

REFOUT

7

6

(2.5V)

(2.5V)

OUT

MAX6325

MAX115

MAX116

Figure 7. External Reference

011 . . . 111

011 . . . 110

000 . . . 010

000 . . . 001

000 . . . 000

111 . . . 111

111 . . . 110

111 . . . 101

100 . . . 001

100 . . . 000

- FS

ZERO

INPUT VOLTAGE (LSB)

OUTPUT CODE

+FS - 1LSB

4096

4096

Figure 8. Bipolar Transfer Function