MAX9939AUB 데이터 시트보기 (PDF) - Maxim Integrated

부품명

상세내역

제조사

MAX9939AUB

SPI Programmable-Gain Amplifier with Input VOS Trim and Output Op Amp

Maxim Integrated 

SPI Programmable-Gain Amplifier

with Input VOS Trim and Output Op Amp

SHDN: Set SHDN to 0 for normal operation. Set SHDN

to 1 to place the device in a low-power 13µA shutdown

mode. In shutdown mode, the outputs OUTA and OUTB

are high impedance, however, the SPI decode circuitry

is still active. Each instruction requires a write to the

SHDN bit.

MEAS: The MAX9939 provides a means for measuring

its own input offset voltage. When MEAS is set to 1, the

INA- input is disconnected from the input signal path

and internally shorted to INA+. This architecture thus

allows the input common-mode voltage to be compen-

sated at the application-specific input common-mode

voltage of interest. The input offset voltage of the PGA

is the output offset voltage divided by the programmed

gain without any VOS trim (i.e., V3:V0 set to 0):

VOS-INHERENT = (VOUTA - VCC/2)/Gain

Program VOS to offset VOS-INHERENT. The input VOS

also includes the effect of mismatches in the resistor-

dividers. Setting MEAS to 0 switches the inputs back to

the signals on INA+ and INA-. Each instruction requires

a write to the MEAS bit.

Programming Gain

The PGA’s gain is set by the bits G3:G0 in the Gain reg-

ister. Table 3 shows the relationship between the bits

G3:G0 and the amplifier’s gain. The slew rate and

small-signal bandwidth (SSBW) of the PGA depend on

its gain setting as shown in Table 3.

Programming Input Offset Voltage (VOS)

The input offset voltage is set by the bits V4:V0 in the

Input Offset Voltage Trim register. Bit V4 determines the

polarity of the offset. Setting V4 to 0 makes the offset

positive, while setting V4 to 1 makes the offset negative.

Table 4 shows the relationship between V3:V0 and VOS.

To determine the effect of VOS at the output of the ampli-

fier for gains other than 1, use the following formula:

VOUTA = VCC/2 + Gain x (VOS-INHERENT + VOS)

where VOS-INHERENT is the inherent input offset voltage

of the amplifier, which can be measured by setting

MEAS to 1.

Applications Information

Use of Output Amplifier as Active Filter

The output amplifier can be configured as a multiple-

feedback active filter as shown in Figure 3, which tradi-

tionally has better stopband attenuation characteristics

than Sallen-Key filters. These filters also possess inher-

ently better distortion performance since there are no

common-mode induced effects (i.e., the common-

mode voltage of the operational amplifier is always

fixed at VCC/2 instead of it being signal dependent

such as in Sallen-Key filters). Choose external resistors

and capacitors to create lowpass, bandpass, or high-

pass filters.

Table 3. Gain

G3:G0

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

GAIN

(V/V)

1

10

20

30

40

60

80

120

157

0.2 (VCC = 5V)

0.25 (VCC = 3.3V)

1

SLEW RATE

(V/µs)

2.90

8.99

8.70

12.80

12.50

13.31

12.15

18.53

16.49

2.86

2.90

SMALL-SIGNAL BANDWIDTH (MHz)

2.15

2.40

1.95

3.40

2.15

2.60

1.91

2.30

1.78

1.95

2.15

_______________________________________________________________________________________ 9

Share Link: