Datasheet

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LTC6912

6912fa

FEATURES

TYPICAL APPLICATIO

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2 Channels with Independent Gain Control

LTC6912-1: (0, 1, 2, 5, 10, 20, 50, and 100V/V)

LTC6912-2: (0, 1, 2, 4, 8, 16, 32, and 64V/V)

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Offset Voltage = 2mV Max (–40°C to 85°C)

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Channel-to-Channel Gain Matching of 0.1dB Max

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3-Wire SPI

Interface

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Extended Gain-Bandwidth at High Gains

■

Wired-OR Outputs Possible (2:1 Analog MUX

Function)

■

Low Power Hardware Shutdown (GN-16 Only,

2µA Max at 2.7V)

■

Rail-to-Rail Input Range

■

Rail-to-Rail Output Swing

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Single or Dual Supply: 2.7V to 10.5V Total

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Input Noise: 12.6nV/√Hz

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Total System Dynamic Range to 115dB

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16-Pin GN (SSOP) or 12-Pin DFN Package Options

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Data Acquisition Systems

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Dynamic Gain Changing

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Automatic Ranging Circuits

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Automatic Gain Control

Dual Programmable

Gain Amplifiers with

Serial Digital Interface

The LTC

6912 is a family of dual channel, low noise,

digitally programmable gain amplifiers (PGA) that are

easy to use and occupy very little PC board space. The

gains for both channels are independently programmable

using a 3-wire SPI interface to select voltage gains of 0, 1,

2, 5, 10, 20, 50, and 100V/V (LTC6912-1 ); and 0, 1, 2, 4,

8, 16, 32, and 64V/V (LTC6912-2). All gains are inverting.

The LTC6912 family consists of 2 matched amplifiers with

rail-to-rail outputs. When operated with unity gain, they

will also process rail-to-rail input signals. A half-supply

reference generated internally at the AGND pin supports

single power supply applications. Operating from single

or split supplies from 2.7V to 10.5V total, the LTC6912-X

family is offered in tiny SSOP and DFN-12 Packages.

, LTC and LT are registered trademarks of Linear Technology Corporation.

INA

AGND

INB

1µF

0.1µF

INA

INB

OUTA

= GAIN

• V

INA

OUTB

= GAIN

• V

INB

OUT A

OUT B

LTC6912-X

–

SHDN

CS/LD

DATA

CLK

SHDN

CS/LD

DGND

OUT

12 14

CHB CHA

3-WIRE

SPI

INTERFACE

6912 TA01a

FREQUENCY (kHz)

0.1

GAIN (dB)

–10

10 100 1000

6912 TA01b

10000

GAIN OF 64

GAIN OF 32

GAIN OF 16

GAIN OF 8

GAIN OF 4

GAIN OF 2

GAIN OF 1

= ±2.5V

= 10mV

RMS

LTC6912-2

Frequency Response

A Dual, Matched Low Noise PGA (16-Lead SSOP Package)

DESCRIPTIO

All other trademarks are the property of their respective owners.

APPLICATIO S

Summary of content (24 pages)

PAGE 1
LTC6912 Dual Programmable Gain Amplifiers with Serial Digital Interface DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 2 Channels with Independent Gain Control LTC6912-1: (0, 1, 2, 5, 10, 20, 50, and 100V/V) LTC6912-2: (0, 1, 2, 4, 8, 16, 32, and 64V/V) Offset Voltage = 2mV Max (–40°C to 85°C) Channel-to-Channel Gain Matching of 0.
PAGE 2
LTC6912 W W U W ABSOLUTE AXI U RATI GS (Note 1) Total Supply Voltage (V + to V –) ............................... 11V Input Current ...................................................... ±10mA Operating Temperature Range (Note 2) LTC6912C-1, LTC6912C-2 ..................–40°C to 85°C LTC6912I-1, LTC6912I-2 .....................–40°C to 85°C LTC6912H-1, LTC6912H-2 (GN-16 Only) .....................................–40°C to 125°C Specified Temperature Range (Note 3) LTC6912C-1, LTC6912C-2 .............
PAGE 3
LTC6912 U U U GAI SETTI GS A D PROPERTIES Table 1. LTC6912-1 GAIN SETTINGS AND PROPERTIES UPPER/LOWER NIBBLE NOMINAL VOLTAGE GAIN MAXIMUM LINEAR INPUT RANGE (VP-P) Q7 Q3 Q6 Q2 Q5 Q1 Q4 Q0 Volts/Volt dB Dual 5V Supply Single 5V Supply Single 3V Supply NOMINAL INPUT NOMINAL OUTPUT IMPEDANCE (kΩ) IMPEDANCE (Ω) 0 0 0 0 0 –120 10 5 3 (Open) 0.4 0 0 0 1 –1 0 10 5 3 10 0.7 0 0 1 0 –2 6 5 2.5 1.5 5 3.4 0 0 1 1 –5 14 2 1 0.6 2 3.4 0 1 0 0 –10 20 1 0.
PAGE 4
LTC6912 ELECTRICAL CHARACTERISTICS The ● denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V, AGND = 2.5V, Gain = 1, RL = 10k to midsupply point, unless otherwise noted. PARAMETER CONDITIONS MIN C, I GRADES TYP MAX MIN H GRADE TYP MAX UNITS 2.7 10.5 2.7 10.5 V Specifications for Both the LTC6912-1 and the LTC6912-2 ● Total Supply Voltage (VS) Supply Current per Channel Both Amplifiers Active (Gain = 1) VS = 2.
PAGE 5
LTC6912 ELECTRICAL CHARACTERISTICS The ● denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V, AGND = 2.5V, Gain = 1, RL = 10k to midsupply point, unless otherwise noted. PARAMETER CONDITIONS MIN C, I GRADES TYP MAX MIN H GRADE TYP MAX UNITS Specifications for Both the LTC6912-1 and the LTC6912-2 SHDN Input High Voltage (GN-16 Package Only) VS = Single 2.
PAGE 6
LTC6912 ELECTRICAL CHARACTERISTICS The ● denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V, AGND = 2.5V, Gain = 1, RL = 10k to midsupply point, unless otherwise noted. PARAMETER CONDITIONS MIN C, I GRADES TYP MAX MIN H GRADE TYP MAX UNITS Specifications for the LTC6912-1 ONLY Channel-to-Channel Voltage Gain Match (Note 6) VS = 2.7V, Gain = 1, RL = 10k VS = 2.7V, Gain = 1, RL = 500Ω VS = 2.
PAGE 7
LTC6912 ELECTRICAL CHARACTERISTICS The ● denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V, AGND = 2.5V, Gain = 1, RL = 10k to midsupply point, unless otherwise noted. PARAMETER CONDITIONS MIN C, I SUFFIXES TYP MAX MIN H SUFFIX TYP MAX UNITS Specifications for the LTC6912-1 ONLY Offset Voltage Magnitude (Internal Op-Amp, Note 8) Gain = 1 ● 0.125 2 0.125 3.
PAGE 8
LTC6912 ELECTRICAL CHARACTERISTICS The ● denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V, AGND = 2.5V, Gain = 1, RL = 10k to midsupply point, unless otherwise noted.
PAGE 9
LTC6912 ELECTRICAL CHARACTERISTICS The ● denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V, AGND = 2.5V, Gain = 1, RL = 10k to midsupply point, unless otherwise noted. PARAMETER CONDITIONS MIN C, I GRADES TYP MAX MIN H GRADE TYP MAX UNITS Specifications for the LTC6912-2 ONLY Channel-to-Channel Voltage Gain Match (Note 6) VS = 2.7V, Gain = 1, RL = 10k VS = 2.7V, Gain = 1, RL = 500Ω VS = 2.
PAGE 10
LTC6912 ELECTRICAL CHARACTERISTICS The ● denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V, AGND = 2.5V, Gain = 1, RL = 10k to midsupply point, unless otherwise noted. PARAMETER CONDITIONS MIN C, I GRADES TYP MAX MIN H GRADE TYP MAX 0.25 0.14 6.5 4 UNITS Specifications for the LTC6912-2 ONLY Offset Voltage Magnitude Referred to INA or INB Pins (Note 8) Gain = 1 Gain = 8 ● ● 0.25 0.
PAGE 11
LTC6912 ELECTRICAL CHARACTERISTICS The ● denotes the specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V, AGND = 2.5V, Gain = 1, RL = 10k to midsupply point, unless otherwise noted.
PAGE 12
LTC6912 U U SERIAL I TERFACE SPECIFICATIO S SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Serial Interface Timing, Dual ±4.5V ~ ±5.
PAGE 13
LTC6912 U W TYPICAL PERFOR A CE CHARACTERISTICS 40 GAIN OF 50 GAIN OF 20 GAIN OF 10 20 GAIN OF 5 10 GAIN OF 2 GAIN OF 1 0 –10 10 1 100 1000 FREQUENCY (kHz) 10000 0.05 GAIN OF 100 0 GAIN OF 1 GAIN OF 10 –0.05 –0.10 –0.
PAGE 14
LTC6912 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC6912-1 Hardware Shutdown Total Supply Current vs Temperature 10 VS = 5V VS = 3V VS = 2.7V 100 500 VS = 5V 400 VS = 2.7V 300 200 50 25 75 0 TEMPERATURE (°C) 100 3.75 –0.10 GAIN OF 100 –0.15 0 –25 25 50 75 125 100 6912 G12 LTC6912-2 Frequency Response 40 30 GAIN OF 1 0 GAIN OF 10 VS = 2.7V 3.50 VS = 5V RL = 500Ω GAIN CHANGE (dB) GAIN CHANGE (dB) VS = 5V 4.00 3.00 –50 125 0.5 GAIN OF 1 –0.05 4.
PAGE 15
LTC6912 U W TYPICAL PERFOR A CE CHARACTERISTICS 90 VOLTAGE NOISE DENSITY (nV/Hz) 80 70 60 +SUPPLY –SUPPLY 40 30 20 VS = ±2.
PAGE 16
LTC6912 U W TYPICAL PERFOR A CE CHARACTERISTICS LTC6912-2 Gain Shift vs Temperature (Heavy Load) 0.25 GAIN = 1 GAIN CHANGE (dB) 0 VS = 5V RL = 500 GAIN = 8 –0.25 GAIN = 64 –0.50 –0.75 –1.00 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 6912 G26 U U U PI FU CTIO S INA, INB: Analog Inputs. The input signal to the A channel amplifier of the LTC6912-X is the voltage difference between the INA pin and AGND pin.
PAGE 17
LTC6912 U U U PI FU CTIO S AGND: Analog Ground. The AGND pin is at the midpoint of an internal resistive voltage divider, developing a potential halfway between the V + and V – pins. In normal operation, the AGND pin has an equivalent input resistance of nominally 50k (Figure 1).
PAGE 18
LTC6912 U U U PI FU CTIO S ANALOG GROUND PLANE V+ + V– REFERENCE 1 2 2 ≥0.1µF SERIAL INTERFACE DIN: TTL/CMOS Compatible Logic Serial Data Input. The serial interface is synchronously loaded MSB first via DIN on the rising edge of CLK with CS/LD asserted low. 16 LTC6912-X 15 3 14 V – 4 13 5 12 V + 6 11 7 10 8 9 0.1µF 0.1µF SINGLE-POINT SYSTEM GND DIGITAL GROUND PLANE 6912 F04 Figure 4.
PAGE 19
LTC6912 U U U PI FU CTIO S OUT A, OUT B: Analog Output. These pins are the output of the A and B channel amplifiers respectively. Each operational amplifier can swing rail-to-rail (V + to V –) as specified in the Electrical Characteristics table. For best performance, loading the output as lightly as possible will minimize signal distortion and gain error.
PAGE 20
LTC6912 U W U U APPLICATIO S I FOR ATIO configuration. It is recommended the serial interface signals should remain idle in between data transfers in order to minimize digital noise coupling into the analog path. Power On Reset On the initial application of power, the power on reset state of both amplifiers is low power software shutdown (state = 8) (see Tables 1 and 2). In this state, both analog amplifiers are disabled and have their inputs and outputs opened.
PAGE 21
LTC6912 U W U U APPLICATIO S I FOR ATIO Offset Voltage vs Gain Setting The electrical tables list DC offset (error), VOS(OA), at the inputs of the internal op amp (See Figure 1). The electrical tables also show the resulting, gain dependent offset voltage referred to the INA, or INB pins, VOS(IN).
PAGE 22
LTC6912 U W U U APPLICATIO S I FOR ATIO SNR from an amplifier is the ratio of input level to inputreferred noise, and can be 108dB with the LTC6912 family at unity gain. Construction and Instrumentation Cautions Electrically clean construction is important in applications seeking the full dynamic range of the LTC6912 family of dual amplifiers.
PAGE 23
LTC6912 U PACKAGE DESCRIPTIO DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695) 4.00 ±0.10 (2 SIDES) 7 0.65 ±0.05 3.50 ±0.05 1.70 ±0.05 2.20 ±0.05 (2 SIDES) R = 0.115 TYP 0.38 ± 0.10 12 R = 0.20 TYP 1.70 ± 0.10 (2 SIDES) 3.00 ±0.10 (2 SIDES) PIN 1 TOP MARK (NOTE 6) PACKAGE OUTLINE PIN 1 NOTCH (UE12/DE12) DFN 0603 0.25 ± 0.05 3.30 ±0.05 (2 SIDES) 6 0.25 ± 0.05 0.75 ±0.05 0.200 REF 0.50 BSC 3.30 ±0.10 (2 SIDES) 0.00 – 0.05 1 0.
PAGE 24
LTC6912 U TYPICAL APPLICATIO A 2:1 PGA MUX V+ 0.1µF 12 14 V+ V– 2 INA CHANNEL A INPUT OUT A 15 VOUT (TO ADC) 1µF 3 LTC6912-X 4 INB CHANNEL B INPUT SHDN 3-WIRE SPI INTERFACE AGND CS/LD DATA CLK 5 6 7 8 OUT B CHB SHDN CS/LD DIN 13 CHA DGND DOUT 10 9 6912 TA02 MUX OPERATION: IF THE LOWER NIBBLE (Q3, Q2, Q1, Q0) IS (1, 0, 0, 0) THEN OUTA IS IN TRI-STATE AND THE UPPER NIBBLE (Q7, Q6, Q5, Q4) CONTROLS THE ACTIVE CHANNEL B.