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MAX5168中文资料

General Description

The MAX5168 contains 32 sample/hold amplifiers and four 1-of-8 multiplexers. The logic controlling the muxes and sample/hold amplifiers combines the four muxes into a unified 1-of-32 multiplexer with a sample/hold at each output. Additional logic allows two devices to function as a single 64-channel unit. The MAX5168 is available with an output impedance of 50?, 500?, or 1k ?.

The MAX5168 operates with +10V and -5V supplies, and a separate +5V digital logic supply. Manufactured with a proprietary BiCMOS process, it provides high accuracy,fast acquisition time, a low droop rate, and a low hold step. The MAX5168 has a typical linearity error of less than 0.01% and can accurately acquire 8V step input sig-nals to 0.01% accuracy in 2.5μs within the +7V to -4V input signal range. Transitions from sample mode to hold mode result in only a 0.5mV error. While in hold mode, the output voltage slowly droops at a rate of 1mV/s.

The MAX5168 is available in a 48-pin TQFP package and is specified for both the commercial (0°C to +70°C) and extended industrial (-40°C to +85°C) temperature ranges.

________________________Applications

Automatic Test Systems (ATE)Industrial Process Controls Arbitrary Function Generators Avionics Equipment

Features

o 32-Channel Sample/Hold

o 0.01% Accuracy of Acquired Signal o 0.01% Linearity Error o Fast Acquisition Time: 2.5μs o Low Droop Rate: 1mV/s o Low Hold Step: 0.25mV

o Wide Output Voltage Range: +7V to -4V

MAX5168

32-Channel Sample/Hold Amplifier

with a Single Multiplexed Input

________________________________________________________________Maxim Integrated Products

Pin Configuration

19-1674; Rev 0; 4/00

Ordering Information

For free samples and the latest literature, visit https://www.wendangku.net/doc/4b15671471.html, or phone 1-800-998-8800.For small orders, phone 1-800-835-8769.

M A X 5168

32-Channel Sample/Hold Amplifier with a Single Multiplexed Input 2_______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(V DD = +10.0V, V SS = -5.0V, V L = +5.0V ±5%, AGND = DGND = 0, R L = 5k ?, C L = 50pF, T A = T MIN to T MAX , unless otherwise noted.Typical values are at T = +25°C.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

V DD to AGND.......................................................-0.3V to +11.0V V SS to AGND.........................................................-6.0V to +0.3V V DD to V SS ......................................................................+15.75V V L to DGND...........................................................-0.3V to +6.0V V L to AGND...........................................................-0.3V to +6.0V DGND to AGND.....................................................-0.3V to +2.0V IN, OUT_.....................................................................V SS to V DD Logic Inputs to DGND...........................................-0.3V to +6.0V Maximum Current into OUT_............................................±10mA

Maximum Current into Logic Inputs .................................±20mA Continuous Power Dissipation (T A = +70°C)

48-Pin TQFP (derate 12.5mW/°C above +70°C)......1000mW Operating Temperature Ranges

MAX5168_CCM ................................................0°C to +70°C MAX5168_ECM..............................................-40°C to +85°C Storage Temperature Range.............................-65°C to +150°C Lead Temperature (soldering, 10s).................................+300°C

MAX5168

32-Channel Sample/Hold Amplifier

with a Single Multiplexed Input

_______________________________________________________________________________________3

ELECTRICAL CHARACTERISTICS (continued)

(V DD = +10.0V, V SS = -5.0V, V L = +5.0V ±5%, AGND = DGND = 0, R L = 5k ?, C L = 50pF, T A = T MIN to T MAX , unless otherwise noted.Typical values are at T

= +25°C.)

Note 1:Guaranteed by design.

Note 2:Do not exceed the absolute maximum rating for V DD to V SS of +15.75V (see Absolute Maximum Ratings ).

M A X 5168

32-Channel Sample/Hold Amplifier with a Single Multiplexed Input 4_______________________________________________________________________________________

Typical Operating Characteristics

(V DD = +10V, V SS = -5V, V L = +5V, V IN = +5V, R L = ∞, C L = 0, AGND = DGND = 0, V CH = V DD , V CL = V SS , T A = +25°C, unless otherwise noted.)

0.40.21.00.80.61.21.41.81.62.0-4-2-1

-30

DROOP RATE vs. INPUT VOLTAGE

M A X 5168 T O C 01

INPUT VOLTAGE (V)

D R O O P R A T

E (m V /s )

4050-40

-15

DROOP RATE vs. TEMPERATURE

TEMPERATURE (°C)

D R O O P R A T

E (m V /s )

0-40

-20-80-60-100-120

0.1

100

1000

10,000

POWER-SUPPLY REJECTION RATIO

SAMPLE MODE

FREQUENCY (kHz)

P S R R (d B )

0-40-20-80-60-100-120

0.1

100

1000

10,000

POWER-SUPPLY REJECTION RATIO

HOLD MODE

FREQUENCY (kHz)

P S R R (d B )

-20-140-60-40-80-100-120-160-4-2-1

-31

7HOLD STEP vs. INPUT VOLTAGE

M A X 5168 T O C 05

INPUT VOLTAGE (V)H O L D S T E P (μV )80

908510095115110105120

-55-15-35525456585

HOLD STEP vs. TEMPERATURE

M A X 5168 T O C 06

TEMPERATURE (°C)

H O L D S T E P (μV )

-5.0

-4.6-4.8-4.0-4.2-4.4-3.8-3.6-3.2-3.4-3.0-4-2-1

-30

7OFFSET VOLTAGE vs. INPUT VOLTAGE

M A X 5168 T O C 07

INPUT VOLTAGE (V)O F F S E T V O L T A G E (m V )

-7

-5-6-3-4-1-20-4010-15356085

OFFSET VOLTAGE vs. TEMPERATURE

M A X 5168 T O C 08

TEMPERATURE (°C)

O F F S E T V O L T A G E (m V )

MAX5168

32-Channel Sample/Hold Amplifier

with a Single Multiplexed Input

_______________________________________________________________________________________5

Pin Description

M A X 5168

Detailed Description

Digital Interface

The MAX5168 has three logic control inputs and five address lines. The address lines are inputs to a demul-tiplexer that selects one of the 32 outputs in a standard addressing scheme (Table 1). The analog input is con-nected to the addressed sample/hold when directed by the control logic (Table 2).

The three logic control lines determine the state of the addressed sample/hold. The normal circuit connection for this device is to hardwire CONFIG and SELECT to opposing logic voltages. When SELECT and CONFIG are in opposite states (one high and the other low), the five address lines select one of the sample/holds. Use the S /H line to place the selected channel into sample or hold mode. The other 31 channels will remain in hold mode.

If an active-high sampling mode is desired, tie S /H and CONFIG low. In this case, SELECT controls the addressed channel with a high state putting that chan-nel into sample mode.

The SELECT and CONFIG pins allow the design of a virtual 64-channel device using two of the MAX5168s.See the Applications Information section for more infor-mation about 64-plus output addressing schemes.

Sample/Hold

The MAX5168 contains 32 buffered sample/hold circuits with internal hold capacitors. Internal hold capacitors minimize leakage current, dielectric absorption,feedthrough, and required board space. The value of the hold capacitor affects acquisition time and droop rate. Smaller capacitance allows faster acquisition times but increases the droop rate. Larger values increase hold acquisition time. The hold capacitor used in the MAX5168 provides fast 2.5μs (typ) acquisition time while maintaining a relatively low 1mV/s (typ)droop rate, making the sample/hold ideal for high-speed sampling.

Sample Mode

When SELECT and CONFIG are in opposing logic states,the S /H line controls the mode of operation. Sample mode is entered when S /H is low. During sample mode, the

32-Channel Sample/Hold Amplifier with a Single Multiplexed Input 6

_______________________________________________________________________________________

Figure 1. Functional Diagram

MAX5168

32-Channel Sample/Hold Amplifier

with a Single Multiplexed Input

_______________________________________________________________________________________

X = Don’t care.

M A X 5168

selected multiplexer channel connects to IN, allowing the hold capacitor to acquire the input signal. To guarantee an accurate sample, maintain sample mode for at least 4μs. The output of the sample/hold amplifier tracks the input after 4μs. Only the addressed channel on the selected multiplexer samples the input; all other channels remain in hold mode.

Hold Mode

No matter what the condition of the other control lines,S /H = high places the MAX5168 into an all-channel hold mode. H old mode disables the multiplexer and disconnects all 32 sample/holds from the input. When a channel is disconnected, the hold capacitor maintains the sampled voltage at the output with a 1mV/s typical droop rate (towards V DD ).

Hold Step

When switching between sample mode and hold mode,the voltage of the hold capacitor changes due to charge injection from stray capacitance. This voltage change, called a hold step, is minimized by limiting the amount of stray capacitance seen by the hold capacitor.The MAX5168 limits the hold step to 0.25mV (typ). An output capacitor to ground can be used to filter out this small hold-step error.

Output

The MAX5168 contains an output buffer for each multi-plexer channel (32 total), so the hold capacitor sees a high-impedance input that reduces the droop rate. The capacitor droops at 1mV/s (typ) while in hold mode. The buffer also provides a low output impedance; however,the device contains output resistors in series with the buffer output (Figure 1) for selected output filtering. To provide greater design flexibility, the MAX5168 is avail-able with an output impedance of 50?, 500?, or 1k ?.

Output loads increase the analog supply current (I DD and I SS ). Excessive loading of the output(s) drastically increases power dissipation. Do not exceed the maximum power dissipation specified in the Absolute Ma ximum Ratings .

The resistor-divider formed by the output resistor (R O ) and load impedance (R L ) scales the sampled voltage (V SAMP ). Determine the output voltage (V OUT_) as follows:Voltage Gain = A V = R L / (R L + R O )

V OUT_= V SAMP ?A V

The maximum output voltage range depends on the ana-log supply voltages available and the scaling factor used:

(V SS + 0.75V) ?A V ≤V OUT_≤(V DD - 2.4V) ?A V

when R L = ∞, then A V = 1, and this equation becomes

(V SS + 0.75V) ≤V OUT ≤(V DD - 2.4V)

Timing Definitions

Acquisition time (t AQ ) is the time the MAX5168 must remain in sample mode for the hold capacitor to acquire an accurate sample. The hold-mode settling time (t H ) is the time necessary for the output voltage to settle to its final value. Aperture delay (t AP ) is the time interval required to disconnect the input from the hold capacitor. The hold pulse width (t PW ) is the time the MAX5168 must remain in hold mode while the address is changed. Data setup time (t DS ) is the time an address must be maintained at the digital input pins before the address becomes valid. Data hold time (t DH )is the time an address must be maintained after the device is placed in hold mode (Figure 2).

Applications Information

Multiplexing a DAC

Figure 3 shows a typical demultiplexer application.Different digital codes are converted by the digital-to-analog converter (DAC) and then stored on 32 different channels of the MAX5168. The 40mV/s (max) droop rate requires refreshing the hold capacitors every 250ms before the voltage droops by 1/2LSB for an 8-bit DAC with a 5V full-scale voltage.

Virtual 64 Output Sample/Hold

Two MAX5168s can be configured to operate as a single 64 output sample/hold. The upper and lower addressed devices are identified by CONFIG’s logic level. Connect the CONFIG pin of the upper device low, making its SELECT pin active high. Connect the CONFIG pin of the lower device high to make the SELECT pin active low.Figure 4 shows how to configure the devices.

The devices now use only six address lines and a sin-gle S /H control to decode 64 outputs. Address lines A0–A4 from the control logic connect to ADDR0–ADDR4 on both of the 32-channel devices. The A5 line toggles the SELECT pins of both devices to select the active one. The device that has CONFIG tied high responds to the lower 32 addresses (000000 through 011111). The device that has CONFIG grounded responds to the upper 32 addresses (100000 through 111111).

32-Channel Sample/Hold Amplifier with a Single Multiplexed Input 8_______________________________________________________________________________________

MAX5168

32-Channel Sample/Hold Amplifier

with a Single Multiplexed Input

_______________________________________________________________________________________9

Figure 2. Timing Diagram

Figure 3. Multiplexing a DAC

M A X 5168

Input Drive Requirements

The input of the MAX5168 feeds the inputs of 32 high-impedance buffers. These buffers are what charge the sample/hold capacitor through the multiplexer switch resistance. The bias current of a selected buffer is 10μA, and this feeds into the 10pF input capacitance.Figure 5 shows an equivalent input circuit. The bias cur-rents of the other 31 sample and holds are very small in comparison to the bias current of the selected channel.

Powering the MAX5168

The MAX5168 does not require a special power-up sequence to avoid latchup. The device requires three separate supply voltages for operation. However, when one or two of the voltages are not available, DC-DC charge-pump (switched-capacitor) converters provide a simple, efficient solution. The MAX860 provides volt-age doubling or inversion, ideal for conversions from +5V to +10V or from +5V to -5V.

Chip Information

TRANSISTOR COUNT: 6961

32-Channel Sample/Hold Amplifier with a Single Multiplexed Input 10______________________________________________________________________________________

Figure 4. 64-Output Sample/Hold Circuit

Figure 5. Input Equivalent Circuit

MAX5168

32-Channel Sample/Hold Amplifier

with a Single Multiplexed Input

______________________________________________________________________________________11

Package Information

M A X 5168

32-Channel Sample/Hold Amplifier with a Single Multiplexed Input Ma xim ca nnot a ssume responsibility for use of a ny circuitry other tha n circuitry entirely embodied in a Ma xim product. No circuit pa tent licenses a re implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

12____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600?2000 Maxim Integrated Products

Printed USA

is a registered trademark of Maxim Integrated Products.

NOTES