EVALUATION KIT AVAILABLE
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
General Description
Features
The MAX155/MAX156 are high-speed, 8-bit, multichannel analog-to-digital converters (ADCs) with simultaneous
track/holds (T/Hs) to eliminate timing differences between
input channel samples. The MAX155 has 8 analog input
channels and the MAX156 has 4 analog input channels.
Each channel has its own T/H, and all T/Hs sample at the
same instant. The ADC converts a channel in 3.6µs and
stores the result in an internal 8x8 RAM. The MAX155/
MAX156 also feature a 2.5V internal reference and
power-down capability, providing a complete, sampling
data-acquisition system.
●● 8 Simultaneously Sampling Track/Hold Inputs
●● 3.6µs Conversion Time Per Channel
●● Unipolar or Bipolar Input Range
●● Single-Ended or Differential Inputs
●● Mixed Input Configurations Possible
●● 2.5V Internal Reference
●● Single +5V or Dual ±5V Supply Operation
Applications
●●
●●
●●
●●
●●
When operating from a single +5V supply, the MAX155/
MAX156 perform either unipolar or bipolar, single-ended
or differential conversions. For applications requiring
wider dynamic range or bipolar conversions around
ground, the VSS supply pin may be connected to -5V.
Conversions are initiated with a pulse to the WR pin, and data
is accessed from the ADC’s RAM with a pulse to the RD pin.
A bidirectional interface updates the channel configuration
and provides output data. The ADC may also be wired for
output-only operation.The MAX155 comes in 28-pin PDIP
and wide SO packages, and the MAX156 comes in 24-pin
narrow PDIP and 28-pin wide SO packages.
Phase-Sensitive Data Acquisition
Vibration and Waveform Analysis
DSP Analog Input
AC Power Meters
Portable Data Loggers
Ordering Information appears at end of data sheet.
For related parts and recommended products to use with this part, refer
to www.maximintegrated.com/MAX155.related.
Functional Diagram
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
MAX155
T/H
T/H
CLK
8-BIT
A/D
3.6µs
T/H
T/H
REFIN
8
T/H
8x8
RAM
T/H
T/H
REFOUT
2.5V
VREF
8
THREESTATE
BUFFER
T/H
8
8-BIT
DATA
8 BUS
CS
8
CONTROL
LOGIC
RD
WR
MODE
19-2949; Rev 2; 1/12
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
Absolute Maximum Ratings
VDD to AGND.............................................................. -0.3V, +6V
VDD to DGND.............................................................. -0.3V, +6V
AGND to DGND............................................-0.3V, (VDD + 0.3V)
VSS to AGND.............................................................. +0.3V, -6V
VSS to DGND.............................................................. +0.3V, -6V
CS, WR, RD, CLK, MODE to DGND............-0.3V, (VDD + 0 3V)
BUSY, D0–D7 to DGND................................-0.3V, (VDD + 0 3V)
REFOUT to AGND........................................-0.3V, (VDD + 0 3V)
REFIN to AGND............................................-0.3V, (VDD + 0 3V)
AIN to AGND..................................... (VSS - 0.3V), (VDD + 0 3V)
Output Current (REFOUT)..................................................30mA
Continuous Power Dissipation (TA = +70°C)
24-Pin PDIP (derate 8.7mW/°C above +70°C).............696mW
28-Pin PDIP (derate 9.09mW/°C above +70°C)...........727mW
28-Pin Wide SO (derate 12.5mW/°C above +70°C)...1000mW
Operating Temperature Ranges:
MAX155/MAX156_C_ _.......................................0°C to +70°C
MAX155/MAX156_E_ _................................... -40°C to +85°C
Storage Temperature Range............................. -65°C to +150°C
Lead Temperature (soldering, 10s).................................. +300°C
Soldering Temperature (reflow)........................................+260°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.
Electrical Characteristics
(VDD = +5V, VREFIN = +2.5V. External Reference, VAGND = VDGND = 0V, VSS = 0V or -5V, fCLK = 5MHz external, Unipolar range
single-ended mode, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
ACCURACY (Note 1)
Resolution
8
Integral Linearity Error
No Missing Codes Resolution
±½
MAX15_B
±1
Guaranteed monotonic
Offset Error (Unipolar)
Offset Error (Bipolar)
8
±½
MAX15_B
±1
MAX15_A
±1
MAX15_B
±2
Gain Error
Bipolar
LSB
Bits
MAX15_A
Unipolar
Channel-to-Channel Matching
Bits
MAX15_A
MAX15_A
±1
MAX15_B
±1
MAX15_A
±1
MAX15_B
±2
MAX15_A
±½
MAX15_B
±1
LSB
LSB
LSB
LSB
DYNAMIC PERFORMANCE (VIN = 50kHz, 2.5VP-P sine wave sampled at 220ksps)
Signal-to-Noise and Distortion
Ratio
Total Harmonic Distortion
SINAD
MAX15_A
48
MAX15_B
47
dB
THD
-60
dB
SFDR
-62
dB
Small-Signal Bandwidth
4
MHz
Aperture Delay
20
Spurious-Free Dynamic Range
Aperture Delay Matching (Note 2)
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ns
4
ns
Maxim Integrated │ 2
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
Electrical Characteristics (continued)
(VDD = +5V, VREFIN = +2.5V. External Reference, VAGND = VDGND = 0V, VSS = 0V or -5V, fCLK = 5MHz external, Unipolar range
single-ended mode, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
ANALOG INPUT
Voltage Range, Unipolar, SingleEnded
AIN_(+) to AGND
Unipolar Differential
Bipolar, Single-Ended
0
VREF
AIN_(+) to AIN_(-)
0
VREF
AIN_(+) to AGND
-VREF
VREF
Bipolar, Differential
AIN_(+) to AIN_(-)
-VREF
VREF
Common-Mode Range
Differential mode
VSS
VDD
DC Input Impedance
AIN = VDD
10
V
MΩ
REFERENCE INPUT
REFIN Range (For Specified
Performance) (Note 2)
2.375
IREF
2.500
VREFIN = 2.5V
2.625
V
1
mA
REFERENCE OUTPUT (CL = 4.7µF)
TA = +25°C
2.44
2.50
2.56
TA = TMIN to
TMAX
2.38
2.50
2.62
Output Voltage
IL = 0mA
Load Regulation
TA = +25°C, IOUT = 0 to 10mA
Power-Supply Sensitivity
TA = +25°C, VDD = 5V ±5%
±1
Temperature Drift
V
-10
mV
±3
mV
±100
ppm/°C
LOGIC INPUTS (Mode = Open Circuit)
CS, RD, WR, CLK, D0–D7 (When
Inputs) Input Low Voltage
VIL
Input High Voltage
VIH
0.8
2.4
V
V
Input Current
IIN
±10
µA
Input Capacitance (Note 2)
CIN
15
pF
Input Low Voltage
VIL
0.5
V
Input High Voltage
VIH
VDD 0.5
Input Midlevel Voltage
VMID
VDD/2
- 0.5
Input Floating Voltage
VFLT
VDD/2
IIN
±50
MODE
Input Current
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V
VDD/2
+ 0.5
V
±100
µA
V
Maxim Integrated │ 3
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
Electrical Characteristics (continued)
(VDD = +5V, VREFIN = +2.5V. External Reference, VAGND = VDGND = 0V, VSS = 0V or -5V, fCLK = 5MHz external, Unipolar range
single-ended mode, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
0.4
V
LOGIC OUTPUTS
BUSY, D0–D7 Output Low Voltage
VOL
IOUT = 1.6mA
Output High Voltage
VOH
IOUT = -360µA
4
V
D0–D7 Floating State Leakage
Floating State Output Capacitance
(Note 2)
COUT
Conversion Time
fCLK = 5MHz, single channel
3.6
±10
µA
15
pF
3.8
µs
5.25
V
POWER REQUIREMENTS
Positive Power-Supply Voltage
VDD
4.75
PD = 0
Positive Power-Supply Current
IDD
PD = 1
Negative Power-Supply Voltage
VSS
Negative Power-Supply Current
ISS
MAX155
18
24
MAX156
9
12
CLK, CS, WR,
RD = 0V or VDD;
DOUT = 0V or
VDD
25
100
µA
-5
V
0
Power-Supply Rejection (Change
in Full-Scale Error)
PD = 0
2
50
PD = 1
2
50
VDD = 5V ±5%, VSS = 0V
±0.1
±0.25
VDD = 5V, VSS = -5V ±5%
±0.1
mA
µA
LSB
TIMING CHARACTERISTICS (Note 3, Figures 1–7)
(VDD = +5V, VREFIN = +2.5V. External Reference, VAGND = VDGND = 0V, VSS = 0V or -5V, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CS to WR Setup Time
tCWS
0
ns
CS to WR Hold Time
tCWH
0
ns
CS to RD Setup Time
tCRS
0
ns
CS to RD Hold Time (Note 2)
tCRH
0
ns
WR Low Pulse Width
tWR
MAX15_C/E
100
RD Low Pulse Width
tRDL
MAX15_C/E
100
ns
RD High Pulse Width (Note 2)
tRDH
MAX15_C/E
180
ns
WR to RD Delay (Note 2)
tWRD
MAX15_C/E
280
ns
WR to BUSY Low Delay
tWBD
MAX15_C/E
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2000
220
ns
ns
Maxim Integrated │ 4
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
TIMING CHARACTERISTICS (Note 3, Figures 1-7) (continued)
(VDD = +5V, VREFIN = +2.5V. External Reference, VAGND = VDGND = 0V, VSS = 0V or -5V, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
BUSY High to WR Delay (to update
configuration register) (Notes 2, 3)
tBWD
50
ns
CLK to WR Delay (Acquisition Time)
(Note 2)
tACQ
800
ns
BUSY High to RD Delay (Notes 2, 3)
tBRD
50
ns
Address-Setup Time
tAS
120
ns
Address-Hold Time
tAH
0
ns
RD to Data Valid (Note 4)
tDV
MAX15_C/E
100
ns
RD to Data Three-State Output (Note 5)
tTR
MAX15_C/E
80
ns
CLK to BUSY Delay (Note 2)
tCB
100
CLK Frequency
0.5
300
ns
5.0
MHz
Note 1: VDD = +5V, VREFIN = +2.5V, VSS = 0V. Performance at ±5% power-supply tolerance is guaranteed by Power-Supply
Rejection test.
Note 2: Guaranteed by design, not production tested.
Note 3: All input control signals are specified with tr = tf = 20ns (10% to 90% of +5V) and timed from a +1.6V voltage level. Output
signals are timed from VOH and VOL.
Note 4: tDV is the time required for an output to cross +0.8V or +2.4V measured with load circuit of Figure 1.
Note 5: tTR is the time required for the data lines to change 0.5V, measured with load circuits of Figure 2.
+5V
+5V
3kΩ
DN
3kΩ
DN
100pF
3kΩ
100pF
DGND
DN
DN
10pF
HIGH-Z TO VOL
DGND
HIGH-Z TO VOH
Figure 1. Load Circuits for Data-Access Timing
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10pF
3kΩ
VOL TO HIGH-Z
VOH TO HIGH-Z
Figure 2. Load Circuits for Three-State Output Timing
Maxim Integrated │ 5
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
tCRS
tCWS
tCWH
tCRS
tCRH
tCRS
tCRH
CS
tWR
tWRD
WR
tRDL
tRDH
tRDL
RD
tWBD
tBRD
tCONV
tBWD
BUSY
tDV
ttR
DATA IN
D0–D7
tAS
tDV
ttR
DATA OUT
DATA OUT
tACQ
tAH
Figure 3. Write and Read Timing
Pin Configuration
TOP VIEW
+
+
+
1
AIN3
AIN4
28
1
AIN1
AIN2
24
N.C
1
2
AIN2
AIN5
27
2
AIN0
AIN3
23
AIN1
2
27 N.C.
3
AIN1
AIN6
26
3
MODE
VDD
22
N.C.
3
26 AIN3
4
AIN0
AIN7
25
4
VSS
AGND
21
AIN0
4
5
MODE
VDD
24
5
CS
REFIN
20
6
VSS
AGND
23
6
RD
REFOUT
19
7
CS
REFIN
22
7
WR
D0/A0
18
8
RD
REFOUT
21
8
BUSY
D1/A1
17
9
WR
D0/A0
20
9
CLK
D2
16
10
BUSY
D1/A1
19
10
D7/ALL
D3/PD
15
11
CLK
D2/A2
18
11
D6/DIFF
D4/INH
14
12
DGND
D5/BIP
13
MAX155
12
D7/ALL
D3/PD
17
13
D6/DIFF
D4/INH
16
14
DGND
D5/BIP
15
MAX156
PDIP
28 AIN2
25 N.C.
MAX156
MODE
5
24 VDD
VSS
6
23 AGND
CS
7
22 REFIN
RD
8
21 REFOUT
WR
9
20 D0/A0
BUSY
10
19 D1/A1
CLK
11
18 D2
D7/ALL
12
17 D3/PD
D6/DIFF
13
16 D4/INH
DGND
14
15 D5/BIP
WIDE SO
PDIP/SO
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Maxim Integrated │ 6
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
Pin Description
PIN
MAX155
MAX156
NAME
FUNCTION
PDIP/SO
PDIP
SO
1
23
26
AIN3
Sampling Analog Input, Channel 3
2
24
28
AIN2
Sampling Analog Input, Channel 2
3
1
2
AIN1
Sampling Analog Input, Channel 1
4
2
4
AIN0
Sampling Analog Input, Channel 0
5
3
5
MODE
6
4
6
VSS
Negative Supply. Power VSS with -5V for extended input range.
7
5
7
CS
CHIP SELECT Input must be low for the ADC to recognize RD, or WR
8
6
8
RD
READ Input reads data sequentially from RAM
9
7
9
WR
WRITE Input’s rising edge initiates conversion and updates channel configuration
register. Falling edge samples inputs.
10
8
10
BUSY
11
9
11
CLK
12
10
12
D7/ALL
Three-State Data Output Bit 7 (MSB)/Sequential or Specific Conversion
13
11
13
D6/DIFF
Three-State Data Output Bit 6/Single-Ended/Differential Select
14
12
14
DGND
Digital Ground
15
13
15
D5/BIP
Three-State Data Output Bit 5/Unipolar/Bipolar Conversion
16
14
16
D4/INH
Three-State Data Output Bit 4/Inhibit Conversion Input
17
15
17
D3/PD
Three-State Data Output Bit 3/Power-Down Input
18
16
18
D2/A2
Three-State Data Output Bit 2/RAM Address Bit A2 (MAX155 Only)
19
17
19
D1/A1
Three-State Data Output Bit 1/RAM Address Bit A1
20
18
20
D0/A0
Three-State Data Output Bit 0/RAM Address Bit A0
21
19
21
REFOUT
22
20
22
REFIN
Reference Input, +2.5 Normally
23
21
23
AGND
Analog Ground
24
22
24
VDD
Power-Supply Voltage, +5V Normally
25–28
—
—
AIN7–4
Sampling Analog Input, Channels 7–4
—
—
1, 3,
25, 27
N.C.
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Mode configures multiplexer and converter. See Table 4.
BUSY Output low when conversion is in progress
External Clock Input
Reference Output, +2.5V
No Connection. No internal connection—pin unconnected.
Maxim Integrated │ 7
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
Detailed Description
ADC Operation
The MAX155/MAX156 contain a 3.6µs successive approximation ADC and 8/4 track-and-hold (T/H) inputs. When a
conversion is started, all AIN inputs are simultaneously
sampled. All channels sample whether or not they are
selected for the conversion. Either a single-channel or
multichannel conversion may be requested and channel
configurations may be mixed, ADC results are then stored
in an internal RAM.
In hard-wired mode (see the Multiplexer and AID
Configurations section) multichannel conversions are
initiated with one write operation. In input/output (I/O)
mode, multichannel configurations are set up prior to the
conversion by loading channel selections into the con-
figuration register. This register also selects single-ended/
differential, unipolar/bipolar (Figure 9), power-down, and
other functions. Each channel selection requires a separate write operation (i.e. 8 writes for 8 channels), but only
after power-up. Once the desired channel arrangement
is loaded, each subsequent write converts all selected
channels without reconfiguring the multiplexer (mux). I/O
mode requires more write operations, but provides more
flexibility than hard-wired mode.
To access conversion results, successive RD pulses automatically sence through RAM, beginning with channel 0.
Each RD pulse increments the RAM address counter,
which resets to 0 when WR goes low in multichannel
conversions. An arbitrary RAM location may also be read
by writing a 1 to INH while loading the RAM address (A0–
A2), and then performing a read operation.
Table 1. Multiplexer Configurations
PIN
NAME
D0/A0
D1/A1
D2/A2
1 or 0
D3/PD
D4/INH
D5/BIP**
D6/DIFF**
FUNCTION
A0–A2 select a multiple channel for the configurations described below, or select a RAM address
for reading with a subsequent RD.
0
Normal ADC operation
1
Power-down reduces the power-supply current. Configuration data may be loaded and is
maintained during power-down.
0
A conversion starts when WR goes high
1
Inhibits the conversion when WR goes high. Allows mux configuration to be loaded and RAM
locations to be accessed without starting a conversion.
0
Unipolar conversion (Figure 9a) for the channel specified by A0–A2. Input range = 0V to VREF.
1
Bipolar conversion (Figure 9b) for the channel specified by A0–A2. Input range = ±VREF.
0
Single-ended configuration for the channel specified by A0–A2 as described in Table 2
1
Differential contiguration for the channel specified by A0–A2 as described in Table 2
0
All previously configured channels are converted. Data is read with consecutive RD pulses,
beginning with the lowest configured channel.
1
Only the channel specified by A2–A0 is converted. A single RD pulse reads the result of that
conversion.
D7/ALL
•Configuration inputs are shared with data outputs D0-D7. The functions of D0-D7 are not described in this table.
••DIFF and BIP are not implemented on the current conversion, but go into effect on the.following conversion.
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Maxim Integrated │ 8
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
Multiplexer and A/D Configuration
select from 4 mux configurations as listed in Table 4 (see the
Hard-Wired Mode section).
A conversion is started with a WR pulse. All channels
sample on WR’s falling edge. Mux configuration data is
loaded on WR’s rising edge. In I/O mode (MODE = Open
Circuit), selections for channel number, singleor multichannel conversion, unipolar or bipolar input, and singleended or differential input are made with A0-A2, ALL, BIP,
and DIFF (Table 1). These input pins are also shared with
the RAM data outputs D0–D7. An alternate, simpler interface is provided by the hard-wired mode, which selects
some general mux configurations without requiring ADC
programming. Hard-wired connections of MODE and VSS
On the rising edge of WR, the mux configuration register
is updated; falling edge initiates sampling of all inputs.
A channel selection can be implemented on the current
conversion, but changes from unipolar to bipolar (with
BIP) or from singleended to differential operation (with
DIFF) do not go into effect until the following WR. This can
be overcome by writing to the configuration register while
inhibiting the conversion (INH = 1), or by changing DIFF
and BIP one conversion early, i.e. on the previous write.
Table 2. Single-Ended Channel Selection (MODE = Open Circuit)
MUX ADDRESS
SINGLE-ENDED CHANNEL SELECTION
A0
A1
A2
DIFF
0
0
0
0
0
+
1
0
0
0
0
1
0
0
1
1
0
0
0
0
1
0
1
0
1
0
0
1
1
0
1
1
1
0
1
2
3
4
5
6
7
AGND
-
+
+
+
+
+
+
+
-
Note: Shaded areas represent MAX156 operation.
Table 3. Differential Channel Selection (MODE = Open Circuit)
MUX ADDRESS
DIFFERENTIAL CHANNEL SELECTION
A0
A1
A2
DIFF
0
1
0
0
0
1
+
-
0
1
0
1
0
0
1
1
0
1
1
1
1
0
0
1
1
1
0
1
1
0
1
1
1
1
1
1
-
2
3
+
-
4
5
+
-
6
7
+
-
-
+
+
-
+
-
+
Note: Shaded areas represent MAX156 operation.
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Maxim Integrated │ 9
MAX155/MAX156
Interface Timing
Input/Output Mode, Multichannel Conversion
Timing
I/O mode is selected when the MODE input is open
circuit. In I/O mode, the mux configuration register determines the conversion type. The register is updated on the
rising edge of WR.
Table 1 lists all conversion options. For example, at
D6/DIFF, a logic 0 or 1 selects a single-ended or differential conversion. Data is loaded into addressed locations
in the configuration register with a series of WR pulses.
If INH is high while writing, no conversion takes place. A
conversion is started by writing INH = 0 to the configuration register. When a change is made to the contents of
the configuration register, a “dummy” conversion may be
necessary. This is due to a built-in latency of one full conversion for unipolar/bipolar and single-ended/differential
selections.
It is not necessary to update the configuration register
before every conversion. A particular mux configuration
must be loaded only once after power-up (but the configuration may require several writes to be loaded). A
mux configuration is retained for successive conversions
and during power-down (PD = 1) so that reconfiguring is
unnecessary when the ADC returns to normal operation
(PD = 0). Configuration and RAM data is lost only when
power is removed from the ADC at VDD.
When updating the configuration register, INH should be
high for all except the last WR so the conversion is not
started until the mux is set. On WR’s falling edge, all input
channels sample simultaneously. BUSY goes low at the
beginning of the conversion, and channels are converted
sequentially starting with the lowest selected channel.
When BUSY goes high, conversion results are stored
in RAM. At conversion end, a microprocessor (µP) can
access the RAM contents with consecutive RD pulses.
The first accessed data is the lowest channel’s result.
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
The configuration data determines which RAM locations
are sequentially read by consecutive RD pulses, so new
data should be placed in the configuration register only
after a full RD operation. It is not necessary to update the
configuration register for every conversion. A new conversion is initiated with a WR pulse (when INH = 0), regardless of the number of channe ls that have been read.
Figure 4a shows the MAX155 timing for an 8-channel
unipolar configuration. 8 channels are configured and
8 consecutive RD pulses access data. Figure 4b illustrates 4-channel differential conversion timing involving
4 sampled channels and 4 RD pulses. In cases where
conflicting differential configurations are loaded, the last
channel selected with DIFF = 1 will be the positive input
of the differential channel.
Input/Output Mode, Single-Channel Conversion Timing
Figure 5a shows timing for a single-channel (ALL = 1),
single-ended conversion; Figure 5b shows a differential
conversion. With MODE floating, the configuration register is updated on the rising edge of WR. BUSY goes
low at the beginning of the conversion and returns high
when the channel designated by the configuration register has been converted. All channels are sampled on
the falling edge of WR even if only a single channel has
been requested. At conversion end, the µP can read the
result for the selected channel with a single RD pulse.
Subsequent RD pulses will access old conversion results
remaining in other RAM locations. The next conversion
is initiated with a WR pulse, regardless of the number of
channels that have been read.
INH and A0–A2, in the configuration register, access locations in RAM. INH = 1 allows the RAM address pointer to
be updated without starting a conversion. A READ pulse
then reads the contents of the addressed location.
Subsequent RD pulses access conversion results for the
remaining channels.
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Maxim Integrated │ 10
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
CS
WR
RD
tCONV
BUSY
D0-D7
DATA IN
CH0
NOTE: After power-up, and prior to the above
timing sequence, all single-ended channels must
be set up by writing the following data into the
configuration register. 8 WRs (see Figure 3) are
needed for 8 channels:
A2
0
1
0
1
0
1
0
1
0
0
1
1
0
0
1
1
0
0
0
0
1
1
1
1
PD INH BIP DIFF ALL
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
S
S
S
S
S
S
S
S
0
0
0
0
0
0
0
0
CH3
CONSECUTIVE RAM LOCATIONS ARE
CONVERSION END
OF ALL 8 CHANNELS
ALL 8 CHANNELS ARE SAMPLED HERE
A1
CH2
THE FIRST RAM
LOCATION READ
IS CH 0
UPDATE CONFIGURATION
REGISTER AND BEGIN NEW
CONVERSION
A0
CH1
ACCESSED BY CONSECUTIVE RD PULSES
Once the above data is loaded, all channels are
converted with a single WR to any address
(this is where the above timing diagram begins).
With INH = 0, and ALL = 0:
A0
A1
A2
0
0
0
0
0
0
0
0
0
0
0
PD INH BIP DIFF ALL
0
0
S
0
0
S = May be selected
Figure 4a. Input/Output Mode Timing–Eight Single-Ended Conversions
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Maxim Integrated │ 11
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
CS
WR
RD
tCONV
BUSY
D0-D7
DATA IN
0,1
UPDATE CONFIGURATION
REGISTER AND BEGIN NEW
CONVERSION
A2
0
1
0
1
0
1
0
1
0
0
1
1
PD INH BIP DIFF ALL
0
0
0
0
1
1
1
1
S
S
S
S
0
0
0
0
6,7
CONSECUTIVE RAM LOCATIONS ARE
ACCESSED BY CONSECUTIVE RD PULSES
CONVERSION END
OF ALL 4 DIFFERENTIAL CHANNELS
NOTE: After power-up, and prior to the above
timing sequence, all differential channels must
be set up by writing to the configuration register.
(AIN0, 2, 4, 6 are +, and AIN1, 3, 5, 7 are - for
this example). 4 WRs (see Figure 3) are needed
for 8 channels:
A1
4,5
THE FIRST RAM
LOCATION READ
IS CH 0,1
ALL 4 DIFFERENTIAL CHANNELS
ARE SAMPLED HERE
A0
2,3
Once the above data is loaded, all channels
are converted with a single WR to any address
(this is where the above timing diagram begins).
With INH = 0, and ALL = 0:
A0
A1
A2
0
0
0
PD INH BIP DIFF ALL
0
0
S
0
0
0
0
0
0
S = May be selected
Figure 4b. Input/Output Mode Timing–Four Differential Conversions
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Maxim Integrated │ 12
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
CS
WR
RD
tCONV
BUSY
D0-D7
DATA IN
DATA OUT
UPDATE CONFIGURATION
REGISTER AND BEGIN NEW
CONVERSION
END OF CONVERSION
READ DATA INDICATED
BY ADDRESS
CHANNEL IS SAMPLED HERE
NOTE: A single-ended channel is converted by writing
the following data into the configuration register
(see Figure 3) The BIP and DIFF bits are not implemented
until the next WR
A0
A1
A2
PD
INH
BIP
DIFF
ALL
S
S
S
0
0
S
0
1
S = May be selected
Figure 5a. Input/Output Mode Timing–Single-Channel, Single-Ended Conversion
CS
WR
RD
tCONV
BUSY
D0-D7
DATA IN
DATA OUT
UPDATE CONFIGURATION
REGISTER AND BEGIN NEW
CONVERSION
END OF CONVERSION
READ DATA INDICATED
BY ADDRESS
CHANNEL IS SAMPLED HERE
NOTE: A differential channel is converted by writing
the following data into the configuration register
(see Figure 3) The BIP and DIFF bits are not
implemented until the next WR
A0
A1
A2
PD
INH
BIP
DIFF
ALL
S
S
S
0
0
S
1
1
S = May be selected
Figure 5b. Input/Output Mode Timing–Single-Channel, Differential Conversion
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Maxim Integrated │ 13
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
CS
WR
RD
tCONV
BUSY
INH = 0
DATA IN
D0-D7
INH = 1
DATA OUT
DATA OUT
INH = 0
DATA IN
DATA OUT
READ DATA
AT ADDRESS
END OF
CONVERSION
READ DATA INDICATED
BY ADDRESS
UPDATE CONFIGURATION REGISTER
AND BEGIN NEW CONVERSION
ALL CHANNELS ARE
SAMPLED HERE
UPDATE CONFIGURATION
REGISTER WITH NEW
ADDRESS
UPDATE
CONFIGURATION
REGISTER BEGIN
CONVERSION
NOTE: A RAM location is read by writing the following
data into the configuration register and when performing
a RD. If INH = 0, a conversion will begin.
A0
A1
A2
S
S
S
PD INH BIP DIFF ALL
0
1
X
X
1
S = May be selected
X = Don’t Care for this WR if INH = 0, but may effect next conversion.
Figure 6. Input/Output Mode Timing–Reading Arbitrary RAM Locations
Hard-Wired Mode
For simpler applications, the MODE and VSS pins can be
hard-wired to specify the type of conversion as outlined
in Table 4. In this mode, the configuration register is not
used, so input data on DO-D7 is ignored. For example,
with MODE tied low, an 8-channel, single-ended conver
sion begins with WR With MODE tied high, a 4-channel,
differential conversion is init iated with WR. Again, the
configuration register is not affected by the data present
on 00-07. These conversions are otherwise identical to
those shown in Figure 4.
Analog Considerations
lntemal Reference
The internal 2.5V reference (REFOUT) must be bypassed
to AGND (Figure 8a) with a 4.7µF electrolytic and a 0.1µF
ceramic capacitor to ensure stability.
www.maximintegrated.com
Table 4. Hard-Wired Mode—Multiplexer
Selections
MODE
VSS
CONVERSION TYPE
OPEN
CIRCUIT
X
0
AGND
8-Channel, Single-Ended, Unipolar
Conversion
1
AGND
4-Channel, Differential, Unipolar
Conversion
0
-5V
8-Channel, Single-Ended, Bipolar
Conversion
1
-5V
4-Channel, Differential, Bipolar
Conversion
Multiplexer configuration register
determines conversion type. Not
hard-wired.
Maxim Integrated │ 14
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
CS
WR
RD
tCONV
BUSY
CH0
D0-D7
ALL 8 CHANNELS ARE
SAMPLED HERE
END OF CONVERSION
OF 8 CHANNELS
CH1
THE FIRST RAM
LOCATION
READ IS CH 0
CH6
CH7
CONSECUTIVE RAM LOCATIONS ARE
ACCESSED BY CONSECUTIVE RD PULSES
MODE = 0
Figure 7a. Hard-Wired Mode Timing—Eight Single-Ended Conversions
CS
WR
RD
tCONV
BUSY
0, 1
D0–D7
ALL 4 DIFFERENTIAL CHANNELS
SAMPLED HERE
END OF CONVERSION
OF 4 DIFFERENTIAL
CHANNELS
2, 3
THE FIRST RAM
LOCATION
READ IS CH 0, 1
4, 5
6, 7
CONSECUTIVE RAM LOCATIONS ARE
ACCESSED BY CONSECUTIVE RD PULSES
MODE = 1
Figure 7b. Hard-Wired Mode Timing—Eight Single-Ended Conversions
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Maxim Integrated │ 15
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
AINx (+)
AINx (+)
AINx
MAX155
MAX156
AINx (-)
VDD
+5V
47µF
0.1µF
MAX155
MAX156
AINx (-)
VDD
+5V
47µF
0.1µF
REFOUT
MAX584
4.7µF
REFIN
4.7µF
AINx
+2.5V
REFIN
0.1µF
AGND
0.1µF
VSS
AGND
VSS
4.7µF
Figure 8a. Internal Reference
Figure 8b. External Reference, +2.5V Full Scale
Extemal Reference
Bypassing
If an external voltage reference is used at REFIN,
REFOUT must either be bypassed (Figure 8b) or disabled to prevent its output from oscillating and generating
unwanted conversion noise elsewhere in the ADC. If component count is critical when using an external reference,
REFOUT may be disabled by connecting it to VDD. In
this case, the unused internal reference does not need a
bypass cap. A disadvantage of tying REFOUT to VDD is
that power-down current will be increased by about 250µA
above the specification limits.
Power-Down Mode
The MAX155/MAX156 may be placed in a powered-down
state by writing a 1 to the PD location in the configuration
register (Table 1). The register may be updated while in
this state (to change mux configurations or exit power
down mode) and all register contents are retained; however no data can be read from RAM and no conversions
can be started. The power-down command is implemented on WR’s rising edge.
To minimize current drain, the MAX155/MAX156 internal reference is turned off during power-down. When
returning to normal operation (PD = 0), up to 5ms may
be needed to allow the reference to recharge its 4.7µF
bypass capacitor before a conversion is performed. If an
external reference is used, and remains on during power
down, a conversion can be started within 50µs after loading PD with a 0.
www.maximintegrated.com
REFOUT
A 47µF electrolytic and a 0.1µF ceramic capacitor should
bypass VDD to AGND. If input signals below ground are
expected, a negative supply is necessary. In that case,
VSS should be bypassed to AGND with a 4.7µF and
0.1µF combination.
The internal reference requires a 4.7µF and 0.1µF combination. If an external voltage reference is used, bypass
REFIN to AGND with a 4.7µF capacitor close to the chip.
When an external reference is used, REFOUT must still
be either bypassed or connected to VDD.
Track/Hold Amplifiers
The MAX155/MAX156 T/H amplifiers’ high input impedance usually requires no input buffering. All T/Hs sample
simultaneously. For best results, the analog inputs should
not exceed the power-supply rails (VDD, VSS) by more
than 50mV.
The time required for the T/H to acquire an input signal
for one channel is a function of how quickly the channel
input capacitance is charged. If the source impedance of
the input signal is high, acquisition takes longer, and more
time must be allowed between conversions. Acquisition
time is calculated by:
tACQ = 8(RS + RIN) x 4pF (but never less than 800ns)
where RIN = 15kΩ, and RS = source impedance of the
ADC’s input signal.
Maxim Integrated │ 16
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
Applications Information
OUTPUT
CODE
9-Bit A/D Conversion
(FS - 3/2 LSB)
1111 1111
1111 1110
1111 1101
FS = VREF
FS
256
1 LSB =
0000 0011
0000 0010
0000 0001
0000 0000
0 1 LSB 3 LSBs
2 LSBs
AIN
FS - 1 LSB
FS
In I/O mode, a 9th bit of resolution can be created by performing two unipolar differential conversions with opposite
input polarities (i.e., first with AIN0[+] and AIN1[-], then with
AINO[-] and AIN1[+]). Only the A0 bit must be changed to
reverse input channel polarity (Table 3). The sign reversal
also occurs on the current write without a one conversion
delay. For a differential input signal, one of the two conversions will read 0 while the other will contain an 8-bit result.
The input polarity that provides the 8-bit result indicates
the 9th (sign) bit. 4 channels can be measured this way. A
major drawback of this technique is that many of the sampling features of the MAX155/MAX156 are defeated since
two separate samples are needed
If only two 9-bit channels are needed, then two separate
differential channels with reversed input polarities can be
connected so that both input pairs sample at the same
time. This way the simultaneoussampling advantages of
the MAX155/MAX156 are retained.
AIN, INPUT VOLTAGE (LSB)
Figure 9a. Transfer Function—Unipolar Operation
OUTPUT
CODE
Typical I/O Mode Application
0111 1111
The MAX155/MAX156 address and configuration inputs
for this example were determined by selecting the desired
channel configurations in Tables 2 and 3. Figure 10 illustrates the configuration outlined in Table 5.
0111 1110
0000 0010
0000 0001
-1/2 LSB
0000 0000
+1/2 LSB
1111 1111
+FS - 1 LSB
AIN
FS = 2VREF
FS
1 LSB =
256
1111 1110
1000 0001
1000 0000
Figure 9b. Transfer Function—Bipolar Operation
Conversion Time
Conversion time is calculated by:
tCONV = (9 x N x 2)/fCLK
where N is the number of channels converted. This
includes one clock cycle of uncertainty. For a single
channel and 5MHz clock, the conversion time is (9 x 1 x
2)/5MHz = 3.6µs. For the MAX155, the maximum conversion time for 8 channels is (9 x 8 x 2)/5MHz = 28.8µs. In
the application example (Figure 10), six conversions are
configured, and the conversion time is (9 x 6 x 2}/5MHz
= 21.6µs.
www.maximintegrated.com
Table 5. Typical Multiplexer Configuration
A2
A1
A0
DIFF
BIP
FUNCTION
0
0
1
1
1
Channel (1, 0) Differential
Bipolar
0
1
0
0
0
Channel 2 Single-Ended,
Unipolar
0
1
1
0
1
Channel 3 Single-Ended,
Bipolar
1
0
0
0
1
Channel 4 Single-Ended,
Bipolar
1
0
1
0
0
Channel 5 Single-Ended,
Unipolar
1
1
0
1
0
Channel (6. 7)
Differential, Unipolar
An A/D conversion in I/O mode involves the following
steps:
1) Configure the mux by loading data into the configuration register based on selections from Table 2
and/or 3 (with INH = 1 and MODE = open circuit).
Maxim Integrated │ 17
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
For this example, 6 write operations (with each
address and data setting in Table 5 above) load the
mux after power-up.
When the conversion starts, BUSY goes low while all
selected channels are sequentially converted. Conversion
results are stored in RAM and are ready to read when
BUSY returns high.
2) Sample all selected channels with a WR pulse (and
INH = 0), and update or rewrite any one location of
the configuration register.
3) Data is read from RAM with INH = L and consecutive
RD strobes. Note that in the 6 channel configurations
described in this example (Figure 10), 6 RD pulses
access all available data, start with the differential
channel (1, 0). Additional RD pulses loop around,
accessing the lowest channel data again.
This write operation may be skipped by loading INH with a
0 on the last WR of the above step. The conversion then
starts on the 6th WR. DIFF and SIP cannot be changed
on the 6th WR in the conversion is started at that time.
4) To start a new conversion cycle with the same mux
configuration, repeat steps 2 and 3.
+5V
+24
VDD
(-) 3 AIN
(1)
DIFFERENTIAL
BIPOLAR
(+) 4
2
REFOUT
REFIN
(0)
CLK
(3) BIPOLAR
MODE
28
CS
(4) BIPOLAR
RD
SENSOR
27
(+) 26
(5) BIPOLAR
WR
BUSY
(6)
0.1µF
47µF
21
22
2.5V
AGND
23
DGND
VSS
14
6
0.1µF
CLOCK
5
7
8
9
10
D0–D7
(7)
-1.75V
11
20...15, 13, 12
DIFFERENTIAL
UNIPOLAR
(-) 25
47µF
(2) BIPOLAR
MAX155
1
0.1µF
8
DATA I/0 LINES
-5V
47µF
Figure 10. MAX155/MAX156 Typical Operating Circuit
www.maximintegrated.com
Maxim Integrated │ 18
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
Ordering Information
Package Information
PART
PINPACKAGE
TEMP RANGE
ERROR
(LSBs)
MAX155ACPI+
0°C to +70°C
MAX155BCPI+
0°C to +70°C
28 PDIP
±1
MAX155ACWI+
0°C to +70°C
28 Wide SO
±½
MAX155BCWI+
0°C to +70°C
28 Wide SO
MAX155BC/D
0°C to +70°C
Dice*
MAX155AEPI+
-40°C to +85°C
28 PDIP
±½
MAX155BEPI+
-40°C to +85°C
28 PDIP
±1
MAX155AEWI+
-40°C to +85°C
28 Wide SO
±½
MAX155BEWI+
-40°C to +85°C
28 Wide SO
±1
MAX156ACNG+
0°C to +70°C
24 PDIP
±½
MAX156BCNG+
0°C to +70°C
24 PDIP
±1
MAX156ACWI+
0°C to +70°C
28 Wide SO
±½
MAX156BCWI+
0°C to +70°C
28 Wide SO
±1
0°C to +70°C
MAX156BC/D
28 PDIP
±½
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
±1
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE NO.
±1
LAND
PATTERN
NO.
24 PDIP
N24+8
21-0043
—
28 PDIP
P28+7
21-0044
—
28 Wide SO
W28+3
21-0042
90-0109
Dice*
±1
MAX156AENG+
-40°C to +85°C
24 PDIP
±½
MAX156BENG+
-40°C to +85°C
24 PDIP
±1
MAX156AEWI+
-40°C to +85°C
28 Wide SO
±½
MAX156BEWI+
-40°C to +85°C
28 Wide SO
±1
Chip Information
PROCESS: BiCMOS
+Denotes a lead(Pb)-free/RoHS-compliant package.
*Contact factory for dice specifications.
www.maximintegrated.com
Maxim Integrated │ 19
MAX155/MAX156
8-/4-Channel ADCs with Simultaneous
T/Hs and Reference
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
0
11/91
Initial release
1
6/94
Revised Figure 9a
2
1/12
Removed military grade packages and updated stylistic changes
DESCRIPTION
—
16
1–5, 18–20
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
© 2012 Maxim Integrated Products, Inc. │ 20
Mouser Electronics
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