Maxim MAX1110 2.7v, low-power, multichannel, serial 8-bit adc Datasheet

19-1194; Rev 2; 10/98
KIT
ATION
EVALU
E
L
B
A
AVAIL
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
____________________________Features
The MAX1110/MAX1111 are low-power, 8-bit, 8-channel analog-to-digital converters (ADCs) that feature an
internal track/hold, voltage reference, clock, and serial
interface. They operate from a single +2.7V to +5.5V
supply and consume only 85µA while sampling at rates
up to 50ksps. The MAX1110’s 8 analog inputs and the
MAX1111’s 4 analog inputs are software-configurable,
allowing unipolar/bipolar and single-ended/differential
operation.
♦ +2.7V to +5.5V Single Supply
Successive-approximation conversions are performed
using either the internal clock or an external serial-interface clock. The full-scale analog input range is determined by the 2.048V internal reference, or by an
externally applied reference ranging from 1V to V DD.
The 4-wire serial interface is compatible with the SPI™,
QSPI™, and MICROWIRE™ serial-interface standards.
A serial-strobe output provides the end-of-conversion
signal for interrupt-driven processors.
♦ Internal Track/Hold; 50kHz Sampling Rate
The MAX1110/MAX1111 have a software-programmable, 2µA automatic power-down mode to minimize
power consumption. Using power-down, the supply
current is reduced to 6µA at 1ksps, and only 52µA at
10ksps. Power-down can also be controlled using the
SHDN input pin. Accessing the serial interface automatically powers up the device.
The MAX1110 is available in 20-pin SSOP and DIP
packages. The MAX1111 is available in small 16-pin
QSOP and DIP packages.
♦ Low Power: 85µA at 50ksps
6µA at 1ksps
♦ 8-Channel Single-Ended or 4-Channel Differential
Inputs (MAX1110)
♦ 4-Channel Single-Ended or 2-Channel Differential
Inputs (MAX1111)
♦ Internal 2.048V Reference
♦ SPI/QSPI/MICROWIRE-Compatible Serial Interface
♦ Software-Configurable Unipolar or Bipolar Inputs
♦ Total Unadjusted Error: ±1LSB max
±0.3LSB typ
Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX1110CPP
0°C to +70°C
20 Plastic DIP
MAX1110CAP
0°C to +70°C
20 SSOP
MAX1110C/D
0°C to +70°C
Dice*
*Dice are specified at TA = +25°C, DC parameters only.
Ordering Information continued at end of data sheet.
________________Functional Diagram
________________________Applications
Portable Data Logging
Hand-Held Measurement Devices
Medical Instruments
System Diagnostics
Solar-Powered Remote Systems
4–20mA-Powered Remote
Data-Acquisition Systems
CS
SCLK
DIN
INPUT
SHIFT
REGISTER
SHDN
CH0
CH1
CH2
CH3
CH4*
CH5*
CH6*
CH7*
INT
CLOCK
CONTROL
LOGIC
OUTPUT
SHIFT
REGISTER
ANALOG
INPUT
MUX
REFOUT
SSTRB
T/H
COM
Pin Configurations appear at end of data sheet.
DOUT
+2.048V
REFERENCE
CLOCK
IN
8-BIT
SAR ADC
OUT
REF
VDD
DGND
MAX1110
MAX1111
AGND
REFIN
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corp.
*MAX1110 ONLY
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
For small orders, phone 1-800-835-8769.
MAX1110/MAX1111
General Description
MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
ABSOLUTE MAXIMUM RATINGS
VDD to AGND ..............................................................-0.3V to 6V
AGND to DGND .......................................................-0.3V to 0.3V
CH0–CH7, COM, REFIN,
REFOUT to AGND ......................................-0.3V to (VDD + 0.3V)
Digital Inputs to DGND ...............................................-0.3V to 6V
Digital Outputs to DGND ............................-0.3V to (VDD + 0.3V)
Continuous Power Dissipation (TA = +70°C)
16 Plastic DIP (derate 10.53mW/°C above +70°C) ......842mW
16 QSOP (derate 8.30mW/°C above +70°C) ................667mW
16 CERDIP (derate 10.00mW/°C above +70°C) ..........800mW
20 Plastic DIP (derate 11.11mW/°C above +70°C) ......889mW
20 SSOP (derate 8.00mW/°C above +70°C) ................640mW
20 CERDIP (derate 11.11mW/°C above +70°C) ..........889mW
Operating Temperature Ranges
MAX1110C_P/MAX1111C_E................................0°C to +70°C
MAX1110E_P/MAX1111E_E .............................-40°C to +85°C
MAX1110MJP/MAX1111MJE..........................-55°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10sec) .............................+300°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 = +2.7V to +5.5V; unipolar input mode; COM = 0V; fSCLK = 500kHz, external clock (50% duty cycle); 10 clocks/conversion
cycle (50ksps); 1µF capacitor at REFOUT; TA = TMIN to TMAX; unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DC ACCURACY
Resolution
8
Relative Accuracy (Note 1)
INL
Differential Nonlinearity
DNL
Offset Error
Gain Error (Note 3)
VDD = 2.7V to 3.6V
±0.15
VDD = 5.5V (Note 2)
±0.2
No missing codes over temperature
VDD = 2.7V to 3.6V
±0.35
VDD = 5.5V (Note 2)
±0.5
External reference, 2.048V
TUE
±1
±1
±0.8
±0.3
Channel-to-Channel
Offset Matching
±0.5
±1
Internal or external reference
Gain Temperature Coefficient
Total Unadjusted Error
Bits
LSB
LSB
LSB
LSB
ppm/°C
±1
LSB
±0.1
LSB
SINAD
49
dB
Total Harmonic Distortion
(up to the 5th harmonic)
THD
-70
dB
Spurious-Free Dynamic Range
SFDR
DYNAMIC SPECIFICATIONS (10.034kHz sine-wave input, 2.048Vp-p, 50ksps, 500kHz external clock)
Signal-to-Noise
and Distortion Ratio
Channel-to-Channel Crosstalk
VCH_ = 2.048Vp-p, 25kHz (Note 4)
Small-Signal Bandwidth
-3dB rolloff
Full-Power Bandwidth
2
68
dB
-75
dB
1.5
MHz
800
kHz
_______________________________________________________________________________________
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
(VDD = +2.7V to +5.5V; unipolar input mode; COM = 0V; fSCLK = 500kHz, external clock (50% duty cycle); 10 clocks/conversion
cycle (50ksps); 1µF capacitor at REFOUT; TA = TMIN to TMAX; unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
External clock, 500kHz, 10 clocks/conversion
20
External clock, 2MHz
1
TYP
MAX
25
55
UNITS
CONVERSION RATE
Conversion Time (Note 5)
tCONV
Track/Hold Acquisition Time
tACQ
Internal clock
µs
µs
Aperture Delay
10
ns
Aperture Jitter
<50
ps
Internal Clock Frequency
400
kHz
(Note 6)
External Clock-Frequency Range
50
Used for data transfer only
500
kHz
2
MHz
ANALOG INPUT
Unipolar input, COM = 0V
Input Voltage Range, SingleEnded and Differential (Note 7)
Bipolar input, COM = VREFIN / 2
Multiplexer Leakage Current
On/off-leakage current, VCH_ = 0V or VDD
0
VREFIN
COM ±
VREFIN / 2
±0.01
Input Capacitance
±1
18
V
V
µA
pF
INTERNAL REFERENCE
REFOUT Voltage
1.968
2.048
2.128
V
REFOUT Short-Circuit Current
3.5
mA
REFOUT Temperature Coefficient
±50
ppm/°C
2.5
mV
Load Regulation (Note 8)
0mA to 0.5mA output load
Capacitive Bypass at REFOUT
1
µF
EXTERNAL REFERENCE AT REFIN
VDD +
50mV
1
Input Voltage Range
Input Current
(Note 9)
1
V
20
µA
5.5
V
POWER REQUIREMENTS
Supply Voltage
VDD
Supply Current (Note 2)
IDD
2.7
VDD = 2.7V to 3.6V
Full-scale input
CLOAD = 10pF
Operating mode
85
Reference disabled
45
VDD = 5.5V
Full-scale input
CLOAD = 10pF
Operating mode
120
Reference disabled
80
Software
2
Power-down
Power-Supply Rejection
(Note 10)
PSR
SHDN at DGND
VDD = 2.7V to 3.6V; external reference,
2.048V; full-scale input
250
250
3.2
10
±0.4
±4
µA
mV
_______________________________________________________________________________________
3
MAX1110/MAX1111
ELECTRICAL CHARACTERISTICS (continued)
MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
ELECTRICAL CHARACTERISTICS (continued)
(VDD = +2.7V to +5.5V; unipolar input mode; COM = 0V; fSCLK = 500kHz, external clock (50% duty cycle); 10 clocks/conversion
cycle (50ksps); 1µF capacitor at REFOUT; TA = TMIN to TMAX; unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DIGITAL INPUTS: DIN, SCLK, CS
DIN, SCLK, CS Input High Voltage
VIH
DIN, SCLK, CS Input Low Voltage
VIL
DIN, SCLK, CS Input Hysteresis
VDD ≤ 3.6V
2
VDD > 3.6V
3
V
0.8
VHYST
0.2
V
V
DIN, SCLK, CS Input Leakage
IIN
Digital inputs = 0V or VDD
±1
µA
DIN, SCLK, CS Input Capacitance
CIN
(Note 6)
15
pF
SHDN INPUT
SHDN Input High Voltage
VSH
VDD - 0.4
SHDN Input Mid-Voltage
VSM
1.1
SHDN Voltage, Floating
VFLT
SHDN Input Low Voltage
VSL
SHDN = open
SHDN Input Current
SHDN = 0V or VDD
SHDN Maximum Allowed Leakage
for Mid-Input
SHDN = open
V
VDD - 1.1
VDD / 2
V
V
0.4
V
±4
µA
±100
nA
DIGITAL OUTPUTS: DOUT, SSTRB
Output Low Voltage
VOL
Output High Voltage
VOH
Three-State Leakage Current
Three-State Output Capacitance
4
IL
COUT
ISINK = 5mA
0.4
ISINK = 16mA
0.8
ISOURCE = 0.5mA
CS = VDD
VDD - 0.5
V
V
±0.01
CS = VDD (Note 6)
_______________________________________________________________________________________
±10
µA
15
pF
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
MAX1110/MAX1111
TIMING CHARACTERISTICS (Figures 8 and 9)
(VDD = +2.7V to +5.5V, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
Track/Hold Acquisition Time
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
tACQ
1
µs
DIN to SCLK Setup
tDS
100
ns
DIN to SCLK Hold
tDH
0
ns
SCLK Fall to Output Data Valid
tDO
Figure 1,
CLOAD = 100pF
CS Fall to Output Enable
tDV
Figure 1, CLOAD = 100pF
240
ns
CS Rise to Output Disable
tTR
Figure 2, CLOAD = 100pF
240
ns
MAX111_C/E
20
200
MAX111_M
20
240
ns
CS to SCLK Rise Setup
tCSS
100
ns
CS to SCLK Rise Hold
tCSH
0
ns
SCLK Pulse Width High
tCH
200
ns
SCLK Pulse Width Low
SCLK Fall to SSTRB
tCL
tSSTRB
200
ns
CLOAD = 100pF
240
ns
CS Fall to SSTRB Output Enable
(Note 6)
tSDV
Figure 1, external clock mode only,
CLOAD = 100pF
240
ns
CS Rise to SSTRB Output
Disable (Note 6)
tSTR
Figure 2, external clock mode only,
CLOAD = 100pF
240
ns
SSTRB Rise to SCLK Rise
(Note 6)
tSCK
Figure 11, internal clock mode only
Wake-Up Time
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
Note 10:
Note 11:
tWAKE
0
ns
External reference
20
µs
Internal reference (Note 11)
12
ms
Relative accuracy is the analog value’s deviation (at any code) from its theoretical value after the full-scale range is calibrated.
See Typical Operating Characteristics.
VREFIN = 2.048V, offset nulled.
On-channel grounded; sine wave applied to all off-channels.
Conversion time is defined as the number of clock cycles multiplied by the clock period; clock has 50% duty cycle.
Guaranteed by design. Not subject to production testing.
Common-mode range for the analog inputs is from AGND to VDD.
External load should not change during the conversion for specified accuracy.
External reference at 2.048V, full-scale input, 500kHz external clock.
Measured as | VFS (2.7V) - VFS (3.6V) |.
1µF at REFOUT; internal reference settling to 0.5LSB.
_______________________________________________________________________________________
5
__________________________________________Typical Operating Characteristics
(VDD = +2.7V; fSCLK = 500kHz; external clock (50% duty cycle); RL = ∞; TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT (µA)
140
300
250
CLOAD = 60pF
200
150
120
VDD = 5.5V
100
VDD = 3.6V
80
CLOAD = 30pF
100
5.0
3.0
3.5
4.0
4.5
5.0
5.5
6.0
SHDN = DGND
4.5
4.0
3.5
3.0
2.5
2.0
60
2.5
-60
-20
20
60
100
-60
140
-20
20
60
100
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
TEMPERATURE (°C)
OFFSET ERROR vs. SUPPLY VOLTAGE
INTEGRAL NONLINEARITY vs.
SUPPLY VOLTAGE
DIFFERENTIAL NONLINEARITY
vs. CODE
0.2
0.4
0.6
MAX1110-06
0.7
140
0.3
MAX1110-05
0.5
MAX1110-04
0.8
0.1
0.4
0.3
0.3
DNL (LSB)
0.5
INL (LSB)
0.2
0
-0.1
0.2
0.1
-0.2
0.1
0
0
3.0
3.5
4.0
4.5
5.0
5.5
-0.3
2.5
6.0
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
OFFSET ERROR vs. TEMPERATURE
INTEGRAL NONLINEARITY
vs. CODE
0.20
MAX1110-07
0.6
0.5
5.5
6.0
0
0.15
64
128
192
256
DIGITAL CODE
FFT PLOT
20
MAX1110-08
2.5
fCH_ = 10.034kHz, 2Vp-p
fSAMPLE = 50ksps
0
MAX1110-09
OFFSET ERROR (LSB)
OUTPUT CODE = FULL SCALE
CLOAD = 10pF
SHUTDOWN SUPPLY CURRENT (µA)
350
MAX1110-02
OUTPUT CODE = 10101010
SUPPLY CURRENT (µA)
160
MAX1110-01
400
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
SUPPLY CURRENT vs. TEMPERATURE
MAX1110-03
SUPPLY CURRENT vs. SUPPLY VOLTAGE
0.3
AMPLITUDE (dB)
0.10
0.4
INL (LSB)
OFFSET ERROR (LSB)
MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
0.05
0
-0.05
0.2
-20
-40
-60
-0.10
0.1
-0.20
0
-60
-20
20
60
TEMPERATURE (°C)
6
-80
-0.15
100
140
-100
0
64
128
DIGITAL CODE
192
256
0
5
10
15
FREQUENCY (kHz)
_______________________________________________________________________________________
20
25
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
PIN
NAME
FUNCTION
MAX1110
MAX1111
1–4
1–4
CH0–CH3
Sampling Analog Inputs
5–8
—
CH4–CH7
Sampling Analog Inputs
9
5
COM
Ground Reference for Analog Inputs. Sets zero-code voltage in single-ended mode.
Must be stable to ±0.5LSB.
10
6
SHDN
Three-Level Shutdown Input. Normally floats. Pulling SHDN low shuts the MAX1110/
MAX1111 down to 10µA (max) supply current; otherwise, the devices are fully operational. Pulling SHDN high shuts down the internal reference.
11
7
REFIN
Reference Voltage Input for Analog-to-Digital Conversion. Connect to REFOUT to use
the internal reference.
12
8
REFOUT
Internal Reference Generator Output. Bypass with a 1µF capacitor to AGND.
13
9
AGND
Analog Ground
14
10
DGND
Digital Ground
15
11
DOUT
Serial-Data Output. Data is clocked out on SCLK’s falling edge. High impedance when
CS is high.
16
12
SSTRB
Serial-Strobe Output. In internal clock mode, SSTRB goes low when the MAX1110/
MAX1111 begin the A/D conversion and goes high when the conversion is done.
In external clock mode, SSTRB pulses high for two clock periods before the MSB is
shifted out. High impedance when CS is high (external clock mode only).
17
13
DIN
Serial-Data Input. Data is clocked in at SCLK’s rising edge. The voltage at DIN may
exceed VDD (up to 5.5V).
18
14
CS
Active-Low Chip Select. Data is not clocked into DIN unless CS is low. When CS is
high, DOUT is high impedance. The voltage at CS may exceed VDD (up to 5.5V).
19
15
SCLK
20
16
VDD
Serial-Clock Input. Clocks data in and out of serial interface. In external clock mode,
SCLK also sets the conversion speed (duty cycle must be 45% to 55%). The voltage at
SCLK may exceed VDD (up to 5.5V).
Positive Supply Voltage, +2.7V to +5.5V
+3V
+3V
DOUT
DOUT
3k
3k
CLOAD
CLOAD
DGND
DGND
a) High-Z to VOH and VOL to VOH
b) High-Z to VOL and VOH to VOL
Figure 1. Load Circuits for Enable Time
3k
DOUT
DOUT
3k
CLOAD
DGND
a) VOH to High-Z
CLOAD
DGND
b) VOL to High-Z
Figure 2. Load Circuits for Disable Time
_______________________________________________________________________________________
7
MAX1110/MAX1111
______________________________________________________________Pin Description
MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
_______________Detailed Description
The MAX1110/MAX1111 analog-to-digital converters
(ADCs) use a successive-approximation conversion
technique and input track/hold (T/H) circuitry to convert
an analog signal to an 8-bit digital output. A flexible serial interface provides easy interface to microprocessors
(µPs). Figure 3 shows the Typical Operating Circuit.
Pseudo-Differential Input
The sampling architecture of the ADC’s analog comparator is illustrated in Figure 4, the equivalent input circuit. In single-ended mode, IN+ is internally switched to
the selected input channel, CH_, and IN- is switched to
COM. In differential mode, IN+ and IN- are selected
from the following pairs: CH0/CH1, CH2/CH3,
CH4/CH5, and CH6/CH7. Configure the MAX1110
channels with Table 1 and the MAX1111 channels with
Table 2.
In differential mode, IN- and IN+ are internally switched
to either of the analog inputs. This configuration is
pseudo-differential to the effect that only the signal at
IN+ is sampled. The return side (IN-) must remain stable within ±0.5LSB (±0.1LSB for best results) with
respect to AGND during a conversion. To accomplish
this, connect a 0.1µF capacitor from IN- (the selected
analog input) to AGND.
During the acquisition interval, the channel selected as
the positive input (IN+) charges capacitor CHOLD. The
acquisition interval spans two SCLK cycles and ends
on the falling SCLK edge after the last bit of the input
control word has been entered. At the end of the acquisition interval, the T/H switch opens, retaining charge
on CHOLD as a sample of the signal at IN+. The conversion interval begins with the input multiplexer switching
CHOLD from the positive input (IN+) to the negative
input (IN-). In single-ended mode, IN- is simply COM.
This unbalances node ZERO at the input of the comparator. The capacitive DAC adjusts during the remainder of the conversion cycle to restore node ZERO to 0V
within the limits of 8-bit resolution. This action is equivalent to transferring a charge of 18pF x (VIN+ - VIN-) from
CHOLD to the binary-weighted capacitive DAC, which in
turn forms a digital representation of the analog input
signal.
Track/Hold
The T/H enters its tracking mode on the falling clock
edge after the sixth bit of the 8-bit control byte has
been shifted in. It enters its hold mode on the falling
clock edge after the eighth bit of the control byte has
been shifted in. If the converter is set up for singleended inputs, IN- is connected to COM, and the converter samples the “+” input; if it is set up for differential
inputs, IN- connects to the “-” input, and the difference
(IN+ - IN-) is sampled. At the end of the conversion, the
positive input connects back to IN+, and C HOLD
charges to the input signal.
+2.7V
CAPACITIVE DAC
CH0
VDD
CH7
AGND
DGND
COM
VDD
0.1µF
ANALOG
INPUTS
REFIN
1µF
CPU
REFIN
1µF
CS
SCLK
DIN
DOUT
CH3
I/O
SCK (SK)
MOSI (SO)
MISO (SI)
SSTRB
SHDN
VSS
CH4*
CH5*
CH6*
CH7*
ZERO
18pF
CH2
MAX1110
MAX1111
REFOUT
CH0
CH1
COMPARATOR
CHOLD
INPUT
MUX –
+
6.5k
RIN
CSWITCH
TRACK
T/H
SWITCH
COM
HOLD
AT THE SAMPLING INSTANT,
THE MUX INPUT SWITCHES
FROM THE SELECTED IN+
CHANNEL TO THE SELECTED
IN- CHANNEL.
SINGLE-ENDED MODE: IN+ = CHO–CH7, IN- = COM.
DIFFERENTIAL MODE: IN+ AND IN- SELECTED FROM PAIRS OF
CH0/CH1, CH2/CH3, CH4*/CH5*, CH6*/CH7*.
*MAX1110 ONLY
Figure 3. Typical Operating Circuit
8
Figure 4. Equivalent Input Circuit
_______________________________________________________________________________________
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
MAX1110/MAX1111
Table 1a. MAX1110 Channel Selection in Single-Ended Mode (SGL/DIF = 1)
SEL2
SEL1
SEL0
CH0
0
0
0
+
1
0
0
0
0
1
1
0
1
0
1
0
1
1
0
0
1
1
1
1
1
CH1
CH2
CH3
CH4
CH5
CH6
CH7
COM
–
+
–
+
–
+
–
+
–
+
–
+
–
+
–
Table 1b. MAX1110 Channel Selection in Differential Mode (SGL/DIF = 0)
SEL2
SEL1
SEL0
CH0
CH1
0
0
0
+
–
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
–
CH2
CH3
+
–
CH4
CH5
+
–
CH6
CH7
+
–
–
+
+
–
+
–
+
Table 2a. MAX1111 Channel Selection in Single-Ended Mode (SGL/DIF = 1)
SEL2
SEL1
SEL0
CH0
0
0
X
+
1
0
X
0
1
X
1
1
X
CH1
CH2
CH3
COM
–
+
–
+
–
+
–
Table 2b. MAX1111 Channel Selection in Differential Mode (SGL/DIF = 0)
SEL2
SEL1
SEL0
CH0
CH1
0
0
X
+
–
0
1
X
1
0
X
–
+
1
1
X
CH2
CH3
+
–
–
+
_______________________________________________________________________________________
9
MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
The time required for the T/H to acquire an input signal
is a function of how quickly its input capacitance is
charged. If the input signal’s source impedance is high,
the acquisition time lengthens, and more time must be
allowed between conversions. The acquisition time,
tACQ, is the minimum time needed for the signal to be
acquired. It is calculated by:
tACQ = 6 x (RS + RIN) x 18pF
where RIN = 6.5kΩ, RS = the source impedance of the
input signal, and tACQ is never less than 1µs. Note that
source impedances below 2.4kΩ do not significantly
affect the AC performance of the ADC.
Input Bandwidth
The ADC’s input tracking circuitry has a 1.5MHz smallsignal bandwidth, so it is possible to digitize highspeed transient events and measure periodic signals
with bandwidths exceeding the ADC’s sampling rate by
using undersampling techniques. To avoid highfrequency signals being aliased into the frequency
band of interest, anti-alias filtering is recommended.
Analog Inputs
Internal protection diodes, which clamp the analog
input to VDD and AGND, allow the channel input pins to
swing from (AGND - 0.3V) to (VDD + 0.3V) without dam-
age. However, for accurate conversions near full scale,
the inputs must not exceed VDD by more than 50mV or
be lower than AGND by 50mV.
If the analog input exceeds 50mV beyond the supplies, do not forward bias the protection diodes of
off channels over 2mA.
The MAX1110/MAX1111 can be configured for differential or single-ended inputs with bits 2 and 3 of the control byte (Table 3). In single-ended mode, the analog
inputs are internally referenced to COM with a full-scale
input range from COM to VREFIN + COM. For bipolar
operation, set COM to VREFIN / 2.
In differential mode, choosing unipolar mode sets the
differential input range at 0V to VREFIN. In unipolar
mode, the output code is invalid (code zero) when a
negative differential input voltage is applied. Bipolar
mode sets the differential input range to ±VREFIN / 2.
Note that in this mode, the common-mode input range
includes both supply rails. Refer to Table 4 for input
voltage ranges.
Quick Look
To quickly evaluate the MAX1110/MAX1111’s analog
performance, use the circuit of Figure 5. The
MAX1110/MAX1111 require a control byte to be written
to DIN before each conversion. Tying DIN to +3V feeds
Table 3. Control-Byte Format
10
BIT 7
(MSB)
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
(LSB)
START
SEL2
SEL1
SEL0
UNI/BIP
SGL/DIF
PD1
PD0
BIT
NAME
7 (MSB)
START
6
5
4
SEL2
SEL1
SEL0
3
UNI/BIP
1 = unipolar, 0 = bipolar. Selects unipolar or bipolar conversion mode. Select differential operation
if bipolar mode is used. See Table 4.
2
SGL/DIF
1 = single ended, 0 = differential. Selects single-ended or differential conversions. In singleended mode, input signal voltages are referred to COM. In differential mode, the voltage difference between two channels is measured. See Tables 1 and 2.
1
PD1
1 = fully operational, 0 = power-down.
Selects fully operational or power-down mode.
0 (LSB)
PD0
1 = external clock mode, 0 = internal clock mode.
Selects external or internal clock mode.
DESCRIPTION
The first logic “1” bit after CS goes low defines the beginning of the control byte.
Select which of the input channels are to be used for the conversion (Tables 1 and 2).
______________________________________________________________________________________
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
UNIPOLAR MODE
BIPOLAR MODE
Full Scale
Zero Scale
Positive
Full Scale
Zero
Scale
Negative
Full Scale
VREFIN + COM
COM
+VREFIN / 2
+ COM
COM
-VREFIN / 2
+ COM
in control bytes of $FF (hex), which trigger singleended, unipolar conversions on CH7 (MAX1110) or
CH3 (MAX1111) in external clock mode without powering down between conversions. In external clock mode,
the SSTRB output pulses high for two clock periods
before the most significant bit of the 8-bit conversion
result is shifted out of DOUT. Varying the analog input
alters the output code. A total of 10 clock cycles is
required per conversion. All transitions of the SSTRB
and DOUT outputs occur on SCLK’s falling edge.
How to Start a Conversion
A conversion is started by clocking a control byte into
DIN. With CS low, each rising edge on SCLK clocks a bit
from DIN into the MAX1110/MAX1111’s internal shift reg-
ister. After CS falls, the first arriving logic “1” bit at DIN
defines the MSB of the control byte. Until this first start bit
arrives, any number of logic “0” bits can be clocked into
DIN with no effect. Table 3 shows the control-byte format.
The MAX1110/MAX1111 are compatible with MICROWIRE,
SPI, and QSPI devices. For SPI, select the correct clock
polarity and sampling edge in the SPI control registers:
set CPOL = 0 and CPHA = 0. MICROWIRE, SPI, and
QSPI all transmit a byte and receive a byte at the same
time. Using the Typical Operating Circuit (Figure 3), the
simplest software interface requires three 8-bit transfers
to perform a conversion (one 8-bit transfer to configure
the ADC, and two more 8-bit transfers to clock out the
8-bit conversion result). Figure 6 shows the MAX1110/
MAX1111 common serial-interface connections.
VDD
OSCILLOSCOPE
+3V
0.1µF
1µF
SCLK
DGND
MAX1110
MAX1111
0V TO
+2.048V
ANALOG 0.01µF
INPUT
CH7 (CH3)
AGND
SSTRB
CS
DOUT*
SCLK
COM
+3V
DIN
500kHz
OSCILLATOR
CH1
CH2
CH3
CH4
SSTRB
REFOUT
DOUT
REFIN
SHDN
N.C.
C1
1µF
*FULL-SCALE ANALOG INPUT, CONVERSION RESULT = $FF (HEX)
( ) ARE FOR THE MAX1111.
Figure 5. Quick-Look Circuit
______________________________________________________________________________________
11
MAX1110/MAX1111
Table 4. Full-Scale and Zero-Scale Voltages
MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
I/O
Simple Software Interface
Make sure the CPU’s serial interface runs in master
mode so the CPU generates the serial clock. Choose a
clock frequency from 50kHz to 500kHz.
CS
SCK
SCLK
MISO
1) Set up the control byte for external clock mode and
call it TB1. TB1 should be of the format 1XXXXX11
binary, where the Xs denote the particular channel
and conversion mode selected.
2) Use a general-purpose I/O line on the CPU to pull
CS low.
DOUT
+3V
MAX1110
MAX1111
SS
a) SPI
CS
3) Transmit TB1 and, simultaneously, receive a byte
and call it RB1. Ignore RB1.
CS
SCK
SCLK
MISO
4) Transmit a byte of all zeros ($00 hex) and, simultaneously, receive byte RB2.
DOUT
+3V
5) Transmit a byte of all zeros ($00 hex) and, simultaneously, receive byte RB3.
MAX1110
MAX1111
SS
6) Pull CS high.
b) QSPI
I/O
CS
SK
SCLK
SI
DOUT
Figure 7 shows the timing for this sequence. Bytes RB2
and RB3 contain the result of the conversion padded
with two leading zeros and six trailing zeros. The total
conversion time is a function of the serial-clock
frequency and the amount of idle time between 8-bit
transfers. Make sure that the total conversion time does
not exceed 1ms, to avoid excessive T/H droop.
MAX1110
MAX1111
Digital Inputs
CS, SCLK, and DIN can accept input signals up to
5.5V, regardless of the supply voltages. This allows the
MAX1110/MAX1111 to accept digital inputs from both
3V and 5V systems.
c) MICROWIRE
Figure 6. Common Serial-Interface Connections to the
MAX1110/MAX1111
CS
tACQ
SCLK
1
4
SEL2 SEL1 SEL0 UNI/
BIP
DIN
8
SGL/ PD1
DIF
12
16
20
24
PD0
START
SSTRB
A/D STATE
B7
IDLE
RB3
RB2
RB1
DOUT
B6
ACQUISITION
4µs
B5
B4
B3
B2
B1
B0
FILLED WITH ZEROS
CONVERSION
(fSCLK = 500kHz)
Figure 7. Single-Conversion Timing, External Clock Mode, 24 Clocks
12
______________________________________________________________________________________
IDLE
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
conversion steps. SSTRB pulses high for two clock
periods after the last bit of the control byte. Successiveapproximation bit decisions are made and appear at
DOUT on each of the next eight SCLK falling edges
(Figure 7). After the eight data bits are clocked out,
subsequent clock pulses clock out zeros from the
DOUT pin.
SSTRB and DOUT go into a high-impedance state
when CS goes high; after the next CS falling edge,
SSTRB outputs a logic low. Figure 9 shows the SSTRB
timing in external clock mode.
The conversion must complete in 1ms, or droop on the
sample-and-hold capacitors may degrade conversion
results. Use internal clock mode if the serial-clock frequency is less than 50kHz, or if serial-clock interruptions
could cause the conversion interval to exceed 1ms.
Clock Modes
The MAX1110/MAX1111 can use either an external serial clock or the internal clock to perform the successiveapproximation conversion. In both clock modes, the
external clock shifts data in and out of the devices. Bit
PD0 of the control byte programs the clock mode.
Figures 8–11 show the timing characteristics common
to both modes.
External Clock
In external clock mode, the external clock not only
shifts data in and out, it also drives the analog-to-digital
CS
•••
tCSH
tCSS
tCL
tCH
SCLK
tCSH
•••
tDS
tDH
•••
DIN
tDO
tDV
tDO
tTR
•••
DOUT
Figure 8. Detailed Serial-Interface Timing
CS
•••
•••
tSTR
tSDV
SSTRB
•••
•••
tSSTRB
SCLK
tSSTRB
••••
••••
PD0 CLOCKED IN
Figure 9. External Clock Mode SSTRB Detailed Timing
______________________________________________________________________________________
13
MAX1110/MAX1111
Digital Output
In unipolar input mode, the output is straight binary
(Figure 15). For bipolar inputs, the output is two’s-complement (Figure 16). Data is clocked out at SCLK’s
falling edge in MSB-first format.
MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
CS
SCLK
DIN
1
4
5
SEL2 SEL1 SEL0
UNI/
BIP
2
3
7
8
SGL/
DIF PD1
PD0
6
9
10
11
12
15
16
17
18
START
SSTRB
tCONV
DOUT
A/D STATE
B7
B6
B1
B0
FILLED WITH
ZEROS
CONVERSION
25µs TYP
IDLE
IDLE
tACQ
4µs (fSCLK = 500kHz)
Figure 10. Internal Clock Mode Timing
CS
tCONV
tCSS
tSCK
tCSH
SSTRB
tSSTRB
SCLK
PD0 CLOCK IN
NOTE: FOR BEST NOISE PERFORMANCE, KEEP SCLK LOW DURING CONVERSION.
Figure 11. Internal Clock Mode SSTRB Detailed Timing
Internal Clock
Internal clock mode frees the µP from the burden of
running the SAR conversion clock. This allows the conversion results to be read back at the processor’s convenience, at any clock rate up to 2MHz. SSTRB goes
low at the start of the conversion and then goes high
when the conversion is complete. SSTRB is low for
25µs (typically), during which time SCLK should remain
low for best noise performance.
An internal register stores data when the conversion is
in progress. SCLK clocks the data out of this register at
any time after the conversion is complete. After SSTRB
goes high, the second falling clock edge produces the
MSB of the conversion at DOUT, followed by the
14
remaining bits in MSB-first format (Figure 10). CS does
not need to be held low once a conversion is started.
Pulling CS high prevents data from being clocked into
the MAX1110/MAX1111 and three-states DOUT, but it
does not adversely affect an internal clock-mode conversion already in progress. When internal clock mode
is selected, SSTRB does not go into a high-impedance
state when CS goes high.
Figure 11 shows the SSTRB timing in internal clock
mode. In this mode, data can be shifted in and out of
the MAX1110/MAX1111 at clock rates up to 2MHz, provided that the minimum acquisition time, tACQ, is kept
above 1µs.
______________________________________________________________________________________
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
MAX1110/MAX1111
CS
1
8
10
1
8
10
1
8
10
1
SCLK
S
DIN
CONTROL BYTE 0
S
B7
DOUT
S
CONTROL BYTE 1
B0
B7
B0
CONVERSION RESULT 1
CONVERSION RESULT 0
S
CONTROL BYTE 2
CONTROL BYTE 3
B7
CONVERSION RESULT 2
SSTRB
Figure 12a. Continuous Conversions, External Clock Mode, 10 Clocks/Conversion Timing
CS
SCLK
DIN
DOUT
S
S
CONTROL BYTE 0
B7
CONTROL BYTE 1
B0
CONVERSION RESULT 0
B7
CONVERSION RESULT 1
Figure 12b. Continuous Conversions, External Clock Mode, 16 Clocks/Conversion Timing
Data Framing
The falling edge of CS does not start a conversion. The
first logic high clocked into DIN is interpreted as a start
bit and defines the first bit of the control byte. A conversion starts on the falling edge of SCLK, after the eighth
bit of the control byte (the PD0 bit) is clocked into DIN.
The start bit is defined as:
The first high bit clocked into DIN with CS low any
time the converter is idle; e.g., after VDD is applied.
OR
The first high bit clocked into DIN after the MSB of a
conversion in progress is clocked onto the DOUT
pin.
If CS is toggled before the current conversion is complete, then the next high bit clocked into DIN is recognized as a start bit; the current conversion is
terminated, and a new one is started.
The fastest the MAX1110/MAX1111 can run is 10
clocks per conversion. Figure 12a shows the serialinterface timing necessary to perform a conversion
every 10 SCLK cycles in external clock mode.
Many microcontrollers require that conversions occur in
multiples of eight SCLK clocks; 16 clocks per conversion is typically the fastest that a microcontroller can
drive the MAX1110/MAX1111. Figure 12b shows the
serial-interface timing necessary to perform a conversion every 16 SCLK cycles in external clock mode.
______________________________________________________________________________________
15
Power-On Reset
When power is first applied, and if SHDN is not pulled
low, internal power-on reset circuitry activates the
MAX1110/MAX1111 in internal clock mode. SSTRB is
high on power-up and, if CS is low, the first logical 1 on
DIN is interpreted as a start bit. Until a conversion takes
place, DOUT shifts out zeros. No conversions should
be performed until the reference voltage has stabilized
(see Electrical Characteristics).
Power-Down
When operating at speeds below the maximum sampling rate, the MAX1110/MAX1111’s automatic powerdown mode can save considerable power by placing
the converters in a low-current shutdown state between
conversions. Figure 13 shows the average supply current as a function of the sampling rate.
Select power-down with PD1 of the DIN control byte
with SHDN high or floating (Table 3). Pull SHDN low at
any time to shut down the converters completely. SHDN
overrides PD1 of the control byte. Figures 14a and 14b
illustrate the various power-down sequences in both
external and internal clock modes.
Software Power-Down
Software power-down is activated using bit PD1 of the
control byte. When software power-down is asserted, the
ADCs continue to operate in the last specified clock
mode until the conversion is complete. The ADCs then
power down into a low quiescent-current state. In internal
clock mode, the interface remains active, and conversion
results may be clocked out after the MAX1110/
MAX1111 have entered a software power-down.
The first logical 1 on DIN is interpreted as a start bit,
which powers up the MAX1110/MAX1111. If the DIN byte
contains PD1 = 1, then the chip remains powered up. If
PD1 = 0, power-down resumes after one conversion.
Hard-Wired Power-Down
Pulling SHDN low places the converters in hard-wired
power-down. Unlike software power-down, the conversion is not completed; it stops coincidentally with SHDN
being brought low. SHDN also controls the state of the
internal reference (Table 5). Letting SHDN float enables
the internal 2.048V voltage reference. When returning to
normal operation with SHDN floating, there is a tRC
delay of approximately 1MΩ x CLOAD, where CLOAD is
the capacitive loading on the SHDN pin. Pulling SHDN
high disables the internal reference, which saves power
when using an external reference.
External Reference
An external reference between 1V and VDD should be
connected directly at the REFIN terminal. The DC input
impedance at REFIN is extremely high, consisting of
leakage current only (typically 10nA). During a conversion, the reference must be able to deliver up to 20µA
average load current and have an output impedance of
1kΩ or less at the conversion clock frequency. If the
reference has higher output impedance or is noisy,
bypass it close to the REFIN pin with a 0.1µF capacitor.
If an external reference is used with the MAX1110/
MAX1111, tie SHDN to VDD to disable the internal reference and decrease power consumption.
1000
MAX1110-fig13
Applications Information
CLOAD = 60pF
CODE = 10101010
SUPPLY CURRENT (µA)
MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
100
CLOAD = 30pF
CODE = 10101010
CLOAD = 30pF
CODE = 11111111
10
Table 5. Hard-Wired Power-Down and
Internal Reference State
VDD = VREFIN = 3V
CLOAD AT DOUT AND SSTRB
1
16
SHDN
STATE
DEVICE
MODE
INTERNAL
REFERENCE
1
Enabled
Disabled
Floating
Enabled
Enabled
0
Power-Down
Disabled
0
10
20
30
40
50
SAMPLING RATE (ksps)
Figure 13. Average Supply Current vs. Sampling Rate
______________________________________________________________________________________
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
INTERNAL
EXTERNAL
MAX1110/MAX1111
CLOCK
MODE
EXTERNAL
SHDN
SETS POWERDOWN MODE
SETS EXTERNAL
CLOCK MODE
DIN
S X X X X X 1 1
S X X X X X 0 1
S X X X X X 1 1
DATA VALID
DATA VALID
DOUT
DATA
INVALID
POWERDOWN
POWERED UP
MODE
SETS EXTERNAL
CLOCK MODE
POWERDOWN
POWERED UP
POWERED
UP
Figure 14a. Power-Down Modes, External Clock Timing Diagram
INTERNAL CLOCK MODE
SETS POWER-DOWN MODE
SETS INTERNAL
CLOCK MODE
DIN
S X X X X X 1 0
S X X X X X 0 0
MODE
DATA VALID
DATA VALID
DOUT
SSTRB
S
CONVERSION
CONVERSION
POWERED UP
POWER-DOWN
POWERED
UP
Figure 14b. Power-Down Modes, Internal Clock Timing Diagram
Internal Reference
Transfer Function
To use the MAX1110/MAX1111 with the internal reference, connect REFIN to REFOUT. The full-scale range
of the MAX1110/MAX1111 with the internal reference is
typically 2.048V with unipolar inputs, and ±1.024V with
bipolar inputs. The internal reference should be
bypassed to AGND with a 1µF capacitor placed as
close to the REFIN pin as possible.
Table 4 shows the full-scale voltage ranges for unipolar
and bipolar modes. Figure 15 depicts the nominal, unipolar I/O transfer function, and Figure 16 shows the bipolar
I/O transfer function when using a 2.048V reference.
Code transitions occur at integer LSB values. Output coding is binary, with 1LSB = 8mV (2.048V/256) for unipolar
operation and 1LSB = 8mV [(2.048V/2 - -2.048V/2)/256]
for bipolar operation.
______________________________________________________________________________________
17
MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
OUTPUT CODE
FULL-SCALE
TRANSITION
11111111
SUPPLIES
11111110
+3V
GND
11111101
FS = VREFIN + COM
1LSB = VREFIN
256
00000011
R* = 10Ω
VDD
00000010
AGND
DGND
+3V
DGND
00000001
MAX1110
MAX1111
00000000
0
(COM)
1
2
3
FS
INPUT VOLTAGE (LSB)
FS - 1LSB
Figure 15. Unipolar Transfer Function
DIGITAL
CIRCUITRY
* OPTIONAL
Figure 17. Power-Supply Grounding Connections
Layout, Grounding, and Bypassing
OUTPUT CODE
01111111
01111110
00000010
00000001
00000000
V
+FS = REFIN + COM
2
VREFIN
COM =
2
-VREFIN
-FS =
+ COM
2
VREFIN
1LSB =
256
11111111
11111110
11111101
10000001
10000000
-FS
COM
INPUT VOLTAGE (LSB)
1
+FS - 2 LSB
For best performance, use printed circuit boards. Wirewrap boards are not recommended. Board layout
should ensure that digital and analog signal lines are
separated from each other. Do not run analog and digital (especially clock) lines parallel to one another, or
digital lines underneath the ADC package.
Figure 17 shows the recommended system ground
connections. A single-point analog ground (star ground
point) should be established at AGND, separate from
the logic ground. Connect all other analog grounds and
DGND to the star ground. No other digital system
ground should be connected to this ground. The
ground return to the power supply for the star ground
should be low impedance and as short as possible for
noise-free operation.
High-frequency noise in the VDD power supply may
affect the comparator in the ADC. Bypass the supply to
the star ground with 0.1µF and 1µF capacitors close to
the V DD pin of the MAX1110/MAX1111. Minimize
capacitor lead lengths for best supply-noise rejection. If
the +3V power supply is very noisy, a 10Ω resistor can
be connected to form a lowpass filter.
Figure 16. Bipolar Transfer Function
18
______________________________________________________________________________________
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
TOP VIEW
CH0 1
20 VDD
CH1 2
19 SCLK
CH0 1
16 VDD
CH2 3
18 CS
CH1 2
15 SCLK
17 DIN
CH2 3
16 SSTRB
CH3 4
CH3 4
MAX1110
CH4 5
14 CS
MAX1111
13 DIN
15 DOUT
COM 5
12 SSTRB
CH6 7
14 DGND
SHDN 6
11 DOUT
CH7 8
13 AGND
REFIN 7
10 DGND
COM 9
12 REFOUT
CH5 6
SHDN 10
11 REFIN
9
REFOUT 8
AGND
DIP/QSOP
DIP/SSOP
Ordering Information (continued)
PART
TEMP. RANGE
PIN-PACKAGE
MAX1110EPP
-40°C to +85°C
20 Plastic DIP
MAX1110EAP
MAX1110MJP
MAX1111CPE
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
20 SSOP
20 CERDIP**
16 Plastic DIP
MAX1111CEE
0°C to +70°C
MAX1111EPE
MAX1111EEE
MAX1111MJE
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
Chip Information
TRANSISTOR COUNT: 1996
SUBSTRATE CONNECTED TO DGND
16 QSOP
16 Plastic DIP
16 QSOP
16 CERDIP**
**Contact factory for availability.
______________________________________________________________________________________
19
MAX1110/MAX1111
Pin Configurations
QSOP.EPS
________________________________________________________Package Information
SSOP.EPS
MAX1110/MAX1111
+2.7V, Low-Power, Multichannel,
Serial 8-Bit ADCs
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 1998 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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