MAXIM MAX1113CEE

19-1231; Rev 2; 4/11
KIT
ATION
EVALU
E
L
B
AVAILA
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
The MAX1112/MAX1113 low-power, 8-bit, 8-channel
analog-to-digital converters (ADCs) feature an internal
track/hold, voltage reference, clock, and serial interface. They operate from a single 4.5V to 5.5V supply
and consume only 135µA while sampling at rates up to
50ksps. The MAX1112’s 8 analog inputs and the
MAX1113’s 4 analog inputs are software-configurable,
allowing unipolar/bipolar and single-ended/differential
operation.
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 4.096V internal reference, or by an
externally applied reference ranging from 1V to VDD.
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.
The MAX1112/MAX1113 have a software-programmable, 2µA automatic power-down mode to minimize
power consumption. Using power-down, the supply
current is reduced to 13µA at 1ksps, and only 82µA at
10ksps. Power-down can also be controlled using the
SHDN input pin. Accessing the serial interface automatically powers up the device.
The MAX1112 is available in a 20-pin SSOP package.
The MAX1113 is available in a small 16-pin QSOP
package.
________________________Applications
Portable Data Logging
Hand-Held Measurement Devices
Medical Instruments
System Diagnostics
Solar-Powered Remote Systems
4mA to 20mA-Powered Remote
Data-Acquisition Systems
Pin Configurations appear at end of data sheet.
____________________________Features
♦ 4.5V to 5.5V Single Supply
♦ Low Power: 135µA at 50ksps
13µA at 1ksps
♦ 8-Channel Single-Ended or 4-Channel Differential
Inputs (MAX1112)
♦ 4-Channel Single-Ended or 2-Channel Differential
Inputs (MAX1113)
♦ Internal Track/Hold; 50kHz Sampling Rate
♦ Internal 4.096V Reference
♦ SPI/QSPI/MICROWIRE-Compatible Serial Interface
♦ Software-Configurable Unipolar or Bipolar Inputs
♦ Total Unadjusted Error: ±1 LSB (max)
±0.3 LSB (typ)
Ordering Information continued at end of data sheet.
Functional Diagram
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
SSTRB
T/H
COM
REFOUT
DOUT
+4.096V
REFERENCE
CLOCK
IN
8-BIT
SAR ADC
OUT
REF
VDD
DGND
MAX1112
MAX1113
AGND
REFIN
*MAX1112 ONLY
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corp.
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAX1112/MAX1113
General Description
MAX1112/MAX1113
+5V, Low-Power, Multi-Channel,
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)
QSOP (derate 8.30mW/°C above +70°C) .....................667mW
SSOP (derate 8.00mW/°C above +70°C) .....................640mW
Operating Temperature Ranges
MAX1112CAP/MAX1113CEE...............................0°C to +70°C
MAX1112EAP/MAX1113EEE ............................-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 = 4.5V to 5.5V; unipolar input mode; VCOM = 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
±0.1
No missing codes over temperature
Offset Error
±0.3
Gain Error (Note 2)
Internal or external reference
Gain Temperature Coefficient
External reference, 4.096V
Total Unadjusted Error
Bits
TUE
LSB
±1
LSB
±1
LSB
±1
±0.8
±0.3
Channel-to-Channel
Offset Matching
±0.5
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, 4.096VP-P, 50ksps, 500kHz external clock)
Signal-to-Noise
and Distortion Ratio
Channel-to-Channel Crosstalk
VCH_ = 4.096VP-P, 25kHz (Note 3)
Small-Signal Bandwidth
-3dB rolloff
Full-Power Bandwidth
2
68
dB
-75
dB
1.5
MHz
800
kHz
_______________________________________________________________________________________
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
(VDD = 4.5V to 5.5V; unipolar input mode; VCOM = 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 4)
tCONV
Track/Hold Acquisition Time
tACQ
Internal clock
µs
µs
Aperture Delay
10
Aperture Jitter
< 50
ps
Internal Clock Frequency
400
kHz
(Note 5)
External Clock-Frequency Range
50
Used for data transfer only
ns
500
kHz
2
MHz
ANALOG INPUT
Unipolar input, VCOM = 0V
Input Voltage Range, SingleEnded and Differential (Note 6)
0
VREFIN
COM ±
VREFIN/2
Bipolar input, VCOM = VREFIN/2
Multiplexer Leakage Current
On/off leakage current, VCH_ = 0V or VDD
±0.01
Input Capacitance
±1
18
V
µA
pF
INTERNAL REFERENCE
REFOUT Voltage
3.936
REFOUT Short-Circuit Current
REFOUT Temperature Coefficient
Load Regulation (Note 7)
0 to 0.5mA output load
Capacitive Bypass at REFOUT
4.096
4.256
V
6
mA
±50
ppm/°C
4.5
mV
1
µF
EXTERNAL REFERENCE AT REFIN
VDD +
50
1
Input Voltage Range
Input Current
(Note 8)
V
1
20
µA
5.5
V
Operating mode
135
250
Reference disabled
95
Software
2
POWER REQUIREMENTS
Supply Voltage
VDD
Supply Current
IDD
4.5
Full-scale input
CLOAD = 10pF
Power-down
Power-Supply Rejection
(Note 9)
PSR
SHDN at DGND
VDD = 4.5V to 5.5V; external reference,
4.096V; full-scale input
µA
µA
3.2
10
±0.4
±4
mV
_______________________________________________________________________________________
3
MAX1112/MAX1113
ELECTRICAL CHARACTERISTICS (continued)
MAX1112/MAX1113
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
ELECTRICAL CHARACTERISTICS (continued)
(VDD = 4.5V to 5.5V; unipolar input mode; VCOM = 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
3
VHYST
V
0.8
V
0.2
V
DIN, SCLK, CS Input Leakage
IIN
Digital inputs = 0V or VDD
±1
µA
DIN, SCLK, CS Input Capacitance
CIN
(Note 5)
15
pF
SHDN INPUT
SHDN Input High Voltage
VSH
VDD - 0.4
SHDN Input Mid-Voltage
VSM
1.1
SHDN Voltage, High Impedance
VFLT
SHDN Input Low Voltage
VSL
VSHDN = 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 5)
_______________________________________________________________________________________
±10
µA
15
pF
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
MAX1112/MAX1113
TIMING CHARACTERISTICS (Figures 8 and 9)
(VDD = 4.5V 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
200
ns
CS Fall to Output Enable
tDV
Figure 1, CLOAD = 100pF
240
ns
CS Rise to Output Disable
tTR
Figure 2, CLOAD = 100pF
240
ns
20
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 5)
tSDV
Figure 1, external clock mode only,
CLOAD = 100pF
240
ns
CS Rise to SSTRB Output
Disable (Note 5)
tSTR
Figure 2, external clock mode only,
CLOAD = 100pF
240
ns
SSTRB Rise to SCLK Rise
(Note 5)
tSCK
Figure 11, internal clock mode only
Wakeup Time
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
Note 10:
tWAKE
0
ns
External reference
20
µs
Internal reference (Note 10)
24
ms
Relative accuracy is the analog value’s deviation (at any code) from its theoretical value after the full-scale range is calibrated.
VREFIN = 4.096V, 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 4.096V, full-scale input, 500kHz external clock.
Measured as | VFS (4.5V) - VFS (5.5V) |.
1µF at REFOUT; internal reference settling to 0.5 LSB.
_______________________________________________________________________________________
5
__________________________________________Typical Operating Characteristics
(VDD = 5.0V; fSCLK = 500kHz; external clock (50% duty cycle); RL = ∞; TA = +25°C, unless otherwise noted.)
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
140
VDD = 4.5V
120
MAX1112/13-02
0.3
8
0.2
0.1
6
4
-0.1
2
-0.2
0
100
-60
-20
20
60
100
-0.3
-60
140
-20
20
60
100
TEMPERATURE (°C)
TEMPERATURE (°C)
OFFSET ERROR vs. TEMPERATURE
INTEGRAL NONLINEARITY
vs. CODE
0.5
140
0
64
128
192
256
DIGITAL CODE
0.20
MAX1112/13-04
0.6
0
FFT PLOT
20
0.15
fCH_ = 10.034kHz, 4VP-P
fSAMPLE = 50ksps
0
MAX1112/13-06
VDD = 5.5V
SHDN = DGND
DNL (LSB)
MAX1112/13-01
160
10
MAX1112/13-05
0.10
INL (LSB)
0.4
0.3
AMPLITUDE (dB)
SUPPLY CURRENT (µA)
OUTPUT CODE = FULL SCALE
CLOAD = 10pF
SHUTDOWN SUPPLY CURRENT (µA)
180
DIFFERENTIAL NONLINEARITY
vs. CODE
MAX1112/13-03
SUPPLY CURRENT vs. TEMPERATURE
OFFSET ERROR (LSB)
MAX1112/MAX1113
+5V, Low-Power, Multi-Channel,
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
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
PIN
NAME
FUNCTION
MAX1112
MAX1113
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 ±0.5 LSB.
10
6
SHDN
Three-Level Shutdown Input. Normally high impedance. Pulling SHDN low shuts the
MAX1112/MAX1113 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
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.
Serial-Strobe Output. In internal clock mode, SSTRB goes low when the MAX1112/
MAX1113 begin the A/D conversion and goes high when the conversion is complete.
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).
Internal Reference Generator Output. Bypass with a 1µF capacitor to AGND.
16
12
SSTRB
17
13
DIN
Serial-Data Input. Data is clocked in at SCLK’s rising edge.
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.
19
15
SCLK
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%).
20
16
VDD
Positive Supply Voltage, 4.5V to 5.5V. Bypass to AGND with 0.1µF and 1µF capacitor
as close as possible to the device. Place the 0.1µF capacitor closer to VP-P.
+5V
DOUT
DOUT
3kΩ
+5V
DOUT
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
3kΩ
3kΩ
DOUT
3kΩ
CLOAD
DGND
a) VOH to High-Z
CLOAD
DGND
b) VOL to High-Z
Figure 2. Load Circuits for Disable Time
_______________________________________________________________________________________
7
MAX1112/MAX1113
Pin Description
MAX1112/MAX1113
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
_______________Detailed Description
The MAX1112/MAX1113 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 MAX1112
channels with Table 1 and the MAX1113 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 ±0.5 LSB (±0.1 LSB 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 if necessary.
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.
+5V
VDD
VDD
CH0
0.1μF
ANALOG
INPUTS
CH7
CAPACITIVE DAC
REFIN
1μF
AGND
DGND
COM
CH0
CH1
CPU
MAX1112
MAX1113
REFOUT
REFIN
1μF
CS
SCLK
DIN
DOUT
CH4*
I/O
SCK (SK)
MOSI (SO)
MISO (SI)
Figure 3. Typical Operating Circuit
8
CH6*
CH7*
6.5kΩ
RIN
CSWITCH
TRACK
HOLD
T/H
SWITCH
COM
SSTRB
SHDN
CH5*
ZERO
18pF
CH2
CH3
COMPARATOR
CHOLD
INPUT
MUX –
+
VSS
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*.
*MAX1112 ONLY
Figure 4. Equivalent Input Circuit
_______________________________________________________________________________________
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
MAX1112/MAX1113
Table 1a. MAX1112 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. MAX1112 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. MAX1113 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. MAX1113 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
MAX1112/MAX1113
+5V, Low-Power, Multi-Channel,
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 MAX1112/MAX1113 can be configured for differential or single-ended inputs with bits 2 and 3 of the control byte (Table 3). In single-ended mode, 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 V REFIN. 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. See Table 4 for input voltage
ranges.
Quick Look
To quickly evaluate the MAX1112/MAX1113’s analog
performance, use the circuit of Figure 5. The
MAX1112/MAX1113 require a control byte to be written
to DIN before each conversion. Tying DIN to +5V 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 (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 (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).
______________________________________________________________________________________
+5V, Low-Power, Multi-Channel,
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 (MAX1112) or
CH3 (MAX1113) 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 (MSB) 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 MAX1112/MAX1113’s internal shift register. 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 MAX1112/MAX1113 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
VDD
OSCILLOSCOPE
+5V
0.1µF
1µF
DGND
MAX1112
MAX1113
0V TO
+4.096V
ANALOG 0.01µF
INPUT
CH7 (CH3)
SCLK
AGND
SSTRB
CS
DOUT*
SCLK
COM
+5V
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 MAX1113.
Figure 5. Quick-Look Circuit
______________________________________________________________________________________
11
MAX1112/MAX1113
Table 4. Full-Scale and Zero-Scale Voltages
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
MAX1112/MAX1113
8-bit conversion result). Figure 6 shows the MAX1112/
MAX1113 common serial-interface connections.
I/O
CS
SCK
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.
SCLK
MISO
DOUT
+5V
MAX1112
MAX1113
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.
SS
a) SPI
CS
CS
SCK
SCLK
MISO
DOUT
3) Transmit TB1 and, simultaneously, receive a byte
and call it RB1. Ignore RB1.
4) Transmit a byte of all zeros ($00 hex) and, simultaneously, receive byte RB2.
+5V
MAX1112
MAX1113
SS
5) Transmit a byte of all zeros ($00 hex) and, simultaneously, receive byte RB3.
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.
MAX1112
MAX1113
c) MICROWIRE
Figure 6. Common Serial-Interface Connections to the
MAX1112/MAX1113
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
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
Clock Modes
The MAX1112/MAX1113 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.
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 can 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.
External Clock
In external clock mode, the external clock not only
shifts data in and out, it also drives the analog-to-digital
CS
•••
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
MAX1112/MAX1113
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.
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.
MAX1112/MAX1113
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
CS
SCLK
DIN
1
2
3
4
5
SEL2 SEL1 SEL0 UNI/
BIP
7
8
SGL/ PD1
DIF
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 (typ), 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 MAX1112/MAX1113 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 MAX1112/MAX1113 at clock rates up to 2MHz, provided that the minimum acquisition time, tACQ, is kept
above 1µs.
______________________________________________________________________________________
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
MAX1112/MAX1113
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 MAX1112/MAX1113 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 MAX1112/MAX1113. Figure 12b shows the
serial-interface timing necessary to perform a conversion every 16 SCLK cycles in external clock mode.
______________________________________________________________________________________
15
__________Applications Information
Power-On Reset
When power is first applied, and if SHDN is not pulled
low, internal power-on reset circuitry activates the
MAX1112/MAX1113 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 the Wakeup Time specifications in the Timing
Characteristics).
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 high impedance
enables the internal 4.096V voltage reference. When
returning to normal operation with SHDN high impedance,
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.
Power-Down
External Reference
When operating at speeds below the maximum sampling rate, the MAX1112/MAX1113’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 high impedance (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.
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.
Table 5. Hard-Wired Power-Down and
Internal Reference State
SHDN
STATE
DEVICE
MODE
INTERNAL
REFERENCE
1
Enabled
Disabled
High Impedance
Enabled
Enabled
0
Power-Down
Disabled
16
1000
MAX1112/13-fig13
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 can be clocked out after the MAX1112/
MAX1113 have entered a software power-down.
The first logical 1 on DIN is interpreted as a start bit,
which powers up the MAX1112/MAX1113. If the DIN byte
contains PD1 = 1, then the chip remains powered up. If
PD1 = 0, power-down resumes after one conversion.
If an external reference is used with the MAX1112/
MAX1113, connect SHDN to VDD to disable the internal
reference and decrease power consumption.
SUPPLY CURRENT (μA)
MAX1112/MAX1113
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
CLOAD = 60pF
CODE = 10101010
100
CLOAD = 30pF
CODE = 10101010
CLOAD = 30pF
CODE = 11111111
VDD = VREFIN = 5V
CLOAD AT DOUT + SSTRB
10
0
10
20
30
40
50
SAMPLING RATE (ksps)
Figure 13. Average Supply Current vs. Sampling Rate
______________________________________________________________________________________
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
INTERNAL
EXTERNAL
MAX1112/MAX1113
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
POWERED
UP
POWERDOWN
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 MAX1112/MAX1113 with the internal reference, connect REFIN to REFOUT. The full-scale range
of the MAX1112/MAX1113 with the internal reference is
typically 4.096V with unipolar inputs, and ±2.048V 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 4.096V reference. Code transitions occur at integer LSB values.
Output coding is binary, with 1 LSB = 16mV
(4.096V/256) for unipolar operation and 1 LSB = 16mV
[(4.096V/2 - -4.096V/2)/256] for bipolar operation.
______________________________________________________________________________________
17
MAX1112/MAX1113
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
OUTPUT CODE
FULL-SCALE
TRANSITION
11111111
SUPPLIES
11111110
+5V
GND
11111101
FS = VREFIN + COM
V
1 LSB = REFIN
256
00000011
R* = 10Ω
VDD
00000010
AGND
DGND
+5V
DGND
00000001
00000000
0
1
2
(COM)
3
MAX1112
MAX1113
FS
INPUT VOLTAGE (LSB)
FS - 1 LSB
DIGITAL
CIRCUITRY
*OPTIONAL
Figure 17. Power-Supply Grounding Connections
Figure 15. Unipolar Transfer Function
Layout, Grounding, and Bypassing
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.
OUTPUT CODE
01111111
01111110
00000010
00000001
00000000
VREFIN
+ COM
2
V
COM = REFIN
2
-VREFIN
-FS =
+ COM
2
VREFIN
1 LSB =
256
+FS =
11111111
11111110
11111101
10000001
10000000
-FS
COM
INPUT VOLTAGE (LSB)
1
+FS - 2 LSB
High-frequency noise in the VDD power supply can
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 MAX1112/MAX1113. Minimize
capacitor lead lengths for best supply-noise rejection. If
the 5V power supply is very noisy, a 10Ω resistor can
be connected to form a lowpass filter.
Figure 16. Bipolar Transfer Function
18
______________________________________________________________________________________
+5V, Low-Power, Multi-Channel,
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
MAX1112
CH4 5
14 CS
MAX1113
13 DIN
15 DOUT
COM 5
12 SSTRB
CH6 7
14 DGND
SHDN 6
11 DOUT
CH7
13 AGND
REFIN 7
10 DGND
CH5 6
8
COM 9
REFOUT 8
12 REFOUT
SHDN 10
9
11 REFIN
AGND
QSOP
SSOP
Ordering Information
___________________Chip Information
PIN-PACKAGE
PROCESS:CMOS
0°C to +70°C
20 SSOP
SUBSTRATE CONNECTED TO DGND
MAX1112C/D
MAX1112EAP+
MAX1113CEE+
0°C to +70°C
-40°C to +85°C
0°C to +70°C
Dice*
20 SSOP
16 QSOP
MAX1113EEE+
40°C to +85°C
16 QSOP
PART
TEMP RANGE
MAX1112CAP+
+Denotes a lead(Pb)-free/RoHS-compliant package.
*Dice are specified at TA = +25°C, DC parameters only.
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maxim-ic.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.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
20 SSOP
A20+1
21-0056
90-0094
16 QSOP
E16+1
21-0055
90-0167
______________________________________________________________________________________
19
MAX1112/MAX1113
Pin Configurations
MAX1112/MAX1113
+5V, Low-Power, Multi-Channel,
Serial 8-Bit ADCs
Revision History
REVISION
NUMBER
REVISION
DATE
0
6/97
Initial release
4/11
Updated General Description, Features, Ordering Information, Absolute
Maximum Ratings, Electrical Characteristics, Timing Characteristics, Pin
Description, Tables 3 and 4, 5, Power-Down, Software Power-Down, HardWired Power-Down, External Reference and Layout, Grounding, and
Bypassing, and Chip Information sections.
2
DESCRIPTION
PAGES
CHANGED
—
1-8, 10, 11, 13, 14,
16, 18, 19
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
© 2011 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, inc.