MAX5120BEEE+ ,+3V/+5V, 12-Bit, Serial, Voltage-Output DACs with Internal ReferenceFeaturesThe MAX5120/MAX5121 are low-power, 12-bit, voltage-♦ Single-Supply Operationoutput digital- ..
MAX5122AEEE ,+5V/+3V, 12-Bit, Serial, Force/Sense DACs with 10ppm/∑C Internal ReferenceApplicationsPin ConfigurationIndustrial Process ControlAutomatic Test EquipmentTOP VIEWFB 1 16 VDDD ..
MAX5122BEEE ,+5V/+3V, 12-Bit, Serial, Force/Sense DACs with 10ppm/∑C Internal ReferenceELECTRICAL CHARACTERISTICS—MAX5122 (+5V)(V = +5V ±10%, AGND = DGND, 33nF capacitor at REFADJ, inter ..
MAX5122BEEE ,+5V/+3V, 12-Bit, Serial, Force/Sense DACs with 10ppm/∑C Internal Referenceapplications. Bothdevices draw only 500µA of supply current, which' Buffered Output Capable of Driv ..
MAX5123AEEE ,+5V/+3V / 12-Bit / Serial / Force/Sense DACs with 10ppm/C Internal ReferenceFeaturesThe MAX5122/MAX5123 low-power, 12-bit, voltage-out-' Single-Supply Operationput, digital-to ..
MAX5123BEEE ,+5V/+3V / 12-Bit / Serial / Force/Sense DACs with 10ppm/C Internal ReferenceELECTRICAL CHARACTERISTICS—MAX5122 (+5V)(V = +5V ±10%, AGND = DGND, 33nF capacitor at REFADJ, inter ..
MAX951ESA+T ,Ultra-Low-Power, Single-Supply Op Amp + Comparator + ReferenceFeaturesThe MAX951–MAX954 feature combinations of a Op Amp + Comparator + Reference in an 8-Pinmic ..
MAX951EUA+ ,Ultra-Low-Power, Single-Supply Op Amp + Comparator + ReferenceApplicationsInstruments, Terminals, and Bar-Code ReadersTOP VIEWBattery-Powered SystemsAutomotive K ..
MAX9526ATJ , Low-Power, High-Performance NTSC/PAL Video Decoder
MAX952EPA ,Ultra-Low-Power, Single-Supply Op Amp Comparator ReferenceMAX951–MAX95419-0431; Rev 1; 7/97Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference____ ..
MAX952ESA ,Ultra-Low-Power, Single-Supply Op Amp Comparator ReferenceMAX951–MAX95419-0431; Rev 1; 7/97Ultra-Low-Power, Single-Supply Op Amp + Comparator + Reference____ ..
MAX952EUA ,Ultra-Low-Power, Single-Supply Op Amp Comparator ReferenceFeaturesThe MAX951–MAX954 feature combinations of a' Op Amp + Comparator + Reference in an 8-Pinmic ..
MAX5120BEEE+
+3V/+5V, 12-Bit, Serial, Voltage-Output DACs with Internal Reference
General DescriptionThe MAX5120/MAX5121 are low-power, 12-bit, voltage-
output digital-to-analog converters (DACs) with an inter-
nal precision bandgap reference and an output amplifier.
The MAX5120 operates on a +5V supply with an internal
amplifier reference of +2.5V and is capable of a +4.095V
full-scale output range. The MAX5121, operating on +3V,
delivers its +2.0475V full-scale output with an internal
precision reference of +1.25V. If necessary, the user can
override the internal, <10ppm/°C voltage reference with
an external reference. Both devices draw only 500μA of
supply current, which reduces to 3μA in power-down
mode. In addition, their power-up reset feature allows for
a user-selectable initial output state of either 0V or mid-
scale and minimizes output voltage glitches during
power-up.
The serial interface is compatible with SPI™, QSPI™
and MICROWIRE™, which makes the MAX5120/
MAX5121 suitable for cascading multiple devices. Each
DAC has a double-buffered input organized as an input
register followed by a DAC register. A 16-bit shift regis-
ter loads data into the input register. The DAC register
may be updated independently or simultaneously with
the input register.
Both devices are available in a 16-pin QSOP package
and are specified for the extended industrial (-40°C to
+85°C) temperature range. For pin-compatible 14-bit
upgrades, see the MAX5170/MAX5172 data sheet;
for pin-compatible 13-bit versions, see the MAX5130/
MAX5131 data sheet.
________________________ApplicationsIndustrial Process Controls
Automatic Test Equipment (ATE)
Digital Offset and Gain Adjustment
Motion Control
μP-Controlled Systems
FeatureSingle-Supply Operation
+5V (MAX5120)
+3V (MAX5121)Full-Scale Output Range
+4.095V (MAX5120)
+2.0475V (MAX5121)Built-In 10ppm/°C (max) Precision Bandgap
Reference
+2.5V (MAX5120)
+1.25V (MAX5121)Adjustable Output OffsetSPI/QSPI/MICROWIRE-Compatible, 3-Wire Serial
InterfacePin-Programmable Shutdown Mode and Power-
Up Reset (0V or Midscale Output Voltage)Buffered Output Capable of Driving 5kΩ100pF
or 4–20mA LoadsSpace-Saving 16-Pin QSOP PackagePin-Compatible 13-Bit Upgrades Available
(MAX5130/MAX5131)Pin-Compatible 14-Bit Upgrades Available
(MAX5170/MAX5172)V/+5V, 12-Bit, Serial Voltage-Output DACsith Internal ReferencVDD
REFADJ
REF
AGND
UPO
DOUT
DGND
TOP VIEW
MAX5120
MAX5121
QSOPOUT
RSTVAL
PDL
CLR
DIN
SCLK
19-1428; Rev 0; 2/99
PART
MAX5120AEEEMAX5120BEEE-40°C to +85°C
-40°C to +85°C
TEMP. RANGEPIN-
PACKAGE16 QSOP
16 QSOP
Pin ConfigurationOrdering Information
INL
(LSB)±0.5
MAX5121AEEEMAX5121BEEE
-40°C to +85°C
-40°C to +85°C16 QSOP
16 QSOP±2
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corp.
V/+5V, 12-Bit, Serial Voltage-Output DACsith Internal ReferenceABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS—MAX5120 (+5V)(VDD= +5V ±10%, OS = AGND = DGND = 0V, 33nF capacitor at REFADJ, internal reference, RL= 5kΩ, CL= 100pF, TA= TMINto
TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
VDDto AGND, DGND...............................................-0.3V to +6V
AGND to DGND.....................................................-0.3V to +0.3V
Digital Inputs to DGND.............................................-0.3V to +6V
Digital Outputs (DOUT, UPO) to DGND.....-0.3V to (VDD+ 0.3V)
OUT to AGND.............................................-0.3V to (VDD+ 0.3V)
OS to AGND...................................(AGND - 4V) to (VDD+ 0.3V)
REF, REFADJ to AGND..............................-0.3V to (VDD+ 0.3V)
Maximum Current into Any Pin............................................50mA
Continuous Power Dissipation (TA= +70°C)
QSOP (derate 8.00mW/°C above +70°C).....................667mW
Operating Temperature Range ..........................-40°C to +85°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10sec).............................+300°C
VIN= 0 or VDD
MAX5120A
REFADJ = VDD
4.5V ≤VDD≤5.5V
MAX5120B
MAX5120B
MAX5120A
MAX5120A
Code = FFF hex, TA= +25°C= +25°C
CONDITIONS8CINInput Capacitance-10.0011IINInput Leakage Current200VHYSInput Hysteresis0.8VILInput Low Voltage3VIHInput High Voltage3.37REFADJ Current
ppm/°C10TCVREF3Output Voltage Temperature
Coefficient2.5VREFOutput Voltage
Bits12NResolution
μV/V20250PSRRPower-Supply Rejection Ratio
ppm/°C1030TCVFS310Full-Scale Temperature
Coefficient (Note 3)4.04584.0954.1442VFSFull-Scale Voltage
LSB-11DNLDifferential Nonlinearity-1010VOSOffset Error (Note 2)-0.23mVGEGain Error
UNITSMINTYPMAXSYMBOLPARAMETERISINK= 2mA
ISOURCE= 2mA0.130.4VOLOutput Low VoltageVDD- 0.5VOHOutput High Voltage
MAX5120BLSB-11INLIntegral Nonlinearity (Note 1)
0 ≤IOUT≤100μA (sourcing)μV/μA0.11VOUT/IOUTReference External Load Regulation4Reference Short-Circuit Current
STATIC PERFORMANCE
REFERENCE
DIGITAL INPUT
DIGITAL OUTPUTS
V/+5V, 12-Bit, Serial Voltage-Output DACsith Internal ReferencELECTRICAL CHARACTERISTICS—MAX5120 (+5V) (continued)(VDD= +5V ±10%, OS = AGND = DGND = 0V, 33nF capacitor at REFADJ, internal reference, RL= 5kΩ, CL= 100pF, TA= TMIN
TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
To ±0.5LSB, VSTEP= 4V= VDD, fSCLK= 100kHz,
VSCLK= 5Vp-p
CONDITIONS320ISHDNPower-Supply Current in Shutdown500600IDDPower-Supply Current (Note 5)4.55.5VDDPower-Supply Voltage (Note 5)
nV-s5Digital Feedthrough2Time Required to Exit Shutdown83121ROSOS Input Resistance20Output Settling Time0 to VDDOutput Voltage Swing (Note 4)
UNITSMINTYPMAXSYMBOLPARAMETER
ELECTRICAL CHARACTERISTICS—MAX5121 (+3V)(VDD= +3V ±10%, OS = AGND = DGND = 0V, 33nF capacitor at REFADJ, internal reference, RL= 5kΩ, CL= 100pF, TA= TMINto
TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
MAX5121A
REFADJ = VDD
2.7V ≤VDD≤3.3V
MAX5121B
MAX5121B
MAX5121A
MAX5121A
Data = FFFhex, TA= +25°C= +25°C
CONDITIONS200VHYSInput Hysteresis0.8VILInput Low Voltage2.2VIHInput High Voltage3.37REFADJ Current4Reference Short-Circuit Current
ppm/°C10TCVREF
MAX5121B
0 ≤IOUT≤100μA (sourcing)
Output Voltage Temperature
Coefficient1.25VREFOutput Voltage1
μV/μA0.11
Bits12NResolution
μV/V20250PSRRPower-Supply Rejection Ratio
ppm/°C1030TCVFS
LSB10
VOUT/IOUT
Full-Scale Temperature
Coefficient (Note 3)2.02292.04752.0721VFSFull-Scale Voltage
LSB-11DNLDifferential Nonlinearity-1010VOSOffset Error (Note 2)-0.25
Reference External Load RegulationGEGain Error
UNITSMINTYPMAXSYMBOLPARAMETER2INLIntegral Nonlinearity (Note 1)
V/μs0.6SRVoltage Output Slew Rate
DYNAMIC PERFORMANCE
POWER REQUIREMENTS
STATIC PERFORMANCE
REFERENCE
DIGITAL INPUT
V/+5V, 12-Bit, Serial Voltage-Output DACsith Internal ReferenceELECTRICAL CHARACTERISTICS—MAX5121 (+3V) (continued)(VDD= +3V ±10%, OS = AGND = DGND = 0V, 33nF capacitor at REFADJ, internal reference, RL= 5kΩ, CL= 100pF, TA= TMINto
TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
To ±0.5LSB, VSTEP= 2V= VDD, fSCLK= 100kHz,
VSCLK= 3Vp-p
CONDITIONS320ISHDNPower-Supply Current in Shutdown500600IDDPower-Supply Current (Note 5)2.73.6VDDPower-Supply Voltage (Note 5)
nV-s5Digital Feedthrough2Time Required to Exit Shutdown83121ROSOS Input Resistance20Output Settling Time0 to VDDOutput Voltage Swing (Note 4)
UNITSMINTYPMAXSYMBOLPARAMETERISINK= 2mAV0.130.4VOLOutput Low Voltage
ISOURCE= 2mAVVDD- 0.5VOHOutput High Voltage
VIN= 0 or VDDμA-10.0011IINInput Leakage Current8CINInput Capacitance
V/μs0.6SRVoltage Output Slew Rate
TIMING CHARACTERISTICS—MAX5120 (+5V)(VDD= +5V ±10%, OS = AGND = DGND = 0V, 33nF capacitor at REFADJ, internal reference, RL= 5kΩ, CL= 100pF, TA= TMINto
TMAX, unless otherwise noted. Typical values are at TA= +25°C.)40tCSSCSFall to SCLK Rise Setup Time40tCLSCLK Pulse Width Low
CONDITIONS100tCPSCLK Clock Period40tCHSCLK Pulse Width High0tCSHSCLK Rise to CSRise Hold Time10tCS0SCLK Rise to CSFall Delay Time40tDSSDI Setup Time0tDHSDI Hold Time
UNITSMINTYPMAXSYMBOLPARAMETER100tCSWCSPulse Width High40tCS1CSRise to SCLK Rise Hold Time
CLOAD= 200pFns80tDO1SCLK Rise to DOUT Valid
Propagation Delay Time
CLOAD= 200pFns80tDO2SCLK Fall to DOUT Valid
Propagation Delay Time
DIGITAL OUTPUTS
POWER REQUIREMENTS
DYNAMIC PERFORMANCE
V/+5V, 12-Bit, Serial Voltage-Output DACsith Internal ReferencNote 1:Accuracy is guaranteed as shown in the following table:
Note 2:Offset is measured at the code closest to 10mV.
Note 3:The temperature coefficient is determined by the “box” method in which the maximum DVOUTover the temperature range is
divided by DT.
Note 4:Accuracy is better than 1.0LSB for VOUT= 10mV to (VDD- 180mV). Guaranteed by PSR test on end points.
Note 5:RLOAD= ¥and digital inputs are at either VDDor DGND.
TIMING CHARACTERISTICS—MAX5121 (+3V)(VDD= +3V ±10%, OS = AGND = DGND = 0V, 33nF capacitor at REFADJ, internal reference, RL= 5kΩ, CL= 100pF, TA= TMIN
TMAX, unless otherwise noted. Typical values are at TA= +25°C.)60tCSSCSFall to SCLK Rise Setup Time150
CLOAD= 200pF
tCSW
tCLSCLK Pulse Width Low
CONDITIONS150tCPSCLK Clock Period75tCHSCLK Pulse Width High0tCSHSCLK Rise to CSRise Hold TimePulse Width High75tCS1CSRise to SCLK Rise Hold Time
CLOAD= 200pFns200tDO1SCLK Rise to DOUT Valid
Propagation Delay Time200tDO2SCLK Fall to DOUT Valid
Propagation Delay Time10tCS0SCLK Rise to CSFall Delay Time60tDSSDI Setup Time0tDHSDI Hold Time
UNITSMINTYPMAXSYMBOLPARAMETER53
Accuracy Guaranteed
To Code:From Code:
VDD
(V)
Typical Operating Characteristics
(VDD= +5V (MAX5120), VDD= +3V (MAX5121), RL= 5kΩ, CL= 100pF, OS = AGND, TA = +25°C, unless otherwise noted.)
MAX5120
INTEGRAL NONLINEARITY vs.
DIGITAL INPUT CODE
AX5120/21 toc01
DIGITAL INPUT CODE
(L
MAX5120
DIFFERENTIAL NONLINEARITY vs.
DIGITAL INPUT CODE
AX5120/21 toc02
DIGITAL INPUT CODE
(L
MAX5120
REFERENCE VOLTAGE vs. TEMPERATURE
AX5120/21 toc03
TEMPERATURE (°C)
(V
V/+5V, 12-Bit, Serial Voltage-Output DACsith Internal ReferenceTypical Operating Characteristics (continued)(VDD= +5V (MAX5120), VDD= +3V (MAX5121), RL= 5kΩ, CL= 100pF, OS = AGND, TA = +25°C, unless otherwise noted.)
MAX5120
SUPPLY CURRENT vs. TEMPERATURE
AX5120/21 toc04
TEMPERATURE (°C)
(m
(CODE = AAA HEX)
(CODE = 000 HEX)
(CODE = AAA HEX)
(CODE = 000 HEX)
MAX5120
SUPPLY CURRENT vs. SUPPLY VOLTAGE
AX5120/21 toc05
SUPPLY VOLTAGE (V)
(m
MAX5120
SHUTDOWN CURRENT vs. TEMPERATURE
5120/21 toc06
TEMPERATURE (°C)
(m
MAX5120
FULL-SCALE OUTPUT vs. TEMPERATURE
AX5120/21 toc07
TEMPERATURE (°C)
(VRL = 5kW
CL = 100pF
5V/div
OUT
1V/divs/div
MAX5120
DYNAMIC RESPONSE FALL TIMEMAX5120/21-10
MAX5120
FULL-SCALE ERROR vs. RESISTIVE LOAD
AX5120/21 toc08
RL (kW)
(L
0.25CS
5V/div
OUT
1V/divs/div
MAX5120
DYNAMIC RESPONSE RISE TIMEMAX5120/21-09
SCLK
2V/div
OUT
1mV/div
AC COUPLEDs/div
MAX5120
DIGITAL FEEDTHROUGH (SCLK, OUT) MAX5120/21-11
2V/div
OUT
100mV/div
AC COUPLEDs/div
MAX5120
MAJOR CARRY TRANSITION MAX5120/21-12
V/+5V, 12-Bit, Serial Voltage-Output DACsith Internal ReferencMAX5121
INTEGRAL NONLINEARITY
vs. DIGITAL INPUT CODE
AX5120/21 toc-13
DIGITAL INPUT CODE
(L
MAX5121
DIFFERENTIAL NONLINEARITY
vs. DIGITAL INPUT CODE
AX5120/21 toc-14
DIGITAL INPUT CODE
(L
MAX5121
REFERENCE VOLTAGE vs. TEMPERATURE
AX5120/21 toc-15
TEMPERATURE (°C)
(V
MAX5121
SUPPLY CURRENT vs. TEMPERATURE
X5120/21 toc-16
TEMPERATURE (°C)
(m
CODE = AAA HEX
CODE = 000 HEX
MAX5121
FULL-SCALE OUTPUT vs. TEMPERATURE
5120/21 toc-19
TEMPERATURE (°C)
(V
RL = 5kW
CL = 100pF
MAX5121
SUPPLY CURRENT vs. SUPPLY VOLTAGE
5120/21 toc-17
SUPPLY VOLTAGE (V)
(mCODE = AAA HEX
CODE = 000 HEX
MAX5121
SHUTDOWN CURRENT vs. TEMPERATURE
AX5120/21 toc-18
TEMPERATURE (°C)
(m
MAX5121
FULL-SCALE OUTPUT vs. RESISTIVE LOAD
AX5120/21 toc-20
RL (kW)
(L
2V/div
OUT
500mV/divs/div
MAX5121
DYNAMIC RESPONSE RISE TIMEMAX5120/21-21
Typical Operating Characteristics (continued)(VDD= +5V (MAX5120), VDD= +3V (MAX5121), RL= 5kΩ, CL= 100pF, OS = AGND, TA = +25°C, unless otherwise noted.)
V/+5V, 12-Bit, Serial Voltage-Output DACsith Internal ReferenceTypical Operating Characteristics (continued)(VDD= +5V (MAX5120), VDD= +3V (MAX5121), RL= 5kΩ, CL= 100pF, OS = AGND, TA = +25°C, unless otherwise noted.)
2V/div
OUT
500mV/divs/div
MAX5121
DYNAMIC RESPONSE FALL TIMEMAX5120/21-22
SCLK
2V/div
OUT
500mV/div
AC COUPLEDs/div
MAX5121
DIGITAL FEEDTHROUGH (SCLK, OUT)MAX5120/21-23
2V/div
OUT
100mV/div
AC COUPLEDs/div
MAX5121
MAJOR CARRY TRANSITIONMAX5120/21-24
Pin Description
PINOffset Adjust (Analog Input)OS1
FUNCTIONNAMEAnalog Output Voltage. High impedance if part is in shutdown.OUT2
Power-Down Lockout (Digital Input)
1: Normal operation.
0: Disallows shutdown (device cannot be powered down).
PDL4
Reset Value Input (Digital Input)
1: Tie to VDDto select midscale as the output reset value.
0: Tie to DGND to select 0V as the output reset value.
RSTVAL3
Active-Low Chip-Select Input (Digital Input)CS6
Serial Clock InputSCLK8
Serial Data Input. Data is clocked in on the rising edge of SCLK.DIN7
Reset DAC Input (Digital Input). Clears the DAC to its predetermined (RSTVAL) output state. Clearing the
DAC will cause it to exit a software shutdown state.CLR5
Serial Data OutputDOUT10
Power-Down Input (Digital Input). Pulling PD high when PDL= VDDplaces the IC into shutdown with a
maximum shutdown current of 20μA.PD12
User-Programmable Output (Digital Output)UPO11
Buffered Reference Output/Input. In internal reference mode, the reference buffer provides a +2.5V
(MAX5120) or +1.25V (MAX5121) nominal output, externally adjustable at REFADJ. In external reference
mode, disable the internal reference by pulling REFADJ to VDDand applying the external reference to REF.
REF14
Positive Power Supply. Bypass with a 0.1μF capacitor in parallel with a 4.7μF capacitor to AGND.VDD16
Analog Reference Adjust Input. Bypass with a 33nF capacitor to AGND. Connect to VDDwhen using an
external reference.REFADJ15
Analog GroundAGND13
Digital GroundDGND9
V/+5V, 12-Bit, Serial Voltage-Output DACsith Internal Referenc_______________Detailed DescriptionThe MAX5120/MAX5121 12-bit, voltage-output DACs
are easily configured with a 3-wire serial interface. They
include a 16-bit data-in/data-out shift register and have
a double-buffered input consisting of an input register
and a DAC register. In addition, these devices employ
precision bandgap references and trimmed internal
resistors to produce a gain of 1.6384V/V, maximizing
the output voltage swing (Figure 1). The MAX5120/
MAX5121 output amplifier’s offset-adjust pin allows for
a DC shift in the DAC outputs. The full-scale output volt-
age is +4.095V for the MAX5120 and +2.0475V for the
MAX5121. These DACs are designed with an inverted
R-2R ladder network (Figure 2) that produces a weight-
ed output voltage proportional to the digital input code.
nternal ReferenceBoth the MAX5120 and MAX5121 use an on-board pre-
cision bandgap reference to generate an output volt-
age of +2.5V (MAX5120) or +1.25V (MAX5121). With a
low temperature coefficient of only 10ppm/°C (max),
the REF pin can source up to 100μA and may become
unstable with capacitive loads exceeding 100pF.
REFADJ can be used for minor adjustments (1%) to the
reference voltage. Use the circuits shown in Figure 3a
MAX5120
MAX5121
CONTROL
16-BIT
SHIFT REGISTER
DECODE
CONTROL
INPUT
REGISTER
BANDGAP
REFERENCE
REFERENCE
BUFFER
DAC
REGISTERDAC
(1X)
DOUT
UPO
OUT
0.6384R
GAIN = 1.6384X
1.25V
AGNDDGNDVDDDINSCLKCS
2.5V, (1.25V)
LOGIC
OUTPUT
CLR
PDL
RSTVAL
REFADJREF( ) FOR MAX5121 ONLY
Figure 1. Simplified Functional Diagram
OUT
0.6384R
SHOWN FOR ALL 1s ON DAC
*INTERNAL 2.5V (MAX5120) AND 1.25V (MAX5121)
OR EXTERNAL REFERENCE.
D0 D9D10D112R2R2R2RRR
REF*
AGND
Figure 2. Simplified Inverted R-2R DAC Structure
(MAX5120) and Figure 3b (MAX5121) to achieve theseadjustments. Connect a 33nF capacitor from REFADJ
to AGND to establish low-noise operation of the DAC.
Larger capacitor values may be used, but will result in
increased start-up delay. The time constant (t) for the
start-up delay is determined by the REFADJ input
impedance of 4kΩand CREFADJ:= 4kΩ
·CREFADJ
ternal ReferenceAn external reference may be applied to the REF pin.
Disable the internal reference by pulling REFADJ to
VDD. This allows an external reference signal (AC- or
DC-based) to be fed into the REF pin. For proper oper-
ation, do notexceed the input voltage range limits of
0V to (VDD- 1.4V) for VREF.
Determine the output voltage using the following equa-
tion (REFADJ = VDD; OS = AGND):
VOUT= [VREF
·(NB / 4096)] ·1.6384V/V
where NB is the numeric value of the MAX5120/
MAX5121 input code (0 to 4095), VREFis the external
reference voltage, and 1.6384V/V is the gain of the
internal output amplifier. The REF pin has a minimum
input resistance of 40kΩand is code-dependent.
Output AmplifierThe output amplifier of the MAX5120/MAX5121
employs a trimmed resistor-divider to set a gain of
+1.6384V/V and minimize the gain error. With its on-
board laser-trimmed +1.25V reference and the output
buffer gain, the MAX5121 achieves a full-scale output
of +2.0475V, while the MAX5120 provides a +4.095V
full-scale output with a +2.5V reference.
The output amplifier has a typical slew rate of 0.6V/μs
and settles to ±0.5LSB within 20μs, with a load of 5kΩ
in parallel with 100pF. Loads less than 1kΩmay result
in degraded performance.
The OS pin may be used to adjust the output offset volt-
age. For instance, to achieve a +1V offset, apply
-1.566V (Offset = -[Output Buffer Gain - 1] ·VOS) to OS
to produce an output voltage range from +1V to (1V +
VREF
·1.6384V/V). Note that the DAC’s output range is
still limited by the maximum output voltage specifica-
tion.
Power-Down ModeThe MAX5120/MAX5121 feature software- and hard-
ware-programmable (PD pin) shutdown modes that
reduce the typical supply current to 3μA. To enter soft-
ware shutdown mode, program the control sequence
for the DAC as shown in Table 1.
In shutdown mode, the amplifier output becomes high
impedance and the serial interface remains active.
Data in the input registers is saved, allowing the
MAX5120/MAX5121 to recall the output state prior to
entering shutdown when returning to normal operation
mode. To exit shutdown mode, load both input and
DAC registers simultaneously or update the DAC regis-
ter from the input register. When returning from shut-
down mode, wait 2ms for the reference to settle. When
using an external reference, the DAC requires only
20μs for the output to stabilize.
V/+5V, 12-Bit, Serial Voltage-Output DACsith Internal ReferenceREFADJ
+5V
90k
100k
400k
33nF
MAX5120
REFADJ
+3V
15k
100k
400k
33nF
MAX5121
Figure 3a. MAX5120 Reference Adjust CircuitFigure 3b. MAX5121 Reference Adjust Circuit
