LTC2641/LTC2642
16-/14-/12-Bit VOUT DACs in
3mm × 3mm DFN
FEATURES
DESCRIPTION
Tiny 3mm × 3mm 8-Pin DFN Package
Maximum 16-Bit INL Error: ±1LSB over Temperature
Low 120µA Supply Current
Guaranteed Monotonic over Temperature
Low 0.5nV•sec Glitch Impulse
2.7V to 5.5V Single Supply Operation
Fast 1µs Settling Time to 16 Bits
Unbuffered Voltage Output Directly Drives 60k Loads
50MHz SPI/QSPI/MICROWIRE Compatible
Serial Interface
n Power-On Reset Clears DAC Output to Zero Scale
(LTC2641) or Midscale (LTC2642)
n Schmitt-Trigger Inputs for Direct Optocoupler
Interface
n Asynchronous CLR Pin
n 8-Lead MSOP and 3mm × 3mm DFN Packages
(LTC2641)
n 10-Lead MSOP and 3mm × 3mm DFN Packages
(LTC2642)
The LTC®2641/LTC2642 are families of 16-, 14- and 12‑bit
unbuffered voltage output DACs. These DACs operate from
a single 2.7V to 5.5V supply and are guaranteed monotonic over temperature. The LTC2641A-16/LTC2642A‑16
provide 16‑bit performance (±1LSB INL and ±1LSB DNL)
over temperature. Unbuffered DAC outputs result in low
supply current of 120µA and a low offset error of ±1LSB.
n
n
n
n
n
n
n
n
n
APPLICATIONS
n
n
n
n
High Resolution Offset and Gain Adjustment
Process Control and Industrial Automation
Automatic Test Equipment
Data Acquisition Systems
Both the LTC2641 and LTC2642 feature a reference input
range of 2V to VDD. VOUT swings from 0V to VREF . For
bipolar operation, the LTC2642 includes matched scaling
resistors for use with an external precision op amp (such
as the LT1678), generating a ±VREF output swing at RFB.
The LTC2641/LTC2642 use a simple SPI/MICROWIRE
compatible 3-wire serial interface which can be operated
at clock rates up to 50MHz and can interface directly
with optocouplers for applications requiring isolation. A
power-on reset circuit clears the LTC2641’s DAC output
to zero scale and the LTC2642’s DAC output to midscale
when power is initially applied. A logic low on the CLR pin
asynchronously clears the DAC to zero scale (LTC2641)
or midscale (LTC2642). These DACs are all specified over
the commercial and industrial ranges.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
SoftSpan is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
TYPICAL APPLICATION
Bipolar 16-Bit DAC
LTC2642
0.1µF
VDD
1µF
REF
0.1µF
POWER-ON
RESET
CS
SCLK
DIN
CLR
1.0
VDD = 5V
VREF = 2.5V
±2.5V RANGE
0.8
RFB
INV
16-BIT DAC
LTC2642-16 Integral Nonlinearity
VREF
2V TO VDD
0.6
5pF
–
1/2 LT1678
+
VOUT
0.4
BIPOLAR VOUT
–VREF TO VREF
INL (LSB)
2.7V TO 5.5V
0.2
0
–0.2
–0.4
–0.6
CONTROL
LOGIC
16-BIT DATA LATCH
16-BIT SHIFT REGISTER
INL 25°C
INL 90°C
INL –45°C
–0.8
–1.0
GND
26412 TA01a
0
16384
32768
CODE
49152
65535
26412 TA01b
26412fd
For more information www.linear.com/LTC2641
1
LTC2641/LTC2642
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VDD to GND................................................... –0.3V to 6V
CS, SCLK, DIN,
CLR to GND..........................–0.3V to (VDD + 0.3V) or 6V
REF, VOUT, INV to GND.........–0.3V to (VDD + 0.3V) or 6V
RFB to INV........................................................ –6V to 6V
RFB to GND...................................................... –6V to 6V
GND to GND (S8 Package) OBSOLETE ..... –0.3V to 0.3V
Operating Temperature Range
LTC2641C/LTC2642C................................ 0°C to 70°C
LTC2641I/LTC2642I..............................–40°C to 85°C
Maximum Junction Temperature (Note 2)............. 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................... 300°C
PIN CONFIGURATION
LTC2641
LTC2641
LTC2641
TOP VIEW
REF 1
CS 2
SCLK 3
9
DIN 4
TOP VIEW
8
GND
7
VDD
6
VOUT
5
TOP VIEW
REF
CS
SCLK
DIN
CLR
1
2
3
4
8
7
6
5
GND
VDD
VOUT
CLR
VOUT 1
8
VDD
GND 2
7
GND
REF 3
6
DIN
CS 4
5
SCLK
MS8 PACKAGE
8-LEAD PLASTIC MSOP
DD PACKAGE
8-LEAD (3mm × 3mm) PLASTIC DFN
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 125°C (NOTE 2), θJA = 120°C/W
TJMAX = 125°C, θJA = 110°C/W
TJMAX = 125°C (NOTE 2), θJA = 43°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
OBSOLETE PACKAGE
LTC2642
LTC2642
TOP VIEW
REF
1
10 GND
CS
2
9 VDD
SCLK
3
DIN
4
8 RFB
7 INV
CLR
5
6 VOUT
11
TOP VIEW
REF
CS
SCLK
DIN
CLR
1
2
3
4
5
10
9
8
7
6
GND
VDD
RFB
INV
VOUT
MS PACKAGE
10-LEAD PLASTIC MSOP
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C (NOTE 2), θJA = 43°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
TJMAX = 125°C (NOTE 2), θJA = 120°C/W
26412fd
2
For more information www.linear.com/LTC2641
LTC2641/LTC2642
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2641ACDD-16#PBF
LTC2641ACDD-16#TRPBF
LCZP
8-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2641CDD-16#PBF
LTC2641CDD-16#TRPBF
LCZP
8-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2641CDD-14#PBF
LTC2641CDD-14#TRPBF
LCZN
8-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2641CDD-12#PBF
LTC2641CDD-12#TRPBF
LCZM
8-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2641AIDD-16#PBF
LTC2641AIDD-16#TRPBF
LCZP
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2641IDD-16#PBF
LTC2641IDD-16#TRPBF
LCZP
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2641IDD-14#PBF
LTC2641IDD-14#TRPBF
LCZN
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2641IDD-12#PBF
LTC2641IDD-12#TRPBF
LCZM
8-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2641ACMS8-16#PBF
LTC2641ACMS8-16#TRPBF LTCZS
8-Lead Plastic MSOP
0°C to 70°C
LTC2641CMS8-16#PBF
LTC2641CMS8-16#TRPBF
LTCZS
8-Lead Plastic MSOP
0°C to 70°C
LTC2641CMS8-14#PBF
LTC2641CMS8-14#TRPBF
LTCZR
8-Lead Plastic MSOP
0°C to 70°C
LTC2641CMS8-12#PBF
LTC2641CMS8-12#TRPBF
LTCZQ
8-Lead Plastic MSOP
0°C to 70°C
LTC2641AIMS8-16#PBF
LTC2641AIMS8-16#TRPBF
LTCZS
8-Lead Plastic MSOP
–40°C to 85°C
LTC2641IMS8-16#PBF
LTC2641IMS8-16#TRPBF
LTCZS
8-Lead Plastic MSOP
–40°C to 85°C
LTC2641IMS8-14#PBF
LTC2641IMS8-14#TRPBF
LTCZR
8-Lead Plastic MSOP
–40°C to 85°C
LTC2641IMS8-12#PBF
LTC2641IMS8-12#TRPBF
LTCZQ
8-Lead Plastic MSOP
–40°C to 85°C
LTC2642ACDD-16#PBF
LTC2642ACDD-16#TRPBF
LCZW
10-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2642CDD-16#PBF
LTC2642CDD-16#TRPBF
LCZW
10-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2642CDD-14#PBF
LTC2642CDD-14#TRPBF
LCZV
10-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2642CDD-12#PBF
LTC2642CDD-12#TRPBF
LCZT
10-Lead (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC2642AIDD-16#PBF
LTC2642AIDD-16#TRPBF
LCZW
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2642IDD-16#PBF
LTC2642IDD-16#TRPBF
LCZW
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2642IDD-14#PBF
LTC2642IDD-14#TRPBF
LCZV
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2642IDD-12#PBF
LTC2642IDD-12#TRPBF
LCZT
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC2642ACMS-16#PBF
LTC2642ACMS-16#TRPBF
LTCZZ
10-Lead Plastic MSOP
0°C to 70°C
LTC2642CMS-16#PBF
LTC2642CMS-16#TRPBF
LTCZZ
10-Lead Plastic MSOP
0°C to 70°C
LTC2642CMS-14#PBF
LTC2642CMS-14#TRPBF
LTCZY
10-Lead Plastic MSOP
0°C to 70°C
LTC2642CMS-12#PBF
LTC2642CMS-12#TRPBF
LTCZX
10-Lead Plastic MSOP
0°C to 70°C
LTC2642AIMS-16#PBF
LTC2642AIMS-16#TRPBF
LTCZZ
10-Lead Plastic MSOP
–40°C to 85°C
LTC2642IMS-16#PBF
LTC2642IMS-16#TRPBF
LTCZZ
10-Lead Plastic MSOP
–40°C to 85°C
LTC2642IMS-14#PBF
LTC2642IMS-14#TRPBF
LTCZY
10-Lead Plastic MSOP
–40°C to 85°C
LTC2642IMS-12#PBF
LTC2642IMS-12#TRPBF
LTCZX
10-Lead Plastic MSOP
–40°C to 85°C
LTC2641CS8-16#PBF
LTC2641CS8-16#TRPBF
264116
8-Lead Plastic SO
0°C to 70°C
LTC2641IS8-16#PBF
LTC2641IS8-16#TRPBF
264116
8-Lead Plastic SO
–40°C to 85°C
OBSOLETE
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
26412fd
For more information www.linear.com/LTC2641
3
LTC2641/LTC2642
ELECTRICAL
CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VDD = 3V or 5V, VREF = 2.5V, CL = 10pF, GND = 0, RL = ∞ unless
otherwise specified.
LTC2641-12
LTC2642-12
SYMBOL PARAMETER
CONDITIONS
LTC2641-14
LTC2642-14
LTC2641-16
LTC2642-16
MIN TYP MAX MIN TYP MAX MIN TYP
MAX
LTC2641A-16
LTC2642A-16
MIN TYP
MAX
UNITS
Static Performance
N
Resolution
l
12
14
16
16
Bits
Monotonicity
l
12
14
16
16
Bits
DNL
Differential Nonlinearity
(Note 3)
l
±0.5
±0.5
±1
±0.5
±1
±0.5
±1
LSB
INL
Integral Nonlinearity
(Note 3)
l
±0.5
±0.5
±1
±0.5
±2
±0.5
±1
LSB
ZSE
Zero Code Offset Error
Code = 0
l
1
2
LSB
ZSTC
Zero Code Tempco
GE
Gain Error
±0.05
GETC
Gain Error Tempco
ROUT
DAC Output Resistance
(Note 4)
Bipolar Resistor Matching
(LTC2642) RFB/RINV
l
±0.5
Bipolar Zero Offset Error
(LTC2642)
BZSTC
Bipolar Zero Tempco
(LTC2642)
PSR
Power Supply Rejection
ΔVDD = ±10%
l
±0.05
±2
±1
2
±0.05
±4
±2
±0.05
±5
±2
ppm/°C
±5
LSB
±0.1
±0.1
±0.1
±0.1
ppm/°C
6.2
6.2
6.2
6.2
kΩ
1
1
1
1
±0.1
Ratio Error (Note 7) l
BZE
2
±0.5
±2
±0.1
±0.03
±0.5
±0.1
±0.5
l
±0.015
±4
±2
±0.015
±5
±2
±0.1
±0.5
±0.1
±1
%
±5
LSB
ppm/°C
±1
LSB
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VDD = 3V or 5V, VREF = 2.5V, CL = 10pF, GND = 0, RL = ∞ unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
VDD
V
Reference Input
VREF
Reference Input Range
RREF
Reference Input Resistance (Note 5)
Unipolar Mode (LTC2641)
Bipolar Mode (LTC2642)
l
2.0
l
l
11
8.5
14.8
11.4
kΩ
kΩ
15
V/µs
Dynamic Performance—VOUT
SR
Voltage Output Slew Rate
Measured from 10% to 90%
Output Settling Time
To ±0.5LSB of FS
DAC Glitch Impulse
Major Carry Transition
0.5
nV•s
Digital Feedthrough
Code = 0000hex; NCS = VDD;
SCLK, DIN 0V to VDD Levels
0.2
nV•s
10
nV/√Hz
1.3
MHz
1
Output Voltage Noise Density
µs
Dynamic Performance—Reference Input
BW
Reference –3dB Bandwidth
Code = FFFFhex
Reference Feedthrough
Code = 0000hex, VREF = 1VP-P at 100kHz
SNR
Signal-to-Noise Ratio
CIN(REF)
Reference Input Capacitance
Code = 0000hex
Code = FFFFhex
Digital Input High Voltage
VCC = 3.6V to 5.5V
VCC = 2.7V to 3.6V
1
mVP-P
92
dB
75
120
pF
pF
Digital Inputs
VIH
l
l
2.4
2.0
V
V
26412fd
4
For more information www.linear.com/LTC2641
LTC2641/LTC2642
ELECTRICAL
CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VDD = 3V or 5V, VREF = 2.5V, CL = 10pF, GND = 0, RL = ∞ unless
otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
VIL
Digital Input Low Voltage
VCC = 4.5V to 5.5V
VCC = 2.7V to 4.5V
l
l
0.8
0.6
V
V
IIN
Digital Input Current
VIN = GND to VDD
l
±1
µA
CIN
Digital Input Capacitance
(Note 6)
l
10
pF
VH
Hysteresis Voltage
3
MAX
UNITS
0.15
V
Power Supply
VDD
Supply Voltage
IDD
Supply Current, VDD
Digital Inputs = 0V or VDD
PD
Power Dissipation
Digital Inputs = 0V or VDD, VDD = 5V
Digital Inputs = 0V or VDD, VDD = 3V
l
2.7
120
l
5.5
V
200
µA
0.60
0.36
mW
mW
TIMING
CHARACTERISTICS
The l denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. VDD = 3V or 5V, VREF = 2.5V, CL = 10pF, GND = 0, RL = ∞ unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
t1
DIN Valid to SCLK Setup Time
l
10
ns
t2
DIN Valid to SCLK Hold Time
l
0
ns
t3
SCLK Pulse Width High
l
9
ns
t4
SCLK Pulse Width Low
l
9
ns
t5
CS Pulse High Width
l
10
ns
t6
LSB SCLK High to CS High
l
8
ns
t7
CS Low to SCLK High
l
8
ns
t8
CS High to SCLK Positive Edge
l
8
ns
t9
CLR Pulse Width Low
l
15
fSCLK
SCLK Frequency
50% Duty Cycle
VDD High to CS Low (Power-Up Delay)
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Continuous operation above the specified maximum operating
junction temperature may impair device reliability.
Note 3: LTC2641-16/LTC2642-16 ±1LSB = ±0.0015% = ±15.3ppm of full
scale. LTC2641-14/LTC2642-14 ±1LSB = ±0.006% = ±61ppm of full scale.
LTC2641-12/LTC2642-12 ±1LSB = ±0.024% = ±244ppm of full scale.
ns
50
l
MHz
30
µs
Note 4: ROUT tolerance is typically ±20%.
Note 5: Reference input resistance is code dependent. Minimum is at
871Chex (34,588) in unipolar mode and at 671Chex (26, 396) in bipolar
mode.
Note 6: Guaranteed by design and not production tested.
Note 7: Guaranteed by gain error and offset error testing, not production
tested.
26412fd
For more information www.linear.com/LTC2641
5
LTC2641/LTC2642
TYPICAL PERFORMANCE CHARACTERISTICS
Integral Nonlinearity (INL)
vs Supply (VDD)
Integral Nonlinearity (INL)
LTC2642-16
VREF = 2.5V
VDD = 5V
0.8
0.6
INL vs VREF
1.0
VREF = 2.5V
0.8
0.4
0.2
0.2
0
–0.2
0.6
+INL
0
–INL
–0.2
–0.6
–0.6
–0.6
–0.8
–0.8
–0.8
–1.0
–1.0
–1.0
32768
CODE
65535
49152
3
2
4
VDD (V)
6
5
1.0
1.0
VREF = 2.5V
0.8
0.6
0.4
0.4
0.2
0.2
DNL (LSB)
DNL (LSB)
–0.2
+DNL
0
–DNL
–0.2
0.2
–0.4
–0.4
–0.6
–0.6
–0.8
–0.8
–0.8
–1.0
–1.0
–1.0
32768
CODE
49152
65535
3
2
4
VDD (V)
6
5
INL vs Temperature
DNL vs Temperature
1.0
VREF = 2.5V
VDD = 5V
0.8
+INL
VREF = 2.5V
VDD = 5V
4
DNL (LSB)
0
–INL
–0.2
2
0.2
+DNL
0
–DNL
–0.2
1
0
–1
–0.4
–0.4
–2
–0.6
–0.6
–3
–0.8
–0.8
–4
–1.0
–40
–1.0
–40
–15
35
10
TEMPERATURE (°C)
60
85
26412 G07
VREF = 2.5V
VDD = 5V
3
0.4
0.2
6
5
Bipolar Zero Error vs Temperature
5
0.6
0.6
0.4
4
VREF (V)
26412 G06
BZE (LSB)
0.8
3
2
26412 G05
26412 G04
1.0
–DNL
–0.2
–0.6
16384
+DNL
0
–0.4
0
VDD = 5.5V
0.8
0.6
0
6
5
DNL vs VREF
1.0
0.4
0.6
4
VREF (V)
3
2
26412 G03
Differential Nonlinearity (DNL)
vs Supply (VDD)
LTC2642-16
VREF = 2.5V
VDD = 5V
0.8
–INL
26412 G02
Differential Nonlinearity (DNL)
DNL (LSB)
0
–0.2
–0.4
26412 G01
INL (LSB)
0.2
–0.4
16384
+INL
0.4
–0.4
0
VDD = 5.5V
0.8
0.6
0.4
INL (LSB)
INL (LSB)
1.0
INL (LSB)
1.0
–15
35
10
TEMPERATURE (°C)
60
85
26412 G08
–5
–40
–15
35
10
TEMPERATURE (°C)
60
85
26412 G09
26412fd
6
For more information www.linear.com/LTC2641
LTC2641/LTC2642
TYPICAL PERFORMANCE CHARACTERISTICS
Unbuffered Zero Scale Error vs
Temperature (LTC2641-16)
Bipolar Gain Error vs Temperature
5
VREF = 2.5V
VDD = 5V
1.0
0.8
0.6
0.6
2
0.4
0.4
1
0.2
0.2
0
–1
FSE (LSB)
0.8
ZSE (LSB)
BGE (LSB)
1.0
3
4
0
–0.2
–0.4
–0.4
–3
–0.6
–0.6
–4
–0.8
–0.8
–5
–40
–1.0
–40
–15
35
10
TEMPERATURE (°C)
60
85
–15
35
10
TEMPERATURE (°C)
60
14-Bit Differential Nonlinearity
(DNL) (LTC2642-14)
1.0
LTC2642-14
VREF = 2.5V
VDD = 5V
0.8
0.6
0.6
0.4
0.2
DNL (LSB)
0.4
0.2
–0.2
–0.2
–0.4
–0.6
–0.6
–0.8
–0.8
0
4096
8192
CODE
12288
–1.0
16383
0
4096
8192
CODE
1.0
0.6
0.4
0.2
DNL (LSB)
0.4
0.2
–0.2
–0.6
–0.6
–0.8
–0.8
1024
2048
CODE
3072
4095
26412 G16
32768
49152
–1.0
65535
IREF vs Code (Bipolar LTC2642)
VREF = 2.5V
200
–0.2
–0.4
0
16384
26412 G15
250
0
–0.4
–1.0
0
CODE
LTC2642-12
VREF = 2.5V
VDD = 5V
0.8
0
100
0
16383
12288
IREF (µA)
0.6
150
12-Bit Differential Nonlinearity
(DNL) (LTC2642-12)
LTC2642-12
VREF = 2.5V
VDD = 5V
0.8
VREF = 2.5V
26412 G14
12-Bit Integral Nonlinearity (INL)
(LTC2642-12)
85
50
26412 G13
1.0
60
200
0
–0.4
–1.0
35
10
TEMPERATURE (°C)
IREF vs Code (Unipolar LTC2641)
250
LTC2642-14
VREF = 2.5V
VDD = 5V
0.8
0
–15
26412 G12
IREF (µA)
1.0
–1.0
–40
85
26412 G11
14-Bit Integral Nonlinearity (INL)
(LTC2642-14)
INL (LSB)
0
–0.2
–2
26412 G10
INL (LSB)
Unbuffered Full-Scale Error vs
Temperature (LTC2641-16)
150
100
50
0
1024
2048
CODE
3072
4095
0
0
16384
32768
49152
65535
CODE
26412 G17
26412 G18
26412fd
For more information www.linear.com/LTC2641
7
LTC2641/LTC2642
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current (IDD) vs
Temperature
150
VREF = 2.5V
125
800
700
75
50
75
–15
10
35
TEMPERATURE (°C)
0
85
60
2.5
3.5
3
4
4.5
5
150
100
IDD (µA)
100
IDD (µA)
125
75
50
25
25
2.5
3
3.5
4
4.5
5
0
VREF (V)
1.5
2
VREF (V)
2.5
3
26412 G25
CODE
32768
500ns/DIV
CODE
32767
26412 G24
VOUT vs VDD = 0V to 5.5V
(POR Function) LTC2641
VDD = VREF
0V TO 5.5V
2V/DIV
SETTLE
RESIDUE
250µV/DIV
500ns/DIV
LTC2641-16
UNBUFFERED
CL = 10pF
Full-Scale Settling (Zoomed In)
CS
5V/DIV
LTC2641-16
UNBUFFERED
CL = 10pF
VREF = 2.5V
VDD = 5V
CODE
32767
VOUT
20mV/DIV
1
5
26412 G23
Full-Scale Transition
VOUT
1V/DIV
1 1.5 2 2.5 3 3.5 4 4.5
DIGITAL INPUT VOLTAGE (V)
CS
5V/DIV
VDD = 3V
26412 G22
CS
5V/DIV
0.5
Midscale Glitch Impulse
75
50
2
0
26412 G21
Supply Current (IDD) vs VREF ,
VDD = 3V
125
1.5
0
26412 G20
VDD = 5V
1
5.5
VDD (V)
Supply Current (IDD) vs VREF ,
VDD = 5V
0
VDD = 3V
100
26412 G19
150
400
200
25
0
–40
500
300
50
25
VDD = 5V
600
100
VDD = 3V
IDD (µA)
IDD (µA)
900
VREF = 2.5V
125
VDD = 5V
100
Supply Current (IDD) vs Digital
Input Voltage
IDD (µA)
150
Supply Current (IDD) vs Supply
Voltage (VDD)
VOUT
10mV/DIV
LTC2641-16
500ns/DIV
VREF = 2.5V
CONSULT FACTORY FOR
MEASUREMENT CIRCUIT
26412 G26
LTC2641-16
UNBUFFERED
CL = 10pF
50ms/DIV
26412 G27
26412fd
8
For more information www.linear.com/LTC2641
LTC2641/LTC2642
PIN FUNCTIONS
LTC2641 – MSOP, DFN Packages
REF (Pin 1): Reference Voltage Input. Apply an external
reference at REF between 2V and VDD.
CS (Pin 2): Serial Interface Chip Select/Load Input. When
CS is low, SCLK is enabled for shifting in data on DIN.
When CS is taken high, SCLK is disabled, the 16-bit input
word is latched and the DAC is updated.
SCLK (Pin 3): Serial Interface Clock Input. CMOS and
TTL compatible.
DIN (Pin 4): Serial Interface Data Input. Data is applied to
DIN for transfer to the device at the rising edge of SCLK.
CLR (Pin 5): Asynchronous Clear Input. A logic low clears
the DAC to code 0.
VOUT (Pin 6): DAC Output Voltage. The output range is
0V to VREF .
VDD (Pin 7): Supply Voltage. Set between 2.7V and 5.5V.
GND (Pin 8): Circuit Ground.
Exposed Pad (DFN Pin 9): Circuit Ground. Must be soldered to PCB ground.
LTC2641 – SO Package OBSOLETE
VOUT (Pin 1): DAC Output Voltage. The output range is
0V to VREF.
GND (Pin 2): Circuit Ground.
REF (Pin 3): Reference Voltage Input. Apply an external
reference at REF between 2V and VDD.
CS (Pin 4): Serial Interface Chip Select/Load Input. When
CS is low, SCLK is enabled for shifting in data on DIN.
When CS is taken high, SCLK is disabled, the 16-bit input
word is latched and the DAC is updated.
GND (Pin 7): Circuit Ground Pin. Must be connected to
Pin 2 (GND).
VDD (Pin 8): Supply Voltage. Set between 2.7V and 5.5V.
LTC2642 – MSOP, DFN Packages
REF (Pin 1): Reference Voltage Input. Apply an external
reference at REF between 2V and VDD.
CS (Pin 2): Serial Interface Chip Select/Load Input. When
CS is low, SCLK is enabled for shifting in data on DIN.
When CS is taken high, SCLK is disabled, the 16-bit input
word is latched and the DAC is updated.
SCLK (Pin 3): Serial Interface Clock Input. CMOS and
TTL compatible.
DIN (Pin 4): Serial Interface Data Input. Data is applied to
DIN for transfer to the device at the rising edge of SCLK.
CLR (Pin 5): Asynchronous Clear Input. A logic low clears
the DAC to midscale.
VOUT (Pin 6): DAC Output Voltage. The output range is
0V to VREF .
INV (Pin 7): Center Tap of Internal Scaling Resistors.
Connect to an external amplifier’s inverting input in bipolar mode.
RFB (Pin 8): Feedback Resistor. Connect to an external
amplifier’s output in bipolar mode. The bipolar output
range is –VREF to VREF .
VDD (Pin 9): Supply Voltage. Set between 2.7V and 5.5V.
GND (Pin 10): Circuit Ground.
Exposed Pad (DFN Pin 11): Circuit Ground. Must be
soldered to PCB ground.
SCLK (Pin 5): Serial Interface Clock Input. CMOS and
TTL compatible.
DIN (Pin 6): Serial Interface Data Input. Data is applied to
DIN for transfer to the device at the rising edge of SCLK.
26412fd
For more information www.linear.com/LTC2641
9
LTC2641/LTC2642
BLOCK DIAGRAMS
LTC2641 - SO
OBSOLETE PACKAGE
LTC2641 - MSOP, DFN
7
VDD
1
8
REF
LTC2641-16
LTC2641-14
LTC2641-12
POWER-ON
RESET
2
3
4
5
DIN
16-/14-/12-BIT DAC
VOUT
6
CLR
4
CONTROL
LOGIC
REF
LTC2641-16
CS
SCLK
3
VDD
5
16-BIT DATA LATCH
6
16-BIT SHIFT REGISTER
GND
7
8
POWER-ON
RESET
16-/14-/12-BIT DAC
CONTROL
LOGIC
16-BIT DATA LATCH
VOUT
1
CS
SCLK
DIN
GND
16-BIT SHIFT REGISTER
2641 BD01a
GND
2
2641 BD01b
LTC2642
9
VDD
1
REF
RFB
LTC2642-16
LTC2642-14
LTC2642-12
2
3
4
5
INV
POWER-ON
RESET
16-/14-/12-BIT DAC
CONTROL
LOGIC
16-BIT DATA LATCH
VOUT
8
7
6
CS
SCLK
DIN
CLR
16-BIT SHIFT REGISTER
GND
10
2642 BD
26412fd
10
For more information www.linear.com/LTC2641
LTC2641/LTC2642
TIMING DIAGRAM
t1
t2
t3
1
SCK
2
t4
t6
3
15
16
t8
SDI
t5
t7
26412 TD
CS/LD
OPERATION
General Description
The digital-to-analog transfer function at the VOUT pin is:
The LTC2641/LTC2642 family of 16-/14-/12-bit voltage
output DACs offer full 16-bit performance with less than
±1LSB integral linearity error and less than ±1LSB differential linearity error, guaranteeing monotonic operation.
They operate from a single supply ranging from 2.7V to
5.5V, consuming 120µA (typical). An external voltage
reference of 2V to VDD determines the DAC’s full-scale
output voltage. A 3-wire serial interface allows the LTC2641/
LTC2642 to fit into a small 8-/10-pin MSOP or DFN 3mm
× 3mm package.
k
VOUT(IDEAL) = VREF
2N
Digital-to-Analog Architecture
The DAC architecture is a voltage switching mode resistor ladder using precision thin-film resistors and CMOS
switches. The LTC2641/LTC2642 DAC resistor ladders are
composed of a proprietary arrangement of matched DAC
sections. The four MSBs are decoded to drive 15 equally
weighted segments, and the remaining lower bits drive
successively lower weighted sections. Major carry glitch
impulse is very low at 500pV•sec, CL = 10pF, ten times
lower than previous DACs of this type.
where k is the decimal equivalent of the binary DAC input
code, N is the resolution, and VREF is between 2.0V and
VDD (see Tables 1a, 1b and 1c).
The LTC2642 includes matched resistors that are tied
to an external amplifier to provide bipolar output swing
(Figure 2). The bipolar transfer function at the RFB pin is:
k
VOUT _BIPOLAR(IDEAL) = VREF
– 1
2N–1
(see Tables 2a, 2b and 2c).
Serial Interface
The LTC2641/LTC2642 communicates via a standard
3‑wire SPI/QSPI/MICROWIRE compatible interface. The
chip select input (CS) controls and frames the loading of
serial data from the data input (DIN). Following a CS highto-low transition, the data on DIN is loaded, MSB first, into
the shift register on each rising edge of the serial clock
26412fd
For more information www.linear.com/LTC2641
11
LTC2641/LTC2642
OPERATION
input (SCLK). After 16 data bits have been loaded into the
serial input register, a low-to-high transition on CS transfers the data to the 16-bit DAC latch, updating the DAC
output (see Figures 1a, 1b, 1c). While CS remains high,
the serial input shift register is disabled. If there are less
than 16 low-to-high transitions on SCLK while CS remains
low, the data will be corrupted, and must be reloaded.
Also, if there are more than 16 low-to-high transitions
on SCLK while CS remains low, only the last 16 data bits
loaded from DIN will be transferred to the DAC latch. For
the 14-bit DACs, (LTC2641-14/LTC2642-14), the MSB
remains in the same (left-justified) position in the input
16-bit data word. Therefore, two “don’t-care” bits must
be loaded after the LSB, to make up the required 16 data
bits (Figure 1b). Similarly, for the 12-bit family members
(LTC2641-12/LTC2642-12) four “don’t-care” bits must
follow the LSB (Figure 1c).
Power-On Reset
The LTC2641/LTC2642 include a power-on reset circuit
to ensure that the DAC output comes up in a known
state. When VDD is first applied, the power-on reset circuit sets the output of the LTC2641 to zero-scale (code
0). The LTC2642 powers up to midscale (bipolar zero).
Depending on the DAC number of bits, the midscale code
is: 32,768 (LTC2642-16); 8,192 (LTC2642-14); or 2,048
(LTC2642-12).
Clearing the DAC
A low pulse meeting the t9 (minimum) specification on
the CLR pin asynchronously clears the DAC latch to code
zero (LTC2641) or to midscale (LTC2642).
CS
SCLK
DIN
1
2
3
4
5
6
D15 D14 D13 D12 D11 D10
7
D9
8
D8
9
D7
10
D6
11
D5
12
D4
13
D3
14
D2
15
D1
MSB
16
DAC
UPDATED
D0
LSB
26412 F01a
DATA (16 BITS)
Figure 1a. 16-Bit Timing Diagram (LTC2641-16/LTC2642-16)
CS
SCLK
DIN
1
2
3
4
D13 D12 D11 D10
5
D9
6
D8
7
D7
8
D6
9
D5
10
D4
11
D3
12
D2
13
D1
MSB
14
D0
15
X
16
DAC
UPDATED
X
LSB
26412 F01b
DATA (14 BITS + 2 DON’T-CARE BITS)
Figure 1b. 14-Bit Timing Diagram (LTC2641-14/LTC2642-14)
CS
SCLK
DIN
1
2
D11 D10
3
D9
4
D8
5
D7
6
D6
7
D5
8
D4
9
D3
10
D2
11
D1
MSB
12
D0
13
X
14
X
15
X
LSB
16
DAC
UPDATED
X
26412 F01c
DATA (12 BITS + 4 DON’T-CARE BITS)
Figure 1c. 12-Bit Timing Diagram (LTC2641-12/LTC2642-12)
26412fd
12
For more information www.linear.com/LTC2641
LTC2641/LTC2642
APPLICATIONS INFORMATION
Unipolar Configuration
The external amplifier provides a unity-gain buffer. The
LTC2642 can also be used in unipolar configuration by
tying RFB and INV to REF . This provides power-up and
clear to midscale.
Figure 2 shows a typical unipolar DAC application for
the LTC2641. Tables 1a, 1b and 1c show the unipolar
binary code tables for 16-bit, 14-bit and 12-bit operation.
VREF
2.5V
0.1µF
5V/3V
4.7µF
OUT
IN
5V
Table 1a. 16-Bit Unipolar Binary Code Table
(LTC2641-16)
LT®1019CS8-2.5
GND
DIGITAL INPUT
BINARY NUMBER
IN DAC LATCH
0.1µF
7
VDD
5V/3V 0.1µF
1
REF
–
MSB
1/2 LTC6078
1111 1111 1111 1111 VREF (65,535/65,536)
1000 0000 0000 0000 VREF (32,768/65,536) = VREF/2
LTC2641-16
2
16-BIT DAC
CS
3
SCLK
4
DIN
5
CLR
VOUT 6
ANALOG OUTPUT
(VOUT)
+
UNIPOLAR VOUT
0V TO 2.5V
LSB
0000 0000 0000 0001 VREF (1/65,536)
0000 0000 0000 0000 0V
GND
26412 F02
8
Figure 2. 16-Bit Unipolar Output (LTC2641-16) Unipolar VOUT = 0V to VREF
Table 1b. 14-Bit Unipolar Binary Code Table
(LTC2641-14)
DIGITAL INPUT
BINARY NUMBER
IN DAC LATCH
MSB
ANALOG OUTPUT
(VOUT)
LSB
Table 1c. 12-Bit Unipolar Binary Code Table
(LTC2641-12)
DIGITAL INPUT
BINARY NUMBER
IN DAC LATCH
MSB
ANALOG OUTPUT
(VOUT)
LSB
1111 1111 1111 11xx VREF (16,383/16,384)
1111 1111 1111 xxxx VREF (4,095/4,096)
1000 0000 0000 00xx VREF (8,192/16,384) = VREF/2
1000 0000 0000 xxxx VREF (2,048/4,096) = VREF/2
0000 0000 0000 01xx VREF (1/16,384)
0000 0000 0001 xxxx VREF (1/4,096)
0000 0000 0000 00xx 0V
0000 0000 0000 xxxx 0V
26412fd
For more information www.linear.com/LTC2641
13
LTC2641/LTC2642
APPLICATIONS INFORMATION
Bipolar Configuration
The amplifier circuit provides a gain of +2 from the VOUT
pin, and gain of –1 from VREF . Tables 2a, 2b and 2c show
the bipolar offset binary code tables for 16-bit, 14-bit and
12-bit operation.
Figure 3 shows a typical bipolar DAC application for the
LTC2642. The on-chip bipolar offset/gain resistors, RFB
and RINV , are connected to an external amplifier to produce
a bipolar output swing from –VREF to VREF at the RFB pin.
VREF
2.5V
5V/3V
0.1µF
0.1µF
9
VDD
OUT
4.7µF
RFB 8
C1
10pF
LTC2642-16
INV 7
2
16-BIT DAC
CS
3
SCLK
4
DIN
5
CLR
5V
GND
1
REF
IN
LT1019CS8-2.5
5V
0.1µF
–
1/2 LT1678
+
VOUT 6
0.1µF
BIPOLAR VOUT
–2.5V TO 2.5V
–5V
GND
26412 F02
10
Figure 3. 16-Bit Bipolar Output (LTC2642-16) VOUT = –VREF to VREF
Table 2a. 16-Bit Bipolar Offset Binary
Code Table (LTC2642-16)
DIGITAL INPUT
BINARY NUMBER
IN DAC LATCH
MSB
ANALOG OUTPUT
(VOUT)
LSB
Table 2b. 14-Bit Bipolar Offset Binary
Code Table (LTC2642-14)
DIGITAL INPUT
BINARY NUMBER
IN DAC LATCH
MSB
ANALOG OUTPUT
(VOUT)
LSB
Table 2c. 12-Bit Bipolar Offset Binary
Code Table (LTC2642-12)
DIGITAL INPUT
BINARY NUMBER
IN DAC LATCH
MSB
ANALOG OUTPUT
(VOUT)
LSB
1111 1111 1111 1111 VREF (32,767/32,768)
1111 1111 1111 11xx VREF (8,191/8,192)
1111 1111 1111 xxxx VREF (2,047/2,048)
1000 0000 0000 0001 VREF (1/32,768)
1000 0000 0000 01xx VREF (1/8,192)
1000 0000 0001 xxxx VREF (1/2,048)
1000 0000 0000 0000 0V
1000 0000 0000 00xx 0V
1000 0000 0000 xxxx 0V
0111 1111 1111 1111 –VREF (1/32,768)
0000 0000 0000 0000 –VREF
0111 1111 1111 11xx –VREF (1/8,192)
0000 0000 0000 00xx –VREF
0111 1111 1111 xxxx –VREF (1/2048)
0000 0000 0000 xxxx –VREF
26412fd
14
For more information www.linear.com/LTC2641
LTC2641/LTC2642
APPLICATIONS INFORMATION
Unbuffered Operation and VOUT Loading
Unbuffered VOUT Settling Time
The DAC output is available directly at the VOUT pin, which
swings from GND to VREF . Unbuffered operation provides
the lowest possible offset, full-scale and linearity errors,
the fastest settling time and minimum power consumption.
The settling time at the VOUT pin can be closely approximated by a single-pole response where:
However, unbuffered operation requires that appropriate
loading be maintained on the VOUT pin. The LTC2641/
LTC2642 VOUT can be modeled as an ideal voltage source
in series with a source resistance of ROUT , typically 6.2k
(Figure 4). The DAC’s linear output impedance allows it to
drive medium loads (RL > 60k) without degrading INL or
DNL; only the gain error is increased. The gain error (GE)
caused by a load resistance, RL, (relative to full scale) is:
GE =
–1
R
1+ OUT
RL
t = ROUT • (COUT + CL)
(Figure 4). Settling to 1/2LSB at 16-bits requires about
12 time constants (ln(2 • 65,536)). The typical settling
time of 1µs corresponds to a time constant of 83ns, and
a total (COUT + CL) of about 83ns/6.2k = 13pF . The internal
capacitance, COUT is typically 10pF, so an external CL of
3pF corresponds to 1µs settling to 1/2LSB.
VREF
LTC2641
LTC2642
+
( )–
CODE
VREF
2N
REF
ROUT
VOUT
COUT
GND
RL
CL
IL
VOUT
0V TO VREF
26412 F04
In 16-bit LSBs:
GE =
Figure 4. VOUT Pin Equivalent Circuit
–65536
LSB
R
OUT
1+
RL
Op Amp Selection
ROUT has a low tempco (typically < ±50ppm/°C), and is
independent of DAC code. The variation of ROUT, part-topart, is typically less than ±20%.
Note on LSB units:
For the following error descriptions, “LSB” means 16-bit
LSB and 65,536 is rounded to 66k.
To convert to 14-bit LSBs (LTC2641-14/LTC2642-14)
divide by 4.
To convert to 12-bit LSBs (LTC2641-12/LTC2642-12)
divide by 16.
A constant current, IL, loading VOUT will produce an offset of:
VOFFSET = –IL • ROUT
For VREF = 2.5V, a 16-bit LSB equals 2.5V/65,536, or
38µV. Since ROUT is 6.2k, an IL of 6nA produces an offset
of 1LSB. Therefore, to avoid degrading DAC performance,
it is critical to protect the VOUT pin from any sources of
leakage current.
The optimal choice for an external buffer op amp depends
on whether the DAC is used in the unipolar or bipolar
mode of operation, and also depends on the accuracy,
speed, power dissipation and board area requirements of
the application. The LTC2641/LTC2642’s combination of
tiny package size, rail-to-rail single supply operation, low
power dissipation, fast settling and nearly ideal accuracy
specifications makes it impractical for one op amp type
to fit every application.
In bipolar mode (LTC2642 only), the amplifier operates
with the internal resistors to provide bipolar offset and
scaling. In this case, a precision amplifier operating from
dual power supplies, such as the the LT1678 provides the
±VREF output range (Figure 3).
In unipolar mode, the output amplifier operates as a unity
gain voltage follower. For unipolar, single supply applications a precision, rail-to-rail input, single supply op amp
26412fd
For more information www.linear.com/LTC2641
15
LTC2641/LTC2642
APPLICATIONS INFORMATION
such as the LTC6078 is suitable, if the application does
not require linear operation very near to GND, or zero scale
(Figure 2). The LTC6078 typically swings to within 1mV of
GND if it is not required to sink any load current. For an
LSB size of 38µV, 1mV represents 26 missing codes near
zero scale. Linearity will be degraded over a somewhat
larger range of codes above GND. It is also unavoidable
that settling time and transient performance will degrade
whenever a single supply amplifier is operated very close
to GND, or to the positive supply rail.
voltage temperature coefficient (referenced to 25°C) of
0.6μV/°C will add 1LSB of zero-scale error. Also, IBIAS and
the VOFFSET error it causes, will typically show significant
relative variation over temperature.
The small LSB size of a 16-bit DAC, coupled with the tight
accuracy specifications on the LTC2641/LTC2642, means
that the accuracy and input specifications for the external
op amp are critical for overall DAC performance.
Op amp input common mode rejection ratio (CMRR) is an
input-referred error that corresponds to a combination of
gain error (GE) and INL, depending on the op amp architecture and operating conditions. A conservative estimate
of total CMRR error is:
Op Amp Specifications and Unipolar DAC Accuracy
Most op amp accuracy specifications convert easily to
DAC accuracy.
Op amp input bias current on the noninverting (+) input is
equivalent to an IL loading the DAC VOUT pin and therefore
produces a DAC zero-scale error (ZSE) (see Unbuffered
Operation):
ZSE = –IB(IN+) • ROUT [Volts]
In 16-bit LSBs:
66k
ZSE = –IB IN+ • 6.2k •
LSB
VREF
( )
Op amp input impedance, RIN, is equivalent to an RL
loading the LTC2641/LTC2642 VOUT pin, and produces
a gain error of:
GE =
–66k
LSB
6.2k
1+
RIN
Op amp offset voltage, VOS, corresponds directly to DAC
zero code offset error, ZSE:
ZSE = VOS •
66k
[LSB]
VREF
Temperature effects also must be considered. Over the
–40°C to 85°C industrial temperature range, an offset
16
Op amp open-loop gain, AVOL, contributes to DAC gain
error (GE):
GE =
66k
[LSB]
A VOL
CMRR
V
Error = 10 20 • CMRR _RANGE • 66k LSB
VREF
where VCMRR_RANGE is the voltage range that CMRR (in
dB) is specified over. Op amp Typical Performance Characteristics graphs are useful to predict the impact of CMRR
errors on DAC performance. Typically, a precision op amp
will exhibit a fairly linear CMRR behavior (corresponding
to DAC gain error only) over most of the common mode
input range (CMR), and become nonlinear and produce
significant errors near the edge of the CMR.
Rail-to-rail input op amps are a special case, because they
have 2 distinct input stages, one with CMR to GND and
the other with CMR to V+. This results in a “crossover”
CM input region where operation switches between the
two input stages.
The LTC6078 rail-to-rail input op amp typically exhibits
remarkably low crossover linearity error, as shown in the
VOS vs VCM Typical Performance Characteristics graphs
(see the LTC6078 data sheet). Crossover occurs at CM
inputs about 1V below V+, and an LTC6078 operating as
a unipolar DAC buffer with VREF = 2.5V and V+ = 5V will
typically add only about 1LSB of GE and almost no INL
error due to CMRR. Even in a full rail-to-rail application,
with VREF = V+ = 5V, a typical LTC6078 will add only about
1LSB of INL at 16-bits.
For more information www.linear.com/LTC2641
26412fd
LTC2641/LTC2642
APPLICATIONS INFORMATION
Op Amp Specifications and Bipolar DAC Accuracy
The op amp contributions to unipolar DAC error discussed
above apply equally to bipolar operation. The bipolar application circuit gains up the DAC span, and all errors, by
a factor of 2. Since the LSB size also doubles, the errors
in LSBs are identical in unipolar and bipolar modes.
One added error in bipolar mode comes from IB (IN–),
which flows through RFB to generate an offset. The full
bias current offset error becomes:
VOFFSET = (IB (IN–) • RFB – IB (IN+) • ROUT • 2) [Volts]
So:
(
)
VOFFSET = IB (IN– ) • 28k – IB (IN+ ) • 12.4k •
33k
[LSB]
VREF
Settling Time with Op Amp Buffer
When using an external op amp, the output settling time
will still include the single pole settling on the LTC2641/
LTC2642 VOUT node, with time constant ROUT • (COUT +
CL) (see Unbuffered VOUT Settling Time). CL will include
the buffer input capacitance and PC board interconnect
capacitance.
The external buffer amplifier adds another pole to the output
response, with a time constant equal to (fbandwidth/2π).
For example, assume that CL is maintained at the same
value as above, so that the VOUT node time constant is
83ns = 1μs/12. The output amplifier pole will also have a
time constant of 83ns if the closed-loop bandwidth equals
(1/2π • 83ns) = 1.9MHz. The effective time constant of
two cascaded single-pole sections is approximately the
root square sum of the individual time constants, or √2
• 83ns = 117ns, and 1/2 LSB settling time will be ~12 •
117ns = 1.4μs. This represents an ideal case, with no slew
limiting and ideal op amp phase margin. In practice, it
will take a considerably faster amplifier, as well as careful
attention to maintaining good phase margin, to approach
the unbuffered settling time of 1μs.
The output settling time for bipolar applications (Figure 3) will be somewhat increased due to the feedback
resistor network RFB and RINV (each 28k nominal). The
parasitic capacitance, CP, on the op amp (–) input node
will introduce a feedback loop pole with a time constant
of (CP • 28k/2). A small feedback capacitor, C1, should be
included, to introduce a zero that will partially cancel this
pole. C1 should nominally be
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