LTC2421/LTC2422
1-/2-Channel 20-Bit
µPower
No Latency
∆Σ
TM
ADCs in MSOP-10
FEATURES
s
s
s
s
s
s
DESCRIPTIO
s
s
s
s
s
s
s
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s
s
20-Bit ADCs in Tiny MSOP-10 Packages
1- or 2-Channel Inputs
Single Supply 2.7V to 5.5V Operation
Low Supply Current (200µA) and Auto Shutdown
Automatic Channel Selection (Ping-Pong) (LTC2422)
No Latency: Digital Filter Settles in a
Single Conversion Cycle
8ppm INL, No Missing Codes
4ppm Full-Scale Error
0.5ppm Offset
1.2ppm Noise
Zero Scale and Full Scale Set for Reference
and Ground Sensing
Internal Oscillator—No External Components Required
110dB Min, 50Hz/60Hz Notch Filter
Reference Input Voltage: 0.1V to V
CC
Live Zero—Extended Input Range Accommodates
12.5% Overrange and Underrange
Pin Compatible with LTC2401/LTC2402
The LTC
®
2421/LTC2422 are 1- and 2-channel 2.7V to 5.5V
micropower 20-bit analog-to-digital converters with an
integrated oscillator, 8ppm INL and 1.2ppm RMS noise.
These ultrasmall devices use delta-sigma technology and
a new digital filter architecture that settles in a single cycle.
This eliminates the latency found in conventional
∆Σ
converters and simplifies multiplexed applications.
Through a single pin, the LTC2421/LTC2422 can be
configured for better than 110dB rejection at 50Hz or
60Hz
±2%,
or can be driven by an external oscillator for
a user defined rejection frequency in the range 1Hz to
120Hz. The internal oscillator requires no external fre-
quency setting components.
These converters accept an external reference voltage
from 0.1V to V
CC
. With an extended input conversion
range of –12.5% V
REF
to 112.5% V
REF
(V
REF
= FS
SET
–
ZS
SET
), the LTC2421/LTC2422 smoothly resolve the off-
set and overrange problems of preceding sensors or
signal conditioning circuits.
The LTC2421/LTC2422 communicate through a 2- or
3-wire digital interface that is compatible with SPI and
MICROWIRE
TM
protocols.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No Latency
∆Σ
is a trademark of Linear Technology Corporation.
MICROWIRE is a trademark of National Semiconductor Corporation.
APPLICATIO S
s
s
s
s
s
s
s
Weight Scales
Direct Temperature Measurement
Gas Analyzers
Strain Gauge Transducers
Instrumentation
Data Acquisition
Industrial Process Control
TYPICAL APPLICATIO
2.7V TO 5.5V
1µF
1
V
CC
LTC2422
REFERENCE VOLTAGE
ZS
SET
+ 0.1V TO V
CC
ANALOG INPUT RANGE
ZS
SET
– 0.12V
REF
TO
FS
SET
+ 0.12V
REF
(V
REF
= FS
SET
– ZS
SET
)
0V TO FS
SET
– 100mV
2
3
4
5
FS
SET
CH1
CH0
ZS
SET
SCK
SDO
CS
GND
F
O
Pseudo Differential Bridge Digitizer
2.7V TO 5.5V
V
CC
10
= INTERNAL OSC/50Hz REJECTION
= EXTERNAL CLOCK SOURCE
= INTERNAL OSC/60Hz REJECTION
9
8
7
3-WIRE
SPI INTERFACE
6
24212 TA01
U
1
2
4
3
5
V
CC
LTC2422
FS
SET
9
SCK
CH0
CH1
ZS
SET
GND
6
SDO
CS
F
O
8
7
10
INTERNAL OSCILLATOR
60Hz REJECTION
3-WIRE
SPI INTERFACE
24012TA02
U
U
24212f
1
LTC2421/LTC2422
ABSOLUTE
MAXIMUM
RATINGS
Supply Voltage (V
CC
) to GND .......................– 0.3V to 7V
Analog Input Voltage to GND ....... – 0.3V to (V
CC
+ 0.3V)
Reference Input Voltage to GND .. – 0.3V to (V
CC
+ 0.3V)
Digital Input Voltage to GND ........ – 0.3V to (V
CC
+ 0.3V)
Digital Output Voltage to GND ..... – 0.3V to (V
CC
+ 0.3V)
PACKAGE/ORDER INFORMATION
ORDER PART NUMBER
TOP VIEW
V
CC
FS
SET
V
IN
NC
ZS
SET
1
2
3
4
5
10
9
8
7
6
F
O
SCK
SDO
CS
GND
TOP VIEW
LTC2421CMS
LTC2421IMS
MS10 PART MARKING
LTUX
LTUY
MS10 PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/W
Consult factory for parts specified with wider operating temperature ranges.
CONVERTER CHARACTERISTICS
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
REF
= FS
SET
– ZS
SET
. (Notes 3, 4)
PARAMETER
Resolution
No Missing Codes Resolution
Integral Nonlinearity
Offset Error
Offset Error Drift
Full-Scale Error
Full-Scale Error Drift
Total Unadjusted Error
Output Noise
Normal Mode Rejection 60Hz
±2%
Normal Mode Rejection 50Hz
±2%
Power Supply Rejection, DC
Power Supply Rejection, 60Hz
±2%
Power Supply Rejection, 50Hz
±2%
0.1V
≤
FS
SET
≤
V
CC
, ZS
SET
= 0V (Note 5)
FS
SET
= 2.5V, ZS
SET
= 0V (Note 6)
FS
SET
= 5V, ZS
SET
= 0V (Note 6)
2.5V
≤
FS
SET
≤
V
CC
, ZS
SET
= 0V
2.5V
≤
FS
SET
≤
V
CC
, ZS
SET
= 0V
2.5V
≤
FS
SET
≤
V
CC
, ZS
SET
= 0V
2.5V
≤
FS
SET
≤
V
CC
, ZS
SET
= 0V
FS
SET
= 2.5V, ZS
SET
= 0V
FS
SET
= 5V, ZS
SET
= 0V
V
IN
= 0V (Note 13)
(Note 7)
(Note 8)
FS
SET
= 2.5V, ZS
SET
= 0V, V
IN
= 0V
FS
SET
= 2.5V, ZS
SET
= 0V, V
IN
= 0V, (Notes 7, 15)
FS
SET
= 2.5V, ZS
SET
= 0V, V
IN
= 0V, (Notes 8, 15)
q
q
q
CONDITIONS
q
q
q
q
q
2
U
U
W
W W
U
W
(Notes 1, 2)
Operating Temperature Range
LTC2421/LTC2422C ................................ 0°C to 70°C
LTC2421/LTC2422I ............................ – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART NUMBER
V
CC
FS
SET
CH1
CH0
ZS
SET
1
2
3
4
5
10
9
8
7
6
F
O
SCK
SDO
CS
GND
LTC2422CMS
LTC2422IMS
MS10 PART MARKING
LTUZ
LTVA
MS10 PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/W
U
MIN
20
20
TYP
MAX
UNITS
Bits
Bits
4
8
0.5
0.04
4
0.04
8
16
6
110
110
130
130
100
110
110
10
20
10
10
ppm of V
REF
ppm of V
REF
ppm of V
REF
ppm of V
REF
/°C
ppm of V
REF
ppm of V
REF
/°C
ppm of V
REF
ppm of V
REF
µV
RMS
dB
dB
dB
dB
dB
24212f
LTC2421/LTC2422
A ALOG I PUT A D REFERE CE
SYMBOL
V
IN
FS
SET
ZS
SET
C
S(IN)
C
S(REF)
I
IN(LEAK)
I
REF(LEAK)
PARAMETER
Input Voltage Range
Full-Scale Set Range
Zero-Scale Set Range
Input Sampling Capacitance
Reference Sampling Capacitance
Input Leakage Current
Reference Leakage Current
CS = V
CC
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
REF
= FS
SET
– ZS
SET
. (Note 3)
CONDITIONS
(Note 14)
q
q
q
V
REF
= 2.5V, CS = V
CC
DIGITAL I PUTS A D DIGITAL OUTPUTS
SYMBOL
V
IH
V
IL
V
IH
V
IL
I
IN
I
IN
C
IN
C
IN
V
OH
V
OL
V
OH
V
OL
I
OZ
PARAMETER
High Level Input Voltage
CS, F
O
Low Level Input Voltage
CS, F
O
High Level Input Voltage
SCK
Low Level Input Voltage
SCK
Digital Input Current
CS, F
O
Digital Input Current
SCK
Digital Input Capacitance
CS, F
O
Digital Input Capacitance
SCK
High Level Output Voltage
SDO
Low Level Output Voltage
SDO
High Level Output Voltage
SCK
Low Level Output Voltage
SCK
High-Z Output Leakage
SDO
(Note 9)
I
O
= – 800µA
I
O
= 1.6mA
I
O
= – 800µA (Note 10)
I
O
= 1.6mA (Note 10)
CONDITIONS
2.7V
≤
V
CC
≤
5.5V
2.7V
≤
V
CC
≤
3.3V
4.5V
≤
V
CC
≤
5.5V
2.7V
≤
V
CC
≤
5.5V
The
q
denotes specifications which apply over the full
operating temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
MIN
q
q
q
q
q
q
2.7V
≤
V
CC
≤
5.5V (Note 9)
2.7V
≤
V
CC
≤
3.3V (Note 9)
4.5V
≤
V
CC
≤
5.5V (Note 9)
2.7V
≤
V
CC
≤
5.5V (Note 9)
0V
≤
V
IN
≤
V
CC
0V
≤
V
IN
≤
V
CC
(Note 9)
POWER REQUIRE E TS
SYMBOL
V
CC
I
CC
PARAMETER
Supply Voltage
Supply Current
Conversion Mode
Sleep Mode
The
q
denotes specifications which apply over the full operating temperature range,
otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
q
CS = 0V (Note 12)
CS = V
CC
(Note 12)
U
U W
U
U
U
U
U
MIN
ZS
SET
– 0.12V
REF
0.1 + ZS
SET
0
TYP
MAX
FS
SET
+ 0.12V
REF
V
CC
FS
SET
– 0.1
UNITS
V
V
V
pF
pF
1
1.5
q
q
–100
– 100
1
1
100
100
nA
nA
TYP
MAX
UNITS
V
V
2.5
2.0
0.8
0.6
2.5
2.0
0.8
0.6
–10
–10
10
10
10
10
V
V
V
V
V
V
µA
µA
pF
pF
V
q
q
q
q
q
V
CC
– 0.5
0.4
V
CC
– 0.5
0.4
–10
10
V
V
V
µA
MIN
2.7
TYP
MAX
5.5
UNITS
V
µA
µA
24212f
q
q
200
20
300
30
3
LTC2421/LTC2422
TI I G CHARACTERISTICS
SYMBOL
f
EOSC
t
HEO
t
LEO
t
CONV
PARAMETER
External Oscillator Frequency Range
External Oscillator High Period
External Oscillator Low Period
Conversion Time
F
O
= 0V
F
O
= V
CC
External Oscillator (Note 11)
Internal Oscillator (Note 10)
External Oscillator (Notes 10, 11)
(Note 10)
(Note 9)
(Note 9)
(Note 9)
Internal Oscillator (Notes 10, 12)
External Oscillator (Notes 10, 11)
(Note 9)
q
q
q
q
q
q
q
q
The
q
denotes specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
q
q
q
q
q
q
f
ISCK
D
ISCK
f
ESCK
t
LESCK
t
HESCK
t
DOUT_ISCK
t
DOUT_ESCK
t
1
t
2
t
3
t
4
t
KQMAX
t
KQMIN
t
5
t
6
Note 1:
Absolute Maximum Ratings are those values beyond which the
life of the device may be impaired.
Note 2:
All voltage values are with respect to GND.
Note 3:
V
CC
= 2.7 to 5.5V unless otherwise specified. Input source
resistance = 0Ω.
Note 4:
Internal Conversion Clock source with the F
O
pin tied
to GND or to V
CC
or to external conversion clock source with
f
EOSC
= 153600Hz unless otherwise specified.
Note 5:
Guaranteed by design, not subject to test.
Note 6:
Integral nonlinearity is defined as the deviation of a code from
a straight line passing through the actual endpoints of the transfer
curve. The deviation is measured from the center of the quantization
band.
Note 7:
F
O
= 0V (internal oscillator) or f
EOSC
= 153600Hz
±2%
(external oscillator).
Note 8:
F
O
= V
CC
(internal oscillator) or f
EOSC
= 128000Hz
±2%
(external oscillator).
4
UW
MIN
2.56
0.5
0.5
TYP
MAX
307.2
390
390
UNITS
kHz
µs
µs
ms
ms
ms
kHz
kHz
130.86
133.53
136.20
157.03
160.23
163.44
20510/f
EOSC
(in kHz)
19.2
f
EOSC
/8
45
250
250
1.23
1.25
1.28
192/f
EOSC
(in kHz)
24/f
ESCK
(in kHz)
0
0
0
50
200
15
50
50
150
150
150
55
2000
Internal SCK Frequency
Internal SCK Duty Cycle
External SCK Frequency Range
External SCK Low Period
External SCK High Period
Internal SCK 24-Bit Data Output Time
External SCK 24-Bit Data Output Time
CS
↓
to SDO Low Z
CS
↑
to SDO High Z
CS
↓
to SCK
↓
CS
↓
to SCK
↑
SCK
↓
to SDO Valid
SDO Hold After SCK
↓
SCK Set-Up Before CS
↓
SCK Hold After CS
↓
%
kHz
ns
ns
ms
ms
ms
ns
ns
ns
ns
ns
ns
ns
ns
(Note 10)
(Note 9)
(Note 5)
q
q
q
q
q
q
Note 9:
The converter is in external SCK mode of operation such that
the SCK pin is used as digital input. The frequency of the clock signal
driving SCK during the data output is f
ESCK
and is expressed in kHz.
Note 10:
The converter is in internal SCK mode of operation such that
the SCK pin is used as digital output. In this mode of operation, the
SCK pin has a total equivalent load capacitance C
LOAD
= 20pF.
Note 11:
The external oscillator is connected to the F
O
pin. The external
oscillator frequency, f
EOSC
, is expressed in kHz.
Note 12:
The converter uses the internal oscillator.
F
O
= 0V or F
O
= V
CC
.
Note 13:
The output noise includes the contribution of the internal
calibration operations.
Note 14:
V
REF
= FS
SET
– ZS
SET
. The minimum input voltage is limited
to – 0.3V and the maximum to V
CC
+ 0.3V.
Note 15:
V
CC
(DC) = 4.1V, V
CC
(AC) = 2.8V
P-P
.
24212f
LTC2421/LTC2422
TYPICAL PERFOR A CE CHARACTERISTICS
Total Unadjusted Error (3V Supply)
10
8
6
4
V
CC
= 3V
V
REF
= 2.5V
10
8
6
4
ERROR (ppm)
ERROR (ppm)
ERROR (ppm)
2
0
–2
–4
–6
–8
–10
0
0.5
1.5
2.0
1.0
INPUT VOLTAGE (V)
2.5
24212 G01
T
A
= –55°C, –45°C, 25°C, 90°C
Positive Extended Input Range
Total Unadjusted Error (3V Supply)
10
8
6
4
ERROR (ppm)
V
CC
= 3V
V
REF
= 2.5V
ERROR (ppm)
2
0
–2
–4
–6
–8
–10
2.50
2.55
2.60 2.65 2.70
INPUT VOLTAGE (V)
2.75
2.80
T
A
= –55°C, –45°C, 25°C, 90°C
2
0
–2
–4
–6
–8
–10
0
1
3
2
INPUT VOLTAGE (V)
4
5
24212 G05
ERROR (ppm)
Negative Extended Input Range
Total Unadjusted Error (5V Supply)
10
8
6
4
ERROR (ppm)
2
0
–2
–4
–6
–8
–10
0
–0.05 –0.10 –0.15 –0.20 –0.25 –0.30
INPUT VOLTAGE (V)
24212 G07
V
CC
= 5V
V
REF
= 5V
T
A
= 25°C
T
A
= 90°C
T
A
= –45°C
ERROR (ppm)
T
A
= –55°C
4
2
0
–2
–4
–6
–8
–10
5.00
T
A
= 90°C
5.05
T
A
= 25°C
T
A
= –55°C
T
A
= –45°C
OFFSET ERROR (ppm)
U W
24212 G04
INL (3V Supply)
V
CC
= 3V
V
REF
= 2.5V
Negative Extended Input Range
Total Unadjusted Error (3V Supply)
10
8
6
4
2
0
–2
–4
T
A
= –55°C
V
CC
= 3V
V
REF
= 2.5V
T
A
= 90°C
T
A
= 25°C
T
A
= –45°C
2
0
–2
–4
–6
–8
–10
0
0.5
1.5
2.0
1.0
INPUT VOLTAGE (V)
2.5
24212 G02
T
A
= –55°C, –45°C, 25°C, 90°C
–6
–8
–10
0
–0.05 –0.10 –0.15 –0.20 –0.25 –0.30
INPUT VOLTAGE (V)
24212 G03
Total Unadjusted Error (5V Supply)
10
8
6
4
V
CC
= 5V
V
REF
= 5V
10
8
6
4
2
0
–2
–4
–6
–8
–10
INL (5V Supply)
V
CC
= 5V
V
REF
= 5V
T
A
= –55°C, –45°C, 25°C, 90°C
T
A
= –55°C, –45°C, 25°C, 90°C
0
1
3
2
INPUT VOLTAGE (V)
4
5
24212 G06
Positive Extended Input Range
Total Unadjusted Error (5V Supply)
10
8
6
V
CC
= 5V
V
REF
= 5V
150
Offset Error vs Reference Voltage
V
CC
= 5V
T
A
= 25°C
120
90
60
30
0
5.10 5.15 5.20
INPUT VOLTAGE (V)
5.25
5.30
0
1
3
4
2
REFERENCE VOLTAGE (V)
5
24212 G09
24212 G08
24212f
5
