LTC2424/LTC2428
4-/8-Channel 20-Bit
µPower
No Latency
∆Σ
TM
ADCs
FEATURES
s
s
s
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
Pin Compatible 4-/8-Channel 20-Bit ADCs
8ppm INL, No Missing Codes at 20 Bits
4ppm Full-Scale Error and 0.5ppm Offset
1.2ppm Noise
Digital Filter Settles in a Single Cycle. Each
Conversion is Accurate, Even After Changing
Channels
Fast Mode: 16-Bit Noise, 12-Bit TUE at 100sps
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
Single Supply 2.7V to 5.5V Operation
Low Supply Current (200µA) and Auto Shutdown
Can Be Interchanged with 24-Bit LTC2404/LTC2408
if ZS
SET
Pin is Grounded
The LTC
®
2424/LTC2428 are 4-/8-channel 2.7V to 5.5V
micropower 20-bit A/D converters with an integrated
oscillator, 8ppm INL and 1.2ppm RMS noise. They use
delta-sigma technology and provide single cycle digital
filter settling time (no latency delay) for multiplexed
applications. The first conversion after the channel is
changed is always valid. Through a single pin the LTC2424/
LTC2428 can be configured for better than 110dB rejec-
tion at 50Hz or 60Hz
±2%,
or can be driven by an external
oscillator for a user defined rejection frequency in the
range 1Hz to 800Hz. The internal oscillator requires no
external frequency setting components.
The converters accept any external reference voltage from
0.1V to V
CC
. With their extended input conversion range of
–12.5% V
REF
to 112.5% V
REF
(V
REF
= FS
SET
– ZS
SET
) the
LTC2424/LTC2428 smoothly resolve the offset and
overrange problems of preceding sensors or signal con-
ditioning circuits.
The LTC2424/LTC2428 communicate through a flexible
4-wire digital interface which 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
s
Weight Scales
Direct Temperature Measurement
Gas Analyzers
Strain-Gage Transducers
Instrumentation
Data Acquisition
Industrial Process Control
4-Digit DVMs
TYPICAL APPLICATIO
7
MUXOUT
9 CH0
10 CH1
11 CH2
ANALOG
INPUTS
–0.12V
REF
TO
1.12V
REF
12 CH3
4-/8-CHANNEL
13 CH4*
MUX
14 CH5*
15 CH6*
17 CH7*
5 ZS
SET
4
ADCIN
0.1V TO V
CC
3
2, 8
FS
SET
V
CC
CSADC
CSMUX
20-BIT
∆Σ
ADC
SCK
CLK
D
IN
SDO
23
20
25
19
21
24
V
CC
2.7V TO 5.5V
1µF
SERIAL DATA LINK
MICROWIRE AND
SPI COMPATABLE
ERROR (ppm)
+
MPU
–
LTC2424/LTC2428
GND
F
O
24248 TA01
26
= INTERNAL OSC/50Hz REJECTION
= EXTERNAL CLOCK SOURCE
= INTERNAL OSC/60Hz REJECTION
1, 6, 16, 18, 22, 27, 28
*THESE PINS ARE NO CONNECTS ON THE LTC2404
U
Total Unadjusted Error (3V Supply)
10
8
6
4
2
0
–2
–4
–6
–8
–10
0
0.5
1.5
2.0
1.0
INPUT VOLTAGE (V)
2.5
24248 G01
U
U
V
CC
= 3V
V
REF
= 2.5V
T
A
= –55°C, –45°C, 25°C, 90°C
1
LTC2424/LTC2428
ABSOLUTE
MAXIMUM
RATINGS
(Notes 1, 2)
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
TOP VIEW
GND
V
CC
FS
SET
ADCIN
ZS
SET
GND
MUXOUT
V
CC
CH0
1
2
3
4
5
6
7
8
9
28 GND
27 GND
26 F
O
25 SCK
24 SDO
23 CSADC
22 GND
21 D
IN
20 CSMUX
19 CLK
18 GND
17 NC
16 GND
15 NC
ORDER
PART NUMBER
LTC2424CG
LTC2424IG
CH1 10
CH2 11
CH3 12
NC 13
NC 14
G PACKAGE
28-LEAD PLASTIC SSOP
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. (Notes 3, 4)
PARAMETER
Resolution (No Missing Codes)
Integral Nonlinearity
Integral Nonlinearity (Fast Mode)
Offset Error
Offset Error (Fast Mode)
Offset Error Drift
Full-Scale Error
Full-Scale Error (Fast Mode)
Full-Scale Error Drift
CONDITIONS
0.1V
≤
V
REF
≤
V
CC
, (Note 5)
V
REF
= 2.5V (Note 6)
V
REF
= 5V (Note 6)
2.5V < V
REF
< V
CC
, 100 Samples/Second, f
O
= 2.051MHz
2.5V
≤
V
REF
≤
V
CC
2.5V < V
REF
< 5V, 100 Samples/Second, f
O
= 2.051MHz
2.5V
≤
V
REF
≤
V
CC
2.5V
≤
V
REF
≤
V
CC
2.5V < V
REF
< 5V, 100 Samples/Second, f
O
= 2.051MHz
2.5V
≤
V
REF
≤
V
CC
q
q
q
q
q
q
2
U
U
W
W W
U
W
Operating Temperature Range
LTC2424C/LTC2428C .............................. 0°C to 70°C
LTC2424I/LTC2428I ........................... – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
GND
V
CC
FS
SET
ADCIN
ZS
SET
GND
MUXOUT
V
CC
CH0
1
2
3
4
5
6
7
8
9
28 GND
27 GND
26 F
O
25 SCK
24 SDO
23 CSADC
22 GND
21 D
IN
20 CSMUX
19 CLK
18 GND
17 CH7
16 GND
15 CH6
ORDER
PART NUMBER
LTC2428CG
LTC2428IG
CH1 10
CH2 11
CH3 12
CH4 13
CH5 14
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/W
U
MIN
20
TYP
4
8
40
0.5
3
0.04
4
10
0.04
MAX
10
20
250
10
UNITS
Bits
ppm of V
REF
ppm of V
REF
ppm of V
REF
ppm of V
REF
ppm of V
REF
ppm of V
REF
/°C
15
ppm of V
REF
ppm of V
REF
ppm of V
REF
/°C
LTC2424/LTC2428
CONVERTER CHARACTERISTICS
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Notes 3, 4)
PARAMETER
Total Unadjusted Error
Output Noise
Output Noise (Fast Mode)
Normal Mode Rejection 60Hz
±2%
Normal Mode Rejection 50Hz
±2%
Power Supply Rejection, DC
Power Supply Rejection, 60Hz
±2%
Power Supply Rejection, 50Hz
±2%
CONDITIONS
V
REF
= 2.5V
V
REF
= 5V
V
IN
= 0V, V
REF
= 5V (Note 13)
V
REF
= 5V, 100 Samples/Second, f
O
= 2.051MHz
(Note 7)
(Note 8)
V
REF
= 2.5V, V
IN
= 0V
V
REF
= 2.5V, V
IN
= 0V, (Notes 7, 16)
V
REF
= 2.5V, V
IN
= 0V, (Notes 8, 16)
q
q
A ALOG I PUT A D REFERE CE
SYMBOL
V
IN
V
REF
C
S(IN)
C
S(REF)
I
IN(LEAK)
I
REF(LEAK)
I
IN(MUX)
R
ON
PARAMETER
Input Voltage Range
Reference Voltage Range
Input Sampling Capacitance
Reference Sampling Capacitance
Input Leakage Current
Reference Leakage Current
On Channel Leakage Current
MUX On-Resistance
MUX
∆R
ON
vs Temperature
∆R
ON
vs V
S
(Note 15)
I
S(OFF)
I
D(OFF)
t
OPEN
t
ON
t
OFF
C
S(OFF)
C
D(OFF)
MUX Off Input Leakage
MUX Off Output Leakage
MUX Break-Before-Make Interval
Enable Turn-On Time
Enable Turn-Off Time
Input Off Capacitance (MUX)
Output Off Capacitance (MUX)
MUX OFF Isolation Channel-to-Channel
CS = V
CC
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
(Note 14)
q
q
V
REF
= 2.5V, CS = V
CC
V
S
= 2.5V (Note 15)
I
OUT
= 1mA, V
CC
= 2.7V
I
OUT
= 1mA, V
CC
= 5V
Channel Off, V
S
= 2.5V
Channel Off, V
D
= 2.5V
V
S
= 1.5V, R
L
= 3.4k, C
L
= 15pF
V
S
= 1.5V, R
L
= 3.4k, C
L
= 15pF
DC
at 1Hz
at f
S
= 15,360Hz
U
U
U
U
MIN
TYP
8
16
6
20
MAX
UNITS
ppm of V
REF
ppm of V
REF
µV
RMS
µV
RMS
dB
dB
dB
dB
dB
110
110
130
130
100
110
110
U
MIN
– 0.125 • V
REF
0.1
TYP
MAX
1.125 • V
REF
V
CC
UNITS
V
V
pF
pF
1
1.5
q
q
q
q
q
–100
– 100
1
1
250
120
0.5
20
100
100
±20
300
250
nA
nA
nA
Ω
Ω
%/°C
%
q
q
±20
±20
290
490
190
10
10
120
120
120
nA
nA
ns
ns
ns
pF
pF
dB
dB
dB
3
LTC2424/LTC2428
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
V
IN
H
MUX
V
IN
L
MUX
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
MUX High Level Input Voltage
MUX Low Level Input Voltage
V
+
= 3V
V
+
= 2.4V
(Note 9)
I
O
= – 800µA
I
O
= 1.6mA
I
O
= – 800µA (Note 10)
I
O
= 1.6mA (Note 10)
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
2.7V
≤
V
CC
≤
5.5V
2.7V
≤
V
CC
≤
3.3V
4.5V
≤
V
CC
≤
5.5V
2.7V
≤
V
CC
≤
5.5V
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)
q
q
q
q
q
q
POWER REQUIRE E TS
SYMBOL
V
CC
I
CC
PARAMETER
Supply Voltage
Supply Current (Pin 2)
Conversion Mode
Sleep Mode
Multiplexer Supply Current (Pin 8)
The
q
denotes specifications which apply over the full operating temperature range,
otherwise specifications are at T
A
= 25°C. (Note 3)
CONDITIONS
q
I
CC(MUX)
4
U W
U
U
MIN
2.5
2.0
TYP
MAX
UNITS
V
V
0.8
0.6
2.5
2.0
0.8
0.6
–10
–10
10
10
V
CC
– 0.5
0.4
V
CC
– 0.5
0.4
–10
2
0.8
10
10
10
V
V
V
V
V
V
µA
µA
pF
pF
V
V
V
V
µA
V
V
MIN
2.7
TYP
MAX
5.5
UNITS
V
µA
µA
µA
CS = 0V (Note 12)
CS = V
CC
(Note 12)
All Logic Inputs Tied Together
V
IN
= 0V or 5V
q
q
q
200
20
15
300
30
40
LTC2424/LTC2428
TI I G CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range,
otherwise specifications are at T
A
= 25°C. (Note 3)
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
SYMBOL
f
EOSC
t
HEO
t
LEO
t
CONV
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, source input
is 0Ω. CSADC = CSMUX = CS. V
REF
= FS
SET
– ZS
SET
.
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).
UW
CONDITIONS
20-Bit Effective Resolution
12-Bit Effective Resolution
q
q
q
q
q
q
q
MIN
2.56
2.56k
0.5
0.5
TYP
MAX
307.2
2.048M
390
390
UNITS
kHz
Hz
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
S
is the voltage applied to a channel input. V
D
is the voltage
applied to the MUX output.
Note 16:
V
CC(DC)
= 4.1V, V
CC(AC)
= 2.8V
P-P
.
5
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