LTC6943
Micropower, Dual Precision
Instrumentation Switched
Capacitor Building Block
DESCRIPTIO
The LTC
®
6943 is a monolithic, charge-balanced, dual
switched capacitor instrumentation building block. A pair
of switches alternately connects an external capacitor to
an input voltage and then connects the charged capacitor
across an output port. The internal switches have a
break-before-make action. An internal clock is provided
and its frequency can be adjusted with an external
capacitor. The LTC6943 can also be driven with an external
CMOS clock.
The LTC6943, when used with low clock frequencies,
provides ultra precision DC functions without requiring
precise external components. Such functions are
differential voltage to single-ended conversion, voltage
inversion, voltage multiplication and division by 2, 3, 4, 5,
etc.
The LTC6943 is manufactured using Linear Technology’s
enhanced LTCMOS
TM
silicon gate process, and it is func-
tionally compatible with the LTC1043.
FEATURES
■
■
■
■
■
■
■
■
■
Low Power, I
S
= 60µA(Max)
Robust, Latch Up Proof
Instrumentation Front End with 120dB CMRR
Precise, Charge-Balanced Switching
Operates from 5V to 18V
Internal or External Clock
Operates up to 5MHz Clock Rate
Two Independent Sections with One Clock
Tiny SSOP-16 Package
APPLICATIO S
■
■
■
■
■
Ultra Precision Voltage Inverters, Multipliers
and Dividers
V–F and F–V Converters
Sample-and-Hold
Current Sources
Precision Instrumentation Amplifiers
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTCMOS is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
5V
INPUT
0V TO 3.7V
3
Precision Voltage Controlled Current Source
with Ground Referred Input and Output
Precision Current Sensing in Supply Rails
1
+
–
5
LTC2050
4
2
0.68µF
5V
1k
7
3
1/2 LTC6943
POSITIVE OR
NEGATIVE RAIL
I
E
R
SHUNT
1/2 LTC6943
11
12
6
9
1µF
10
1µF
1k
12
15
0.001µF
11
14
I
OUT
=
V
IN
1000Ω
OPERATES FROM A
SINGLE 5V SUPPLY
6943 • TA01a
U
U
U
10
1µF
9
1µF
E I=
E
R
SHUNT
6
7
14
0.01µF
15
6943 • TA01b
6943f
1
LTC6943
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
CB
+
1
CB
–
2
V
+
3
S2B 4
S1B 5
S1A 6
S2A 7
SHA 8
16 S3B
15 V
–
14 C
OSC
13 S4B
12 S4A
11 S3A
10 CA
–
9
CA
+
Supply Voltage ........................................................ 18V
Input Voltage at Any Pin .......... –0.3V
≤
V
IN
≤
V
+
+ 0.3V
Operating Temperature Range
(Note 2) ............................................ –40°C to 125°C
Specified Temperature Range
(Note 2) .............................................–40°C to 125°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC6943CGN
LTC6943IGN
LTC6943HGN
GN PART
MARKING
6943C
6943I
6943H
GN PACKAGE
16-LEAD NARROW PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 110°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
+
range, otherwise specifications are at T
A
= 25°C. V
SYMBOL PARAMETER
I
S
Power Supply Current
CONDITIONS
The
●
denotes specifications which apply over the full operating temperature
–
= 0V
= 10V, V
LTC6943C
LTC6943I
MIN TYP MAX
40
●
LTC6943H
MIN TYP MAX
40
80
6
240
400
185
30
40
25
75
5
120
60
90
150
170
100
200
400
700
700
1
50
75
70
100
UNITS
µA
µA
µA
µA
pA
nA
Ω
Ω
Ω
kΩ
kHz
kHz
kHz
µA
µA
ns
ns
MHz
dB
Pin 14 Connected High or Low
C
OSC
(Pin 14 to V
–
) = 100pF
60
90
150
170
100
40
400
700
700
1
50
75
70
100
20
10
80
●
I
I
R
ON
R
ON
f
OSC
OFF Leakage Current
ON Resistance
ON Resistance
Internal Oscillator Frequency
Any Switch, Test Circuit 1 (Note 3)
●
6
240
●
Test Circuit 2, V
IN
= 7V, 1 =
±0.5mA
V
+
= 10V, V
–
= 0V
Test Circuit 2, V
IN
= 3.1V, 1 =
±0.5mA
V
+
= 5V, V
–
= 0V
C
OSC
(Pin 14 to V
–
) = 0pF
C
OSC
(Pin 14 to V
–
) = 100pF
Test Circuit 3
Pin 14 at V
+
or V
–
400
●
●
●
20
12
185
30
40
25
I
OSC
Pin Source or Sink Current
Break-Before-Make Time
Clock to Switching Delay
C
OSC
Pin Externally Driven
75
5
120
f
M
CMRR
Maximum External CLK Frequency C
OSC
Pin Externally Driven with CMOS Levels
Common Mode Rejection Ratio
V
+
= 5V, V
–
= –5V, –5V < V
CM
< 5V
DC to 400Hz
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
All versions of the LTC6943 are guaranteed functional over the
operating temperature range of –40°C to 125°C. The LTC6943CGN is
guaranteed to meet 0°C to 70°C specifications and is designed,
characterized and expected to meet the specified performance from –40°C
to 85°C but it is not tested or QA sampled at these temperatures.
The LTC6943IGN is guaranteed to meet specified performance from –40°C
to 85°C. The LTC6943HGN is guaranteed to meet specified performance
from –40°C to 125°C.
Note 3:
OFF leakage current at 25°C is guaranteed by design and it is not
100% tested in production.
6943f
2
U
W
U
U
W W
W
LTC6943
TYPICAL PERFOR A CE CHARACTERISTICS
Power Supply Current vs
Power Supply Voltage
0.50
0.45
0.40
SUPPLY CURRENT (mA)
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
0
C
OSC
= 0pF, T
A
= –55°C
C
OSC
= 0pF, T
A
= 25°C
C
OSC
= 0pF, T
A
= 125°C
C
OSC
= 4700pF, T
A
= –55°C
C
OSC
= 4700pF, T
A
= 25°C
C
OSC
= 4700pF, T
A
= 125°C
R
ON
(Ω)
R
ON
(Ω)
2
4
6
10 12
V
SUPPLY
(V)
8
14
R
ON
vs V
IN
260
240
220 V
IN
200
R
ON
(Ω)
R
ON
(Ω)
180
160
140
120
100
80
0
2
4
6
8
10 12 14 16 18 20
V
IN
(V)
LTC1043 • TPC04
R
ON
(PEAK)
I = 100µA
V+ = 15V
V – = 0V
T
A
= 25°C
I = 100µA
I = mA
500
400
300
200
100
0
0
R
ON
(Ω)
Oscillator Frequency, f
OSC
vs C
OSC
1000
T
A
= 25°C
250
225
200
OSCILLATOR FREQUENCY NORMALIZED
TO f
OSC
AT 5V SUPPLY
100
f
OSC
(kHz)
I
OSC
(kHz)
10
V
S
= 5V
V
S
= 10V
1
V
S
= 15V
0.1
0
1000
2000
3000
C
OSC
(pF)
4000
5000
6943 TPC07
U W
16
18
6943 TPC01
(Test Circuits 2 through 4)
R
ON
vs V
IN
550
500
450 V
IN
400
350
300
250
200
150
100
0
1
2
V
IN
(V)
LTC1043 • TPC02
R
ON
vs V
IN
V+ = 5V
V – = 0V
T
A
= 25°C
280
260
240 V
IN
220
200
180
160
140
120
100
3
4
5
0
1
2
3
4
5 6
V
IN
(V)
7
8
9
10
I = 100µA
I = mA
R
ON
(PEAK)
I = 100µA
V+ = 10V
V – = 0V
T
A
= 25°C
R
ON
(PEAK)
I = 100µA
I = 100µA
I = mA
LTC1043 • TPC03
R
ON
(Peak) vs Power Supply
Voltage
1000
900
800
700
600
V
IN
≈
3.2V
V
IN
≈
7V
3V
≤
V+ +
≤18V
V – = 0V
T
A
= 25°C
2
4
6
V
IN
= 1.6V
V
IN
R
ON
(PEAK)
I = 100µA
1100
1000
900
800
700
600
500
400
300
200
100
R
ON
(Peak) vs Power Supply
Voltage and Temperature
R
ON
(PEAK)
V
IN
I = 100µA
T
A
= 125°C
V
IN
≈
11V
T
A
= 70°C
T
A
= –55°C
0
2
4
6
8 10 12 14 16 18 20
V
SUPPLY
(V)
LTC1043 • TPC06
V
IN
≈
15.1V
8 10 12 14 16 18 20
V
SUPPLY
(V)
LTC1043 • TPC05
Oscillator Frequency, f
OSC
vs Supply Voltage
T
A
= 25°C
Normalized Oscillator Frequency,
f
OSC
vs Supply Voltage
1.5
T
A
= 25°C
1.3
C
OSC
= 0pF
1.0
C
OSC
= 100pF
0.5
C
OSC
= 10,000pF
0.3
C
OSC
= 1,000pF
175
150
125
100
75
50
25
0
0
2
4
6
8
C
OSC
= 0pF
C
OSC
= 100pF
10 12
V
SUPPLY
(V)
14
16
18
0
0
2
4
6
8 10 12
V
SUPPLY
(V)
14
16
18
6943 TPC08
6943 TPC09
6943f
3
LTC6943
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency, f
OSC
vs Ambient Temperature
350
300
V
S
= 5V
250
f
OSC
(kHz)
PIN 14 SOURCE OR SINK CURRENT (µA)
C
OSC
= 0pF
50
I
SOURCE,
T
A
= –55°C
I
SOURCE,
T
A
= 25°C
t
NOV
(ns)
200
150
100
50
V
S
= 10V
V
S
= 15V
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
BLOCK DIAGRA
4
U W
100
6943 TPC10
(Test Circuits 2 through 4)
Break-Before-Make Time, t
NOV
,
vs Supply Voltage
80
T
A
= 25°C
70
60
50
40
30
C
OSC
Pin I
SINK
, I
SOURCE
vs Supply Voltage
100
I
SINK,
T
A
= –55°C
75
I
SINK,
T
A
= 25°C
25
I
SINK,
T
A
= 125°C
I
SOURCE,
T
A
= 125°C
0
0
2
4
6
8
10
12
14
16
18
20
10
0
2
4
6
8 10 12 14 16 18 20
V
SUPPLY
(V)
LTC1043 • TPC12
125
LTC1043 • TPC11
W
S1A 6
7 S2A
SH
A
8
9 C
A+
10 C
A–
S3A 11
CHARGE
BALANCING
CIRCUITRY
S1B 5
4 S2B
12 S4A
1 C
B+
2 C
B–
S3B 16
CHARGE
BALANCING
CIRCUITRY
13 S4B
NON-OVERLAPPING
CLOCK
V
+
V
–
3 V
+
C
OSC
14
OSCILLATOR
15 V
–
THE CHARGE BALANCING CIRCUITRY SAMPLES THE VOLTAGE
AT S3 WITH RESPECT TO S4 (PIN 14 HIGH) AND INJECTS A
SMALL CHARGE AT THE C
+
PIN (PIN 14 LOW).
THIS BOOSTS THE CMRR WHEN THE LTC6943 IS USED AS AN
INSTRUMENTATION AMPLIFIER FRONT END.
FOR MINIMUM CHARGE INJECTION IN OTHER TYPES OF
APPLICATIONS, S3A AND S3B SHOULD BE GROUNDED
THE SWITCHES ARE TIMED AS SHOWN WITH PIN 14 HIGH
6943 • BD01
6943f
LTC6943
TEST CIRCUITS
Test Circuit 1. Leakage Current Test
(6, 11, 5, 16)
(7, 12, 4, 13)
NOTE: TO OPEN SWITCHES,
S1 AND S3 PIN 14,
SHOULD BE CONNECTED
TO V –. TO OPEN S2, S4, THE
C
OSC
PIN 14 SHOULD BE
CONNECTED TO V+ C
OSC
6943 • TC01
Test Circuit 2. R
ON
Test
(6, 11, 5, 16)
(7, 12, 4, 13)
A
+
0V TO 10V
+
(9, 10, 1, 2)
VIN
(9, 10, 1, 2)
100µA to 1mA
CURRENT SOURCE
A
6943 • TC02
Test Circuit 3. Oscillator Frequency, f
OSC
6
(TEST PIN) 1
V+
V–
C
OSC
Test Circuit 4. CMRR Test
7
V
OUT
15
8
14
9
1µF
1µF
CAPACITORS ARE
NOT ELECTROLYTIC
+
3
LTC6943
4
10
+
5
IV
6943 • TC03
11
12
+
V
–
≤
V
CM
≤
V
+
CMRR = 20 LOG
( )
V
CM
V
OUT
6943 • TC04
NOTE: FOR OPTIMUM CMRR, THE C
OSC
SHOULD
BE LARGER THAN 0.0047µF, AND
THE SAMPLING CAPACITOR ACROSS
PINS 9 AND 10 SHOULD BE PLACED
OVER A SHIELD TIED TO PIN 8
APPLICATIO S I FOR ATIO
Common Mode Rejection Ratio (CMRR)
The LTC6943, when used as a differential to single-ended
converter rejects common mode signals and preserves
differential voltages (Figure 1). Unlike other techniques,
the LTC6943’s CMRR does not degrade with increasing
common mode voltage frequency. During the sampling
mode, the impedance of Pins 1, 2 (and 9, 10) should be
balanced, otherwise, common mode signals will appear
differentially. The value of the CMRR depends on the value
of the sampling and holding capacitors (C
S
, C
H
) and on the
sampling frequency. Since the common mode voltages
are not sampled, the common mode signal frequency can
well exceed the sampling frequency without experiencing
aliasing phenomena. The CMRR of Figure 1 is measured
by shorting Pins 6 and 11 and by observing, with a
U
1/2 LTC6943
6
7
C
+
V
D
9
W
U U
+
+
C
S
C
–
10
V
D
C
H
11
V
CM
12
+
C
S
, C
H
ARE MYLAR OR POLYPROPYLENE
6943 • AI01
Figure 1. Differential to Single-Ended Converter
6943f
5
京公网安备 11010802033920号
EEWORLD
