TSH350
550MHz low noise current feedback amplifier
Features
■
Bandwidth: 550MHz in unity gain
■
Quiescent current: 4.1mA
■
Slew rate: 940V/μs
■
Input noise: 1.5nV/√Hz
■
Distortion: SFDR=-66dBc (10MHz, 1Vpp)
■
2.8Vpp minimum output swing on 100Ω load for
a 5V supply
■
Tested on 5V power supply
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SO-8
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Pin connections (top view)
Applications
■
Communication & video test equipment
■
Medical instrumentation
■
ADC drivers
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Description
VCC - 2
du
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4 Inv. In.
NC 1
8 NC
Inv. In. 2
_
7 VCC +
Non-Inv. In. 3
+
6 Output
5 NC
VCC - 4
The TSH350 is a single operator available in the
tiny SOT23-5 and SO-8 plastic packages, saving
board space as well as providing excellent
thermal and dynamic performance.
June 2007
+-
SOT23-5
so
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5 VCC +
Output 1
Non-Inv. In. 3
The TSH350 is a current feedback operational
amplifier using a very high-speed complementary
technology to provide a bandwidth up to 410MHz
while drawing only 4.1mA of quiescent current.
With a slew rate of 940V/µs and an output stage
optimized for driving a standard 100Ω load, this
circuit is highly suitable for applications where
speed and power-saving are the main
requirements.
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SOT23-5
SO-8
Rev 4
1/22
www.st.com
22
Absolute maximum ratings
1
TSH350
Absolute maximum ratings
Table 1.
Absolute maximum ratings (AMR)
Symbol
Value
Unit
6
V
+/-0.5
V
+/-2.5
V
-65 to +150
°C
Maximum junction temperature
150
°C
Rthja
Thermal resistance junction to ambient
SOT23-5
SO-8
250
150
Rthjc
Thermal resistance junction to case
SOT23-5
SO-8
Pmax
VCC
Vid
Parameter
Supply voltage (1)
(2)
Differential input voltage
(3)
Vin
Input voltage range
Tstg
Storage temperature
Tj
ESD
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°C/W
80
28
°C/W
Maximum power dissipation(4) (@Tamb=25°C) for Tj=150°C
SOT23-5
SO-8
500
830
mW
HBM: human body model (5)
pins 1, 4, 5, 6, 7 and 8
pins 2 and 3
2
0.5
kV
MM: machine model (6)
pins 1, 4, 5, 6, 7 and 8
pins 2 and 3
200
60
V
CDM: charged device model(7)
pins 1, 4, 5, 6, 7 and 8
pins 2 and 3
1.5
1.5
kV
Latch-up immunity
200
mA
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1. All voltage values are measured with respect to the ground pin.
2. Differential voltage is the non-inverting input terminal with respect to the inverting input terminal.
3. The magnitude of input and output voltage must never exceed VCC +0.3V.
4. Short-circuits can cause excessive heating. Destructive dissipation can result from short-circuits on all
amplifiers.
5. Human body model: A 100pF capacitor is charged to the specified voltage, then discharged through a
1.5kΩ resistor between two pins of the device. This is done for all couples of connected pin combinations
while the other pins are floating.
6. Machine model: A 200pF capacitor is charged to the specified voltage, then discharged directly between
two pins of the device with no external series resistor (internal resistor < 5Ω). This is done for all couples of
connected pin combinations while the other pins are floating.
7. Charged device model: all pins and the package are charged together to the specified voltage and then
discharged directly to the ground through only one pin. This is done for all pins.
2/22
TSH350
Absolute maximum ratings
Table 2.
Operating conditions
Symbol
Parameter
(1)
VCC
Supply voltage
Vicm
Common mode input voltage
Toper
Operating free air temperature range
Value
Unit
4.5 to 5.5
V
-VCC+1.5V to +VCC-1.5V
V
-40 to + 85
°C
1. Tested in full production at 5V (±2.5V) supply voltage.
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3/22
Electrical characteristics
TSH350
2
Electrical characteristics
Table 3.
Electrical characteristics for VCC = ±2.5V, Tamb = 25°C (unless otherwise specified)
Symbol
Parameter
Test conditions
Min.
Typ.
Max.
0.8
4
Unit
DC performance
Tamb
Vio
Input offset voltage
Offset voltage between both inputs
Tmin < Tamb < Tmax
1
ΔVio
Vio drift vs. temperature
Tmin < Tamb < Tmax
0.9
Non inverting input bias current
DC current necessary to bias the input +
Tamb
12
Iib+
Tmin < Tamb < Tmax
13
Inverting input bias current
DC current necessary to bias the input -
Tamb
1
Iib-
CMR
SVR
Supply voltage rejection ratio
20 log (ΔVCC/ΔVio)
ΔVCC=+3.5V to +5V
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Positive supply current
DC consumption with no input signal
ICC
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35
20
2.5
ΔVic = ±1V
Tmin < Tamb < Tmax
μV/°C
uc
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Tmin < Tamb < Tmax
Common mode rejection ratio
20 log (ΔVic/ΔVio)
Power supply rejection ratio
20 log (ΔVCC/ΔVout)
PSR
mV
68
μA
μA
60
dB
58
81
dB
Tmin < Tamb < Tmax
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78
AV = +1, ΔVCC=±100mV
at 1kHz
51
Tmin < Tamb < Tmax
48
No load
4.1
dB
4.9
mA
Dynamic performance and output characteristics
Pr
Transimpedance
Output voltage/input current gain in open
loop of a CFA.
For a VFA, the analog of this feature is the
open loop gain (AVD)
ΔVout = ±1V, RL = 100Ω
-3dB bandwidth
Frequency where the gain is 3dB below the
DC gain AV
Note: Gain bandwidth product criterion is not
applicable for current-feedback-amplifiers
Small signal
Vout=20mVpp
AV = +1, RL = 100Ω
AV = +2, RL = 100Ω
AV = +10, RL = 100Ω
AV = -2, RL = 100Ω
Gain flatness @ 0.1dB
Band of frequency where the gain variation
does not exceed 0.1dB
Small signal
Vout=100mVp
AV = +1, RL = 100Ω
65
SR
Slew rate
Maximum output speed of sweep in large
signal
Vout = 2Vpp, AV = +2,
RL = 100Ω
940
V/μs
1.56
V
VOH
High level output voltage
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Bw
4/22
170
Tmin < Tamb < Tmax
RL = 100Ω
Tmin < Tamb < Tmax
250
1.44
270
kΩ
250
kΩ
550
390
125
370
MHz
1.49
TSH350
Electrical characteristics
Table 3.
Electrical characteristics for VCC = ±2.5V, Tamb = 25°C (unless otherwise specified)
Symbol
VOL
Parameter
Test conditions
Low level output voltage
Min.
Typ.
Max.
RL = 100Ω
-1.53 -1.44
Tmin < Tamb < Tmax
-1.49
Output to GND
Isink
Short-circuit output current coming in the opTmin < Tamb < Tmax
amp (see Figure 9)
135
Isource
Output current coming out from the op-amp
(see Figure 10)
-140
Unit
V
205
195
mA
Iout
Output to GND
Tmin < Tamb < Tmax
-210
-185
)
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Noise and distortion
eN
Equivalent input noise voltage
See Section 5: Noise measurements
F = 100kHz
Equivalent input noise current (+)
See Section 5: Noise measurements
F = 100kHz
Equivalent input noise current (-)
See Section 5: Noise measurements
F = 100kHz
1.5
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SFDR
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20
pA/√Hz
13
pA/√Hz
-66
-57
-46
-42
dBc
Closed-loop gain and feedback components
VCC (V)
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Gain
Rfb (Ω)
-3dB Bw (MHz)
0.1dB Bw (MHz)
+10
300
125
22
-10
300
120
20
+2
300
390
110
-2
300
370
70
+1
820
550
65
-1
300
350
120
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AV = +1, Vout = 1Vpp
Spurious free dynamic range
F = 10MHz
The highest harmonic of the output spectrum F = 20MHz
F = 50MHz
when injecting a filtered sine wave
F = 100MHz
Table 4.
nV/√Hz
Pr
5/22
Electrical characteristics
Frequency response, positive gain Figure 2.
24
22
20
18
16
14
12
10
8
6
4
2
0
-2
-4 Small Signal
-6
Vcc=5V
-8
Load=100Ω
-10
1M
Gain=+10
Gain=+4
Gain (dB)
Gain (dB)
Figure 1.
TSH350
Gain=+2
Gain=+1
10M
100M
1G
Frequency response, negative gain
24
22
20
18
16
14
12
10
8
6
4
2
0
-2
-4 Small Signal
-6
Vcc=5V
-8
Load=100Ω
-10
1M
Gain=-10
Gain=-4
Gain=-2
Gain=-1
10M
Frequency (Hz)
Figure 3.
Compensation, gain=+4
Vin
Vout
)-
-
4pF
300R
100R
Gain=+4, Vcc=5V,
Small Signal
du
10M
Frequency (Hz)
Figure 5.
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5,9
5,8
Figure 6.
300R
100R
10M
100M
1G
Step response vs. capacitor load
C-Load=1pF
R-iso=22ohms
6
2
Output step (Volt)
4
Gain (dB)
8k2
2pF
3
s
b
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C-Load=10pF
R-iso=39ohms
2
0
C-Load=22pF
R-iso=27ohms
Vin
+
-
Vout
R-iso
-4
300R
300R
C-Load=10pF
R-iso=39ohms
C-Load=22pF
R-iso=27ohms
1
Vin
+
-
300R
300R
0
1k
C-Load
Vout
R-iso
1k
C-Load
Gain=+2, Vcc=5V,
Small Signal
Gain=+2, Vcc=5V,
Small Signal
10M
100M
Frequency (Hz)
6/22
-
Frequency (Hz)
C-Load=1pF
R-iso=22ohms
8
-10
1M
Vout
+
Gain=+2, Vcc=5V,
Small Signal
5,6
1M
10
-8
Vin
5,7
100M
Frequency response vs. capacitor
load
6,0
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11,7
11,6
1M
Gain Flatness (dB)
Gain Flatness (dB)
11,9
-6
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6,1
12,0
-2
Compensation, gain=+2
6,2
+
1G
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Figure 4.
12,1
11,8
)
s
(
t
100M
Frequency (Hz)
1G
-1
0,0s
2,0ns 4,0ns 6,0ns 8,0ns 10,0ns 12,0ns 14,0ns 16,0ns 18,0ns 20,0ns
Time (ns)
TSH350
Electrical characteristics
Figure 7.
Slew rate
Figure 8.
Output amplitude vs. load
4,0
Max. Output Amplitude (Vp-p)
Output Response (V)
2,0
1,5
1,0
0,5
Gain=+2
Vcc=5V
Load=100 Ω
0,0
-2ns
-1ns
0s
1ns
2ns
3,5
3,0
2,5
Gain=+2
Vcc=5V
Load=100Ω
2,0
3ns
10
100
Time (ns)
Figure 9.
Isink
Figure 10. Isource
300
0
+2.5V
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V OL
without load
+
-50
-1V
Isink
_
Isink (mA)
200
V
- 2.5V
RG
Amplifier in open
loop without load
150
)-
100
t(s
50
0
-2,0
-1,5
-1,0
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V (V)
-0,5
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+2.5V
V OH
without load
+
+1V
-200
-300
0,0
Isource
_
V
RG
0,5
1,0
Amplifier in open
loop without load
1,5
2,0
Figure 12. Input voltage noise vs. frequency
4.0
3.5
Pos. Current
Noise
50
en (nV/sqrt(Hz))
in (pA/sqrt(Hz))
c
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-250
60
Neg. Current
Noise
40
30
20
10
1k
100k
V (V)
P
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-150
)
s
(
t
10k
- 2.5V
0,0
Figure 11. Input current noise vs. frequency
70
-100
s
b
O
Isource (mA)
250
1k
Load (ohms)
3.0
2.5
2.0
1.5
10k
100k
Frequency (Hz)
1M
10M
1.0
1k
10k
100k
1M
10M
Frequency (Hz)
7/22
Electrical characteristics
TSH350
Figure 13. Quiescent current vs. VCC
Figure 14. Distortion vs. output amplitude
0
5
-5
4
Icc(+)
-10
-15
3
-20
HD2 & HD3 (dBc)
Icc (mA)
2
1
Gain=+2
Vcc=5V
Input to ground, no load
0
-1
-2
-25
-30
HD2
-35
-40
-45
-50
-55
-60
-3
Gain=+2
Vcc=5V
F=30MHz
Load=100Ω
HD3
-65
-70
-4
Icc(-)
-5
1,25
-75
1,75
2,00
2,25
0
2,50
1
+/-Vcc (V)
Figure 16. Noise figure
40
-20
-25
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35
-30
-35
30
-40
-45
HD2
-60
-65
)
(s
-70
-75
HD3
-80
-85
ct
-90
-95
du
-100
0
1
2
4
c
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15
10
Gain=+2
Vcc=5V
F=10MHz
Load=100Ω
3
20
5
Gain=?
Vcc=5V
0
4
1
10
100
Output Amplitude (Vp-p)
1k
10k
100k
Rsource (ohms)
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Figure 17. Distortion vs. output amplitude
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3
s
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25
-50
NF (dB)
HD2 & HD3 (dBc)
2
Output Amplitude (Vp-p)
Figure 15. Distortion vs. output amplitude
-55
)
s
(
t
-80
1,50
Figure 18. Output amplitude vs. frequency
-20
5
-25
-30
bs
-35
4
HD2
-45
Vout max. (Vp-p)
O
HD2 & HD3 (dBc)
-40
-50
-55
-60
-65
HD3
-70
-75
-80
Gain=+2
Vcc=5V
F=20MHz
Load=100Ω
-85
-90
-95
1
2
Output Amplitude (Vp-p)
8/22
3
2
1
Gain=+2
Vcc=5V
Load=100Ω
-100
0
3
4
0
1M
10M
100M
Frequency (Hz)
1G
TSH350
Electrical characteristics
Figure 19. Reverse isolation vs. frequency
Figure 20. SVR vs. temperature
0
90
85
-20
-40
SVR (dB)
Isolation (dB)
80
-60
75
70
65
60
-80
Small Signal
Vcc=5V
Load=100Ω
-100
1M
55
Gain=+1
Vcc=5V
Load=100Ω
100M
1G
-40
-20
0
Frequency (Hz)
20
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500
320
450
400
350
)
(s
300
0
20
ct
du
40
60
Temperature (°C)
80
100
280
120
80
100
120
80
100
120
o
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260
240
220
Open Loop
Vcc=5V
200
-40
120
-20
0
20
40
60
Temperature (°C)
o
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Figure 23. CMR vs. temperature
e
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100
s
b
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ROL (MΩ )
Bw (MHz)
300
-20
80
c
u
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340
200
60
Figure 22. ROL vs. temperature
550
Gain=+1
250
Vcc=5V
Load=100 Ω
40
Temperature (°C)
Figure 21. Bandwidth vs. temperature
-40
)
s
(
t
50
10M
Figure 24. Ibias vs. temperature
70
14
68
bs
12
66
8
62
IBIAS (μA)
CMR (dB)
O
Ib(+)
10
64
60
58
6
4
Ib(-)
2
56
0
54
52
Gain=+1
Vcc=5V
Load=100Ω
-2
-4
Gain=+1
Vcc=5V
Load=100Ω
50
-40
-20
0
20
40
60
Temperature (°C)
80
100
120
-40
-20
0
20
40
60
Temperature (°C)
9/22
Electrical characteristics
TSH350
Figure 25. Vio vs. temperature
Figure 26. ICC vs. temperature
6
1000
4
Icc(+)
800
0
600
ICC (mA)
VIO (micro V)
2
400
-2
Icc(-)
-4
-6
200
Gain=+1
Vcc=5V
-8 no Load
In+/In- to GND
Open Loop
Vcc=5V
Load=100Ω
-40
-20
0
20
40
60
80
100
-40
120
-20
0
Temperature (°C)
20
e
t
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ol
200
VOH
bs
Iout (mA)
VOH & OL (V)
0
VOL
-2
)
s
(
t
-3
Gain=+1
Vcc=5V
Load=100Ω
-20
0
c
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20
40
Temperature (°C)
e
t
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s
b
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10/22
100
120
100
120
o
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Isource
100
-5
-40
80
c
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300
-1
60
Figure 28. Iout vs. temperature
2
1
40
Temperature (°C)
Figure 27. VOH and VOL vs. temperature
-4
)
s
(
t
-10
0
o
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60
80
-O
0
-100
Isink
-200
-300
-400
Output: short-circuit
Gain=+1
Vcc=5V
-40
-20
0
20
40
60
Temperature (°C)
80
TSH350
3
Evaluation boards
Evaluation boards
An evaluation board kit optimized for high-speed operational amplifiers is available (order
code: KITHSEVAL/STDL). As well as a CD-ROM containing datasheets, articles, application
notes and a user manual, the kit includes the following evaluation boards:
●
SOT23_SINGLE_HF BOARD
Board for the evaluation of a single high-speed op-amp in SOT23-5 package.
●
SO8_SINGLE_HF
Board for the evaluation of a single high-speed op-amp in SO-8 package.
●
SO8_DUAL_HF
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Board for the evaluation of a dual high-speed op-amp in SO-8 package.
●
SO8_S_MULTI
Board for the evaluation of a single high-speed op-amp in SO-8 package in inverting
and non-inverting configuration, dual and single supply.
●
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SO14_TRIPLE
Board for the evaluation of a triple high-speed op-amp in SO-14 package with video
application considerations.
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Board material:
●
2 layers
●
FR4 (ε r=4.6)
●
epoxy 1.6mm
●
copper thickness: 35µm
)
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Figure 29. Evaluation kit for high-speed op-amps
d
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11/22
Power supply considerations
4
TSH350
Power supply considerations
Correct power supply bypassing is very important for optimizing performance in highfrequency ranges. Bypass capacitors should be placed as close as possible to the IC pins to
improve high-frequency bypassing. A capacitor greater than 1μF is necessary to minimize
the distortion. For better quality bypassing, a capacitor of 10nF can be added which should
also be placed as close as possible to the IC pins.
Bypass capacitors must be incorporated for both the negative and the positive supply.
Note:
On the SO8_SINGLE_HF board, these capacitors are C6, C7, C8, C9.
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Figure 30. Circuit for power supply bypassing
+VCC
u
d
o
10µF
+
r
P
e
10nF
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+
s
b
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-
)
(s
t
c
u
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r
10nF
10µF
+
-VCC
P
e
Single power supply
t
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b
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In the event that a single supply system is used, biasing is necessary to obtain a positive
output dynamic range between 0V and +VCC supply rails. Considering the values of VOH
and VOL, the amplifier will provide an output swing from +0.9V to +4.1V on a 100Ω load.
The amplifier must be biased with a mid-supply (nominally +VCC/2), in order to maintain the
DC component of the signal at this value. Several options are possible to provide this bias
supply, such as a virtual ground using an operational amplifier or a two-resistance divider
(which is the cheapest solution). A high resistance value is required to limit the current
consumption. On the other hand, the current must be high enough to bias the non-inverting
input of the amplifier. If we consider this bias current (35μA maximum) as 1% of the current
through the resistance divider, to keep a stable mid-supply, two resistances of 750Ω can be
used.
The input provides a high-pass filter with a break frequency below 10Hz which is necessary
to remove the original 0 volt DC component of the input signal, and to fix it at +VCC/2.
Figure 31 illustrates a 5V single power supply configuration for the SO8_S_MULTI
evaluation board (see Evaluation boards on page 11).
12/22
TSH350
Power supply considerations
A capacitor CG is added in the gain network to ensure a unity gain in low frequency to keep
the right DC component at the output. CG contributes to a high-pass filter with Rfb//RG and
its value is calculated with a consideration of the cut off frequency of this low-pass filter.
Figure 31. Circuit for +5V single supply (using evaluation board SO8_S_MULTI)
+5V
10µF
+
IN
+5V
Rin
1k
100µF
)
s
(
ct
_
100
R1
750
Rfb
+
)
(s
u
d
o
r
P
e
RG
10nF
+ 1µF
R2
750
OUT
t
e
l
o
CG
s
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13/22
Noise measurements
5
TSH350
Noise measurements
The noise model is shown in Figure 32:
●
eN is the input voltage noise of the amplifier
●
iNn is the negative input current noise of the amplifier
●
iNp is the positive input current noise of the amplifier
Figure 32. Noise model
)
s
(
ct
+
iN+
R3
HP3577
Input noise:
8nV/√Hz
_
N3
r
P
e
eN
iN-
N2
R1
N1
)
(s
u
d
o
output
t
e
l
o
R2
s
b
O
t
c
u
The thermal noise of a resistance R is
d
o
r
4kTR Δ F
P
e
t
e
l
o
where ΔF is the specified bandwidth.
s
b
O
On a 1Hz bandwidth the thermal noise is reduced to:
4kTR
where k is the Boltzmann's constant, equal to 1,374.10-23J/°K. T is the temperature (°K).
The output noise eNo is calculated using the Superposition Theorem. However, eNo is not
the simple sum of all noise sources, but rather the square root of the sum of the square of
each noise source, as shown in Equation 1:
Equation 1
eNo =
14/22
2
2
2
2
2
V1 + V2 + V3 + V4 + V5 + V6
2
TSH350
Noise measurements
Equation 2
2
2
2
2
2
2
2
2
2 R2
R2- 2 × 4kTR3
eNo = eN × g + iNn × R2 + iNp × R3 × g + -------- × 4kTR1 + 4kTR2 + 1 + ------R1
R1
The input noise of the instrumentation must be extracted from the measured noise value.
The real output noise value of the driver is:
Equation 3
eNo =
2
( Measured ) – ( instrumentation )
2
)
s
(
ct
The input noise is called equivalent input noise because it is not directly measured but is
evaluated from the measurement of the output divided by the closed loop gain (eNo/g).
u
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After simplification of the fourth and the fifth term of Equation 2 we obtain:
r
P
e
Equation 4
2
2
2
2
2
2
2
2
R2- 2 × 4kTR3
eNo = eN × g + iNn × R2 + iNp × R3 × g + g × 4kTR2 + 1 + ------R1
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s
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Measurement of the input voltage noise eN
If we assume a short-circuit on the non-inverting input (R3=0), from Equation 4 we can
derive:
)
(s
Equation 5
t
c
u
2
2
2
2
eN × g + iNn × R2 + g × 4kTR2
d
o
r
eNo =
P
e
In order to easily extract the value of eN, the resistance R2 will be chosen to be as low as
possible. In the other hand, the gain must be large enough:
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s
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R3=0, gain: g=100
Measurement of the negative input current noise iNn
To measure the negative input current noise iNn, we set R3=0 and use Equation 5. This
time, the gain must be lower in order to decrease the thermal noise contribution:
R3=0, gain: g=10
Measurement of the positive input current noise iNp
To extract iNp from Equation 3, a resistance R3 is connected to the non-inverting input. The
value of R3 must be chosen in order to keep its thermal noise contribution as low as
possible against the iNp contribution:
R3=100W, gain: g=10
15/22
Intermodulation distortion product
6
TSH350
Intermodulation distortion product
The non-ideal output of the amplifier can be described by the following series:
V out = C 0 + C 1 V in + C 2 V
2
in
+ …+ Cn V
n
in
where the input is Vin=Asinωt, C0 is the DC component, C1(Vin) is the fundamental and Cn is
the amplitude of the harmonics of the output signal Vout.
A one-frequency (one-tone) input signal contributes to harmonic distortion. A two-tone input
signal contributes to harmonic distortion and to the intermodulation product.
)
s
(
ct
The study of the intermodulation and distortion for a two-tone input signal is the first step in
characterizing the driving capability of multi-tone input signals.
u
d
o
In this case:
r
P
e
V in = A sin ω1 t + A sin ω2 t
t
e
l
o
then:
bs
2
V out = C 0 + C 1 ( A sin ω1 t + A sin ω2 t ) + C 2 ( A sin ω1 t + A sin ω2 t ) …+ C n ( A sin ω1 t + A sin ω2 t )
n
O
)
From this expression, we can extract the distortion terms, and the intermodulation terms
from a single sine wave:
s
(
t
c
●
second order intermodulation terms IM2 by the frequencies (ω1-ω2) and (ω1+ω2) with an
amplitude of C2A2
●
third order intermodulation terms IM3 by the frequencies (2ω1-ω2), (2ω1+ω2), (−ω1+2ω2)
and (ω1+2ω2) with an amplitude of (3/4)C3A3
u
d
o
r
P
e
The intermodulation product of the driver is measured by using the driver as a mixer in a
summing amplifier configuration (see Figure 33). In this way, the non-linearity problem of an
external mixing device is avoided.
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bs
O
Figure 33. Inverting summing amplifier (using evaluation board SO8_S_MULTI)
Vin1
R1
Vin2
R2
Rfb
_
Vout
+
R
16/22
100
TSH350
7
Inverting amplifier biasing
Inverting amplifier biasing
A resistance is necessary to achieve good input biasing, such as resistance R shown in
Figure 34.
The magnitude of this resistance is calculated by assuming the negative and positive input
bias current. The aim is to compensate for the offset bias current, which could affect the
input offset voltage and the output DC component. Assuming Iib-, Iib+, Rin, Rfb and a zero
volt output, the resistance R is:
R in × R fb
R = ----------------------R in + R fb
)
s
(
ct
Figure 34. Compensation of the input bias current
Rfb
Rin
Iib-
_
s
b
O
+
Iib+
)
(s
t
c
u
r
P
e
t
e
l
o
VCC+
VCC-
u
d
o
Output
Load
R
d
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P
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t
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s
b
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17/22
Active filtering
8
TSH350
Active filtering
Figure 35. Low-pass active filtering, Sallen-Key
C1
R2
R1
+
IN
OUT
C2
_
100
)
s
(
ct
Rfb
910
RG
u
d
o
r
P
e
From the resistors Rfb and RG we can directly calculate the gain of the filter in a classic noninverting amplification configuration:
t
e
l
o
R fb
A V = g = 1 + -------Rg
s
b
O
We assume the following expression as the response of the system:
)
(s
t
c
u
Vout jω
g
T jω = ---------------- = ---------------------------------------Vin jω
j----ω- ( j ω) 2
1 + 2 ζ + -----------ωc ω 2
c
The cut-off frequency is not gain-dependent and so becomes:
d
o
r
P
e
t
e
l
o
1
ωc = -----------------------------------R1R2C1C2
The damping factor is calculated by the following expression:
s
b
O
1
ζ = --- ωc ( C 1 R 1 + C 1 R 2 + C 2 R1 – C 1 R 1 g )
2
The higher the gain, the more sensitive the damping factor is. When the gain is higher than
1, it is preferable to use some very stable resistor and capacitor values. In the case of
R1=R2=R:
R fb
2C 2 – C 1 -------Rg
ζ = -------------------------------2 C1 C2
Due to a limited selection of values of capacitors in comparison with resistors, we can set
C1=C2=C, so that:
R fb
2R 2 – R 1 -------Rg
ζ = -------------------------------2 R1 R2
18/22
TSH350
9
Package information
Package information
Figure 36. SOT23-5 package mechanical data
Dimensions
Ref.
Millimeters
Min.
Typ.
Mils
Max.
Min.
Typ.
Max.
A
0.90
1.45
35.4
57.1
A1
0.00
0.15
0.00
5.9
A2
0.90
1.30
35.4
b
0.35
0.50
13.7
C
0.09
0.20
3.5
D
2.80
3.00
110.2
E
2.60
3.00
102.3
E1
1.50
1.75
e
t
e
ol
e
0.95
e1
1.9
L
0.35
s
b
O
0.55
)
(s
59.0
13.7
)
s
(
ct
51.2
19.7
du
o
r
P
7.8
118.1
118.1
68.8
37.4
74.8
21.6
t
c
u
d
o
r
P
e
t
e
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o
s
b
O
19/22
Package information
TSH350
Figure 37. SO-8 package mechanical data
Dimensions
Ref.
Millimeters
Min.
Typ.
Inches
A
Max.
0.25
0.069
0.10
A2
1.25
0.004
b
0.28
0.48
0.011
0.019
c
0.17
0.23
0.007
0.010
D
4.80
4.90
5.00
0.189
0.193
H
5.80
6.00
6.20
0.228
0.236
E1
3.80
3.90
4.00
0.150
1.27
h
0.25
0.50
L
0.40
1.27
k
1°
s
(
t
c
u
d
o
0.010
e
t
e
l
o
s
b
8°
0.10
r
P
e
0.010
0.049
O
)
20/22
Max.
A1
ccc
s
b
O
Typ.
1.75
e
t
e
l
o
Min.
0.016
1°
u
d
o
)
s
(
ct
0.154
Pr
0.197
0.244
0.157
0.050
0.020
0.050
8°
0.004
TSH350
10
Ordering information
Ordering information
Table 5.
Order codes
Temperature
range
Part number
TSH350ILT
TSH350ID
-40°C to +85°C
TSH350IDT
11
Package
Packing
Marking
SOT23-5
Tape & reel
K305
SO-8
Tube
TSH350I
SO-8
Tape & reel
TSH350I
)
s
(
ct
Revision history
u
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Date
Revision
Changes
1-Oct-2004
1
First release corresponding to Preliminary Data version of datasheet.
10-Dec-2004
2
Release of mature product datasheet.
21-Jun-2005
3
In Table 1 on page 2, Rthjc thermal resistance junction to ambient
replaced by thermal resistance junction to case.
8-Jun-2007
4
Format update.
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21/22
TSH350
)
s
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u
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r
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22/22
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