P-1
LTC324H
General Description
The LTC324H of quad-channel amplifiers provides input offset voltage correction for
positive low offset (2.5 mV maximum) and drift (1 µV/℃) through the use of proprietary
techniques. Featuring rail-to-rail input and output swings, and low quiescent current
(total 375 µA typically) combined with a wide bandwidth of 1.2 MHz and low noise (30
nV/√Hz at 1 kHz) makes this family very attractive for a variety of battery-powered
applications such as handsets, tablets, notebooks, and portable medical devices. The low
input bias current supports these amplifiers to be used in applications with mega-ohm
source impedances.
The robust design of the LTC324H amplifiers provides ease-of-use to the circuit
designer: unity-gain stability with capacitive loads of up to 500 pF, integrated RF/EMI
rejection filter, no phase reversal in overdrive conditions, and high electro-static
discharge (ESD) protection (5-kV HBM). The LTC324H amplifiers are optimized for
operation at voltages as low as +1.8 V (±0.9 V) and up to +5.5 V (±2.75 V) at the
temperature range of 0 ℃ to 70 ℃, and operation at voltages from +2.0 V (±1.0 V) to +5.5
V (±2.75 V) over the extended temperature range of −40 ℃ to +125 ℃.
The quad-channel LTC324H is offered in both SOIC-14L and TSSOP-14L packages.
Features and Benefits
Precision: 2.5 mV Maximum Positive Input Offset Voltage
Low Noise: 30 nV/√Hz at 1 kHz
1.2 MHz GBW for Unity-Gain Stable
Micro-Power: Total 375 μA Supply Current
Single 1.8 V to 5.5 V Supply Voltage Range at 0 ℃ to 70 ℃
Rail-to-Rail Input and Output
Internal RF/EMI Filter
Extended Temperature Range: −40℃ to +125℃
Applications
Battery-Powered Instruments:
– Consumer, Industrial, Medical, Notebooks
Wireless Chargers
Audio Outputs
Sensor Signal Conditioning:
– Sensor Interfaces, Loop-Powered, Active Filters
Wireless Sensors:
– Home Security, Remote Sensing, Wireless Metering
Pin Configurations (Top View)
LTC324H
SOIC-14L / TSSOP-14L
OUT A
1
﹣IN A
2
A
14
OUT D
13
﹣IN D
D
﹢IN A
3
12
﹢IN D
﹢VS
4
11
﹣VS
﹢IN B
5
10
﹢IN C
B
C
﹣IN B
6
9
﹣IN C
OUT B
7
8
OUT C
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
P-2
LTC324H
Pin Description
Symbol
Description
–IN
Inverting input of the amplifier. The voltage range is from (VS– – 0.1V) to (VS+ + 0.1V).
+IN
Non-inverting input of the amplifier. This pin has the same voltage range as –IN.
+VS
Positive power supply. The voltage is from 2.0V to 5.5V. Split supplies are possible
as long as the voltage between VS+ and VS– is from 2.0V to 5.5V.
–VS
Negative power supply. It is normally tied to ground. It can also be tied to a voltage
other than ground as long as the voltage between VS+ and VS– is from 2.0V to 5.5V.
OUT
Amplifier output.
Ordering Information
Type Number
Package Name
Package Quantity
Marking Code (1)
LTC324HXS14/R5
SO-14
Tape and Reel, 2 500
324 T, AG4IX
LTC324HXT14/R6
TSSOP-14
Tape and Reel, 3 000
324 T, AG4IX
(1) There may be multiple device markings, a varied marking character of “x” , or additional marking, which relates to the
logo, the lot trace code information, or the environmental category on the device.
Limiting Value
In accordance with the Absolute Maximum Rating System (IEC 60134).
Parameter
Absolute Maximum Rating
Supply Voltage, VS+ to VS–
10.0 V
Signal Input Terminals: Voltage, Current
VS– – 0.3 V to VS+ + 0.3 V, ±10 mA
Output Short-Circuit
Continuous
Storage Temperature Range, Tstg
–65 ℃ to +150 ℃
Junction Temperature, TJ
150 ℃
Lead Temperature Range (Soldering 10 sec)
260 ℃
ESD Rating
Parameter
Electrostatic
Discharge
Voltage
Item
Value
Human body model (HBM), per MIL-STD-883J / Method 3015.9 (1)
±5 000
Charged device model (CDM), per ESDA/JEDEC JS-002-2014 (2)
±2 000
Machine model (MM), per JESD22-A115C
±250
Unit
V
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
Manufacturing with less than 500-V HBM is possible if necessary precautions are taken.
(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
Manufacturing with less than 250-V CDM is possible if necessary precautions are taken.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
LTC324H
P-3
Electrical Characteristics
VS = 5.0V, TA = +25℃, VCM = VS /2, VO = VS /2, and RL = 10kΩ connected to VS /2, unless otherwise noted.
Boldface limits apply over the specified temperature range, TA = −40 to +125 ℃.
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Unit
+2.5
mV
3
μV/℃
OFFSET VOLTAGE
VOS
Input offset voltage
0
VOS TC
Offset voltage drift
TA = −40 to +125 ℃
PSRR
Power supply
rejection ratio
VS = 2.0 to 5.5 V, VCM < VS+ − 2V
80
TA = −40 to +125 ℃
75
±1
106
dB
INPUT BIAS CURRENT
1
IB
IOS
Input bias current
TA = +85 ℃
150
TA = +125 ℃
500
Input offset current
pA
5
pA
μVP-P
NOISE
Vn
Input voltage noise
f = 0.1 to 10 Hz
6
en
Input voltage noise
density
f = 10 kHz
27
f = 1 kHz
30
In
Input current noise
density
f = 1 kHz
10
nV/√Hz
fA/√Hz
INPUT VOLTAGE
VCM
CMRR
Common-mode
voltage range
Common-mode
rejection ratio
VS––0.1
VS = 5.5 V, VCM = −0.1 to 5.6 V
80
VCM = 0 to 5.3 V, TA = −40 to +125 ℃
72
VS = 2.0 V, VCM = −0.1 to 2.1 V
74
VCM = 0 to 1.8 V, TA = −40 to +125 ℃
66
VS++0.1
V
94
86
dB
INPUT IMPEDANCE
CIN
Input capacitance
Differential
2.0
Common mode
3.5
pF
OPEN-LOOP GAIN
AVOL
Open-loop voltage
gain
RL = 10 kΩ, VO = 0.05 to 3.5 V
90
TA = −40 to +125 ℃
85
RL = 600 Ω, VO = 0.15 to 3.5 V
85
TA = −40 to +125 ℃
80
105
100
dB
FREQUENCY RESPONSE
GBW
Gain bandwidth
product
SR
Slew rate
G = +1, CL = 100 pF,
VO = 1.5 to 3.5 V
THD+N
Total harmonic
distortion + noise
G = +1, f = 1 kHz, VO = 1 VRMS
tS
Settling time
tOR
Overload recovery
time
1.2
MHz
1.0
V/μs
0.003
%
To 0.1%, G = +1, 1V step
1.5
To 0.01%, G = +1, 1V step
1.8
To 0.1%, VIN * Gain > VS
2.5
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
μs
μs
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
LTC324H
P-4
Electrical Characteristics (continued)
VS = 5.0V, TA = +25℃, VCM = VS /2, VO = VS /2, and RL = 10kΩ connected to VS /2, unless otherwise noted.
Boldface limits apply over the specified temperature range, TA = −40 to +125 ℃.
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Unit
OUTPUT
VOH
High output voltage
swing
RL = 50 kΩ
VS+–6
VS+–3
RL = 2 kΩ
VS+–100
VS+–65
VOL
Low output voltage
swing
RL = 50 kΩ
VS–+2
VS–+4
RL = 2 kΩ
VS–+42
VS–+65
ISC
Short-circuit current
Source current through 10Ω
45
Sink current through 10Ω
55
mV
mV
mA
POWER SUPPLY
VS
Operating supply
voltage
IQ
Quiescent current
TA = 0 to +70 ℃
1.8
5.5
TA = −40 to +125 ℃
2.0
5.5
375
V
490
μA
+125
℃
THERMAL CHARACTERISTICS
TA
Operating
temperature range
θJA
Package Thermal
Resistance
–40
TSSOP-14L
112
SOIC-14L
115
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
℃/W
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
LTC324H
P-5
Typical Performance Characteristics
At TA = +25℃, VCM = VS /2, and RL = 10kΩ connected to VS /2, unless otherwise noted.
AOL (dB)
80
60
40
20
0
-20
-40
10
100
1k
10k
100k
1M
100
90
80
70
PSRR (dB)
100
140
120
100
80
60
40
20
0
-20
-40
-60
-80
10M
Phase (deg)
120
60
50
40
30
20
10
0
10
100
1k
Frequency (Hz)
Open-loop Gain and Phase as a function of
Frequency.
1M
1,000
Voltage Noise (nV/√Hz)
120
100
CMRR (dB)
100k
Power Supply Rejection Ratio as a function of
Frequency.
140
100
80
60
40
20
0
10
1
10
100
1k
10k
100k
1M
1
100
Frequency (Hz)
10k
1M
Frequency (Hz)
Common-mode Rejection Ratio as a function of
Frequency.
Input Voltage Noise Spectral Density as a function of
Frequency.
500
Quiescent Current (μA)
140
120
Channel Separation(dB)
10k
Frequency (Hz)
100
80
60
40
400
300
200
100
20
0
0
10
100
1k
10k
100k
1M
10M
1.5
2.5
3
3.5
4
4.5
5
5.5
Supply Voltage (V)
Frequency (Hz)
Channel Separation as a function of Frequency.
2
Quiescent Current as a function of Supply Voltage.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
LTC324H
P-6
Typical Performance Characteristics (continued)
At TA = +25℃, VCM = VS /2, and RL = 10kΩ connected to VS /2, unless otherwise noted.
5
Sourcing Current
500
4
Output Voltage (V)
Quiescent Current (μA)
600
400
300
200
100
0
125℃
25℃
2
1
Sinking Current
0
-50
-25
0
25
50
75
100
125
0
Temperature (℃)
10
20
30
40
50
60
70
Output Current (mA)
Output Voltage Swing as a function of Output
Current.
Quiescent Current as a function of Temperature.
60
Short-circuit Current (mA)
80
Short-circuit Current (mA)
–40℃
3
60
40
–ISC
20
+ISC
0
–ISC
50
40
30
+ISC
20
2
2.5
3
3.5
4
4.5
5
Supply Voltage (V)
Short-circuit Current as a function of Supply
Voltage.
5.5
-50
-25
0
25
50
75
100
Temperature (℃)
Short-circuit Current as a function of Temperature.
CL=100pF
25mV/div
CL=100pF
1V/div
125
5μs/div
Large Signal Step Response.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
2μs/div
Small Signal Step Response.
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
P-7
LTC324H
Application Notes
The LTC324H operational amplifier is unity-gain
stable and free from unexpected output phase
reversal. These devices use proprietary techniques
to provide positive low offset voltage and low drift
over temperature. For lowest offset voltage and
precision performance, optimize circuit layout and
mechanical conditions. Avoid temperature gradients
that create thermoelectric (Seebeck) effects in the
thermocouple junctions formed from connecting
dissimilar conductors. Cancel these thermallygenerated potentials by assuring they are equal on
both input terminals. Other layout and design
considerations include:
• Use low thermoelectric-coefficient conditions
(avoid dissimilar metals).
• Thermally isolate components from power supplies
or other heat sources.
• Shield operational amplifiers and input circuitry
from air currents, such as cooling fans.
Following these guidelines reduces the likelihood of
junctions being at different temperatures, which can
cause thermoelectric voltages of 0.1μV/℃ or higher,
depending on materials used.
OPERATING VOLTAGE
The LTC324H family is fully specified and ensured for
operation from 2.0 V to 5.5 V (±1.0 V to ±2.75 V). In
addition, many specifications apply from –40 ℃ to
+125 ℃. Parameters that vary significantly with
operating voltages or temperature are illustrated in
the typical characteristics graphs.
NOTE: Supply voltages (VS+ to VS–) higher than +10 V
can permanently damage the device.
RAIL-TO-RAIL INPUT
The input common-mode voltage range of the
LTC324H series extends 100 mV beyond the negative
and positive supply rails. This performance is
achieved with a complementary input stage: an Nchannel input differential pair in parallel with a Pchannel differential pair. The N-channel pair is active
for input voltages close to the positive rail, typically
VS+–1.4 V to the positive supply, whereas the Pchannel pair is active for inputs from 100 mV below
the negative supply to approximately VS+–1.4 V. There
is a small transition region, typically VS+–1.2 V to VS+–1
V, in which both pairs are on. This 200 mV transition
region can vary up to 200 mV with process variation.
Thus, the transition region (both stages on) can range
from VS+–1.4 V to VS+–1.2 V on the low end, up to VS+–1
V to VS+–0.8 V on the high end. Within this transition
region, PSRR, CMRR, offset voltage, offset drift, and
THD can be degraded compared to device operation
outside this region.
The typical input bias current of the LTC324H during
normal operation is approximately 1 pA. In overdriven
conditions, the bias current can increase significantly.
The most common cause of an overdriven condition
occurs when the operational amplifier is outside of
the linear range of operation. When the output of the
operational amplifier is driven to one of the supply
rails, the feedback loop requirements cannot be
satisfied and a differential input voltage develops
across the input pins. This differential input voltage
results in activation of parasitic diodes inside the
front-end input chopping switches that combine with
electromagnetic interference (EMI) filter resistors to
create the equivalent circuit. Notice that the input
bias current remains within specification in the linear
region.
INPUT EMI FILTER AND CLAMP CIRCUIT
Figure 1 shows the input EMI filter and clamp circuit.
The LTC324H op-amps have internal ESD protection
diodes (D1, D2, D3, and D4) that are connected
between the inputs and each supply rail. These
diodes protect the input transistors in the event of
electrostatic discharge and are reverse biased
during normal operation. This protection scheme
allows voltages as high as approximately 500 mV
beyond the rails to be applied at the input of either
terminal without causing permanent damage. These
ESD protection current-steering diodes also provide
in-circuit, input overdrive protection, as long as the
current is limited to 20 mA as stated in the Absolute
Maximum Ratings.
Operational amplifiers vary in susceptibility to EMI. If
conducted EMI enters the operational amplifier, the
dc offset at the amplifier output can shift from its
nominal value when EMI is present. This shift is a
result of signal rectification associated with the
internal semiconductor junctions. Although all
operational amplifier pin functions can be affected by
EMI, the input pins are likely to be the most
susceptible. The EMI filter of the LTC324H family is
composed of two 5 kΩ input series resistors (RS1 and
RS2), two common-mode capacitors (CCM1 and CCM2),
and a differential capacitor (CDM). These RC networks
set the −3dB low-pass cutoff frequencies at 35 MHz
for common-mode signals, and at 22 MHz for
differential signals.
VS+
D1
RS1
5kΩ
IN+
D2
D3
CCM1
RS2 CDM
5kΩ
IN–
D4
CCM2
VS–
Figure 1. Input EMI Filter and Clamp Circuit
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
P-8
LTC324H
Application Notes (continued)
RAIL-TO-RAIL OUTPUT
feedback loop.
Designed as a micro-power, low-noise operational
amplifier, the LTC324H delivers a robust output drive
capability. A class AB output stage with commonsource transistors is used to achieve full rail-to-rail
output swing capability. For resistive loads up to 100
kΩ, the output swings typically to within 5 mV of
either supply rail regardless of the power-supply
voltage applied. Different load conditions change the
ability of the amplifier to swing close to the rails. For
resistive loads up to 2 kΩ, the output swings typically
to within 65 mV of the positive supply rail and within
42 mV of the negative supply rail.
For no-buffer configuration, there are two others
ways to increase the phase margin: (a) by increasing
the amplifier’s gain, or (b) by placing a capacitor in
parallel with the feedback resistor to counteract the
parasitic capacitance associated with inverting node.
CF
VIN
CL
The LTC324H family can safely drive capacitive loads
of up to 500 pF in any configuration. As with most
amplifiers, driving larger capacitive loads than
specified may cause excessive overshoot and ringing,
or even oscillation. A heavy capacitive load reduces
the phase margin and causes the amplifier frequency
response to peak. Peaking corresponds to overshooting or ringing in the time domain. Therefore, it
is recommended that external compensation be used
if the LTC324H op-amps must drive a load exceeding
500 pF. This compensation is particularly important
in the unity-gain configuration, which is the worst
case for stability.
A quick and easy way to stabilize the op-amp for
capacitive load drive is by adding a series resistor,
RISO, between the amplifier output terminal and the
load capacitance, as shown in Figure 2. RISO isolates
the amplifier output and feedback network from the
capacitive load. The bigger the RISO resistor value, the
more stable VOUT will be. Note that this method
results in a loss of gain accuracy because RISO forms
a voltage divider with the RL.
RISO
VIN
VOUT
LTC324H
CAPACITIVE LOAD AND STABILITY
LTC324H
RF
RISO
VOUT
CL
Figure 2. Indirectly Driving Heavy Capacitive Load
An improvement circuit is shown in Figure 3. It
provides DC accuracy as well as AC stability. The RF
provides the DC accuracy by connecting the inverting
signal with the output.
The CF and RISO serve to counteract the loss of phase
margin by feeding the high frequency component of
the output signal back to the amplifier’s inverting
input, thereby preserving phase margin in the overall
RL
Figure 3. Indirectly Driving Heavy Capacitive Load
with DC Accuracy
OVERLOAD RECOVERY
Overload recovery is defined as the time required for
the operational amplifier output to recover from a
saturated state to a linear state. The output devices
of the operational amplifier enter a saturation region
when the output voltage exceeds the rated operating
voltage, either because of the high input voltage or
the high gain. After the device enters the saturation
region, the charge carriers in the output devices
require time to return back to the linear state. After
the charge carriers return back to the linear state,
the device begins to slew at the specified slew rate.
Thus, the propagation delay in case of an overload
condition is the sum of the overload recovery time
and the slew time. The overload recovery time for
the LTC324H family is approximately 2.5 μs.
EMI REJECTION RATIO
Circuit performance is often adversely affected by
high frequency EMI. When the signal strength is low
and transmission lines are long, an op-amp must
accurately amplify the input signals. However, all opamp pins — the non-inverting input, inverting input,
positive supply, negative supply, and output pins —
are susceptible to EMI signals. These high frequency
signals are coupled into an op-amp by various
means, such as conduction, near field radiation, or
far field radiation. For example, wires and printed
circuit board (PCB) traces can act as antennas and
pick up high frequency EMI signals.
Amplifiers do not amplify EMI or RF signals due to
their relatively low bandwidth. However, due to the
nonlinearities of the input devices, op-amps can
rectify these out of band signals. When these high
frequency signals are rectified, they appear as a dc
offset at the output.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
LTC324H
P-9
Application Notes (continued)
The LTC324H op-amps have integrated EMI filters at
their input stage. A mathematical method of
measuring EMIRR is defined as follows:
EMIRR = 20 log (VIN_PEAK / ΔVOS)
thermocouple error. Maintaining a constant ambient
temperature on the circuit board further reduces this
error. The use of a ground plane helps distribute heat
throughout the board and reduces EMI noise pickup.
INPUT-TO-OUTPUT COUPLING
To minimize capacitive coupling, the input and output
signal traces should not be parallel. This helps
reduce unwanted positive feedback.
MAXIMIZING PERFORMANCE THROUGH PROPER
LAYOUT
To achieve the maximum performance of the
extremely high input impedance and low offset
voltage of the LTC324H op-amps, care is needed in
laying out the circuit board. The PCB surface must
remain clean and free of moisture to avoid leakage
currents between adjacent traces. Surface coating of
the circuit board reduces surface moisture and
provides a humidity barrier, reducing parasitic
resistance on the board. The use of guard rings
around the amplifier inputs further reduces leakage
currents. Figure 4 shows proper guard ring
configuration and the top view of a surface-mount
layout. The guard ring does not need to be a specific
width, but it should form a continuous loop around
both inputs. By setting the guard ring voltage equal to
the voltage at the non-inverting input, parasitic
capacitance is minimized as well. For further
reduction of leakage currents, components can be
mounted to the PCB using Teflon standoff insulators.
Guard
Ring
+IN
–IN
+VS
Figure 4. Use a guard ring around sensitive pins
Other potential sources of offset error are
thermoelectric voltages on the circuit board. This
voltage, also called Seebeck voltage, occurs at the
junction of two dissimilar metals and is proportional
to the temperature of the junction. The most common
metallic junctions on a circuit board are solder-toboard trace and solder-to-component lead. If the
temperature of the PCB at one end of the component
is different from the temperature at the other end,
the resulting Seebeck voltages are not equal,
resulting in a thermal voltage error.
This thermocouple error can be reduced by using
dummy components to match the thermoelectric
error source. Placing the dummy component as
close as possible to its partner ensures both
Seebeck voltages are equal, thus canceling the
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
LTC324H
P-10
Typical Application Circuits
DIFFERENTIAL AMPLIFIER
eliminates expansive low-leakage cables that that is
required to connect a pH probe (general purpose
combination pH probes, e.g Corning 476540) to metering
ICs such as ADC, AFE and/or MCU. A LTC324H op-amp and
a lithium battery are housed in the probe assembly. A
conventional low-cost coaxial cable can be used to carry
the op-amp’s output signal to subsequent ICs for pH
reading.
R2
R1
Vn
LTC324H
VOUT
Vp
R3
MOTOR PHASE CURRENT SENSING AMPLIFIER
R4
VREF
Figure 5. Differential Amplifier
The circuit shown in Figure 5 performs the difference
function. If the resistors ratios are equal R4/R3 = R2/R1, then:
VOUT = (Vp – Vn) × R2/R1 + VREF
INSTRUMENTATION AMPLIFIER
RG
VREF
R1
R2
R2
LTC324H
R1
LTC324H
VOUT
V1
V2
VOUT =(V1 V2 )(1
R1 2 R1
) VREF
R2 RG
The current sensing amplification shown in Figure 8 has a
slew rate of 2πfVPP for the output of sine wave signal, and
has a slew rate of 2fVPP for the output of triangular wave
signal. In most of motor control systems, the PWM
frequency is at 10 kHz to 20 kHz, and one cycle time is 100
μs for a 10 kHz of PWM frequency. In current shunt
monitoring for a motor phase, the phase current is
converted to a phase voltage signal for ADC sampling. This
sampling voltage signal must be settled before entering the
ADC. As the Figure 8 shown, the total settling time of a
current shunt monitor circuit includes: the rising edge delay
time (tSR) due to the op-amp’s slew rate, and the
measurement settling time (tSET). For a 3-shunt solution in
motor phase current sensing, if the smaller duty cycle of
the PWM is defined at 45% (In fact, the phase with minimum
PWM duty cycle, such as 5%, is not detected current directly,
and it can be calculated from the other two phase currents),
and the tSR is required at 20% of a total time window for a
phase current monitoring, in case of a 3.3 V motor control
system (3.3 V MCU with 12-bit ADC), the op-amp’s slew rate
should be more than:
3.3V / (100μs× 45% × 20%) = 0.37 V/μs
At the same time, the op-amp’s bandwidth should be much
greater than the PWM frequency, like 10 time at least.
Figure 6. Instrumentation Amplifier
The LTC324H family is well suited for conditioning sensor
signals in battery-powered applications. Figure 6 shows a
two op-amp instrumentation amplifier, using the LTC324H
op-amps. The circuit works well for applications requiring
rejection of common-mode noise at higher gains. The
reference voltage (VREF) is supplied by a low-impedance
source. In single voltage supply applications, the VREF is
typically VS/2.
tSR
VBUS
tSET
High side
switch
tSR – Time delay due to op-amp slew rate
tSET – Measurement settling time
tSMP – Sampling time window
To Motor Phase
VM
Low side
switch
BUFFERED CHEMICAL SENSORS
tSMP
R2
R1
RSHUNT
Coax
LTC324H
R1
10MΩ
3V
C1
To MCU
ADC pin
LTC324H
R3
R4
To ADC,
AFE or MCU
R5
C2
Filter
pH
PROBE
Offset
Amplification
Figure 8. Current Shunt Monitor Circuit
R2
10MΩ
All components contained within the pH probe
Figure 7. Buffered pH Probe
The LTC324H family has input bias current in the pA range.
This is ideal in buffering high impedance chemical sensors,
such as pH probes. As an example, the circuit in Figure 7
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
LTC324H
P-11
Package Outlines (continued)
TSSOP-14L
A3 A2
A
Symbol
A1
D
b
e
C
L1 L
E
E1
A
A1
A2
A3
b
C
D
E
E1
e
L1
L
θ
Dimensions
In Millimeters
Min
Max
1.200
0.050
0.150
0.900
1.050
0.390
0.490
0.200
0.290
0.130
0.180
4.860
5.060
6.200
6.600
4.300
4.500
0.650 TYP.
1.000 REF.
0.450
0.750
0°
8°
Dimensions
In Inches
Min
Max
0.0472
0.002
0.006
0.037
0.043
0.016
0.020
0.008
0.012
0.005
0.007
0.198
0.207
0.253
0.269
0.176
0.184
0.0256 TYP.
0.0393 REF.
0.018
0.031
0°
8°
Dimensions
In Millimeters
Min
Max
1.450
1.850
0.100
0.300
1.350
1.550
0.550
0.750
0.406 TYP.
0.203 TYP.
8.630
8.830
5.840
6.240
3.850
4.050
1.270 TYP.
1.040 REF.
0.350
0.750
2°
8°
Dimensions
In Inches
Min
Max
0.059
0.076
0.004
0.012
0.055
0.063
0.022
0.031
0.017 TYP.
0.008 TYP.
0.352
0.360
0.238
0.255
0.157
0.165
0.050 TYP.
0.041 REF.
0.014
0.031
2°
8°
θ
SOIC-14L
A3
A2
A
A1
D
b
C
e
L1 L
E
Symbol
E1
A
A1
A2
A3
b
C
D
E
E1
e
L1
L
θ
θ
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
P-12
LTC324H
IMPORTANT NOTICE
Linearin is a global fabless semiconductor company specializing in advanced high-performance highquality analog/mixed-signal IC products and sensor solutions. The company is devoted to the innovation
of high performance, analog-intensive sensor front-end products and modular sensor solutions, applied
in multi-market of medical & wearable devices, smart home, sensing of IoT, and intelligent industrial &
smart factory (industrie 4.0). Linearin’s product families include widely-used standard catalog products,
solution-based application specific standard products (ASSPs) and sensor modules that help customers
achieve faster time-to-market products. Go to http://www.linearin.com for a complete list of Linearin
product families.
For additional product information, or full datasheet, please contact with the Linearin’s Sales Department
or Representatives.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
Linearin and designs are registered trademarks of Linearin Technology Corporation.
© Copyright Linearin Technology Corporation. All Rights Reserved.
All other trademarks mentioned are the property of their respective owners.
FN1617-34Q.0c — Data Sheet
General-Purpose, Micro-Power 1.2MHz, RRIO Precision Amplifiers
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