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PDF LT1970A Data sheet ( Hoja de datos )
| Número de pieza | LT1970A | |
| Descripción | 500mA Power Op Amp | |
| Fabricantes | Linear | |
| Logotipo |  |
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LT1970A
500mA Power Op Amp with
Adjustable Precision Current Limit
FEATURES
DESCRIPTION
n ± 500mA Minimum Output Current
n Independent Adjustment of Source and
Sink Current Limits
n 1% Current Limit Accuracy
n Improved Reactive Load Driving Stability
n Operates with Single or Split Supplies
n Shutdown/Enable Control Input
n Open-Collector Status Flags:
Sink Current Limit
Source Current Limit
Thermal Shutdown
n Fail-Safe Current Limit and Thermal Shutdown
n 1.6V/µs Slew Rate
n 3.6MHz Gain-Bandwidth Product
n Specified Temperature Range: –40°C to 85°C
n Available in a 20-Lead TSSOP Package
APPLICATIONS
n Automatic Test Equipment
n Laboratory Power Supplies
n Motor Drivers
n Thermoelectric Cooler Driver
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
The LT®1970A is a ± 500mA power op amp with precise
externally controlled current limiting. Separate control
voltages program the sourcing and sinking current limit
sense thresholds with 1% accuracy. Output current may
be boosted by adding external power transistors.
The circuit operates with single or split power supplies
from 5V to 36V total supply voltage. In normal opera-
tion, the input stage supplies and the output stage sup-
plies are connected (VCC to V+ and VEE to V–). To reduce
power dissipation it is possible to power the output stage
(V+, V–) from independent, lower voltage rails. The amplifier
is unity-gain stable with a 3.6MHz gain-bandwidth product
and slews at 1.6V/µs. The LT1970A can drive capacitive
and inductive loads directly.
Open-collector status flags signal current limit circuit
activation, as well as thermal shutdown of the amplifier.
An enable logic input puts the amplifier into a low power,
high impedance output state when pulled low. Thermal
shutdown and a ±800mA fixed current limit protect the
chip under fault conditions.
The LT1970A is packaged in a 20-lead TSSOP package with
a thermally conductive copper bottom plate to facilitate
heat sinking.
TYPICAL APPLICATION
Device Power Supply (DPS) with ±500mA Adjustable Current Limit
VLIMIT
0V TO 5V
VIN
20V 20V
VCC V+
EN
6k
+IN
VCSRC
VCSNK
ISNK
ISRC
LT1970A
SENSTSE+DOUT
SENSE–
–IN
V–
VEE
COMMON
IOUT(MAX)
IOUT
=
±
VLIMIT
10 • RCS
RCS
1Ω
1/4W
TRACE R TRACE L
100mΩ 200nH
SENSE
4.7µF
ESR
0.1Ω
LOAD
1970A TA01
–5V 10k
100pF
CURRENT LIMIT = 500mA
VLOAD, RLOAD = 100Ω
2V/DIV
0V
VLOAD,
RLOAD = 10Ω
VIN, 5V/DIV
100µs/DIV
For more information www.linear.com/LT1970A
1970A TA01b
1970afb
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1970A
Supply Current vs Supply Voltage
4.5
4.0
3.5
IV+
IV–
3.0 IVCC
2.5
2.0 IVEE
1.5
1.0
0.5 VTACC==25V°+C= –VEE = –V–
0
2 4 6 8 10 12 14 16 18 20
SUPPLY VOLTAGE (±V)
1870A G04
Gain Bandwidth vs Supply Voltage
5 AV = 100
4
3
2
Open-Loop Gain and Phase
vs Frequency
70
100
60 90
50 GAIN
40
PHASE
80
70
30 60
20 50
10 40
0 30
–10 20
–20 10
–30 0
100 1k 10k 100k 1M 10M 100M
FREQUENCY (Hz)
1970A G05
Gain vs Frequency
10 AV = 1
0
–10
VS = ±15V
VS = ±5V
–20
1 –30
0
0 4 8 12 16 20 24 28 32 36
TOTAL SUPPLY VOLTAGE (V)
1970A G07
Output Impedance
100
VS = ±15V
10
AV = 100
1
0.1
AV = 10
AV = 1
0.01
0.001
1k
10k 100k 1M 10M 100M
FREQUENCY (Hz)
1970A G10
–40
10k
100k
1M
FREQUENCY (Hz)
10M
1970A G08
Disabled Output Impedance
600k
100k
VS = ±15V
VENABLE = 0.8V
10k
1k
100
10
1
1k 10k 100k 1M 10M 100M
FREQUENCY (Hz)
1970A G11
Phase Margin vs Supply Voltage
60
58
AV = –1
RF = RG = 1k
56
TA = 25°C
VOUT = VS/2
54
52
50
48
46
44
42
40
0
4 8 12 16 20 24 28 32 36
TOTAL SUPPLY VOLTAGE (V)
1970A G06
Gain vs Frequency with CL OAD
10 VS = ±15V
AV = 1
0
30nF
10nF
1nF
–10
0nF
–20
–30
–40
10k
100k
1M
FREQUENCY (Hz)
10M
1970A G09
Slew Rate vs Supply Voltage
1.8
1.7
FALLING
1.6
RISING
1.5
1.4
1.3
1.2
1.1
AV = –1
RF = RG = 1k
1.0 TA = 25°C
46 8
10 12 14
SUPPLY VOLTAGE (±V)
16 18
1970A G12
For more information www.linear.com/LT1970A
1970afb
5
5 Page 
LT1970A
APPLICATIONS INFORMATION
and VCSRC/10 in magnitude, cause the current limit ampli-
fiers to decouple from the signal path. This is functionally
indicated by diodes D1 and D2 in the Block Diagram. When
the voltage VSENSE increases in magnitude sufficient to
equal or overcome one of the offset voltages VCSNK/10 or
VCSRC/10, the appropriate current limit amplifier becomes
active and because of its very high transconductance, takes
control from the input stage, GM1. The output current is
regulated to a value of IOUT = VSENSE/RSENSE = (VCSRC or
VCSNK)/(10 • RSENSE). The time required for the current
limit amplifiers to take control of the output is typically 4µs.
Linear operation of the current limit sense amplifier
occurs with the inputs SENSE+ and SENSE– ranging be-
tween VCC –
connect pins
1S.E5NVSaEn+daVnEdEO+U1T.5toV.gMethoesrt,
applications will
with the load on
the opposite side of the external sense resistor and pin
SENSE–. Feedback to the inverting input of GM1 should
be connected from SENSE– to – IN. Ground side sensing
of load current may be employed by connecting the load
between pins OUT and SENSE+. Pin SENSE– would be
connected to ground in this instance. Load current would
be regulated in exactly the same way as the conventional
connection. However, voltage mode accuracy would be
degraded in this case due to the voltage across RSENSE.
Creative applications are possible where pins SENSE+ and
SENSE– monitor a parameter other than load current. The
operating principle that at most one of the current limit
stages may be active at one time, and that when active,
the current limit stages take control of the output from
GM1, can be used for many different signals.
Current Limit Threshold Control Buffers
Input pins VCSNK and VCSRC are used to set the response
thresholds of current limit amplifiers “ISINK” and “ISRC”.
Each of these inputs may be independently driven by a
voltage of 0V to 5V above the COMMON reference pin.
The 0V to 5V input voltage is attenuated by a factor of 10
and applied as an offset to the appropriate current limit
amplifier. AC signals may be applied to these pins. The AC
bandwidth from a VC pin to the output is typically 2MHz.
For proper operation of the LT1970A, these control inputs
cannot be left floating.
For low VCC supply applications it is important to keep
the maximum input control voltages, VCSRC and VCSNK,
at least 2.5V below the VCC potential. This ensures linear
control of the current limit threshold. Reducing the current
limit sense resistor value allows high output current from
a smaller control voltage which may be necessary if the
VCC supply is only 5V.
The transfer function from VC to the associated VOS is
linear from about 0.1V to 5V in, or 10mV to 500mV at
the current limit amplifier inputs. An intentional nonlinear-
ity is built into the transfer functions at low levels. This
nonlinearity ensures that both the sink and source limit
amplifiers cannot become active simultaneously. Simul-
taneous activation of the limit amplifiers could result in
uncontrolled outputs. As shown in the Typical Performance
Characteristics curves, the control inputs have a “hockey
stick” shape, to keep the minimum limit threshold at 4mV
for each limit amplifier.
Figure 1 illustrates an interesting use of the current
sense input pins. Here the current limit control ampli-
fiers are used to produce a symmetrically limited output
voltage swing. Instead of monitoring the output current,
the output voltage is divided down by a factor of 20 and
applied to the SENSE+ input, with the SENSE– input
grounded. When the threshold voltage between SENSE+
and SENSE– (VCLAMP/10) is reached, the current limit
stage takes control of the output and clamps it a level of
±2 • VCLAMP. With control inputs VCSRC and VCSNK tied
together, a single polarity input voltage sets the same +
and – output limit voltage for symmetrical limiting. In this
circuit the output will current limit at the built-in fail-safe
level of typically 800mA.
ENABLE Control
The ENABLE input pin puts the LT1970A into a low sup-
ply current, high impedance output state. The ENABLE
pin responds to TTL threshold levels with respect to the
COMMON pin. Pulling the ENABLE pin low is the best
way to force zero current at the output. Setting VCSNK =
VCSRC = 0V allows the output current to remain as high
as ± 4mV/RSENSE.
For more information www.linear.com/LT1970A
1970afb
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT1970A.PDF ] | |
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