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PDF LT1970 Data sheet ( Hoja de datos )
| Número de pieza | LT1970 | |
| Descripción | 500mA Power Op Amp with Adjustable Precision Current Limit | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1970
500mA Power Op Amp with
Adjustable Precision Current Limit
FEATURES
s ±500mA Minimum Output Current
s Independent Adjustment of Source and
Sink Current Limits
s 2% Current Limit Accuracy
s Operates with Single or Split Supplies
s Shutdown/Enable Control Input
s Open Collector Status Flags:
Sink Current Limit
Source Current Limit
Thermal Shutdown
s Fail Safe Current Limit and Thermal Shutdown
s 1.6V/µs Slew Rate
s 3.6MHz Gain Bandwidth Product
s Fast Current Limit Response: 2MHz Bandwidth
s Specified Temperature Range: – 40°C to 85°C
U
APPLICATIO S
s Automatic Test Equipment
s Laboratory Power Supplies
s Motor Drivers
s Thermoelectric Cooler Driver
, LTC and LT are registered trademarks of Linear Technology Corporation.
DESCRIPTIO
The LT®1970 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 2% 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 operation, the
input stage supplies and the output stage supplies are con-
nected (VCC to V+ and VEE to V–). To reduce power dissi-
pation 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 current limit circuits operate with a 2MHz re-
sponse between the VCSRC or VCSNK control inputs and
the amplifier output.
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 shut-
down and a ±800mA fixed current limit protect the chip
under fault conditions.
The LT1970 is packaged in a 20-lead TSSOP package with
a thermally conductive copper bottom plate to facilitate
heat sinking.
TYPICAL APPLICATIO
AV = 2 Amplifier with Adjustable ±500mA Full-Scale
Current Limit and Fault indication
VLIMIT
0V TO 5V
15V
15V
IOUT(LIMIT)
=
±
VLIMIT
10 • RCS
VCC V+
3k
VCSRC
VIN
+IN VCSNK
ISNK
ISRC
RCS
IOUT 1Ω
TSD 1/4W
LT1970
OUT
SENSE+
SENSE–
–IN VEE V–
COMMON
–15V
R1 LOAD
10k
R2
10k
1970 TA01
Current Limited Sinewave Into 10Ω Load
4V
2V
VLOAD
0V
– 2V
VCSRC = 4V
VCSNK = 2V
RCS = 1Ω
20µs/DIV
1970 TA02
1970f
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LT1970
Supply Current vs Supply Voltage
4.5
4.0 IV+
IV–
3.5
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)
1870 G16
Slew Rate vs Supply Voltage
1.8
1.7
FALLING
1.6
RISING
1.5
1.4
1.3
1.2
AV = –1
1.1 RF = RG = 1k
TA = 25°C
1.0
46 8
10 12 14
SUPPLY VOLTAGE (±V)
16 18
1970 G23
Large-Signal Response, AV = – 1
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)
1970 G18
Slew Rate vs Temperature
2.5
VS = ±15V
FALLING
2.0
RISING
1.5
1.0
0.5
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
1970 G24
Small-Signal Response, AV = 1
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)
1970 G21
Large-Signal Response, AV = 1
10V
0V
– 10V
RL = 1k
20µs/DIV
1970 G39
Small-Signal Response, AV = – 1
10V
0V
– 10V
RL = 1k
CL = 1000pF
20µs/DIV
1970 G40
RL = 1k
500ns/DIV
1970 G41
RL = 1k
CL = 1000pF
2µs/DIV
1970 G42
1970f
5
5 Page 
LT1970
APPLICATIO S I FOR ATIO
but these supply pins do not carry high currents, and the
power saving is much less. VCC and VEE must be greater
than the maximum output swing by 2V or more.
When V– and V+ are provided separately from VCC and VEE,
care must be taken to insure that V– and V+ are always less
than or equal to the main supplies in magnitude. Protec-
tion Schottky diodes may be required to insure this in all
cases, including power on/off transients.
Operation with reduced V+ and V– supplies does not affect
any performance parameters except maximum output
swing. All DC accuracy and AC performance specifications
guaranteed with VCC = V+ and VEE = V– are still valid within
the reduced signal swing range.
Heat Sinking
The power dissipated in the LT1970 die must have a path
to the environment. With 100°C/W thermal resistance in
free air with no heat sink, the package power dissipation is
limited to only 1W. The 20-pin TSSOP package with
exposed copper underside is an efficient heat conductor if
it is effectively mounted on a PC board. Thermal resis-
tances as low as 40°C/W can be obtained by soldering the
bottom of the package to a large copper pattern on the PC
board. For operation at 85°C, this allows up to 1.625W of
power to be dissipated on the LT1970. At 25°C operation,
up to 3.125W of power dissipation can be achieved. The
PC board heat spreading copper area must be connected
to VEE.
DRIVING REACTIVE LOADS
Capacitive Loads
The LT1970 is much more tolerant of capacitive loading
than most operational amplifiers. In a worst-case configu-
ration as a voltage follower, the circuit is stable for capaci-
tive loads less than 2.5nF. Higher gain configurations
improve the CLOAD handling. If very large capacitive loads
are to be driven, a resistive decoupling of the amplifier
from the capacitive load is effective in maintaining stability
and reducing peaking. The current sense resistor, usually
connected between the output pin and the load can serve
as a part of the decoupling resistance.
Very large capacitive loads above 1µF can also cause
transient overshoots when the current limiting circuits
activate. The FILTER pin is provided to assist in controlling
this problem. Should load capacitance cause transient
overshoot, a 1nF to 100nF capacitor between the FILTER
and SENSE– pins will minimize the overshoot. The best
value of capacitor to use in this situation will likely require
some empirical evaluation, as the optimum is a complex
function of output current, load resistance, sense resistor
and load capacitance.
Inductive Loads
Load inductance is usually not a problem at the outputs of
operational amplifiers, but the LT1970 can be used as a
high output impedance current source. This condition
may be the main operating mode, or when the circuit
enters a protective current limit mode. Just as load capaci-
tance degrades the phase margin of normal op amps, load
inductance causes a peaking in the loop response of the
feedback controlled current source. The inductive load
may be caused by long lead lengths at the amplifier output.
If the amplifier will be driving inductive loads or long lead
lengths (greater than 4 inches) a 500pF capacitor from the
SENSE– pin to the ground plane will cancel the inductive
load and insure stability.
Supply Bypassing
The LT1970 can supply large currents from the power
supplies to a load at frequencies up to 4MHz. Power supply
impedance must be kept low enough to deliver these
currents without causing supply rails to droop. Low ESR
capacitors, such as 0.1µF or 1µF ceramics, located close
to the pins are essential in all applications. When large,
high speed transient currents are present additional ca-
pacitance may be needed near the chip. Check supply rails
with a scope and if signal related ripple is seen on the
supply rail, increase the decoupling capacitor as needed.
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1970f
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LT1970.PDF ] | |
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