DC453B - Demo Manual

DEMO CIRCUIT 453B
QUICK STARTLT1970A
GUIDE
LT1970A
Power Amplifier with
Adjustable Current Limiting
DESCRIPTION
Demonstration circuit 453B is useful for evaluating the
LT1970A, a power amplifier with adjustable current limiting. The demo circuit is available in two versions;
DC453B-A with up to 500mA of output current and
DC453B-B for applications with up to 5 Amps of output
current. For the 5 Amp version a Class B MOSFET based
current boost stage has been added to the output section
with current limit control still provided by the LT1970A.
The maximum output current of the board is set by two
on-board potentiometers to permit independent control
of the sinking and sourcing current limit. The current
limit adjustment can also be provided by external voltage
sources. Symmetrical sourcing and sinking current limit
with a single control is also possible.
LEDs provide an indication of faults detected by the
LT1970A. Separate indicators illuminate when the amplifier enters sourcing or sinking current limit and if the
LT1970A overheats and enters thermal shutdown protection.
Several jumpers enable flexible amplifier operation. Configurations include:
Single or dual power supplies
Separate or common input stage and power output
stage supplies
AC or DC coupled inputs
Non-Inverting gains of 1 or 2, Inverting gain of –1
Separate or common current limit control
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT and
PowerPath are trademarks of Linear Technology Corporation.
TYPICAL PERFORMANCE SUMMARY
TA = 25°C, Common ±12V Supplies
SYMBOL PARAMETER
VSUPPLY Power Supply Range
IOUT
Adjustable Output Current Limit Range
BWS
Small Signal –3dB Bandwidth
BWL
SR
VSATH
Large Signal –3dB Bandwidth
Slew Rate
Output Sat Voltage High
CONDITIONS
Single Supply
Dual Supply
DC453B-A (LT1970A basic amplifier), Vcc ≥ 8V
DC453B-B (Boosted)
DC453B-A (LT1970A basic amplifier)
AV= +1, Vout=200mVP-P, RLOAD=100Ω,
DC453B-B (Boosted)
AV= +1, Vout=200mVP-P, RLOAD=10Ω
DC453B-A (LT1970A basic amplifier)
AV= +1, Vout=20VP-P, RLOAD=100Ω
DC453B-B (Boosted)
AV= +1, Vout=10VP-P, RLOAD=10Ω,
DC453B-A (LT1970A basic amplifier), VSAT=V+VOUT
Common ±12V Supplies, RLOAD=250Ω
Common ±12V Supplies, RLOAD=25Ω
Vcc/Vee=±12V and V+/V-=±5V, RLOAD=100Ω
Vcc/Vee=±12V and V+/V-=±5V, RLOAD=10Ω
MIN
8
±8
±4
±0.04
TYP
MAX
36
±18
±500
±5
UNITS
V
V
mA
A
1.6
MHz
7.2
KHz
58
KHz
7
1.6
KHz
V/μS
1.4
2.1
0.1
0.8
V
V
V
V
1
LT1970A
TYPICAL PERFORMANCE SUMMARY
TA = 25°C, Common ±12V Supplies
SYMBOL PARAMETER
VSATL
IS
Output Sat Voltage Low
Total Quiescent Supply Current
CONDITIONS
DC453B-B (Boosted), See Operational Notes
DC453B-A (LT1970A basic amplifier), VSAT= VOUTVCommon ±12V Supplies, RLOAD=250Ω
Common ±12V Supplies, RLOAD=25Ω
Vcc/Vee=±12V and V+/V-=±5V, RLOAD=100Ω
Vcc/Vee=±12V and V+/V-=±5V, RLOAD=10Ω
MIN
DC453B-B (Boosted), See Operational Notes
No Load
DC453B-A (LT1970A basic amplifier)
DC453B-B (Boosted)
TYP
MAX
UNITS
2.1
2.8
0.3
1.3
V
V
V
V
9
12
mA
mA
QUICK START PROCEDURE
Demonstration circuit 453B is easy to set up to evaluate
the performance of the LT1970A. Before applying power
to the amplifier, configure all on-board jumpers for the
desired operation. Figure 1 provides an overview of how
JP1: Input Signal Coupling, AC or DC
the placement of each of the jumpers adjusts the configuration. Position each jumper for the following results:
DC coupling, non-inverting, applies the input signal directly to the amplifier + input with a 5KΩ input impedance, inverting, directly connects to a 10KΩ resistor to
the amplifier – input.
AC coupling connects the input signal through a series
10μF capacitor. Depending on the amplifier topology the
lower –3dB corner frequency is in the range of 1.6Hz to
6.2Hz.
JP2: Inverting (INV) or Non-Inverting (NI)
Directs the input signal for an Inverting or Non-Inverting
amplifier.
DUAL sets the DC bias of the inputs and output to
ground when symmetrical dual + and - power supplies
are used.
SINGLE sets the DC bias of the inputs and output to ½
Vcc when a single power supply is used. This setting also
biases the inputs and output to the midpoint of asymmetrical dual supplies.
Removing the shunt from this jumper can allow the power amplifier to bias at the same dc potential as the input
signal for DC coupled single supply uses.
JP4: Gain Configuration Setting
The four positions of this jumper configure the amplifier
to one of three gain values. The inset diagram on the
schematic, Figure 4, shows how the amplifier feedback is
arranged for each jumper position. A small table is also
included on the printed circuit board to serve as a ready
reference for the jumper settings.
The jumper position shorting pins 2 and 3 provides the
same configuration as shorting pins 3 and 4.
JP5: Separate (S) or Common (C) Current Limit Control
JP3: Input biasing for SINGLE or DUAL Power Supplies
Separate (S) position allows for the independent setting
of the amplifier sourcing current limit and sinking current
2
LT1970A
limit through two 10K potentiometers and an on-board
5V regulator. Any voltage between 0V and 5V applied to
the LT1970A pins VCSRC and VCSNK sets the output
current limit value.
Common (C) position connects the VCSRC and VCSNK
input pins together to force the sourcing and sinking current limit values to be the same. With this setting, only
the potentiometer labeled VCSRC adjusts the current limit control voltage.
JP6: Vee biasing for SINGLE or DUAL Power Supplies
SINGLE setting connects the Vee supply of the LT1970A
directly to ground.
DUAL setting connects the Vee supply to the VEE input
jack.
.
With the Common (COM) selection just one power
source, a single positive supply, or one pair of plus
and minus supplies, is required. This supply powers both
JP7: Common (COM) or Separate (SEP) Power Supplies
the input stage supplies of the LT1970A, Vcc and Vee,
and the output stage supplies, V+ and V-.
With the Separate (SEP) selection the output stage supplies must be provided separately to the V+ and Vinput
jacks. This feature reduces power dissipation in the output stage by running the supplies at a lower value than
the main amplifier input stage.
COM
S
C
SEP
Note proper shunt
orientation.
JP7
JP5
Separate or Common Source
and Sink Current Limit Control
Common or Separate Input
Stage and Output Stage
Supplies
SINGLE
DUAL
JP6
Single Supply (LT1970
Vee=0V) or Dual Supply
(LT1970 Vee=Vee
Voltage)
DC
AC
JP1
DC or AC
Coupled Input
Gain Setting Table
JP4
INV
JP2
NON
SINGLE
JP3
DUAL
5 4 3 2 1
Amplifier Gain
Configuration
Inverting or NonSingle Supply (DC Vout=Vcc/2) or
Inverting
Dual Supply (DC Vout=0V)
Amplifier
Figure 1. DC453B Jumper Configuration
3
LT1970A
POWER CONNECTIONS
Figure 2 shows how to properly connect power to the
453B demo circuit.
Dual Supplies
Separate Dual Supplies
Single Supply
Figure 2. Power Supply Connections
OPTIONAL EXTERNAL
CONNECTIONS
Several test point turrets have been added, see Figure
3, to make it easy to use external equipment to control
the operation of the power amplifier.
External
Enable(5V)/Disable(0V)
Pulse
Error Flag Monitoring
Thermal Shutdown (TP14)
Sink Current Limit (TP15)
Source Current Limit (TP16)
TP10
External Current Limit
Control
(Use Source Supply
Only for Single
Symmetrical Current
Limit Control)
Sink
0V to 5Vdc
TP3
Source
0V to 5Vdc
TP4
Manual Current Source
Limit Adjustments
Sink
TP11
Input Signal
J6
J4
Load
Output Signal
Figure 3. External Control Options
4
LT1970A
OPERATIONAL NOTES
Minimum Supply Voltage
The LT1970A can operate with a total supply voltage of
only 5 Volts. For convenience, a 5V regulator is included
on DC453B to provide the control voltage for the current
limit adjustments. To keep this regulator properly biased
the minimum positive Vcc supply must be at least 8 Volts
when using either a single or dual power supply. Lower
supply voltage is possible if external current limit control
voltages are provided.
Current Limit Control
To ensure proper operation of the LT1970A two 100kΩ
resistors to ground are connected to the two current limit
control inputs. These resistors prevent open circuit control inputs with jumper JP5 removed. The effect of these
resistors slightly attenuates the current limit control voltages provided by the on-board potentiometers. With
separate limit control, the maximum voltage is 4.6V.
When tied together for common control the maximum
voltage is 4.2V.
The actual current limit of DC453B is actually slightly
greater than the expected nominal value at higher output
current levels (greater than 400mA for the –A version
and 4A for the –B version). The reason for this is the inclusion of diode package D5. The back-to-back diodes
across the current sense inputs prevent erratic behavior
in the unlikely event of an abrupt output short circuit
condition. These diodes limit the maximum voltage difference seen at the sense amplifier inputs. When the voltage across the sense resistor, Rsense, exceeds 0.4
Volts, the diodes begin to conduct current and decrease
the actual voltage difference seen by the sense amplifier.
Boosted Current Version
DC453B-B contains complimentary P and N channel
power MOSFETs for output current up to ±5A. The same
easy voltage control of the output current is provided by
the LT1970A. The current boost stage is a class B design
intended for DC and low frequency applications.
The crossover distortion of this typical Class B design is
apparent at frequencies greater than 7kHz. Above this
frequency, the total time in crossover becomes 10% or
more of the period of a sine wave input.
The frequency response of the current boosted amplifier
will vary as a function of the load resistance. Resistor R9,
100Ω, and the load resistor create an attenuation network inside the feedback loop of the amplifier. This causes the LT1970A to run at a higher closed loop gain than
the overall amplifier gain, limiting the observed output
1
⎛
R ⎞
2πRF C 24 • ⎜⎜ 1 + 9 ⎟⎟
⎝ Rload ⎠
closed loop frequency response. The –3dB corner frequency of the boosted amplifier is:
F−3dB =
Where RF (10KΩ) and C24 (220pf) are feedback components already provided on the board. Refer to the Figure
4 schematic. With no load, the non-inverting unity gain
bandwidth is 72kHz. Depending on signal levels the usable bandwidth may be less due to the 1.6V/μs slew rate.
The large power MOSFETs in the output stage can pull
the output voltage very near the supply voltage rails. This
can cause the sense amplifier inputs to exceed their input
common mode voltage range, which is 1V away from
either the Vcc or Vee supply rail. This can cause what
appears to be a latch-up condition where the output goes
to one rail or the other and illuminates the current limit
indicators. Reducing the input voltage and cycling the
power supplies will reset the amplifier back to normal. To
prevent this from occurring, places for resistor divider
networks to reduce the voltages seen at the sense amplifier inputs are provided. These are resistors R12
through R15 on the board. The identical divider networks
should ensure that the peak voltages at the sense amplifier inputs are never within 1 Volt of the Vcc or Vee
supply rails.
5
A
B
C
D
C16
10uF
35V
7
6
3
DUAL
SINGLE
NC
NC
NC
U2
LTC3010EMS8E-5
+
8
VEE
4
GND
5
OUT
C14
1uF
2
JP2
+5V
R26
10K
DC453B-A
NON BOOSTED
DC453B-B
BOOSTED
Assembly Type
100
0 JUMPER
R9, R10,
R11
25V
C17 10uF
INV
NON
INPUT_OPA
TP1
* VERSION TABLE
VEE_DEVICE
2
1
5
JP4
1
2
3
4
5
3
10uF
AC
R20
4.99K
2
JP3
SHDN
1uF
JP6
2
2
DC
SENSE
GND
IN
25V
C1
JP1
1
C15
R16
2K
VCC
DUAL
SINGLE
2.5K
R19
BNC
TP18 TP19 TP20 TP21 TP22
R17
4.99K
R18
4.99K
VCC
J1 (OPT.)
INPUT
1
3
1
3
VR1
10K
VR2
10K
1
R12,R14
10K
R2
TP4
Q1, Q2
4
VCC
TBD
C2
10K
RF
*
*
2
1
R21
R3
NOT
0 JUMPER
INSTALLED
INSTALLED 0 JUMPER
1 OHM
>=0.5W
R13,R15
TBD
* R14
TBD
* R12
R30
100
3
D5
BAV99
3
3
NOT
INSTALLED
NOT
INSTALLED
R3, R21
R22, R23
TBD
* R15
*
*
R9
1K
(OPT.)
C12
TBD
*
R11
TP7
GND
J6
VEE
TP9
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
2
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A
CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;
HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO
VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL
APPLICATION. COMPONENT SUBSTITUTION AND PRINTED
CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT
PERFORMANCE OR RELIABILITY. CONTACT LINEAR
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
COM
PCB DES.
TIM R.
AK
SCALE = NONE
APP ENG.
10K
10K
-
+
10K
DUAL
SINGLE
SUPPLY
-
+
1
VEE
VCC
V-
V+
C22
10uF
35V
C20
10uF
35V
C10
10uF
35V
C8
10uF
35V
+2
JP2
10K
4-5
10K
2-3
-
+
-
+
10K
DUAL
SUPPLY
ONLY
10K
DUAL
SINGLE
SUPPLY
0.1uF
C23
C21
0.1uF
C11
0.1uF
C9
0.1uF
DATE:
N/A
1
LT1970A
DEMO CIRCUIT 453B
Wednesday, November 28, 2012
IC NO.
SHEET 1
POWER OP AMP WITH ADJUSTABLE CURRENT LIMIT
SIZE
DATE
11-28-12
OF 1
1
REV.
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900 www.linear.com
Fax: (408)434-0507
LTC Confidential-For Customer Use Only
INV NON
JP2
INV NON
TECHNOLOGY
IN
IN
+2
-1, +1
-1, +1
3-4
4-5
+2
-1, +1
-1, +1
2-3
AC GAIN
+1
DC GAIN
1-2
+
+
+
+
TIM R.
APPROVED
JP4
JP4 SETTINGS
VEE
-18V MAX
E3
E2
GND
VCC
+18V MAX
E1
V-18V MAX
E5
GND
E6
V+
+18V MAX
E4
PRODUCTION
DESCRIPTION
REVISION HISTORY
JP4 SETTING DIAGRAM
DUAL
SINGLE
SUPPLY
V-
1
__
V+
REV
ECO
TITLE: SCHEMATIC
10K
3-4
JP2
INV NON
10uF
INV NON
JP2
1-2
SEP
APPROVALS
IN
IN
JP7
OUTPUT
SUPPLIES
VCC
2
OUT FET D
FET_V-
OUTPUT
J4
FET_V-
NFET
J2 (OPT.)
OUTPUT
MONITOR
BNC
S
* IRF530N
D
Q2
IRF9530N
PFET
* Q1
D
S
CUSTOMER NOTICE
TP8
OUTPUT
TBD
* C13
G
G
*
R10
TP6
FET_V+
FET_V+
1/2W
*
R1K_LOAD
*
R_SENSE
1/2W
R8
*100
TP5
OPA OUT
B
A
* R23
TBD
3
R13
220pF
C24
OPA OUT
TBD
TBD
TBD
* R22
0.1 OHM
>=3W
C12, C13
C18
TBD
100K
R29
R_SENSE
3
0.1uF
C7
TP13
VCC
R5 R6 R7
1.5K 1.5K 1.5K
U1
LT1970A
JP5 S C
B
A
10uF
35V
TP3
R28
100K
VCSNK
C5
0.1uF
-IN
COMMON
+IN
C6
R4
10K
VCSRC/VCLCONT
10K
R1
8
14
9
15
NOT
NOT
NOT
INSTALLED INSTALLED INSTALLED
NOT
INSTALLED
INSTALLED
INSTALLED
R8
VCSRC
+5V MAX
2
0-> +5V
2
C4
10uF
35V
VCSNK
TP17
VEE_DEVICE
VEE
D4
BAT54WS
TP2
+IN
VEE_DEVICE
R27
4.99K
TP10
TP14
TP15
ISRC
TP16
ISNK
TSD
ENABLE IN
4
7
VCC
D2
GND
TP12
3
1
3
1
SENSE-
INPUT
TP11
3
1
CW
INCREASE
CW
INCREASE
+
5
13
17
ISNK
D1
18
TSD
VCSRC
6
5
TSD
AMB
ISNK
AMB
ISRC
RED
6
19
4
3
D3
16
ISRC
FILTER
5
ENABLE
VEE
VEE
VEE
VEE
1
10
11
20
2
VCSNK
12
SENSE+
4
V+
V-
2
2
1
+
A
B
C
D
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