DEMO MANUAL DC1698A
LT1999: High Voltage,
Bidirectional Current
Sense Amplifier
DESCRIPTION
Demonstration circuit 1698A features the LT1999, a high
voltage, bi-directional current sense amplifier.
The demo board amplifies the voltage drop across an on
board current sense resistor. The output voltage is a bi-
directional signal that is centered on the V
REF
voltage and
is proportional to the current through the sense resistor.
The output is scaled by one of three fixed gain options. The
gain options are: 10V/V (DC1698A-A), 20V/V (DC1698A-B)
and 50V/V (DC1698A-C). The input voltage range is from
–5V to 80V (independent of the device supply voltage)
allowing the part to be used for high or low side current
sensing. The LT1999 requires a separate 5V supply voltage.
Design files for this circuit board are available at
http://www.linear.com/demo
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.
PERFORMANCE SUMMARY
Table 1. Performance Summary (T
A
= 25°C)
SYMBOL
V
S
V
CM
CMRR
V
OUT
V
OSI
I
Q
V
REF
V
REFIN
PARAMETER
Supply Range
CM Input Voltage Range
Common Mode Rejection Ratio
Swing Output High (with Respect to V
+
)
Swing Output Low (with Respect to V
–
)
Input Referred Offset Voltage
V
+
Quiescent Current
Open Circuit Voltage
REF Pin Input Range
V
CM
= 0V , 7V
P-P
, f = 100kHz
R
LOAD
= Open
R
LOAD
= Open
T
A
= 25°C, V
CM
> 5.5V
V
CM
> 5.5V
V
S
= 5V
2.44
1.25
CONDITIONS
MIN
4.5
–5
80
100
5
150
550
1.55
2.5
2.55
V
+
– 1.5
125
225
TYP
MAX
5.5
80
UNITS
V
V
dB
mV
mV
μV
mA
V
V
OPERATING PRINCIPLES
The LT1999 operates by amplifying the voltage drop
across a user selected sense resistor. The voltage across
the resistor is amplified by a fixed gain of 10V/V, 20V/V
or 50V/V(LT1999-10,LT1999-20,LT1999-50) and is level
shifted to the OUT pin of the device. The voltage difference
and polarity with respect to the V
REF
pin voltage indicates
the magnitude and direction of the current in the sense
resistor.
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DEMO MANUAL DC1698A
BLOCK DIAGRAM
V
+
V
+
1
R
+IN
2
+IN
2k
2k
C
F
4pF
–IN
2k
2k
0.8k
R
+S
0.8k
R
–S
V(G
+IN
)
V(G
–IN
)
SHDN
2μA
4.5k
8
R
G
V+
D1
300Ω
3
R
–IN
V
+
4
LT1999
QUICK START PROCEDURE
Demonstration circuit 1698 is easy to set up and evaluate
the performance of the LT1999. Refer to Figure 1 for proper
measurement equipment setup and follow the procedure:
1. With power off, connect a power supply to V
+
and the
common to GND. This supply should be between 4.5V
and 5.5V. Connect a second supply’s positive terminal
to the V
SENSE+
and connect its common to the circuit
ground. The second supply’s (load supply) output volt-
age can range from –5V to 80V.
2. With power off, connect the load to the V
SENSE–
. If
the load power source does not have accurate current
readout a DMM may be connected in series with the
load as shown in Figure 1.
3. Connect a voltmeter to the V
OUT
terminal, with the com-
mon connected to the V
REF
terminal. An oscilloscope can
also be used to monitor Vout with respect to ground.
4. Turn on the power supply to the device and the load
supply.
5. Measure the output voltage with respect to V
REF
. The
output voltage will be proportional to the load and with
the factory set sense resistor will equal 0.5V per 1A.
2
+
–
+
G
IN
–
A
O
V+
160k
OUT
7
REF
160k
6
GND
5
1999 BD
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DEMO MANUAL DC1698A
QUICK START PROCEDURE
LOAD SUPPLY
(–5V TO 80V)
20V
5.00V
DEVICE SUPPLY
(4.5V TO 5.5V)
1.00V
V
OUT
2.00A
LOAD
10Ω
Figure 1. Proper Measurement Equipment Setup
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DEMO MANUAL DC1698A
PARTS LIST
ITEM
General BOM
1
2
3
DC1698A-A
1
2
3
DC1698A-B
1
2
3
DC1698A-C
1
2
3
1
1
1
DC1698A
R1
U1
General BOM
Resistor, 0.01Ω 1W 1% 2512 SMD
IC, LT1999IMS8-50
Vishay, WSL2512R0100FEA
Linear Technology, LT1999IMS8-50#PBF
1
1
1
DC1698A
R1
U1
General BOM
Resistor, 0.025Ω 1% 2512 1W
IC, LT1999IMS8-20
Vishay, WSL2512R0250FEA
Linear Technology, LT1999IMS8-20#PBF
1
1
1
DC1698A
R1
U1
General BOM
Resistor, 0.05Ω 1% 2512 2W
IC, LT1999IMS8-10
SEI, CSRN2512FT50L0
Linear Technology, LT1999IMS8-10#PBF
2
1
1
C1, C2
C3
R2
Capacitor, 0.1μF 10% 25V X7R 0603
Capacitor, 100pF 10% 16V X7R 0402
Resistor, 0Ω 0603 1% 1/16W
AVX, 06033C104KAT2A
AVX, 0402YC101KAT2A
YAGEO, RC0603FR-070RL
QUANTITY
REFERENCE
DESCRIPTION
MANUFACTURER’S PART NUMBER
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ECO REV
1
CUYLER L.
DESCRIPTION
PRODUCTION
10/01/2010
APPR
DATE
V+
1
4.5V - 5.5V
E6
SCHEMATIC DIAGRAM
E1
1
VSENSE +
V+
1
-5V - +80V
LT1999IMS8*
U1
C3
VSHDN\
8
100pF
E7
1
VSUPPLY
/SHDN
0402
2
IN+
VOUT
7
0 Ohm
E3
1
R2
VOUT
R1
*
2V AT 4A
VREF
2512
3
V+
IN-
6
VREF
1
C1
4
VSUPPLY
5
E5
1
GND
0.1uF
E4
*
ASSY
-A
-B
-C
U1
LT1999IMS8-10
LT1999IMS8-20
LT1999IMS8-50
R1
0.05 ohm
0.025 ohm
0.01 ohm
GND
1
VSENSE -
0.1uF
C2
E2
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 representation
that the interconnection of its circuits as described herein will not infringe on existing patent rights.
NOTES: UNLESS OTHERWISE SPECIFIED
CUSTOMER NOTICE
APPROVALS
PCB DES.
APP ENG.
CL
CUYLER L.
TITLE: SCHEMATIC
1630 McCarthy Blvd.
Milpitas, CA 95035
PH: (408) 432-1900
WWW.LINEAR.COM
1. ALL RESISTORS ARE IN OHMS, 0603
2. ALL CAPACTORS ARE IN MICROFARADS, 0603
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 LAYOUT MAY SIGNIFICANTLY
AFFECT CIRCUIT PERFORMANCE OR RELIABILITY.
CONTACT LINEAR TECHNOLOGY APPLICATIONS
ENGINEERING FOR ASSISTANCE.
LTC CONFIDENTIAL FOR-
CUSTOMER USE ONLY
THIS CIRCUIT IS PROPRIETARY TO
LINEAR TECHNOLOGY AND SUPPLIED FOR
USE WITH LINEAR TECHNOLOGY PARTS.
SCALE = NONE
HIGH VOLTAGE BI-DIRECTIONAL CURRENT SENSE
REV
IC NO.
SIZE
LT1999IMS8-10/-20/-50
1
N/A
DEMO CIRCUIT 1698A
10/2010
DATE:
SH 1 of 1
DEMO MANUAL DC1698A
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