DEMO MANUAL DC1659A
LT6109-1/LT6109-2
High Side Current Sense
Amplifiers with Reference
and Comparators
two inverting inputs available. Both current sense gain
and current fault limits are set by on board resistors and
are the same for both boards. The gain is set at 100V/V
and the comparators are set to trip at current thresholds
of 50mA and 300mA.
The key performance specifications are listed in the table
below.
Design files for this circuit board are available at
http://www.linear.com/demo
L,
LT, LTC, LTM, TimerBlox, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
DESCRIPTION
Demonstration circuit 1659A features the LT
®
6109, a high
side current sense amplifier with two comparators and a
400mV reference.
The demo board circuit amplifies the voltage across an
on-board current sense resistor, to provide a precision
unipolar voltage output that is proportional to the sensed
current. The board has two on-board comparators with
latching outputs and an integrated 400mV reference that
sets the threshold for the comparators. There are two ver-
sions of this demonstration circuit, A and B, depending on
which version of the LT6109 is installed. The DC1659A-A
(LT6109-1) has an inverting and a noninverting compara-
tor input available, while the DC1659A-B (LT6109-2) has
PERFORMANCE SUMMARY
SYMBOL
V
IN
V
IOUT
I
IOUT
I
LOAD
I
Q
V
THR1
V
THR2
PARAMETER
Input Supply Range
Measured Output Signal
Measured Output Current
Output Load Current Range
IN Quiescent Current
Comparator1 Threshold
Comparator2 Threshold
(T
A
= 25°C)
MIN
2.7
TYP
1
100
4
800
300
50
MAX
60
UNITS
V
V
μA
A
μA
mA
mA
CONDITIONS
I
LOAD
= 100mA
V
IOUT
= 1V
Thermal Limit of R
SENSE
V
IN
= 12V
V
IOUT
= 3.0V
V
IOUT
= 0.5V
OPERATING PRINCIPLES
The LT6109 operates by amplifying the voltage drop across
a sense resistor that is in series with the load. The sense
inputs of the amplifier differentially measure the sense
resistor voltage drop to control an internal variable current
source that allows translation of the input voltage level to
a level referenced to the GND. The circuit gain is set by
the ratio of the output resistor to the input resistor. The
comparator thresholds are set by the internal reference
and the current trip points are set by dividing the output
resistance into a network of three resistors. The DC1659
is shipped with a 100mΩ sense resistor, a gain of 100 and
current fault thresholds of 50mA and 300mA.
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DEMO MANUAL DC1659A
BLOCK DIAGRAMS
LT6109-1 (DC1659A-A)
9
LT6109-1
V
+
LT6109-2 (DC1659A-B)
9
LT6109-2
V
+
100Ω
100Ω
10
SENSEHI
3k
–
+
V
–
V
+
200nA
34V
6V
10
SENSEHI
3k
–
+
V
–
V
+
200nA
34V
6V
SENSELO
1
V
–
3k
OUTA
V
–
SENSELO
8
1
V
–
3k
OUTA
V
–
8
2
EN/RST
ENABLE AND
RESET TIMING
RESET
V
+
INC2
2
EN/RST
ENABLE AND
RESET TIMING
RESET
V
+
3
OUTC2
UNDERCURRENT FLAG
7
3
OUTC2
INC2
OVERCURRENT FLAG
V
–
V
+
400mV
REFERENCE
V
+
V
–
V
–
V
+
4
OUTC1
OVERCURRENT FLAG
4
INC1
OUTC1
OVERCURRENT FLAG
6
V
–
5
610912 F01
V
–
5
610912 F02
2
–
–
+
400mV
REFERENCE
+
–
–
+
+
7
V
+
V
–
INC1
6
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DEMO MANUAL DC1659A
QUICK START PROCEDURE
The DC1659A provides a simple way to evaluate the
performance of the LT6109. Refer to Figure 1 for proper
measurement equipment setup and follow the procedure
below:
1. With the power off, connect the power supply positive
to IN and the common to GND. With default board
settings the supply can range from 3.3V to 60V. If the
supply does not have an accurate current readout, a
DMM may be connected in series with the supply as
shown in Figure 1.
2. Connect a DMM or oscilloscope to the I
OUT
with the
common connection connected to ground.
3. Connect a load to the demo boards OUT terminal (posi-
tive) and ground. The load may be a power resistor,
active load instrument or a circuit of interest.
20.0V
4. Turn on the power supply. The comparators start in an
unknown state and must be reset. This can be done
by pressing the reset button. With the load shown in
Figure 1 the comparator outputs should be:
PART
DC1659A-A LT6109-1
DC1659A-B LT6109-2
C
OUT1
High
High
C
OUT2
High
Low
5. Measure the output voltage and confirm it corresponds
to the load current. V
IOUT
= 10 • I
LOAD
for the factory
installed resistors.
6. If able, sweep load current from 0mA to 300mA to verify
the operation of the comparators. The LED will turn on
when the comparator output has latched low. Use the
reset circuitry to reset comparator output.
Reset
0.10A
Load
200Ω
1.0V
Figure 1. Test Setup
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DEMO MANUAL DC1659A
OPERATION
Current Sense Gain
The gain of the LT6109 current sense amplifier is set
by the ratio of R
OUT
and R
IN
resistors. In the demo
circuit this means that the gain is set by the ratio of
(R1 + R2 + R3)/R10. The gain error is primarily controlled
by the precision of the resistors used. The factory resis-
tors are a 1% tolerance which will dominate the gain
error. To reduce system gain error, the resistors can be
replaced with 0.1% resistors.
LED Indicators
The LEDs indicate the state of the comparator outputs.
When the LED is on, the comparator is latched low. When
the LED is off, the comparator output is high. When the
comparator output is latched low, the LT6109 must be reset
to refresh the comparator output and to turn off the LEDs.
Jumper Summary
Reset(JP1): The Reset jumper has two settings for manual
or auto mode. In manual mode, the user must press the
reset button to reset the latching comparators. In auto
mode, the comparators will be continuously reset every
10 seconds. The factory default setting is manual mode.
Optional Settings
1. For supply voltages below 3.3V, remove R20 and install
R21 (0Ω jumper). When R21 is installed, the supply
voltage must stay between 2.7V to 6V to prevent dam-
aging the TimerBlox
®
circuitry that is used to reset the
comparator outputs.
2. To power the LT6109 from a supply separate from the
load, remove R22 and connect the power supply to V
+
turret.
3. There are a number of optional components that (not
installed) allow the DC1659 to be tailored to a specific
application:
A) To free comparator input INC1, remove R2 and R3
and install R19.
B) To free comparator input INC2, remove R1 and R2
and install R18.
C) To add filtering to the amplifier output, install C6.
4. R9 can be set to the same value as R10 to reduce error
caused by input bias current. Typically for values of
R10 (less than 1k) and R9 can be omitted as the error
is negligible.
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DEMO MANUAL DC1659A
PARTS LIST
ITEM
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
28
29
30
DC1659A-A
1
DC1659A-B
1
1
U1
IC, LT6109IMS-2
Linear Technology Corp. LT6109IMS-2
1
U1
IC, LT6109IMS-1
Linear Technology Corp. LT6109IMS-2
QTY
1
1
2
1
1
3
7
1
1
2
1
1
1
3
1
2
1
1
1
1
1
1
1
3
2
1
1
1
1
REFERENCE
C1
C2
C4, C5
C6
C7
E1, E2, E8
E3-E7, E9, E10
JP1
JP1
LED1, LED2
R1
R2
R3
R4, R5, R14
R6
R7, R8
R10
R11, R22
R12
R13
R15
R16, R23
R17
R18, R19, R21
R20, R9
SW1
U2
U3
U4
PART DESCRIPTION
Capacitor, 1μF 20% 1206 100V X7R
Capacitor, 0.47μF 20% 0603 16V X5R
Capacitor, 0.1μF 20% 0402 10V X5R
Capacitor, 0.1μF 20% 0603 X5R Optional
Capacitor, 0.1μF 10% 0603 100V X7R
Turret Terminal
Turret Terminal
Header, 3-Pin, 2mm
Shunt
Red1206 LED
Resistor, 2k 1% 0603 1/16W
Resistor, 6.65k 1% 0603 1/16W
Resistor, 1.33k 1% 0603 1/16W
Resistor, 10k 5% 0402 1/16W
Resistor, 118k 1% 0402 1/16W
Resistor, 1k 5% 0603 1/16W
Resistor, 100Ω 1% 0603 1/16W
Resistor, 0Ω 0402 1/16W
Resistor, 13.7k 1% 0402 1/16W
Resistor, 249k 1% 0402 1/16W
Resistor, 0.1Ω 1% 2512 2W
Resistor, 1M 1% 0402 1/16W
Resistor, 392k 1% 0402 1/16W
Optional
Resistor, 0Ω 0603 1/16W
Switch, Pushbutton
IC, LT3010EMS8E#PBF
IC, LT6993CS6-1#PBF
IC, LT6991CS6#PBF
AAC/CJ06-000M
Panasonic/EVQPPDA25
Linear Technology Corp.
Linear Technology Corp.
Linear Technology Corp.
Murata/GRM188R72A104KA35D
Mill Max 2501-2-00-80-00-00-07-0
Mill Max 2308-2-00-80-00-00-07-0
SAMTEC TMM-103-02-L-S
SAMTEC 2SN-BK-G
Panasonic/LN1251C
AAC/CR16-2001FM
Vishay/CRCW06036K65FKEA
AAC/CR16-1331FM
AAC/CR05-103JM
AAC/CR05-1243FM
Vishay/CRCW04021K00JNED
Vishay/CRCW0603100RFKEA
Vishay/CRCW04020000Z0ED
AAC/CR05-1372FM
AAC/CR05-2493FM
IRC/LR2512LF-01-R100-F
AAC/CR05-1004FM
AAC/CR05-3923FM
MANUFACTURER/PART NUMBER
TDK/C3216X7R2A105M
AVX/0603YD474MAT2A
Taiyo Yuden/LMK105BJ104MV-F
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