DEMO CIRCUIT 1 1 9 2
Q UICK S TA RT
LT6105
G UIDE
L T6 1 0 5
P re c is io n , G a in S e le c ta b le H ig h
S id e Cu rre n t S e n s e A m p lifie r
suitabl f measuring suppl bus l
e or
y
oading as they are
brought up. W hen provided w ith a negative suppl it is
y,
capabl ofmonitoring negative suppl
e
ies.
The key perf
ormance characteristics of the LT6105 and
DC1192 are show n in the Perf
ormance Summary bel .
ow
Design files for this circuit board are available. Call the
LTC factory.
L
, LT, Over-The-Top are registered trademarks ofLinear Technol Corporation. Other
ogy
product names may be trademarks ofthe companies that manuf
acture the products.
DESCRIPTION
Demonstration Circuit 1192 is a Precision, Gain Sel
ect-
abl High Side Current Sense Ampl ier f
e
if eaturing the
LT6105.
This demo board ampl ies a current-sense resistor IR-
if
drop, providing a precision uni-pol output vol
ar
tage pro-
portional to l current. The LT6105 is pow ered f
oad
rom a
suppl vol
y tage (f
rom 2.85V up to 36V) w hil it measures
e
current ofa vol
tage pow er bus (0V to 44V). This device is
suitabl f measuring battery system current since the
e or
monitoring-input current draw s become negl e w hen
igibl
V
CC
is pow ered dow n. Its 0V and up input range makes it
PERF ORM ANCE SU M M ARY
SYM BOL
V
IN
V
CC
A
V
A
Z
V
OUT
I
M AX
I
CC
I
BIAS
I
INPD
t
R
PARAM ETER
M onitored Suppl Input Range
y
Ampl ier Suppl Range
if
y
Vol Gain
tage
TotalCurrent to Vol Gain
tage
Output Vol Range
tage
M aximum Sense Current
V
+
(=Vcc) Suppl Current
y
V
S+
Bias Current
V
S+
Current during Pow er Dow n
V
M ON
step-response time
Specifications are at T
A
= 25°C
CONDI ONS
TI
MI
N
-0.3
2.85
TYP
0… 44
3… 28
50
1
2
150
15
.001
50
M AX
44
36
UNI
TS
V
V
V/
V
V/
A
V
A
µA
µA
µA
µs
R
IN1
= R
IN2
= 100, R
OUT
= 4.99k
R
SENSE
= .020 Ohm
V+ = 3V
Thermall ofR
SENSE
(2W atts)
imit
V+= 36V, V
S+
=3V, V
SENSE
=0V
V
S+
= 3V, V
SENSE
=0V
V
+
= 0V, V
S+
=44V, V
SENSE
=0V
I
OUT
step f 0A to 5A
rom
10
250
25
1
OPERATING PRINCIPL ES
The LT6105 operates by ampl ying the vol
if
tage drop on a
sense resistor pl
aced in series w ith the pow er source ofa
l to be monitored. The sense inputs of the ampl ier
oad
if
diferentialy measure the sense-resistor drop to control
f
l
an internalvariabl current source that alow s transl
e
l
ation
of the input inf
ormation to a l
evel ref
erenced to V
EE
(ground in this demo circuit). An internal post-ampl ier
if
provides additional gain and buf ers the output signal
f
.
The post-ampl ier gain is establ
if
ished by the pin strap
conf
iguration of the part. In DC1192 as shipped, the
sense resistor instaled is 20mΩ and the resistors set the
l
gain to 50V/ so the nominal output scal is 1V per
V,
ing
Ampere of l current. Other scal
oad
ings can be produced
by changing the resistors.
The DC1192 Schematic diagram is show n in Figure 2.
1
LT6105
Q U ICK START PROCEDU RE
Demonstration circuit 1192 is easy to set up to eval
uate
the perf
ormance of the LT6105. Ref to Figure 1 f
er
or
proper measurement equipment setup and f l the
olow
procedure bel :
ow
1.
W ith pow er of, connect the l driving pow er suppl
f
oad
y
positive to SOURCE and the common to GND. This
suppl shoul be in the range of 0V to 44V. If this
y
d
suppl is not equipped w ith an accurate current read-
y
out, a DM M (set to measure Amperes) may be con-
nected in series w ith the suppl as show n in Figure 1.
y
NOTE.
Be sure that the current capacity ofthe DM M is adequate to
handl the intended l current.
e
oad
3.
Connect a vol
tmeter or osciloscope probe to the Vout
l
terminal w ith the common connection or ground cl
,
ip
tied to GND.
4.
Connect a l to the TO LOAD terminal(positive) and
oad
return (negative) to the common of the l driving
oad
pow er suppl The l may be a pow er resistor, ac-
y.
oad
tive l instrument, or other circuit ofinterest.
oad
5.
Turn on the pow er suppl
ies.
6.
Check f an output vol
or
tage that corresponds to the
l current: V
M ON
= 1.0×I
O UT
.
oad
2.
W ith pow er of , connect the ampl ier suppl positive
f
if
y
to VCC and the common to GND. This suppl shoul
y
d
be in the range of2.85V to 36V.
POWER
SUPPLY
3.0
+ COM
POWER
SUPPLY
10.
+
0
COM
1.00
0
DMM
A COM V
1.00
0
DMM
A COM V
LOAD
(10Ω)
Figure 1. Proper M easurem ent Equipm ent Setup
2
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