Datasheet

LTC6103
9
6103f
APPLICATIONS INFORMATION
Care should be taken when designing the printed circuit
board layout to minimize input trace resistance (to Pins 5,
6, 7 and 8), especially for small R
IN
values. Trace resistance
to the –IN terminals will increase the effective R
IN
value,
causing a gain error. Trace resistance on +IN terminals will
have an effect on offset error. These errors are described
in more detail later in this data sheet. In addition, internal
device resistance will add approximately 0.3Ω to R
IN
.
Selection of External Output Resistor, R
OUT
The output resistor, R
OUT
, determines how the output cur-
rent is converted to voltage. V
OUT
is simply I
OUT
• R
OUT
. In
choosing an output resistor, the maximum output voltage
must fi rst be considered. If the circuit following is a buf-
fer or ADC with limited input range, then R
OUT
must be
chosen so that I
OUT(MAX)
• R
OUT
is less than the allowed
maximum input range of this circuit.
In addition, the output impedance is determined by R
OUT
. If
the circuit to be driven has high enough input impedance,
then almost any useful output impedance will be accept-
able. However, if the driven circuit has relatively low input
impedance or draws spikes of current, as an ADC might
do, then a lower R
OUT
value may be required in order to
preserve the accuracy of the output. As an example, if the
input impedance of the driven circuit is 100 times R
OUT
,
then the accuracy of V
OUT
will be reduced by 1% since:
VI
RR
RR
OUT OUT
OUT IN DRIVEN
OUT IN DRIVEN
=
+
=
•
•
()
()
IIR IR
OUT OUT OUT OUT
•• .••
100
101
099=
Figure 3b. The LTC6103 Allows High-Low Current Ranging
6103 F03b
301Ω
3
4
5
6
21
8
7
V
OUT
V
IN
R
SENSE(LO)
100mΩ
M1
Si4465
R5
7.5k
I
LOAD
10k
CMPZ4697
301Ω
87 6 5
421
1.74M
4.7k
Q1
CMPT5551
619k
40.2k
LTC1540
V
LOGIC
(3.3V TO 5V)
7.5k
V
LOGIC
BAT54C
HIGH CURRENT
RANGE OUT
250mV/A
HIGH
RANGE
INDICATOR
(I
LOAD
> 1.2A)
LOW CURRENT
RANGE OUT
250mV/A
R
SENSE(HI)
10mΩ
+
–
(V
LOGIC
+ 5V) ≤ V
IN
≤ 60V
0A ≤ I
LOAD
≤ 10A
LTC6103