LTC6104 LINER [Linear Technology], LTC6104 Datasheet - Page 9

• Manufacturer Part Number: LTC6104
• Description: High Voltage, High Side, Bi-Directional Current Sense Amplifi er
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Selection of External Input Resistor, R
The external input resistor, R
conductance of the current sense circuit.
R
while limiting the output current. At low supply voltage,
I
the largest expected sense voltage gives I
then the maximum output dynamic range is available.
Output dynamic range is limited by both the maximum
allowed output current and the maximum allowed output
voltage, as well as the minimum practical output signal. If
less dynamic range is required, then R
accordingly, reducing the maximum output current and
power dissipation. If low sense currents must be resolved
accurately in a system that has very wide dynamic range,
a smaller R
allows may be used if the maximum current is limited in
another way, such as with a Schottky diode across R
(Figure 3). This will reduce the high current measurement
accuracy by limiting the result, while increasing the low
current measurement resolution. This approach can be
helpful in cases where occasional large burst currents
may be ignored.
Care should be taken when designing the printed circuit
board layout to minimize input trace resistance (to Pins
5, 6, 7 and 8). Trace and interconnect impedances to the
OUT
Figure 3. Shunt Diodes Limit Maximum Input Voltage to Allow
Better Low Input Resolution Without Overranging
IN
For example if R
I
Since I
OUT
should be chosen to allow the required resolution
may be as much as ±1mA. By setting R
= ±
OUT
1
IN
mA for V
=
than the maximum current specifi cation
,
V
LOAD
SENSE
R
IN
IN
SENSE
=
,
R
D
100Ω
transconductance g
SENSE
SENSE
= ±
6104 F03
,
IN
100
then I
BATTERY
, controls the trans-
mV
IN
OUT
IN
.
can be increased
=
OUT
IN
V
m
100
S
such that
= ±1mA,
E E NSE
=
Ω
R R
SENSE
1
IN
or
–IN terminals will increase the effective R
a gain error, especially for small R
internal device resistance will add approximately 0.3Ω
to R
Trace and interconnect impedances to the +INB terminal will
have an effect on offset error. These errors are described
in more detail later in this data sheet.
Selection of External Output Resistor, R
The output resistor, R
rent is converted to voltage. V
V
voltage range must fi rst be considered. If the circuit that
is driven by the output does not limit the output voltage
range, then R
output voltage range does not exceed the LTC6104 maxi-
mum output voltage range (see Electrical Characteristics).
If the following circuit is a buffer or ADC with limited input
range, then R
allowed maximum input range of this circuit.
In addition, the output impedance is determined by R
If the circuit to be driven has high enough input imped-
ance, then almost any useful output impedance will be
acceptable. However, if the driven circuit has relatively low
input impedance, or draws spikes of current, such as an
ADC might do, then a lower R
in order to preserve the accuracy of the output. As an
example, if the input impedance of the driven circuit is
100 times R
by 1% since:
Selection of External Voltage Reference, V
Selection of external reference voltage should be consid-
ered together with selection of R
Example:
Given the conditions: I
REF
V
IN
. In choosing an output resistor, the maximum output
OUT
.
–
V
OUT
REF
OUT
OUT
, then the accuracy of V
=
=
must be chosen such that the maximum
I
must be chosen so that V
I
OUT
OUT
OUT
OUT
•
•
R
R
, determines how the output cur-
R
OUT
OUT
OUT
= –1mA to 1mA, V
OUT
OUT
•
+
•
100
101
R
R
OUT
IN DRIVEN
is simply I
IN DRI
value may be required
IN
(
(
.
=
values. In addition,
OUT
0 99
LTC6104
V V EN
.
IN
OUT
will be reduced
value, causing
)
)
•
OUT
OUT
REF
I
S
OUT
= 12V.
• R
is in the
•
R
OUT
OUT
OUT
9
6104f
+
.