LTC2052 LINER [Linear Technology], LTC2052 Datasheet - Page 11

• Manufacturer Part Number: LTC2052
• Description: High Voltage, High-Side Current Sense
• Manufacturer: LINER [Linear Technology]

Selection of External Input Resistor, R
The external input resistor, R
tance of the current sense circuit. Since I
transconductance g
then I
R
while limiting the output current. At low supply voltage,
I
the largest expected sense voltage gives I
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
reducing the max 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
than the max current spec allows may be used if the max
current is limited in another way, such as with a Schottky
diode across R
current measurement accuracy by limiting the result, while
increasing the low current measurement resolution.
APPLICATIONS INFORMATION
OUT
IN
should be chosen to allow the required resolution
may be as much as 1mA. By setting R
OUT
V
= V
OUT
SENSE
I
LOAD
SENSE
/100 or I
+IN
CMPZ4697
301
V
m
–
(Figure 3a). This will reduce the high
10k
= 1/R
LTC6101
IN
+
R
SENSE LO
OUT
100m
can be increased accordingly,
IN
IN
–
. For example, if R
, controls the transconduc-
= 1mA for V
M1
Si4465
Figure 3b. Dual LTC6101s Allow High-Low Current Ranging
301
–IN
OUT
V
+
V
IN
R
7.5k
OUT
IN
5
OUT
SENSE
+IN
301
V
= V
–
IN
= 1mA, then
LTC6101
SENSE
such that
(
0 ≤ I
= 100mV.
V
IN
+
LOGIC
R
SENSE HI
LOAD
= 100,
10m
–
/R
+5V
≤ 10A
IN
IN
)
,
≤ V
7.5k
–IN
301
V
OUT
IN
+
≤ 60V
Figure 3a. Shunt Diode Limits Maximum Input Voltage to Allow
Better Low Input Resolution Without Overranging
This approach can be helpful in cases where occasional
large burst currents may be ignored. It can also be used
in a multirange confi guration where a low current circuit
is added to a high current circuit (Figure 3b). Note that
a comparator (LTC1540) is used to select the range, and
transistor M1 limits the voltage across R
Care should be taken when designing the board layout
for R
connect impedances will increase the effective R
causing a gain error. In addition, internal device resistance
will add approximately 0.2Ω to R
V
IN
IN,
BAT54C
especially for small R
V
LOGIC
1.74M
619k
40.2k
HIGH CURRENT RANGE OUT
250mV/A
LOW CURRENT RANGE OUT
2.5V/A
LTC6101/LTC6101HV
3
4
5
6
(3.3V TO 5V)
R
+
–
SENSE
V
2
LOGIC
7
1
LOAD
LTC1540
V
+
6101 F03a
(I
INDICATOR
LOAD
IN
8
RANGE
HIGH
values. All trace and inter-
> 1.2A)
D
IN
SENSE
6101 F03b
.
4.7k
SENSE LO
Q1
CMPT5551
IN
11
.
value,
6101fh