isl28006 Intersil Corporation, isl28006 Datasheet - Page 15

• Manufacturer Part Number: isl28006
• Description: Micropower, Rail To Rail Input Current Sense Amplifier With Voltage Output
• Manufacturer: Intersil Corporation

Test Circuits and Waveforms
FIGURE 49. t
Applications Information
Functional Description
The ISL28006-20, ISL28006-50 and ISL28006-100 are
single supply, uni-directional current sense amplifiers
with fixed gains of 20V/V, 50V/V and 100V/V
respectively. The ISL28006-ADJ is a single supply,
uni-directional current sense amplifier with an adjustable
gain via external resistors.
The ISL28006 is a 2-stage amplifier. Figure 52 shows the
active circuitry for high-side current sense applications
where the sense voltage is between 1.35V to 28V.
Figure 53 shows the active circuitry for ground sense
applications where the sense voltage is between 0V to
1.35V.
The first stage is a bi-level trans-conductance amp and
level translator. The gm stage converts the low voltage
drop (V
sense resistor, to a current (@ gm = 21.3µA/V). The
trans-conductance amplifier forces a current through R
resulting to a voltage drop across R
sense voltage (V
mirrored across R
at the input of the second amplifier equal to V
The second stage is responsible for the overall gain and
frequency response performance of the device. The fixed
gains (20, 50, 100) are set with internal resistors R
R
uses external gain resistors to set the gain of the output.
For the fixed gain amps the only external component
needed is a current sense resistor (typically 0.001Ω to
0.01Ω, 1W to 2W).
g
. The variable gain (ADJ) has an additional FB pin and
V
RS+
SENSE
PULSE
GENERATOR
s
) sensed across an external milli-ohm
, SATURATION RECOVERY TIME
V
RS-
SENSE
5
creating a ground-referenced voltage
). The current through R
15
RS+
RS-
V
CC
V
GND
1
RS+
that is equal to the
1MΩ
OUT
PULSE
GENERATOR
R
L
SENSE
FIGURE 51. SLEW RATE
V
1
OUT
is
f
ISL28006
.
(Continued)
and
1
RS+
RS-
The transfer function for the fixed gain parts is given in
Equation 1.
The transfer function for the adjustable gain part is given
in Equation 2.
The input gm stage derives its ~2.86µA supply current
from the input source through the R
as the sensed voltage at the RS+ pin is >1.35V and the
gm
R
amplifier kicks in and the gm
flowing out of the RS- pin.
V
V
S
OUT
OUT
+ drops below the 1.35V threshold, the gm
HI
V
CC
GND
V
amplifier is selected. When the sense voltage at
=
RS+
=
1MΩ
OUT
⎛
⎜
⎝
GAIN
1
+
FIGURE 50. GAIN vs FREQUENCY
------- -
R
R
G
F
R
×
⎞
⎟
⎠
L
SIGNAL
GENERATOR
(
(
V
I
S
I
SENSE
V
S
R
OUT
R
S
S
+
+
V
V
OS
OS
)
)
RS+
RS-
LO
output current reverses,
V
S
CC
+ terminal as long
GND
1MΩ
OUT
February 4, 2010
R
LO
L
V
(EQ. 1)
(EQ. 2)
FN6548.1
OUT