isl28005 Intersil Corporation, isl28005 Datasheet - Page 9

• Manufacturer Part Number: isl28005
• Description: Micropower, Rail-to-rail Input Current Sense Amplifier With Voltage Output
• Manufacturer: Intersil Corporation

Test Circuits and Waveforms
FIGURE 13. SLEW RATE, t
Applications Information
Functional Description
The ISL28005-20, ISL28005-50 and ISL28005-100 are
single supply, uni-directional current sense amplifiers
with fixed gains of 20V/V, 50V/V and 100V/V
respectively.
The ISL28005 is a 2-stage amplifier. Figure 16 shows the
active circuitry for high-side current sense applications
where the sense voltage is between 1.35V to 28V.
Figure 17 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
V
RS+
SENSE
PULSE
GENERATOR
TIME
) sensed across an external milli-ohm
V
RS-
s
RS+
RS-
9
, SATURATION RECOVERY
V
CC
V
GND
1
RS+
that is equal to the
1MΩ
OUT
PULSE
GENERATOR
R
L
FIGURE 15. SLEW RATE
V
OUT
ISL28005
(Continued)
1
RS+
RS-
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
sense resistor (typically 0.001Ω to 0.01Ω, 1W to 2W).
The transfer function is given in Equation 1.
The input gm stage derives its ~2.86µA supply current
from the input source through the RS+ terminal as long
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
g
S
OUT
. The only external component needed is a current
+ drops below the 1.35V threshold, the gm
HI
V
CC
V
GND
amplifier is selected. When the sense voltage at
=
RS+
GAIN
1MΩ
OUT
FIGURE 14. GAIN vs FREQUENCY
×
R
(
SIGNAL
GENERATOR
L
I
S
V
SENSE
SENSE
R
V
5
OUT
S
creating a ground-referenced voltage
+
V
). The current through R
OS
)
RS+
RS-
LO
output current reverses,
V
CC
GND
1MΩ
OUT
February 3, 2010
SENSE
R
LO
L
1
is
V
FN6973.1
(EQ. 1)
OUT
f
.
and