ISL28006_10 Datasheet, PDF (18/25 Pages) Intersil Corporation – Micropower, Rail to Rail Input Current Sense Amplifier with Voltage Output

ISL28006
Test Circuits and Waveforms
V_CC
+
V_RS+
-
+
V_SENSE
-
R_S+
R_S-
GND
OUT
1MΩ R_L ^VOUT
+
V_RS+
-
V_R1
R₁
+
V_SENSE
- R₂
V_R2
V_CC
R_S+
R_S-
GND
OUT
1MΩ
R_L ^VOUT
FIGURE 61. I_S, V_OS, V_OA, CMRR, PSRR, GAIN ACCURACY
V_CC
V_RS+
V_RS-
R_S+
OUT
R_S-
GND
1MΩ R_L ^VOUT
PULSE
GENERATOR
FIGURE 63. t_s, SATURATION RECOVERY TIME
FIGURE 62. INPUT BIAS CURRENT, LEAKAGE CURRENT
SIGNAL
GENERATOR
V_CC
V_RS+
V_SENSE
R_S+
OUT
R_S-
GND
1MΩ R_L ^VOUT
FIGURE 64. GAIN vs FREQUENCY
V_CC
V_RS+
R_S+
OUT
R_S-
GND
1MΩ R_L ^VOUT
PULSE
GENERATOR
FIGURE 65. SLEW RATE
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 single supply,
uni-directional current sense amplifier with an adjustable
gain via external resistors (see Figure 70). The
ISL28006-ADJ is stable for gains of 20 and higher.
The ISL28006 is a 2-stage amplifier. Figure 66 shows the
active circuitry for high-side current sense applications
where the sense voltage is between 1.35V to 28V.
Figure 67 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) sensed across an external milli-ohm
sense resistor, to a current (@ gm = 21.3µA/V). The
trans-conductance amplifier forces a current through R₁
resulting to a voltage drop across R₁ that is equal to the
sense voltage (V_SENSE). The current through R₁ is
mirrored across R₅ creating a ground-referenced voltage
at the input of the second amplifier equal to V_SENSE.
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_f and
R_g. The variable gain (ADJ) has an additional FB pin and
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).
The transfer function for the fixed gain parts is given in
Equation 1.
V_OUT = GAIN × (I_SR_S + V_OS)
(EQ. 1)
The transfer function for the adjustable gain part is given
in Equation 2.
V_OUT
=
⎛
⎜
⎝
1
+
R^-R----_G^-F--_{⎠⎟⎞}
(I_S
R_S
+
V_OS
)
(EQ. 2)
18
FN6548.4
September 16, 2010