ISL28006_11 Datasheet, PDF (17/24 Pages) Intersil Corporation – Micropower, Rail to Rail Input Current Sense Amplifier

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 63. I_S, V_OS, V_OA, CMRR, PSRR, GAIN ACCURACY
V_RS+
V_RS-
V_CC
R_S+
OUT
R_S-
GND
1MΩ R_L ^VOUT
PULSE GENERATOR
FIGURE 65. t_s, SATURATION RECOVERY TIME
V_RS+
FIGURE 64. INPUT BIAS CURRENT, LEAKAGE CURRENT
V_RS+
SIGNAL
GENERATOR
V_CC
V_SENSE
R_S+
OUT
R_S-
GND
1MΩ R_L ^VOUT
FIGURE 66. GAIN vs FREQUENCY
V_CC
R_S+
OUT
R_S-
GND
1MΩ R_L ^VOUT
PULSE
GENERATOR
FIGURE 67. 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 72). The
ISL28006-ADJ is stable for gains of 20 and higher.
The ISL28006 is a 2-stage amplifier. Figure 68 shows the active
circuitry for high-side current sense applications where the sense
voltage is between 1.35V to 28V. Figure 69 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----_GF^-_{⎠⎟⎞}
(
I_S
R_S
+
V_O
S
)
(EQ. 2)
The input gm stage derives its ~2.86µA supply current from the
input source through the R_S+ terminal as long as the sensed
voltage at the R_S+ pin is >1.35V and the gm_HI amplifier is
selected. When the sense voltage at R_S+ drops below the 1.35V
threshold, the gm_LO amplifier kicks in and the gm_LO output
current reverses, flowing out of the R_S- pin.
17
FN6548.5
May 23, 2011