Datasheet

For both positive and negative V
SENSE
voltages, the cur-
rent flowing out of the current mirror is equal to:
I
OUT
= M x |V
SENSE
|/R
G1
For the MAX9928F, the transconductance of the device
is trimmed so that I
OUT
/|V
SENSE
| = 5μA/mV. For the
MAX9929F, the voltage gain of the device is trimmed so
that V
OUT
/|V
SENSE
| = 50V/V. The SIGN output from the
comparator indicates the polarity of V
SENSE
.
Current Output (MAX9928F)
The output voltage equation for the MAX9928_ is given
below:
V
OUT
= (R
SENSE
x I
LOAD
) x (G
m
X R
OUT
)
where V
OUT
= the desired full-scale output voltage, I
LOAD
= the full-scale current being sensed, R
SENSE
= the
current-sense resistor, R
OUT
= the voltage-setting resis-
tor, and G
m
= MAX9928F transconductance (5μA/mV).
The full-scale output voltage range can be set by chang-
ing the R
OUT
resistor value. The above equation can be
modified to determine the R
OUT
required for a particular
full-scale range:
R
OUT
= (V
OUT
)/(I
LOAD
x R
SENSE
x G
m
)
OUT is a high-impedance current source and can drive an
unlimited amount of capacitance.
Figure 2. Ideal Transfer Characteristics with 0mV Amplifier
Input Offset Voltage and -1mV Comparator Input Offset Voltage
Figure 1. Functional Diagram
0-1.2-1.8-3.0 3.02.01.0
0-1.2-1.8-3.0 3.02.01.0
V
SENSE
(mV)
V
SENSE
(mV)
SIGN
I
OUT
(V
OUT
)
( ) FOR THE MAX9929F.
CURRENT
MIRROR
MAX9928F
MAX9929F
C
S2
S1
Q1
Q2
10kΩ*
SIGN
OUT
V
CC
V
IN
-0.1V TO +28V
(V
BATT
)
R
SENSE
V
SENSE
+
-
2.5V TO 5.5V
R
G1
80kΩ
R
G2
80kΩ
R
C2
80kΩ
R
C1
80kΩ
RS-
RS+
TO
LOAD/CHARGER
TO ADC
TO C
*INTERNAL 10kΩ RESISTOR FOR MAX9929_ ONLY.
GND
A
V
CC
1MΩ
MAX9928/MAX9929 -0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Ampliers
www.maximintegrated.com
Maxim Integrated │ 9