MAX9928F Maxim, MAX9928F Datasheet - Page 8

• Manufacturer Part Number: MAX9928F
• Description: The MAX9928F/MAX9929F low-cost, uni-/bidirectional, high-side, current-sense amplifiers are ideal for monitoring battery charge and discharge currents in notebooks, cell phones, and other portable equipment
• Manufacturer: Maxim

-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
The MAX9928F/MAX9929F micropower uni-/bidirectional,
current-sense amplifiers feature -0.1V to +28V input
common-mode range that is independent of the supply
voltage. This wide input voltage range feature allows the
monitoring of the current flow out of a power supply dur-
ing short-circuit/fault conditions, and also enables high-
side current sensing at voltages far in excess of the
supply voltage (V
ate from a 2.5V to 5.5V single supply and draw a low
20µA quiescent supply current.
Current flows through the sense resistor, generating a
sense voltage V
es the direction of the sense voltage and configures the
amplifier for either positive or negative sense voltages
by controlling the S1 and S2 switches.
For positive V
input is high impedance and equals V
amplifier’s output drives the base of Q1, forcing its non-
inverting input terminal to (V
current to flow through R
Transistor Q2 and the current mirror amplify the current
by a factor of M.
For negative V
ing input is high impedance and the voltage on RS- ter-
minal equals V
drives the base of Q1 forcing its inverting input terminal
to match the voltage at the noninverting input terminal;
this causes a current to flow through R
|V
ror amplify the current by a factor of M.
8
SENSE
µMAX
_______________________________________________________________________________________
PIN
4, 5
1
2
3
6
7
8
|/R
G2
BUMP
UCSP
. Again, transistor Q2 and the current mir-
B3
B2
B1
A1
A2
A3
SENSE
—
SENSE
SENSE
IN
CC
+ V
). The MAX9928F/MAX9929F oper-
voltage, the amplifier’s inverting
voltage, the amplifier’s noninvert-
(Figure 1). The comparator sens-
Detailed Description
NAME
SENSE.
SIGN
GND
N.C.
OUT
RS+
V
RS-
CC
G1
IN
- V
equal to |V
The amplifier’s output
Negative Current-Sense Input. Load-side connection for the external sense resistor.
SIGN Output. Indicates polarity of V
SIGN = H indicates V
SIGN = L indicates V
Positive Current-Sense Input. Power-side connection to the external sense resistor.
No Connection. Not internally connected.
Supply Voltage Input. Bypass to GND with a 0.1µF capacitor.
Circuit Ground
Current-Sense Output. MAX9928: Current output (I
Voltage output (V
SENSE
IN
); this causes a
- V
SENSE
G2
SENSE.
equal to
OUT
|/R
RS+
RS+
is proportional to |V
The
G1
< V
> V
.
RS-
RS-
The amplifier is configured for either positive V
negative V
parator has a built-in offset skew of -1.2mV so that ran-
dom offsets in the comparator do not affect the
precision of I
comparator has a small amount of hysteresis (typically
0.6mV) to prevent its output from oscillating at the
crossover sense voltage. The ideal transfer characteris-
tic of I
(SIGN) is shown in Figure 2.
The amplifier V
voltages (V
ures the internal structure of the amplifier to work with
negative V
sion V
is slightly impacted. See details in the Electrical
Characteristics Note 2. The user can choose the direc-
tion that needs the best precision to be the direction
where V
battery currents, the discharge current should be V
V
range. When the battery charger is plugged in, the
charge current flows in the opposite direction and is
usually much larger, and a higher V
tolerated. See the Typical Operating Circuit .
For applications with unidirectional currents (e.g., bat-
tery discharge only), the SIGN output can be ignored.
Note that as V
for the MAX9928 or V
increases. This additional current is supplied from V
RS-
SENSE
to give the best accuracy over the largest dynamic
OS
SENSE
OUT
.
RS+
FUNCTION
trim is no longer effective and the resulting V
SENSE
SENSE
RS+
(V
|).
> V
SENSE
OUT
OUT
OS
OUT
> V
RS-
voltages (V
is only trimmed for the positive V
by the SIGN comparator. The com-
) and the output of the comparator
is proportional to |V
RS-
(V
. For example, when monitoring Li+
Pin/Bump Description
increases, the output current (I
OUT
). The SIGN comparator reconfig-
OUT
) with positive V
/10k
+V
RS-
Ω
SENSE
> V
for the MAX9929) also
SENSE
RS+
OS
) and the preci-
vs. -V
|). MAX9929:
error can be
SENSE
SENSE
SENSE
SENSE
RS+
. The
OUT
CC
OS
or
>
.