LT1638 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LT1638
Linear Technology
'LT1638' PDF : 18 Pages View PDF
LT1638/LT1639
TYPICAL APPLICATION
The battery monitor in Figure 5 also demonstrates the
LT1638’s ability to operate with its inputs above the
positive rail. In this application, a conventional amplifier
would be limited to a battery voltage between 5V and
ground, but the LT1638 can handle battery voltages as
high as 44V. When the battery is charging, Amp B senses
the voltage drop across RS. The output of Amp B causes
Q2 to drain sufficient current through RB to balance the
input of Amp B. Likewise, Amp A and Q1 form a closed
loop when the battery is discharging. The current through
Q1 or Q2 is proportional to the current in RS and this cur-
rent flows into RG and is converted into a voltage. Amp
D buffers and amplifies the voltage across RG. Amp C
compares the output of Amp A and Amp B to determine
the polarity of current through RS. The scale factor for
VOUT with S1 open is 1V/A. With S1 closed the scale
factor is 1V/100mA and currents as low as 500μA can
be measured.
CHARGER
VOLTAGE
RS, 0.2Ω RA, 2k
IBATT
RA', 2k
+
A
1/4 LT1639
–
Q1
2N3904
LOAD
RB, 2k
+
Q2
2N3904
B
RB', 2k
1/4 LT1639
+
–
RG
VBATT = 12V
10k
S1
10k
IBATT
=
VOUT
=
(RS)(RG/RA)(GAIN)
VOUT AMPS
GAIN
S1 = OPEN, GAIN = 1
S1 = CLOSED, GAIN = 10
+
C
1/4 LT1639
–
LOGIC
LOGIC HIGH (5V) = CHARGING
LOGIC LOW (0V) = DISCHARGING
+
D
1/4 LT1639
–
90.9k
RA = RB
VS = 5V, 0V
VOUT
1638/39 F05
Figure 5. Battery Monitor
RELATED PARTS
PART NUMBER
LT1078/LT1079
LT2078/LT2079
LT1178/LT1179
LT2178/LT2179
LT1366/LT1367
LT1490/LT1491
LT1636
DESCRIPTION
Dual/Quad 55μA Max, Single Supply, Precision Op Amps
Dual/Quad 17μA Max, Single Supply, Precison Op Amps
Dual/Quad Precision, Rail-to-Rail Input and Output Op Amps
Dual/Quad Over-The-Top Micropower, Rail-to-Rail Input and
Output Op Amps
Single Over-The-Top Micropower Rail-to-Rail Input and Output
Op Amp
COMMENTS
Input/Output Common Mode Includes Ground, 70μV VOS(MAX)
and 2.5μV/°C Drift (Max), 200kHz GBW, 0.07V/μs Slew Rate
Input/Output Common Mode Includes Ground, 70μV VOS(MAX)
and 4μV/°C Drift (Max), 85kHz GBW, 0.04V/μs Slew Rate
475μV VOS(MAX), 500V/mV AVOL(MIN), 400kHz GBW
Single Supply Input Range: – 0.4V to 44V, Micropower 50μA
per Amplifier, Rail-to-Rail Input and Output, 200kHz GBW
55μA Supply Current, VCM Extends 44V above VEE,
Independent of VCC; MSOP Package, Shutdown Function
18 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
16389fg
LT 1011 REV G • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 1998
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