LM3824
Precision Current Gauge IC with Internal Zero Ohm
Sense Element and PWM Output
General Description
The LM3824 Current Gauge provides easy to use precision
current measurement with virtually zero insertion loss (typi-
cally 0.003
). The LM3824 is used for high-side sensing.
A Delta Sigma analog to digital converter is incorporated to
precisely measure the current and to provide a current aver-
aging function. Current is averaged over 6 msec time peri-
ods in order to provide immunity to current spikes. The ICs
have a pulse-width modulated (PWM) output which indicates
the current magnitude and direction. The shutdown pin can
be used to inhibit false triggering during start-up, or to enter
a low quiescent current mode.
The LM3824 is factory-set in two different current options.
The sense range is -1.0A to +1.0A or -2.0A to +2.0A. The
sampling interval for this part is 6ms. If a more precise mea-
surement is required, please refer to LM3822 datasheet.
Key Specifications
n
Ultra low insertion loss (0.003
)
n
2V to 5.5V supply range
n
3% accuracy at room temperature for the 1A device
(includes accuracy of the internal sense element)
n
Low quiescent current in shutdown mode
(typically 1.8 A)
n
6 msec sampling interval
n
In MSOP-8 Package
Features
n
No external sense element required
n
PWM output indicates the current magnitude and
direction
n
PWM output is easily interfaced with microprocessors
and controllers
n
Precision
current-sense technique
n
Low temperature sensitivity
n
Internal filtering rejects false trips
n
Internal Power-On-Reset (POR)
n
DC Offset is less than 8 mA for 1A part
Applications
n
Battery charge/discharge gauge
n
Motion control diagnostics
n
Power supply load monitoring and management
n
Resettable smart fuse
Connection Diagram
DS200007-1
Top View
LM3824 for High-Side Sensing
July 2000
LM3824
Precision
Current
Gauge
IC
with
Internal
Zero
Ohm
Sense
Element
and
PWM
Output
2000 National Semiconductor Corporation
DS200007
www.national.com
Ordering Information
Order No.
*
Sense
Range
Sampling
Interval
*
Sensing
Method
NS
Package
Number
Package
Type
Supplied As:
LM3824MM-1.0
1.0A
6 ms
High-side
MUA08A
MSOP-8
Tape and Reel
(1000 units/reel)
LM3824MMX-1.0
1.0A
6 ms
High-side
MUA08A
MSOP-8
Tape and Reel
(3500 units/reel)
LM3824MM-2.0
2.0A
6 ms
High-side
MUA08A
MSOP-8
Tape and Reel
(1000 units/reel)
LM3824MMX-2.0
2.0A
6 ms
High-side
MUA08A
MSOP-8
Tape and Reel
(3500 units/reel)
*
Current is sampled over a fixed interval. The average current during this interval is indicated by the duty cycle of the PWM output
during next interval.
Pin Description (High-Side, LM3824)
Pin
Name
Function
1
SENSE+, V
DD
High side of internal current sense, also supply voltage.
2
GND
Supply Ground.
3
FLTR+
Filter input -- provides anti-aliasing for delta sigma modulator.
4
FLTR-
Filter input.
5
SD
Shutdown input. Connected to V
DD
through a pull-up resistor for normal operation.
When low, the LM3824 is put into a low current mode.
6
TEST
Connect to GND for normal operation.
7
PWM
Digital output indicates the current magnitude and direction.
8
SENSE-
Low side of internal current sense.
LM3824
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2
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Absolute Maximum Supply Voltage
5.5V
Power Dissipation
(Note 2)
ESD Susceptibility (Note 3)
1.5 kV
Sense Current (peak, for 200 msec) (Note 4)
10A
Sink Current for PWM pin
1mA
Maximum Junction Temperature
150C
Storage Temperature
-65C to +150C
Lead Temperature (Soldering, 10 sec)
260C
Operating Ratings
(Note 1)
Input Voltage
2.0V to 5.25V
Sense Current (continuous) (Note 4)
5A
Junction Temperature Range
-40C to +85C
Electrical Characteristics
Typical numbers are at 25C and represent the most likely parametric norm.
Specifications in standard type face are for T
J
= 25C and those with boldface type apply over full operating temperature
ranges.
LM3824-1.0
SENSE+V
DD
= 3.6V for the following specifications. Supply bypass capacitor is 1 F and filter capacitor is 0.1 F.
Symbol
Parameter
Conditions
Typ
(Note 5)
Limit
(Note 6)
Units
I
ACC
Average Current Accuracy
(Note 7)
1.0A current
1.0
A
0.97 / 0.95
A (min)
1.03 / 1.05
A (max)
e
n
Effective Output Noise (rms)
12
mA
LM3824-2.0
SENSE+V
DD
= 3.6V for the following specifications. Supply bypass capacitor is 1 F and filter capacitor is 0.1 F.
Symbol
Parameter
Conditions
Typ
(Note 5)
Limit
(Note 6)
Units
I
ACC
Average Current Accuracy
(Note 7)
2.0A current (Note 8)
2.0
A
1.88 / 1.84
A (min)
2.12 / 2.16
A (max)
e
n
Effective Output Noise (rms)
36
mA
Common Device Parameters
Unless otherwise specified, V
DD
= 3.6V for the following specifications. Supply bypass capacitor is 1 F and filter capacitor is
0.1 F.
Symbol
Parameter
Conditions
Typ
(Note 5)
Limit
(Note 6)
Units
I
Q1
Quiescent Current
Normal Mode, SD = high
95
A
150
A (max)
I
Q2
Quiescent Current
Shutdown Mode, SD = low
1.8
A
10
A (max)
D
RES
PWM Resolution
0.8
%
t
S
Sampling Time
6
ms
4
ms (min)
10
ms (max)
f
P
Frequency of PWM Waveform
160
Hz
100
Hz (min)
250
Hz (max)
V
TH
Threshold High Level for SD
1.3
V
1.8
V (min)
LM3824
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Common Device Parameters
(Continued)
Unless otherwise specified, V
DD
= 3.6V for the following specifications. Supply bypass capacitor is 1 F and filter capacitor is
0.1 F.
Symbol
Parameter
Conditions
Typ
(Note 5)
Limit
(Note 6)
Units
V
TL
Threshold Low Level for SD
1.2
V
0.7
V (max)
V
OH
Logic High Level for PWM
Load current = 1 mA, 2V
V
DD
5.25V
V
DD
- 0.05
V
DD
- 0.2
V
V (min)
V
OL
Logic Low Level for PWM
Sink current = 1 mA, 2V
V
DD
5.25V
0.04
V
0.2
V (max)
P
I
Insertion Loss
I
SENSE
= 1A (Note 9)
0.003
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is in-
tended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see Electrical Characteristics. The guar-
anteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.
Note 2: At elevated temperatures, devices must be derated based on package thermal resistance. The device in the surface-mount package must be derated at
JA
= 220C/W (typically), junction-to-ambient.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 k
resistor into each pin.
Note 4: The absolute maximum peak and continuous currents specified are not tested. These specifications are dependent on the
JA
, which is 220C/W for the
MSOP-8 package.
Note 5: Typical numbers are at 25C and represent the most likely parametric norm. Specifications in standard type face are for T
J
= 25C and those with boldface
type apply over full operating temperature ranges.
Note 6: Limits are 100% production tested at 25C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control
(SQC) methods. The limits are used to calculate National's Average Outgoing Quality Level (AOQL).
Note 7: There is a variation in accuracy over time due to thermal effects. Please refer to the "PWM Output and Current Accuracy" section for more information.
Note 8: This parameter is production tested at 1A and guaranteed by design at 2A.
Note 9: The tolerance of the internal lead frame resistor is corrected internally. The temperature coefficient of this resistor is 2600 ppm/C.
LM3824
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Typical Performance Characteristics
Supply bypass capacitor is 0.1 F and filter capacitor is 0.1 F.
Measured Current vs Actual Current
(LM3824-1.0)
DS200007-24
Measured Current vs Actual Current
(LM3824-2.0)
DS200007-25
PWM Frequency vs Supply Voltage
DS200007-33
PWM Frequency vs Temperature
DS200007-23
Operating Current vs Supply Voltage
DS200007-18
Shutdown Current vs Supply Voltage
DS200007-20
LM3824
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