Rainbow Electronics LM3822 User Manual
November 2000
LM3822
Precision Current Gauge IC with Internal Zero Ohm
Sense Element and PWM Output
General Description
The LM3822 Current Gauge provides easy to use precision
current measurement with virtually zero insertion loss (typically 0.003Ω). The LM3822 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 averaging function. Current is averaged over 50 msec time
periods 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 LM3822 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 50ms. If faster sampling is
desired, please refer to the data sheet for the part number
LM3824.
n Low quiescent current in shutdown mode (typically
1.8 µA)
n 50 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 ∆Σ 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 1 mA for 1A part
LM3822 Precision Current Gauge IC with Internal Zero Ohm Sense Element and PWM Output
Key Specifications
n Ultra low insertion loss (typically 0.003Ω)
n 2V to 5.5V supply range
±
n
2% accuracy at room temperature for the 1A device
(includes accuracy of the internal sense element)
Connection Diagram
LM3822 for High-Side Sensing
Applications
n Battery charge/discharge gauge
n Motion control diagnostics
n Power supply load monitoring and management
n Resettable smart fuse
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Top View
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Ordering Information
LM3822
* 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.
Order No.
LM3822MM-1.0
LM3822MMX-1.0
LM3822MM-2.0
LM3822MMX-2.0
*
Sense
Range
±
1.0A 50 ms High-side MUA08A MSOP-8 Tape and Reel
±
1.0A 50 ms High-side MUA08A MSOP-8 Tape and Reel
±
2.0A 50 ms High-side MUA08A MSOP-8 Tape and Reel
±
2.0A 50 ms High-side MUA08A MSOP-8 Tape and Reel
Sampling
Interval*
Sensing
Method
NS
Package
Number
Pin Description (High-Side, LM3822)
Pin Name Function
1 SENSE+, V
2 GND Supply Ground.
3 FLTR+ Filter input — provides anti-aliasing for delta sigma modulator.
4 FLTR− Filter input.
5SD
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.
DD
High side of internal current sense, also supply voltage.
Shutdown input. Connected to VDDthrough a pull-up resistor for normal operation.
When low, the LM3822 is put into a low current mode.
Package
Type
Supplied As:
(1000 units/reel)
(3500 units/reel)
(1000 units/reel)
(3500 units/reel)
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LM3822
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
Storage Temperature −65˚C to +150˚C
Lead Temperature (Soldering, 10 sec) 260˚C
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Operating Ratings (Note 1)
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 150˚C
Input Voltage 2.0V to 5.25V
Sense Current (continuous) (Note 4) 5A
Junction Temperature Range −40˚C to +85˚C
Electrical Characteristics Typical numbers are at 25˚C and represent the most likely parametric norm.
Specifications in standard type face are for T
ranges.
= 25˚C and those with boldface type apply over full operating temperature
J
LM3822-1.0
SENSE+VDD= 3.6V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is 0.1 µF.
Symbol Parameter Conditions
I
ACC
Average Current Accuracy
1.0A current 1.0
(Note 7)
e
n
Effective Output Noise (rms) 2 mA
Typ
(Note 5)
Limit
(Note 6)
0.98 / 0.96 A (min)
1.02 / 1.04 A (max)
Units
A
LM3822-2.0
SENSE+VDD= 3.6V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is 0.1 µF.
Symbol Parameter Conditions
I
ACC
Average Current Accuracy
2.0A current (Note 8) 2.0 A
(Note 7)
Typ
(Note 5)
Limit
(Note 6)
1.94 / 1.90 A (min)
2.06 / 2.10 A (max)
e
n
Effective Output Noise (rms) 6 mA
Common Device Parameters
Unless otherwise specified, VDD= 3.6V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is
0.1 µF.
Symbol Parameter Conditions
I
Q1
I
Q2
D
RES
t
S
f
P
V
TH
Quiescent Current Normal Mode, SD = high 95 µA
Quiescent Current Shutdown Mode, SD = low 1.8 µA
PWM Resolution 0.1 %
Sampling Time 50 ms
Frequency of PWM Waveform 20 Hz
Threshold High Level for SD 1.3 V
Typ
(Note 5)
Limit
(Note 6)
150 µA (max)
10 µA (max)
40 ms (min)
80 ms (max)
12.5 Hz (min)
25 Hz (max)
1.8 V (min)
Units
Units
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Electrical Characteristics Typical numbers are at 25˚C and represent the most likely parametric norm.
Specifications in standard type face are for T
LM3822
ranges. (Continued)
= 25˚C and those with boldface type apply over full operating temperature
J
Common Device Parameters (Continued)
Unless otherwise specified, VDD= 3.6V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is
0.1 µF.
Symbol Parameter Conditions
V
TL
V
OH
Threshold Low Level for SD 1.2 V
Logic High Level for PWM Load current = 1 mA, 2V ≤ VDD≤
Typ
(Note 5)
VDD− 0.05
5.25V
V
OL
Logic Low Level for PWM Sink current = 1 mA, 2V ≤ VDD≤
0.04 V
5.25V
P
I
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see Electrical Characteristics. The
guaranteed 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
θ
JA
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 4: The absolute maximum peak and continuous currents specified are not tested. These specifications are dependent on the θ
MSOP-8 package.
Note 5: Typical numbers are at 25˚C and represent the most likely parametric norm. Specifications in standard type face are for T
typeapply over full operating temperature ranges.
Note 6: Limits are 100% production tested at 25˚C. 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.
Insertion Loss I
= 220˚C/W (typically), junction-to-ambient.
= 1A (Note 9) 0.003 Ω
SENSE
Limit
(Note 6)
0.7 V (max)
− 0.2
V
DD
0.2 V (max)
, which is 220˚C/W for the
JA
= 25˚C and those with boldface
J
Units
V
V (min)
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