NSC LM3813M-7.0, LM3813M-1.0, LM3812MX-7.0, LM3812M-7.0, LM3812M-1.0 Datasheet
...
June 1999
LM3812/LM3813
Precision Current Gauge IC with Ultra Low Loss Sense
Element and PWM Output
General Description
The LM3812/LM3813 Current Gauges provide easy to use precision current measurement with virtually zero insertion loss (typically 0.004Ω). The LM3812 is used for high-side sensing and the LM3813 is used for low-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 LM3812 and LM3813 are factory-set in two different current options. The sense range is −1A to +1A or −7A to +7A. The sampling interval for these parts is 50ms. If faster sampling is desired, please refer to the data sheets for the part numbers LM3814 and LM3815.
Key Specifications
nUltra low insertion loss (typically 0.004Ω)
n2V to 5.25V supply range
n±2% accuracy at room temperature (includes accuracy of the internal sense element) (LM3812-1.0, LM3813-1.0)
nLow quiescent current in shutdown mode (typically 2.5 µA)
n50 msec sampling interval
Features
nNo external sense element required
nPWM output indicates the current magnitude and direction
nPWM output can be interfaced with microprocessors
nPrecision ΔΣ current-sense technique
nLow temperature sensitivity
nInternal filtering rejects false trips
nInternal Power-On-Reset (POR)
Applications
n Battery charge/discharge gauge n Motion control diagnostics
n Power supply load monitoring and management n Resettable smart fuse
Connection Diagrams
DS100122-1
DS100122-3
Top View
LM3812
Top View
for High-Side Sensing
LM3813
for Low-Side Sensing
PWM and Element Sense Loss Low Ultra with IC Gauge Current Precision LM3812/LM3813
Output
© 1999 National Semiconductor Corporation |
DS100122 |
www.national.com |
Ordering Information
|
|
|
|
NS |
|
|
Order No.# |
Sense |
Sampling |
Sensing |
Package |
Package |
|
|
Range |
Interval* |
Method |
Number³ |
Type |
Supplied As: |
LM3812M-1.0 |
±1A |
50 ms |
High-side |
M08A |
SO-8 |
95 units in Rails |
|
|
|
|
|
|
|
LM3812MX-1.0 |
±1A |
50 ms |
High-side |
M08A |
SO-8 |
2.5k units on Tape and Reel |
|
|
|
|
|
|
|
LM3812M-7.0 |
±7A |
50 ms |
High-side |
M08A |
SO-8 |
95 units in Rails |
|
|
|
|
|
|
|
LM3812MX-7.0 |
±7A |
50 ms |
High-side |
M08A |
SO-8 |
2.5k units on Tape and Reel |
|
|
|
|
|
|
|
LM3813M-1.0 |
±1A |
50 ms |
Low-side |
M08A |
SO-8 |
95 units in Rails |
|
|
|
|
|
|
|
LM3813MX-1.0 |
±1A |
50 ms |
Low-side |
M08A |
SO-8 |
2.5k units on Tape and Reel |
|
|
|
|
|
|
|
LM3813M-7.0 |
±7A |
50 ms |
Low-side |
M08A |
SO-8 |
95 units in Rails |
|
|
|
|
|
|
|
LM3813MX-7.0 |
±7A |
50 ms |
Low-side |
M08A |
SO-8 |
2.5k units on Tape and Reel |
|
|
|
|
|
|
|
# Suffix M indicates that the part is available in Surface Mount package. Suffix X indicates that the part is available in 2.5k units on Tape and 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.
³ The Package code M08A is internal to National Semiconductor and indicates an 8-lead surface mount package, SO-8.
Pin Description (High-Side, LM3812)
Pin |
|
|
Name |
Function |
|
|
|
|
|
1 |
|
SENSE+, VDD |
High side of internal current sense, also supply voltage. |
|
2 |
SENSE− |
Low side of internal current sense. |
||
|
|
|
|
|
3 |
FLTR+ |
Filter input Ð provides anti-aliasing for delta sigma modulator. |
||
|
|
|
|
|
4 |
FLTR− |
Filter input. |
||
|
|
|
|
|
5 |
|
Shutdown pin. Connected to VDD through a pull up resistor for normal operation. |
||
|
SD |
|
||
|
|
|
|
When low, the IC goes into a low current mode (typically 3 µA). |
|
|
|
|
|
6 |
PWM |
PWM output indicates the current magnitude and direction. |
||
|
|
|
|
|
7 |
GND |
Ground |
||
|
|
|
|
|
8 |
GND |
Ground |
||
|
|
|
|
|
Pin Description (Low-Side, LM3813)
Pin |
|
|
Name |
Function |
|
|
|
|
|
1 |
|
SENSE+, GND |
High side of internal current sense, also ground. |
|
|
|
|
|
|
2 |
|
SENSE− |
Low side of internal current sense. |
|
|
|
|
|
|
3 |
|
FLTR+ |
Filter input ± provides anti-aliasing for delta sigma modulator. |
|
|
|
|
|
|
4 |
|
FLTR− |
Filter input. |
|
|
|
|
|
|
5 |
|
|
Shutdown pin. Connected to VDD through a pull up resistor for normal operation. |
|
|
SD |
|
||
|
|
|
|
When low, the IC goes into a low current mode (typically 3 µA). |
|
|
|
|
|
6 |
PWM |
PWM output indicates the current magnitude and direction. |
||
|
|
|
|
|
7 |
GND |
Ground |
||
|
|
|
|
|
8 |
VDD |
VDD (supply) |
||
www.national.com |
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 |
Voltage on Pin 5 |
5.25V |
Maximum Junction Temperature |
150ÊC |
Storage Temperature |
−65ÊC to +150ÊC |
Lead Temperature (Soldering, 10 sec) |
260ÊC |
Operating Ratings (Note 1)
Input Voltage |
2.0V to 5.25V |
Sense Current (continuous) (Note 4) |
7A |
Junction Temperature Range |
−40ÊC to +125ÊC |
Electrical Characteristics
LM3812-1.0, LM3813-1.0
VDD = 5.0V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is 0.1 µF.
Symbol |
Parameter |
Conditions |
Typ |
Limit |
Units |
|
(Note 5) |
(Note 6) |
|||||
|
|
|
|
|||
|
|
|
|
|
|
|
IACC |
Average Current Accuracy |
at 0.9A current |
0.9 |
|
A |
|
|
(Note 7) |
|
|
|
||
|
|
|
|
|
||
|
|
|
|
0.882 / 0.864 |
A (min) |
|
|
|
|
|
0.918 / 0.936 |
A (max) |
|
|
|
|
|
|
|
|
en |
Effective Output Noise (rms) |
|
2 |
|
mA |
LM3812-7.0, LM3813-7.0
VDD = 5.0V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is 0.1 µF.
Symbol |
Parameter |
Conditions |
Typ |
Limit |
Units |
|
(Note 5) |
(Note 6) |
|||||
|
|
|
|
|||
|
|
|
|
|
|
|
IACC |
Average Current Accuracy |
at 2.5A current (Note 8) |
2.5 |
|
A |
|
|
(Note 7) |
|
|
2.400 / 2.350 |
A (min) |
|
|
|
|
|
2.600 / 2.650 |
A (max) |
|
|
|
|
|
|
|
|
en |
Effective Output Noise (rms) |
|
20 |
|
mA |
Common Device Parameters
Unless otherwise specified, VDD = 5.0V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is 0.1 µF.
Symbol |
Parameter |
Conditions |
Typ |
Limit |
Units |
|||||||||
(Note 5) |
(Note 6) |
|||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
IQ1 |
Quiescent Current |
Normal Mode, |
|
|
= high |
100 |
|
µA |
||||||
SD |
|
|||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
160 |
µA (max) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
IQ2 |
Quiescent Current |
Shutdown Mode, |
|
= low |
2.5 |
|
µA |
|||||||
SD |
|
|||||||||||||
|
|
|
|
|
|
|
|
|
|
|
|
10 |
µA (max) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
DRES |
PWM Resolution |
|
|
|
|
|
0.1 |
|
% |
|||||
tS |
Sampling Time |
|
|
|
|
|
52 |
|
ms |
|||||
|
|
|
|
|
|
|
|
|
|
|
|
40 |
ms (min) |
|
|
|
|
|
|
|
|
|
|
|
|
|
80 |
ms (max) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
fP |
Frequency of PWM Waveform |
|
|
|
|
|
20 |
|
Hz |
|||||
|
|
|
|
|
|
|
|
|
|
|
|
12.5 |
Hz (min) |
|
|
|
|
|
|
|
|
|
|
|
|
|
25 |
Hz (max) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
VTH |
|
|
|
|
|
|
|
|
|
|
|
|||
Threshold High Level for |
SD |
|
|
|
|
|
|
1.2 |
|
V |
||||
|
|
|
|
|
|
|
|
|
|
|
|
1.8 |
V (min) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
VTL |
|
|
|
|
|
|
|
|
|
|||||
Threshold Low Level for |
SD |
|
|
|
|
|
|
1.3 |
|
V |
||||
|
|
|
|
|
|
|
|
|
|
|
|
0.7 |
V (max) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
3 |
www.national.com |
Common Device Parameters (Continued)
Unless otherwise specified, VDD = 5.0V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is 0.1 µF.
Symbol |
Parameter |
Conditions |
Typ |
Limit |
Units |
|
(Note 5) |
(Note 6) |
|||||
|
|
|
|
|||
|
|
|
|
|
|
|
VOH |
Logic High Level for PWM |
Load current = 1 mA, 2V ≤ VDD ≤ |
VDD − 0.05 |
|
V |
|
|
|
5.25V |
|
VDD − 0.2 |
V (min) |
|
VOL |
Logic Low Level for PWM |
Sink current = 1 mA, 2V ≤ VDD ≤ |
0.04 |
|
V |
|
|
|
5.25V |
|
0.2 |
V (max) |
|
|
|
|
|
|
|
|
PI |
Insertion Loss |
ISENSE = 1A (Note 9) |
0.004 |
|
Ω |
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 θJA= 150ÊC/W (typically), junction-to-ambient.
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 θJA, which is 150ÊC/W for the S08 package.
Note 5: Typical numbers are at 25ÊC and represent the most likely parametric norm. Specifications in standard type face are for TJ= 25ÊC and those with boldface type apply over full operating temperature ranges.
Note 6: Limits are 100% production tested at 25ÊC. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. The limits are used to calculate National's Averaging Outgoing Quality Level (AOQL).
Note 7: There is a variation in accuracy over time due to thermal effects. Please refer to the ªPWM Output and Current Accuracyº section for more information.
Note 8: The PWM accuracy for LM3812-7.0 and LM3813-7.0 depends on the amount of copper area under pins 1 and 2, and the layout. Please refer to the ªPWM Output and Current Accuracyº section for more information.
Note 9: The tolerance of the internal lead frame resistor is corrected internally. The temperature coefficient of this resistor is 2600 ppm/ÊC.
www.national.com |
4 |
Typical Performance Characteristics
Measured Current vs Actual Current (LM3812-1.0 and LM3813-1.0)
Supply bypass capacitor is 0.1 µF and filter capacitor is 0.1 µF.
Measured Current vs Actual Current (LM3812-7.0 and LM3813-7.0)
|
DS100122-15 |
DS100122-24 |
PWM Frequency vs Supply Voltage |
|
PWM Frequency vs Temperature |
DS100122-13 DS100122-16
Operating Current vs Supply Voltage Shutdown Current vs Supply Voltage
DS100122-18 |
DS100122-19 |
5 |
www.national.com |
Loading...