LM3812MX-1.0 [TI]

2-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8, 0.150 INCH, PLASTIC, SOP-8;
LM3812MX-1.0
型号: LM3812MX-1.0
厂家: TEXAS INSTRUMENTS    TEXAS INSTRUMENTS
描述:

2-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8, 0.150 INCH, PLASTIC, SOP-8

光电二极管
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LM3812, LM3813  
www.ti.com  
SNOS028D JUNE 1999REVISED APRIL 2013  
LM3812/LM3813 Precision Current Gauge IC with Ultra Low Loss Sense Element and  
PWM Output  
Check for Samples: LM3812, LM3813  
1
FEATURES  
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.  
2
No External Sense Element Required  
PWM Output Indicates the Current Magnitude  
and Direction  
PWM Output can be Interfaced with  
Microprocessors  
A
Delta Sigma analog to digital converter is  
Precision ΔΣ Current-Sense Technique  
Low Temperature Sensitivity  
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.  
Internal Filtering Rejects False Trips  
Internal Power-On-Reset (POR)  
APPLICATIONS  
Battery Charge/Discharge Gauge  
Motion Control Diagnostics  
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.  
Power Supply Load Monitoring and  
Management  
Resettable Smart Fuse  
KEY SPECIFICATIONS  
Ultra Low Insertion Loss (Typically 0.004Ω)  
2V to 5.25V Supply Range  
±2% Accuracy at Room Temperature (Includes  
Accuracy of the Internal Sense Element)  
( LM3812-1.0, LM3813-1.0)  
Low Quiescent Current In Shutdown Mode  
(Typically 2.5 µA)  
50 msec Sampling Interval  
Connection Diagrams  
Figure 1. LM3812 (Top View)  
for High-Side Sensing  
Figure 2. LM3813 (Top View)  
for Low-Side Sensing  
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of  
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.  
All trademarks are the property of their respective owners.  
2
PRODUCTION DATA information is current as of publication date.  
Products conform to specifications per the terms of the Texas  
Instruments standard warranty. Production processing does not  
necessarily include testing of all parameters.  
Copyright © 1999–2013, Texas Instruments Incorporated  
LM3812, LM3813  
SNOS028D JUNE 1999REVISED APRIL 2013  
www.ti.com  
PIN DESCRIPTIONS (High-Side, LM3812)  
Function  
Pin  
1
Name  
SENSE+, VDD  
High side of internal current sense, also supply voltage.  
Low side of internal current sense.  
Filter input — provides anti-aliasing for delta sigma modulator.  
Filter input.  
2
SENSE  
FLTR+  
FLTR−  
SD  
3
4
5
Shutdown pin. Connected to VDD through a pull up resistor for normal operation. When low, the  
IC goes into a low current mode (typically 3 µA).  
6
7
8
PWM  
GND  
GND  
PWM output indicates the current magnitude and direction.  
Ground  
Ground  
PIN DESCRIPTIONS (Low-Side, LM3813)  
Function  
Pin  
1
Name  
SENSE+, GND  
SENSE−  
FLTR+  
High side of internal current sense, also ground.  
Low side of internal current sense.  
Filter input – provides anti-aliasing for delta sigma modulator.  
Filter input.  
2
3
4
FLTR−  
5
SD  
Shutdown pin. Connected to VDD through a pull up resistor for normal operation. When low, the  
IC goes into a low current mode (typically 3 µA).  
6
7
8
PWM  
GND  
VDD  
PWM output indicates the current magnitude and direction.  
Ground  
VDD (supply)  
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam  
during storage or handling to prevent electrostatic damage to the MOS gates.  
2
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SNOS028D JUNE 1999REVISED APRIL 2013  
(1) (2)  
ABSOLUTE MAXIMUM RATINGS  
Absolute Maximum Supply Voltage  
Power Dissipation  
5.5V  
(3)  
See  
(4)  
ESD Susceptibility  
1.5 kV  
10A  
(5)  
Sense Current (peak, for 200 msec)  
Sink Current for PWM pin  
Voltage on Pin 5  
1mA  
5.25V  
Maximum Junction Temperature  
Storage Temperature  
150°C  
65°C to +150°C  
260°C  
Lead Temperature (Soldering, 10 sec)  
(1) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and  
specification  
(2) 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 ensure specific performance limits. For ensured specifications and test  
conditions, see Electrical Characteristics. The ensured specifications apply only for the test conditions listed. Some performance  
characteristics may degrade when the device is not operated under the listed test conditions.  
(3) At elevated temperatures, devices must be derated based on package thermal resistance. The device in the surface-mount package  
must be derated at θJA= 150°C/W (typically), junction-to-ambient.  
(4) The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.  
(5) The absolute maximum peak and continuous currents specified are not tested. These specifications are dependent on the θJA, which is  
150°C/W for the D0008A package.  
(1)  
OPERATING RATINGS  
Input Voltage  
2.0V to 5.25V  
7A  
(2)  
Sense Current (continuous)  
Junction Temperature Range  
40°C to +125°C  
(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 ensure specific performance limits. For ensured specifications and test  
conditions, see Electrical Characteristics. The ensured specifications apply only for the test conditions listed. Some performance  
characteristics may degrade when the device is not operated under the listed test conditions.  
(2) The absolute maximum peak and continuous currents specified are not tested. These specifications are dependent on the θJA, which is  
150°C/W for the D0008A package.  
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  
IACC  
Parameter  
Conditions  
at 0.9A current  
Typ(1)  
Limit(2)  
Units  
(3)  
Average Current Accuracy  
0.9  
A
0.882 / 0.864  
0.918 / 0.936  
A (min)  
A (max)  
en  
Effective Output Noise (rms)  
2
mA  
(1) Typical numbers are at 25°C and represent the most likely parametric norm. Specifications in standard type face are for TJ= 25°C and  
those with boldface type apply over full operating temperature ranges.  
(2) Limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlation using Statistical  
Quality Control (SQC) methods. The limits are used to calculate Averaging Outgoing Quality Level (AOQL).  
(3) 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.  
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Units  
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  
IACC  
Parameter  
Conditions  
Typ(1)  
Limit(2)  
(3)  
(4)  
Average Current Accuracy  
at 2.5A current  
2.5  
A
2.400 / 2.350  
2.600 / 2.650  
A (min)  
A (max)  
en  
Effective Output Noise (rms)  
20  
mA  
(1) Typical numbers are at 25°C and represent the most likely parametric norm. Specifications in standard type face are for TJ= 25°C and  
those with boldface type apply over full operating temperature ranges.  
(2) Limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlation using Statistical  
Quality Control (SQC) methods. The limits are used to calculate Averaging Outgoing Quality Level (AOQL).  
(3) 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.  
(4) 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 PWM OUTPUT AND CURRENT ACCURACY section for more information.  
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(1)  
Limit(2)  
Units  
100  
µA  
µA (max)  
IQ1  
Quiescent Current  
Normal Mode, SD = high  
160  
2.5  
µA  
µA (max)  
IQ2  
Quiescent Current  
PWM Resolution  
Shutdown Mode, SD = low  
10  
DRES  
0.1  
52  
%
ms  
tS  
Sampling Time  
40  
80  
ms (min)  
ms (max)  
20  
Hz  
fP  
Frequency of PWM Waveform  
12.5  
25  
Hz (min)  
Hz (max)  
1.2  
1.3  
V
VTH  
VTL  
VOH  
Threshold High Level for SD  
Threshold Low Level for SD  
Logic High Level for PWM  
1.8  
0.7  
V (min)  
V
V (max)  
V
DD 0.05  
V
Load current = 1 mA, 2V VDD 5.25V  
Sink current = 1 mA, 2V VDD 5.25V  
V
DD 0.2  
V (min)  
0.04  
V
VOL  
PI  
Logic Low Level for PWM  
Insertion Loss  
0.2  
V (max)  
(3)  
ISENSE = 1A  
0.004  
Ω
(1) Typical numbers are at 25°C and represent the most likely parametric norm. Specifications in standard type face are for TJ= 25°C and  
those with boldface type apply over full operating temperature ranges.  
(2) Limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlation using Statistical  
Quality Control (SQC) methods. The limits are used to calculate Averaging Outgoing Quality Level (AOQL).  
(3) The tolerance of the internal lead frame resistor is corrected internally. The temperature coefficient of this resistor is 2600 ppm/°C.  
4
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SNOS028D JUNE 1999REVISED APRIL 2013  
TYPICAL PERFORMANCE CHARACTERISTICS  
Supply bypass capacitor is 0.1 µF and filter capacitor is 0.1 µF.  
Measured Current vs Actual Current  
Measured Current vs Actual Current  
(LM3812-7.0 and LM3813-7.0)  
(LM3812-1.0 and LM3813-1.0)  
Figure 3.  
Figure 4.  
PWM Frequency vs Supply Voltage  
PWM Frequency vs Temperature  
Figure 5.  
Figure 6.  
Operating Current vs Supply Voltage  
Shutdown Current vs Supply Voltage  
Figure 7.  
Figure 8.  
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)  
Supply bypass capacitor is 0.1 µF and filter capacitor is 0.1 µF.  
Operating Current vs Temperature  
Shutdown Current vs Temperature  
Figure 9.  
Figure 10.  
Current vs Duty Cycle  
Accuracy vs Supply Voltage  
Figure 11.  
Figure 12.  
Accuracy vs Temperature  
(LM3812-1.0 and LM3813-1.0)  
Accuracy vs Temperature  
(LM3812-7.0 and LM3813-7.0)  
Figure 13.  
Figure 14.  
6
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)  
Supply bypass capacitor is 0.1 µF and filter capacitor is 0.1 µF.  
Error vs Current  
(LM3812-1.0 and LM3813-1.0)  
Error vs Current  
(LM3812-7.0 and LM3813-7.0)  
Figure 15.  
Figure 16.  
These curves represent a statistical average such that the noise is insignificant.  
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TYPICAL APPLICATION CIRCUITS  
In the application circuits, the 0.1 µF ceramic capacitor between pins 1 and 8 is used for bypassing, and the 0.1  
µF ceramic capacitor between pins 3 and 4 is used for filtering. Shutdown (SD) is tied to VDD through a 10 kΩ  
resistor.  
Figure 17. High Side Sense  
Figure 18. Low Side Sense  
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ITOTAL = 2.2(D10.5)IMAX + 2.2(D20.5)IMAX  
where D1 is the duty cycle of PWM1 and  
D2 is the duty cycle of PWM2.  
Figure 19. Paralleling LM3812 for Higher Load Current  
Please refer to the PRODUCT OPERATION section for more information.  
Figure 20. High Voltage Operation — VIN Greater Than 5.25V (High Side Sense)  
(PWM output is referred to Pin 7)  
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Figure 21. High Voltage Operation — VIN Greater Than 5.25V (Low Side Sense)  
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PRODUCT OPERATION  
The current is sampled by the delta-sigma modulator, as illustrated in Figure 22. The pulse density output of the  
delta-sigma modulator is digitally filtered. The digital output is then compared to the output of a digital ramp  
generator. This produces a PWM output. The duty cycle of the PWM output is proportional to the amount of  
current flowing. A duty cycle of 50% indicates zero current flow. If the current is flowing in positive direction, the  
duty cycle will be greater than 50%. Conversely, the duty cycle will be less than 50% for currents flowing in the  
negative direction. A duty cycle of 95.5% (4.5%) indicates the current is at IMAX (IMAX). The IC can sense  
currents from IMAX to +IMAX. Options for IMAX are 1A or 10A. The sense current is given by:  
ISENSE = 2.2 (D0.5)(IMAX  
)
where  
D is the duty cycle of the PWM waveform.  
IMAX is the full scale current (1A or 10A).  
(1)  
(2)  
Similarly, the duty cycle is given by:  
D = [ISENSE/(2.2 IMAX)] + 0.5  
For quick reference, see the Conversion Tables in Table 1 and Table 2.  
The user should note that, while the LM3812-7.0/ LM3813-7.0 will read 10A full scale, it is rated for 10A  
operation for a duration of no more than 200 msec, and 7A operation continuously.  
In this IC, the current is averaged over 50 msec time slots. Hence, momentary current surges of less than 50  
msec are tolerated.  
This is a sampled data system which requires an anti-aliasing filter, provided by the filter capacitor.  
The delta-sigma modulator converts the sensed current to the digital domain. This allows digital filtering, and  
provides immunity to current and noise spikes. This type of filtering would be difficult or impossible to accomplish  
on an IC with analog components.  
When ordering, the user has to specify whether the part is being used for low-side or high-side sense. The user  
also needs to specify the full scale value.  
Figure 22. Functional Block Diagram of LM3812 and LM3813  
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PWM OUTPUT AND CURRENT ACCURACY  
Offset  
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The PWM output is quantized to 1024 levels. Therefore, the duty cycle can change only in increments of 1/1024.  
There is a one-half (0.5) quantization cycle delay in the output of the PWM circuitry. That is to say that instead of  
a duty cycle of N/1024, the duty cycle actually is (N+½)/1024.  
The quantization error can be corrected for if a more precise result is desired. To correct for this error, simply  
subtract 1/2048 from the measured duty cycle.  
The extra half cycle delay will show up as a DC offset of ½ bit if it is not corrected for. This is approximately 1.1  
mA for 1 Amp parts, and 11 mA for 7 Amp parts.  
Jitter  
In addition to quantization, the duty cycle will contain some jitter. The jitter is quite small (for example, the  
standard deviation of jitter is only 0.1% for the LM3812/13-1.0). Statistically the jitter can cause an error in a  
current sample. Because the jitter is a random variable, the mean and standard deviation are used. The mean, or  
average value, of the jitter is zero. The standard deviation (0.1%) can be used to define the peak error caused  
from jitter.  
The “crest factor” has often been used to define the maximum error caused by jitter. The crest factor defines a  
limit within which 99.7% of the samples fall. The crest factor is defined as ±0.3% error in the duty cycle.  
Since the jitter is a random variable, averaging multiple outputs will reduce the effective jitter. Obeying statistical  
laws, the jitter is reduced by the square root of the number of readings that are averaged. For example, if four  
readings of the duty cycle are averaged, the resulting jitter (and crest factor) are reduced by a factor of two.  
Jitter and Noise  
Jitter in the PWM output appears as noise in the current measurement. The Electrical Characteristics show noise  
measured in current RMS (root mean square). Arbitrarily one could specify PWM jitter, as opposed to noise. In  
either case the effect results in a random error in an individual current measurement.  
Noise, just like jitter, can be reduced by averaging many readings. The RMS value of the noise corresponds to  
one standard deviation. The “crest factor” can be calculated in terms of current, and is equal to ±3 sigma (RMS  
value of the noise).  
Noise will also be reduced by averaging multiple readings, and follows the statistical laws of a random variable.  
Accuracy of 7A Versions  
The graph of Figure 23 shows two possible responses to a 7A current step. The flat response shows basically a  
7A level with some noise. This is what is possible with a good thick trace and a good thermal connection to the  
IC on the sense pins.  
The second trace that asymptotically approaches a higher value shows what can happen under extremely poor  
thermal conditions. Here a very small wire connects the IC to the current source. The very small wire does not  
allow heat in the sense resistor to dissipate. Hence, as the sense resistor heats up, a temperature difference  
between the sense element and the die gets larger, and an error develops. Eventually the temperature difference  
reaches steady state, which accounts for the under-damped exponential response.  
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Figure 23. Transient Response to 7 Amp Step Current  
Accuracy Versus Noise  
The graph shown in Figure 24 illustrates the typical response of ±1 Ampere current gauges. In this graph, the  
horizontal axis indicates time, and the vertical axis indicates measured current (the PWM duty cycle has been  
converted to current). The graph was generated for an actual current of 500 mA.  
The difference between successive readings manifests itself as jitter in the PWM output or noise in the current  
measurement (when duty cycle of the PWM output is converted to current).  
The accuracy of the measurement depends on the noise in the current waveform. The accuracy can be improved  
by averaging several outputs. Although there is variation in successive readings, a very accurate measurement  
can be obtained by averaging the readings. For example, on averaging the readings shown in this example, the  
average current measurement is 502.3 mA (Figure 24). This value is very close to the actual value of 500 mA.  
Moreover, the accuracy depends on the number of readings that are averaged.  
Figure 24. Typical Response of LM3812-1.0/LM3813-1.0  
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LOOK-UP TABLES  
The following tables show how to convert the duty cycle of the PWM output to a current value, and vice versa.  
The quantization error of ½ bit is not shown in these tables. Please see the PWM OUTPUT AND CURRENT  
ACCURACY section for more details.  
Table 1. Current to Duty Cycle Conversion Table  
Sense Current  
(Amps)(1)  
Duty Cycle  
(%)  
Sense Current  
(Amps)(1)  
Duty Cycle  
(%)  
1.00  
0.95  
0.90  
0.85  
0.80  
0.75  
0.70  
0.65  
0.60  
0.55  
0.50  
0.45  
0.40  
0.35  
0.30  
0.25  
0.20  
0.15  
0.10  
0.05  
0.00  
95.5  
93.2  
90.9  
88.6  
86.4  
84.1  
81.8  
79.5  
77.3  
75.0  
72.7  
70.5  
68.2  
65.9  
63.6  
61.4  
59.1  
56.8  
54.5  
52.3  
50.0  
-1.00  
-0.95  
-0.90  
-0.85  
-0.80  
-0.75  
-0.70  
-0.65  
-0.60  
-0.55  
-0.50  
-0.45  
-0.40  
-0.35  
-0.30  
-0.25  
-0.20  
-0.15  
-0.10  
-0.05  
-0.00  
4.5  
6.8  
9.1  
11.4  
13.6  
15.9  
18.2  
20.5  
22.7  
25.0  
27.3  
29.5  
31.8  
34.1  
36.4  
38.6  
40.9  
43.2  
45.5  
47.7  
50.0  
(1) Maximum Sense Current = 1.0 Amps for LM3812-1.0 and LM3813-1.0.  
The sense current should be multiplied by 10 for LM3812-7.0 and LM3813-7.0.  
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Table 2. Duty Cycle to Current Conversion Table  
Duty Cycle  
Sense Current  
(Amps)(1)  
Duty Cycle  
(%)  
Sense Current  
(Amps)(1)  
(%)  
95.5  
92.5  
90.0  
87.5  
85.0  
82.5  
80.0  
77.5  
75.0  
72.5  
70.0  
67.5  
65.0  
62.5  
60.0  
57.5  
55.0  
52.5  
50.0  
0.990  
0.935  
0.880  
0.825  
0.770  
0.715  
0.660  
0.605  
0.550  
0.495  
0.440  
0.385  
0.330  
0.275  
0.220  
0.165  
0.110  
0.055  
0.000  
50.0  
47.5  
45.0  
42.5  
40.0  
37.5  
35.0  
32.5  
30.0  
27.5  
25.0  
22.5  
20.0  
17.5  
15.0  
12.5  
10.0  
7.5  
-0.000  
-0.055  
-0.110  
-0.165  
-0.220  
-0.275  
-0.330  
-0.385  
-0.440  
-0.495  
-0.550  
-0.605  
-0.660  
-0.715  
-0.770  
-0.825  
-0.880  
-0.935  
-0.990  
5.0  
(1) Maximum Sense Current = 1.0 Amps for LM3812-1.0 and LM3813-1.0.  
The sense current should be multiplied by 10 for LM3812-7.0 and LM3813-7.0.  
TIMING DIAGRAM  
Duty cycle of the PWM waveform during any sampling interval indicates the current magnitude (average) and  
direction during the previous sampling interval.  
Figure 25. Typical Timing Diagram for Mostly Positive Current  
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