Rainbow Electronics LM3815 User Manual
LM3814/LM3815
Fast Current Gauge IC with Ultra Low Loss Sense
Element and PWM Output
±
n
General Description
The LM3814/LM3815 Current Gauges provide easy to use
precision current measurement with virtually zero insertion
loss (typically 0.004Ω). The LM3814 is used for high-side
sensing and the LM3815 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 6 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 LM3814 and LM3815 are factory-set in two different
current options. The sense range is −1A to +1A or −7A to
+7A. The user specifies a particular part number to match
the current range for a given application. The sampling
interval for these parts is 6ms. If larger sampling interval is
desired for better accuracy, please refer to the data sheets
for the part numbers LM3812 and LM3813.
Key Specifications
n Ultra low insertion loss (typically 0.004Ω)
n 2V to 5.25V supply range
3.5% accuracy at room temperature (includes
accuracy of the internal sense element) (LM3814-1.0,
LM3815-1.0)
n Low quiescent current in shutdown mode (typically 2.5
µA)
n 6 msec sampling interval
Features
n No external sense element required
n PWM output indicates the current magnitude and
direction
n PWM output can be interfaced with microprocessors
n Precision ∆Σ current-sense technique
n Low temperature sensitivity
n Internal filtering rejects false trips
n Internal 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
LM3814/LM3815 Fast Current Gauge IC with Ultra Low Loss Sense Element and PWM Output
January 1999
Connection Diagrams
Top View
LM3814
for High-Side Sensing
10101301
Top View
10101303
LM3815
for Low-Side Sensing
© 2004 National Semiconductor Corporation DS101013 www.national.com
Ordering Information
Order No.
LM3814/LM3815
LM3814M-1.0
LM3814MX-1.0
LM3814M-7.0
LM3814MX-7.0
LM3815M-1.0
LM3815MX-1.0
LM3815M-7.0
LM3815MX-7.0
#
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.
#
Sense
Range
±
1A 6 ms High-side M08A SO-8 95 units in Rails
±
1A 6 ms High-side M08A SO-8 2.5k units on Tape and Reel
±
7A 6 ms High-side M08A SO-8 95 units in Rails
±
7A 6 ms High-side M08A SO-8 2.5k units on Tape and Reel
±
1A 6 ms Low-side M08A SO-8 95 units in Rails
±
1A 6 ms Low-side M08A SO-8 2.5k units on Tape and Reel
±
7A 6 ms Low-side M08A SO-8 95 units in Rails
±
7A 6 ms Low-side M08A SO-8 2.5k units on Tape and Reel
Sampling
Interval*
Sensing
MethodNSPackage
Number
‡
The Package code M08A is internal to National Semiconductor and indicates an 8-lead surface mount package,
SO-8.
Pin Description (High-Side, LM3814)
Pin Description (High-Side, LM3814)
Pin Name Function
1 SENSE+, V
2 SENSE− Low side of internal current sense.
3 FLTR+ Filter input — provides anti-aliasing for delta sigma modulator.
4 FLTR− Filter input.
5SD
6 PWM PWM output indicates the current magnitude and direction.
7 GND Ground
8 GND Ground
DD
High side of internal current sense, also supply voltage.
Shutdown pin. Connected to VDDthrough a pull up resistor for normal operation. When
low, the IC goes into a low current mode (typically 3 µA).
‡
Package
Type
Supplied As:
Pin Description (Low-Side, LM3815)
Pin Description (Low-Side, LM3815)
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.
5SD
6 PWM PWM output indicates the current magnitude and direction.
7 GND Ground
8V
www.national.com 2
DD
Shutdown pin. Connected to VDDthrough a pull up resistor for normal operation. When
low, the IC goes into a low current mode (typically 3 µA).
VDD(supply)
LM3814/LM3815
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
Maximum Junction Temperature 150˚C
Storage Temperature −65˚C to +150˚C
Lead Temperature (Soldering, 10 sec) 260˚C
Operating Ratings (Note 1)
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 1 mA
Input Voltage 2.0V to 5.25V
Sense Current (continuous) (Note 4) 7A
Junction Temperature Range −40˚C to +125˚C
Voltage on Pin 5 5.25V
Electrical Characteristics
LM3814-1.0, LM3815-1.0
VDD= 5.0V for the following specifications. Supply bypass capacitor is 1µF and filter capacitor is 0.1µF.
Symbol Parameter Conditions
I
ACC
Average Current Accuracy
at 0.9A current 0.9 A
Typ
(Note 5)
(Note 7)
e
n
Effective Output Noise (rms) 12 mA
LM3814-7.0, LM3815-7.0
VDD= 5.0V for the following specifications. Supply bypass capacitor is 1µF and filter capacitor is 0.1µF.
Symbol Parameter Conditions
I
ACC
Average Current Accuracy
at 2.5A current (Note 8) 2.5 A
(Note 7)
e
n
Effective Output Noise (rms) 120 mA
Typ
(Note 5)
Limit
(Note 6)
Units
0.868 / 0.850 A (min)
0.932 / 0.950 A (max)
Limit
(Note 6)
Units
2.350 / 2.288 A (min)
2.650 / 2.712 A (max)
Common Device Parameters
Unless otherwise specified, VDD= 5.0V for the following specifications. Supply bypass capacitor is 1µF and filter capacitor is
0.1µF.
Symbol Parameter Conditions
I
Q1
I
Q2
D
RES
t
S
f
P
V
TH
V
TL
V
OH
Quiescent Current Normal Mode, SD = high 100 µA
Quiescent Current Shutdown Mode, SD = low 2.5 µA
PWM Resolution 0.8 %
Sampling Time 6 ms
Frequency of PWM Waveform 160 Hz
Threshold High Level for SD 1.2 V
Threshold Low Level for SD 1.3 V
Logic High Level for PWM Load current = 1mA, 2V ≤ VDD≤
5.25V
Typ
(Note 5)
VDD− 0.05
Limit
(Note 6)
160 µA (max)
10 µA (max)
4 ms (min)
10 ms (max)
100 Hz (min)
250 Hz (max)
1.8 V (min)
0.7 V (max)
− 0.2
V
DD
Units
V
V (min)
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Electrical Characteristics (Continued)
Common Device Parameters (Continued)
Unless otherwise specified, VDD= 5.0V for the following specifications. Supply bypass capacitor is 1µF and filter capacitor is
0.1µF.
LM3814/LM3815
Symbol Parameter Conditions
V
OL
Logic Low Level for PWM Sink current = 1mA, 2V ≤ VDD≤
Typ
(Note 5)
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
S08 package.
Note 5: Typical numbers are at 25˚C and represent the most likely parametric norm. Specifications in standard type face are for T
type apply 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 Averaging 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: The PWM accuracy for LM3814-7.0 and LM3815-7.0 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.
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
= 150˚C/W (typically), junction-to-ambient.
= 1A (Note 9) 0.004 Ω
SENSE
Limit
(Note 6)
0.2 V (max)
, which is 150˚C/W for the
JA
= 25˚C and those with boldface
J
Units
Typical Performance Characteristics
Supply bypass capacitor is 0.1µF and filter capacitor is
0.1µF.
Measured Current vs Actual Current
(LM3814-1.0 and LM3815-1.0)
10101315 10101324
Measured Current vs Actual Current
(LM3814-7.0 and LM3815-7.0)
www.national.com 4
Typical Performance Characteristics Supply bypass capacitor is 0.1µF and filter capacitor is
0.1µF. (Continued)
PWM Frequency vs Supply Voltage PWM Frequency vs Temperature
LM3814/LM3815
10101314
10101317
Operating Current vs Supply Voltage Shutdown Current vs Supply Voltage
10101318 10101319
Operating Current vs Temperature Shutdown Current vs Temperature
10101320 10101321
www.national.com5
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