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

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-widthmodulated (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.

Connection Diagrams

Key Specifications

n Ultra low insertion loss (typically 0.004Ω)
n 2V to 5.25V supply range

±

n

2%accuracy at room temperature (includes accuracy
of the internal sense element) (LM3812-1.0,
LM3813-1.0)

n Low quiescent current in shutdown mode (typically

2.5 µA)

n 50 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

DS100122-1

Top View

LM3812

for High-Side Sensing

© 1999 National Semiconductor Corporation DS100122 www.national.com

Top View

LM3813

for Low-Side Sensing

DS100122-3

Ordering Information

Order No.

LM3812M-1.0
LM3812MX-1.0
LM3812M-7.0
LM3812MX-7.0
LM3813M-1.0
LM3813MX-1.0
LM3813M-7.0
LM3813MX-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.

‡

The Package code M08A is internal to National Semiconductor and indicates an 8-lead surface mount package, SO-8.

#

Sense
Range

±
±
±
±
±
±
±
±

Sampling

Interval

1A 50 ms High-side M08A SO-8 95 units in Rails
1A 50 ms High-side M08A SO-8 2.5k units on Tape and Reel
7A 50 ms High-side M08A SO-8 95 units in Rails
7A 50 ms High-side M08A SO-8 2.5k units on Tape and Reel
1A 50 ms Low-side M08A SO-8 95 units in Rails
1A 50 ms Low-side M08A SO-8 2.5k units on Tape and Reel
7A 50 ms Low-side M08A SO-8 95 units in Rails
7A 50 ms Low-side M08A SO-8 2.5k units on Tape and Reel

Sensing

*

Method

NS
Package
Number

Package

‡

Type Supplied As:

Pin Description (High-Side, LM3812)

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).

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.
5SD

6 PWM PWM output indicates the current magnitude and direction.
7 GND Ground
8V

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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)

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

Maximum Junction Temperature 150˚C
Storage Temperature −65˚C to +150˚C
Lead Temperature (Soldering, 10 sec) 260˚C

Operating Ratings (Note 1)

Input Voltage 2.0V to 5.25V
Sense Current (continuous) (Note 4) 7A
Junction Temperature Range −40˚C to +125˚C

Sink Current for PWM pin 1mA
Voltage on Pin 5 5.25V

Electrical Characteristics

LM3812-1.0, LM3813-1.0

=

V

5.0V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is 0.1 µF.

DD

Symbol Parameter Conditions

I

e

ACC

Average Current Accuracy
(Note 7)

n

Effective Output Noise (rms) 2 mA

at 0.9A current 0.9

(Note 5)

LM3812-7.0, LM3813-7.0

=

V

5.0V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is 0.1 µF.

DD

Symbol Parameter Conditions

I

e

ACC

Average Current Accuracy
(Note 7)

n

Effective Output Noise (rms) 20 mA

at 2.5A current (Note 8) 2.5 A

(Note 5)

Typ

Typ

Limit

(Note 6)

Units

A

0.882 / 0.864 A (min)

0.918 / 0.936 A (max)

Limit

(Note 6)

Units

2.400 / 2.350 A (min)

2.600 / 2.650 A (max)

Common Device Parameters

Unless otherwise specified, V

0.1 µF.

Symbol Parameter Conditions

I

Q1

I

Q2

D

RES

t

S

f

P

V

TH

V

TL

Quiescent Current Normal Mode, SD=high 100 µA

Quiescent Current Shutdown Mode, SD=low 2.5 µA

PWM Resolution 0.1
Sampling Time 52 ms

Frequency of PWM Waveform 20 Hz

Threshold High Level for SD 1.2 V

Threshold Low Level for SD 1.3 V

=

5.0V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is

DD

Typ

(Note 5)

Limit

(Note 6)

Units

160 µA (max)

10 µA (max)

40 ms (min)
80 ms (max)

12.5 Hz (min)
25 Hz (max)

1.8 V (min)

0.7 V (max)

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%

Common Device Parameters (Continued)

Unless otherwise specified, V

0.1 µF.

Symbol Parameter Conditions

V

OH

V

OL

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

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

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 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.
Note 9: The tolerance of the internal lead frame resistor is corrected internally. The temperature coefficient of this resistor is 2600 ppm/˚C.

Logic High Level for PWM Load current=1 mA, 2V ≤ VDD≤

Logic Low Level for PWM Sink current=1 mA, 2V ≤ VDD≤

Insertion Loss I

=

150˚C/W (typically), junction-to-ambient.

JA

=

5.0V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is

DD

Typ

(Note 5)

Limit

(Note 6)

VDD− 0.05

5.25V

− 0.2

V

DD

0.04 V

5.25V

SENSE

=

1A (Note 9) 0.004 Ω

0.2 V (max)

, which is 150˚C/W for the S08

JA

=

25˚C and those with boldface

J

Units

V (min)

V

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Typical Performance Characteristics Supply bypass capacitor is 0.1 µF and filter capacitor is 0.1 µF.

Measured Current vs Actual Current
(LM3812-1.0 and LM3813-1.0)

PWM Frequency vs Supply Voltage

DS100122-15

Measured Current vs Actual Current
(LM3812-7.0 and LM3813-7.0)

DS100122-24

PWM Frequency vs Temperature

Operating Current vs Supply Voltage

DS100122-13

DS100122-18

DS100122-16

Shutdown Current vs Supply Voltage

DS100122-19

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