Rainbow Electronics LM3813 User Manual

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

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

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

LM3812/LM3813 Precision Current Gauge IC with Ultra Low Loss Sense Element and PWM

Output

Connection Diagrams

Top View

10012201

LM3812

for High-Side Sensing

Top View

LM3813

for Low-Side Sensing

10012203

Ordering Information

Order No.

LM3812/LM3813

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.

Sense Range

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

Sampling

Interval*

Sensing

Method

NS Package Number

‡

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+, 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

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, 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

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)

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LM3812/LM3813

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 1mA

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 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

ACC

Average Current Accuracy

at 0.9A current 0.9

(Note 7)

Effective Output Noise (rms) 2 mA

Typ

(Note 5)

0.882 / 0.864 A (min)

0.918 / 0.936 A (max)

Limit

(Note 6)

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 Parameter Conditions

ACC

Average Current Accuracy

at 2.5A current (Note 8) 2.5 A

(Note 7)

Typ

(Note 5)

Limit

(Note 6)

2.400 / 2.350 A (min)

2.600 / 2.650 A (max)

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

RES

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

Typ

(Note 5)

Limit

(Note 6)

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)

Units

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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 1 µF and filter capacitor is

0.1 µF.

LM3812/LM3813

Symbol Parameter Conditions

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

Typ

(Note 5)

VDD− 0.05

5.25V

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

0.04 V

5.25V

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

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 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.

Insertion Loss I

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

= 1A (Note 9) 0.004 Ω

SENSE

Limit

(Note 6)

− 0.2

0.2 V (max)

, which is 150˚C/W for the

= 25˚C and those with boldface

Units

V (min)

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)

10012215 10012224

Measured Current vs Actual Current

(LM3812-7.0 and LM3813-7.0)

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

0.1 µF. (Continued)

PWM Frequency vs Supply Voltage PWM Frequency vs Temperature

LM3812/LM3813

10012213

10012216

Operating Current vs Supply Voltage Shutdown Current vs Supply Voltage

10012218 10012219

Operating Current vs Temperature Shutdown Current vs Temperature

10012220 10012221

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Rainbow Electronics LM3813 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

General Description

Key Specifications

Features

Applications

Connection Diagrams

Ordering Information

Pin Description (High-Side, LM3812)

Pin Description (Low-Side, LM3813)

Absolute Maximum Ratings (Note 1)

Operating Ratings (Note 1)

LM3812-7.0, LM3813-7.0

Common Device Parameters

Typical Performance Characteristics