Rainbow Electronics LM3824 User Manual

LM3824
Precision Current Gauge IC with Internal Zero Ohm
Sense Element and PWM Output

LM3824 Precision Current Gauge IC with Internal Zero Ohm Sense Element and PWM Output

July 2000

General Description

The LM3824 Current Gauge provides easy to use precision
current measurement with virtually zero insertion loss (typi­cally 0.003Ω). The LM3824 is used for high-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 LM3824 is factory-set in two different current options.
The sense range is −1.0A to +1.0A or −2.0A to +2.0A. The
sampling interval for this part is 6ms. If a more precise mea­surement is required, please refer to LM3822 datasheet.

Key Specifications

n Ultra low insertion loss (0.003Ω)
n 2V to 5.5V supply range

±

n

3% accuracy at room temperature for the 1A device

(includes accuracy of the internal sense element)

n Low quiescent current in shutdown mode

(typically 1.8 µA)

n 6 msec sampling interval
n In MSOP-8 Package

Features

n No external sense element required
n PWM output indicates the current magnitude and

direction

n PWM output is easily interfaced with microprocessors

and controllers

n Precision ∆Σ current-sense technique
n Low temperature sensitivity
n Internal filtering rejects false trips
n Internal Power-On-Reset (POR)
n DC Offset is less than 8 mA for 1A part

Applications

n Battery charge/discharge gauge
n Motion control diagnostics
n Power supply load monitoring and management
n Resettable smart fuse

Connection Diagram

DS200007-1

Top View

LM3824 for High-Side Sensing

© 2000 National Semiconductor Corporation DS200007 www.national.com

Ordering Information

LM3824

Order No.

LM3824MM-1.0

LM3824MMX-1.0

LM3824MM-2.0

LM3824MMX-2.0

*

Current is sampled over a fixed interval.Theaveragecurrentduringthisintervalisindicatedbythe duty cycle of the PWM output

during next interval.

*

Sense
Range

±

1.0A 6 ms High-side MUA08A MSOP-8 Tape and Reel

±

1.0A 6 ms High-side MUA08A MSOP-8 Tape and Reel

±

2.0A 6 ms High-side MUA08A MSOP-8 Tape and Reel

±

2.0A 6 ms High-side MUA08A MSOP-8 Tape and Reel

Sampling

Interval

*

Sensing

Method

NS

Package

Number

Package

Type

Supplied As:

(1000 units/reel)

(3500 units/reel)

(1000 units/reel)

(3500 units/reel)

Pin Description (High-Side, LM3824)

Pin Name Function

1 SENSE+, V
2 GND Supply Ground.
3 FLTR+ Filter input — provides anti-aliasing for delta sigma modulator.
4 FLTR− Filter input.
5SD

6 TEST Connect to GND for normal operation.
7 PWM Digital output indicates the current magnitude and direction.
8 SENSE− Low side of internal current sense.

DD

High side of internal current sense, also supply voltage.

Shutdown input. Connected to VDDthrough a pull-up resistor for normal operation.
When low, the LM3824 is put into a low current mode.

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LM3824

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

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

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

Operating Ratings (Note 1)

Input Voltage 2.0V to 5.25V
Sense Current (continuous) (Note 4) 5A
Junction Temperature Range −40˚C to +85˚C

Sense Current (peak, for 200 msec) (Note 4) 10A
Sink Current for PWM pin 1mA
Maximum Junction Temperature 150˚C

Electrical Characteristics Typical numbers are at 25˚C and represent the most likely parametric norm.

Specifications in standard type face are for T

ranges.

= 25˚C and those with boldface type apply over full operating temperature

J

LM3824-1.0

SENSE+VDD= 3.6V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is 0.1 µF.

Symbol Parameter Conditions

I

ACC

Average Current Accuracy

1.0A current 1.0

(Note 7)

e

n

Effective Output Noise (rms) 12 mA

Typ

(Note 5)

Limit

(Note 6)

0.97 / 0.95 A (min)

1.03 / 1.05 A (max)

Units

A

LM3824-2.0

SENSE+VDD= 3.6V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is 0.1 µF.

Symbol Parameter Conditions

I

ACC

Average Current Accuracy

2.0A current (Note 8) 2.0 A

(Note 7)

Typ

(Note 5)

Limit

(Note 6)

Units

1.88 / 1.84 A (min)

2.12 / 2.16 A (max)

e

n

Effective Output Noise (rms) 36 mA

Common Device Parameters

Unless otherwise specified, VDD= 3.6V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is

0.1 µF.

Symbol Parameter Conditions

I

Q1

I

Q2

D

RES

t

S

f

P

V

TH

Quiescent Current Normal Mode, SD = high 95 µA

Quiescent Current Shutdown Mode, SD = low 1.8 µA

PWM Resolution 0.8 %
Sampling Time 6 ms

Frequency of PWM Waveform 160 Hz

Threshold High Level for SD 1.3 V

Typ

(Note 5)

Limit

(Note 6)

Units

150 µA (max)

10 µA (max)

4 ms (min)

10 ms (max)

100 Hz (min)
250 Hz (max)

1.8 V (min)

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Common Device Parameters (Continued)

Unless otherwise specified, VDD= 3.6V for the following specifications. Supply bypass capacitor is 1 µF and filter capacitor is

LM3824

0.1 µF.

Symbol Parameter Conditions

V

TL

V

OH

Threshold Low Level for SD 1.2 V

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

Typ

(Note 5)

VDD− 0.05

5.25V

V

OL

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

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
= 220˚C/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 θ

MSOP-8 package.

Note 5: Typicalnumbers 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 Average 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: This parameter is production tested at 1A and guaranteed by design at 2A.
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

= 1A (Note 9) 0.003 Ω

SENSE

Limit

(Note 6)

0.7 V (max)

− 0.2

V

DD

0.2 V (max)

, which is 220˚C/W for the

JA

= 25˚C and those with boldface

J

Units

V

V (min)

JA

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