NSC LM3815MX-7.0, LM3815MX-1.0, LM3814MX-7.0, LM3814MX-1.0, LM3814M-7.0 Datasheet

January 1999

LM3814/LM3815

Fast Current Gauge IC with Ultra Low Loss Sense

Element and PWM Output

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

nUltra low insertion loss (typically 0.004Ω)

n2V to 5.25V supply range

n±3.5% accuracy at room temperature (includes accuracy of the internal sense element) (LM3814-1.0, LM3815-1.0)

nLow quiescent current in shutdown mode (typically 2.5 µA)

n6 msec sampling interval

Features

nNo external sense element required

nPWM output indicates the current magnitude and direction

nPWM output can be interfaced with microprocessors

nPrecision ΔΣ current-sense technique

nLow temperature sensitivity

nInternal filtering rejects false trips

nInternal 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

Connection Diagrams

DS101013-1

DS101013-3

Top View

LM3814

Top View

for High-Side Sensing

LM3815

for Low-Side Sensing

Output PWM and Element Sense Loss Low Ultra with IC Gauge Current Fast LM3814/LM3815

© 1999 National Semiconductor Corporation

DS101013

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Ordering Information

Order No.#	Sense	Sampling	Sensing	NS	Package	Supplied As:
	Range	Interval*	Method	Package	Type
				Number³
LM3814M-1.0	±1A	6 ms	High-side	M08A	SO-8	95 units in Rails
LM3814MX-1.0	±1A	6 ms	High-side	M08A	SO-8	2.5k units on Tape and Reel
LM3814M-7.0	±7A	6 ms	High-side	M08A	SO-8	95 units in Rails
LM3814MX-7.0	±7A	6 ms	High-side	M08A	SO-8	2.5k units on Tape and Reel
LM3815M-1.0	±1A	6 ms	Low-side	M08A	SO-8	95 units in Rails
LM3815MX-1.0	±1A	6 ms	Low-side	M08A	SO-8	2.5k units on Tape and Reel
LM3815M-7.0	±7A	6 ms	Low-side	M08A	SO-8	95 units in Rails
LM3815MX-7.0	±7A	6 ms	Low-side	M08A	SO-8	2.5k units on Tape and Reel

# 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.

³ 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			Name	Function
1		SENSE+, VDD		High side of internal current sense, also supply voltage.
2	SENSE−			Low side of internal current sense.
3	FLTR+			Filter input Ð provides anti-aliasing for delta sigma modulator.
4	FLTR−			Filter input.
5				Shutdown pin. Connected to VDD through a pull up resistor for normal operation.
		SD
				When low, the IC goes into a low current mode (typically 3 µA).
6	PWM			PWM output indicates the current magnitude and direction.
7	GND			Ground
8	GND			Ground

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.
5				Shutdown pin. Connected to VDD through a pull up resistor for normal operation.
		SD
				When low, the IC goes into a low current mode (typically 3 µA).
6	PWM			PWM output indicates the current magnitude and direction.
7	GND			Ground
8	VDD			VDD (supply)

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

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

Operating Ratings (Note 1)

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

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	Typ	Limit	Units
				(Note 5)	(Note 6)
	IACC	Average Current Accuracy	at 0.9A current	0.9		A
		(Note 7)			0.868 / 0.850	A (min)
					0.932 / 0.950	A (max)
	en	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	Typ	Limit	Units
				(Note 5)	(Note 6)
	IACC	Average Current Accuracy	at 2.5A current (Note 8)	2.5		A
		(Note 7)			2.350 / 2.288	A (min)
					2.650 / 2.712	A (max)
	en	Effective Output Noise (rms)		120		mA

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

Typ

Limit

Units

(Note 5)

(Note 6)

IQ1

Quiescent Current

Normal Mode,

= high

100

µA

SD

160

µA (max)

IQ2

Quiescent Current

Shutdown Mode,

= low

2.5

µA

SD

10

µA (max)

DRES

PWM Resolution

0.8

%

tS

Sampling Time

6

ms

4

ms (min)

10

ms (max)

fP

Frequency of PWM Waveform

160

Hz

100

Hz (min)

250

Hz (max)

VTH

Threshold High Level for

SD

1.2

V

1.8

V (min)

VTL

Threshold Low Level for

SD

1.3

V

0.7

V (max)

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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.

	Symbol	Parameter	Conditions	Typ	Limit	Units
				(Note 5)	(Note 6)
	VOH	Logic High Level for PWM	Load current = 1mA, 2V ≤ VDD ≤	VDD − 0.05		V
			5.25V		VDD − 0.2	V (min)
	VOL	Logic Low Level for PWM	Sink current = 1mA, 2V ≤ VDD ≤	0.04		V
			5.25V		0.2	V (max)
	PI	Insertion Loss	ISENSE = 1A (Note 9)	0.004		Ω

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 θJA= 150ÊC/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 θJA, which is 150ÊC/W for the S08 package.

Note 5: Typical numbers are at 25ÊC and represent the most likely parametric norm. Specifications in standard type face are for TJ= 25ÊC and those with boldface type apply over full operating temperature ranges.

Note 6: Limits are 100% production tested at 25ÊC. 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/ÊC.

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Typical Performance Characteristics

Measured Current vs Actual Current (LM3814-1.0 and LM3815-1.0)

Supply bypass capacitor is 0.1µF and filter capacitor is 0.1µF.

Measured Current vs Actual Current (LM3814-7.0 and LM3815-7.0)

	DS101013-15	DS101013-24
PWM Frequency vs Supply Voltage		PWM Frequency vs Temperature

DS101013-14 DS101013-17

Operating Current vs Supply Voltage Shutdown Current vs Supply Voltage

DS101013-18

DS101013-19

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