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LM3420

SNVS116E –MAY 1998–REVISED DECEMBER 2014

LM3420 8.4-V Li-Ion Battery Charge Controller

1 Features 3 Description

The LM3420 series of controllers are monolithic

1• Input Voltage Range: up to 20 V integrated circuits designed for charging and end-of-

• Voltage Options for Charging 1, 2, 3, or 4 Cells charge control for lithium-ion rechargeable batteries.

• Output Current up to 15 mA The LM3420 is available in an 8.4-V version for one

through four cell charger applications.

• Precision (0.5%) End-of-Charge Control

– LM3420 ±1% Included in a very small package is an (internally

compensated) op amp, a bandgap reference, an NPN

– LM3420A ±0.5% output transistor, and voltage setting resistors. The

• Drive Capability for External Power Stage amplifier's inverting input is externally accessible for

• Temperature Drift Curvature Correction for loop frequency compensation. The output is an open-

Voltage Stability emitter NPN transistor capable of driving up to 15 mA

of output current into external circuitry.

• Low Quiescent Current, 85 μA (Typ.)

• Tiny SOT-23-5 package A trimmed precision bandgap reference utilizes

temperature drift curvature correction for excellent

voltage stability over the operating temperature

2 Applications range. The LM3420 series allows for precision end-

• Lithium-Ion Battery Charging of-charge voltage threshold for lithium-ion

• Suitable for Linear and Switching Regulator rechargeable batteries. The premium grade LM3420A

Charger Designs is available with an initial voltage threshold tolerance

of ±0.5%, while the standard grade LM3420 has an

space initial voltage threshold tolerance of ±1%.

space The LM3420 is available in a sub-miniature 5-lead

surface mount package thus allowing very compact

designs.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)

LM3420 SOT-23 (5) 2.90 mm x 1.60 mm

(1) For all available packages, see the orderable addendum at

the end of the datasheet.

Simplified Schematic

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,

intellectual property matters and other important disclaimers. PRODUCTION DATA.

LM3420

SNVS116E –MAY 1998–REVISED DECEMBER 2014

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Table of Contents

8.2 Functional Block Diagram....................................... 10

1 Features.................................................................. 18.3 Feature Description................................................. 10

2 Applications ........................................................... 18.4 Device Functional Modes........................................ 11

3 Description............................................................. 19 Application and Implementation ........................ 12

4 Revision History..................................................... 29.1 Application Information............................................ 12

5 Pin Configuration and Functions......................... 39.2 Typical Application: Constant Current/Constant

6 Specifications......................................................... 4Voltage Li-Ion Battery Charger ................................ 12

6.1 Absolute Maximum Ratings ...................................... 410 Power Supply Recommendations ..................... 17

6.2 ESD Ratings.............................................................. 411 Layout................................................................... 18

6.3 Recommended Operating Conditions....................... 411.1 Layout Guidelines ................................................. 18

6.4 Thermal Information.................................................. 411.2 Layout Example .................................................... 18

6.5 LM3420 Electrical Characteristics............................. 512 Device and Documentation Support ................. 18

6.6 LM3420A Electrical Characteristics .......................... 612.1 Trademarks........................................................... 18

6.7 Typical Characteristics.............................................. 712.2 Electrostatic Discharge Caution............................ 18

7 Parameter Measurement Information .................. 912.3 Glossary................................................................ 18

7.1 Test Circuits.............................................................. 913 Mechanical, Packaging, and Orderable

8 Detailed Description............................................ 10 Information ........................................................... 19

8.1 Overview................................................................. 10

4 Revision History

NOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision D (May 2013) to Revision E Page

• Deleted info re: 4.2-V, 8.2-V, 12.6-V and 16.8 V versions .................................................................................................... 1

• Added Device Information and ESD Ratings tables, Feature Description,Device Functional Modes,Application and

Implementation,Power Supply Recommendations,Layout,Device and Documentation Support, and Mechanical,

Packaging, and Orderable Information sections; moved some curves to Application Curves section .................................. 1

Changes from Revision C (April 2013) to Revision D Page

• Changed layout of National Data Sheet to TI format ........................................................................................................... 13

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5 Pin Configuration and Functions

SOT-23 (DBV) Package

5 Pins

Top

Pin Functions

PIN I/O DESCRIPTION

NAME NUMBER

IN 1 I Input voltage supply

GND 2 — Ground

NC 3 — No connection

OUT 4 O Open emitter output capable of sourcing current

COMP 5 Compensation

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6 Specifications

6.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted) (1)(2)

MIN MAX UNIT

Input voltage VIN 20 V

Output current 20 mA

Junction temperature 150

Vapor phase (60 seconds) 215 °C

Lead temperature Infrared (15 seconds) 220

Power dissipation (TA= 25°C)(3) 300 mV

Storage temperature, Tstg −65 150 °C

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings

only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended

Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and

specifications.

(3) The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax (maximum junction temperature),

RθJA (junction-to-ambient thermal resistance), and TA(ambient temperature). The maximum allowable power dissipation at any

temperature is PDmax = (TJmax −TA)/RθJA or the number given in the Absolute Maximum Ratings, whichever is lower. The typical thermal

resistance (RθJA) when soldered to a printed circuit board is approximately 181.2°C/W for the DBV0005A package.

6.2 ESD Ratings VALUE UNIT

Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2000

V(ESD) Electrostatic discharge V

Charged-device model (CDM), per JEDEC specification JESD22- ±500

C101(2)

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.

6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)(1)(2)

MIN NOM MAX UNIT

Ambient temperature −40 85 °C

Junction temperature −40 125

Output current 15 mA

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings

only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended

Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

(2) The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax (maximum junction temperature),

RθJA (junction to ambient thermal resistance), and TA(ambient temperature). The maximum allowable power dissipation at any

temperature is PDmax = (TJmax −TA)/RθJA or the number given in the Absolute Maximum Ratings, whichever is lower. The typical thermal

resistance (RθJA) when soldered to a printed circuit board is approximately 181.2°C/W for the DBV0005A package.

6.4 Thermal Information LM3420

THERMAL METRIC(1) SOT-23 (DBV) UNIT

5 PINS

RθJA Junction-to-ambient thermal resistance 181.2

RθJC(top) Junction-to-case (top) thermal resistance 91.2

RθJB Junction-to-board thermal resistance 38.2 °C/W

ψJT Junction-to-top characterization parameter 5.3

ψJB Junction-to-board characterization parameter 37.7

(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.

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6.5 LM3420 Electrical Characteristics

Unless otherwise specified, specifications apply over full operating temperature range and VIN = VREG, VOUT = 1.5 V.

PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT

IOUT = 1 mA, TJ= 25°C 8.316 8.4 8.484

Regulation voltage V

IOUT = 1 mA 8.232 8.4 8.568

VREG IOUT = 1 mA, TJ= 25°C –1% 1%

Regulation voltage

tolerance IOUT = 1 mA –2% 2%

IOUT = 1 mA, TJ= 25°C 85 125

IQQuiescent current μA

IOUT = 1 mA 85 150

20 μA≤IOUT ≤1 mA, VOUT = 6 V 1 3.3

TJ= 25°C

Transconductance 20 μA≤IOUT ≤1 mA, VOUT = 6 V 0.50 3.3

GmmA/mV

ΔIOUT/ΔVREG 1 mA ≤IOUT ≤15 mA, VOUT = 6 V 2.5 6

1 mA ≤IOUT ≤15 mA, VOUT = 6 V 1.4 6

1 V ≤VOUT ≤VREG −1.2V, RL= 470 Ω(3) 450 1000

TJ= 25°C V/V

1 V ≤VOUT ≤VREG −1.3 V, RL= 470 Ω200 1000

Voltage gain

AVΔVOUT/ΔVREG 1 V ≤VOUT ≤VREG −1.2 V, RL= 5 kΩ(3) 1000 3500

TJ= 25°C V/V

1 V ≤VOUT ≤VREG −1.3 V, RL= 5 kΩ700 3500

VSAT VIN = VREG + 100 mV 1 1.2

TJ= 25°C

Output saturation(4) V

VIN = VREG + 100 mV 1 1.3

ILVIN = VREG −100 mV, VOUT = 0 V 0.1 0.5

TJ= 25°C

Output leakage current μA

VIN = VREG −100 mV, VOUT = 0 V 0.1 1

RfInternal feedback 135 181 227 kΩ

TJ= 25°C

resistor(5)

EnOutput noise voltage IOUT = 1 mA, 10 Hz ≤f≤10 kHz 140 μVRMS

(1) Limits are 100% production tested at 25°C. Limits over the operating temperature range are specified through correlation using

Statistical Quality Control (SQC) methods. The limits are used to calculate Averaging Outgoing Quality Level (AOQL).

(2) Typical numbers are at 25°C and represent the most likely parametric norm.

(3) Actual test is done using equivalent current sink instead of a resistor load.

(4) VSAT = V(IN) −VOUT, when the voltage at the IN pin is forced 100 mV above the nominal regulating voltage (VREG).

(5) See Application and Implementation and Typical Characteristics sections for information on this resistor.

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6.6 LM3420A Electrical Characteristics

Unless otherwise specified, specifications apply over full operating temperature range and VIN = VREG, VOUT = 1.5 V.

PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT

IOUT = 1 mA, TJ= 25°C 8.358 8.4 8.442

Regulation voltage V

IOUT = 1 mA 8.316 8.4 8.484

VREG IOUT = 1 mA, TJ= 25°C –0.5% 0.5%

Regulation voltage

tolerance IOUT = 1 mA –1% 1%

IOUT = 1 mA, TJ= 25°C 85 110

IQQuiescent current μA

IOUT = 1 mA 85 115

20 μA≤IOUT ≤1 mA, VOUT = 6 V 1.3 3.3

TJ= 25°C

Transconductance 20 μA≤IOUT ≤1 mA, VOUT = 6 V 0.75 3.3

GmmA/mV

ΔIOUT/ΔVREG 1 mA ≤IOUT ≤15 mA, VOUT = 6 V 3 6

1 mA ≤IOUT ≤15 mA, VOUT = 6 V 1.5 6

1 V ≤VOUT ≤VREG −1.2 V, RL= 470 Ω(3) 550 1000

TJ= 25°C V/V

1 V ≤VOUT ≤VREG −1.3 V, RL= 470 Ω250 1000

Voltage gain

AVΔVOUT/ΔVREG 1 V ≤VOUT ≤VREG −1.2 V, RL= 5 kΩ(3) 1500 3500

TJ= 25°C V/V

1 V ≤VOUT ≤VREG −1.3 V, RL= 5 kΩ900 3500

VSAT VIN = VREG + 100 mV 1 1.2

TJ= 25°C

Output saturation(4) V

VIN = VREG + 100 mV 1 1.3

ILVIN = VREG −100 mV, VOUT = 0 V 0.1 0.5

TJ= 25°C

Output leakage current μA

VIN = VREG −100 mV, VOUT = 0 V 0.1 1

Internal feedback kΩ

RfTJ= 25°C 135 181 227

resistor(5)

EnOutput noise voltage IOUT = 1 mA, 10 Hz ≤f≤10 kHz 140 μVRMS

(1) Limits are 100% production tested at 25°C. Limits over the operating temperature range are specified through correlation using

Statistical Quality Control (SQC) methods. The limits are used to calculate Averaging Outgoing Quality Level (AOQL).

(2) Typical numbers are at 25°C and represent the most likely parametric norm.

(3) Actual test is done using equivalent current sink instead of a resistor load.

(4) VSAT = VIN −VOUT, when the voltage at the IN pin is forced 100 mV above the nominal regulating voltage (VREG).

(5) See Application and Implementation and Typical Characteristics sections for information on this resistor.

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6.7 Typical Characteristics

Figure 1. Bode Plot Figure 2. Response Time

Figure 3. Response Time Figure 4. Quiescent Current

Figure 5. Internal Feedback Resistor (Rf) Tempco Figure 6. Normalized Temperature Drift

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Typical Characteristics (continued)

Figure 7. Output Saturation Voltage (VSAT)

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7 Parameter Measurement Information

7.1 Test Circuits

The test circuits shown in Figure 8,Figure 9 and Figure 10 can be used to measure and verify various LM3420

parameters. Test conditions are set by forcing the appropriate voltage at the VOUT Set test point and selecting the

appropriate RLor IOUT as specified in LM3420 Electrical Characteristics. Use a DVM at the “measure” test points

to read the data.

Figure 8. Circuit Used For Bode Plots Figure 9. Circuit Used For Response Time

Figure 10. LM3420 Test Circuit

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OUT

GND

COMP

31 k

1.23 V

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8 Detailed Description

8.1 Overview

The LM3420 is a shunt regulator specifically designed to be the reference and control section in an overall

feedback loop of a lithium-ion battery charger. The regulated output voltage is sensed between the IN pin and

GROUND pin of the LM3420. If the voltage at the IN pin is less than the LM3420 regulating voltage (VREG), the

OUT pin sources no current. As the voltage at the IN pin approaches the VREG voltage, the OUT pin begins

sourcing current. This current is then used to drive a feedback device (opto-coupler), or a power device (linear

regulator, switching regulator, etc.), which servos the output voltage to be the same value as VREG.

In some applications, (even under normal operating conditions) the voltage on the IN pin can be forced above

the VREG voltage. In these instances, the maximum voltage applied to the IN pin should not exceed 20 V. In

addition, an external resistor may be required on the OUT pin to limit the maximum current to 20 mA.

8.2 Functional Block Diagram

8.3 Feature Description

8.3.1 Compensation

The inverting input of the error amplifier is brought out to allow overall closed-loop compensation. In many of the

applications circuits shown here, compensation is provided by a single capacitor (CC) connected from the

compensation pin to the out pin of the LM3420. The capacitor values shown in the schematics are adequate

under most conditions, but they can be increased or decreased depending on the desired loop response.

Applying a load pulse to the output of a regulator circuit and observing the resultant output voltage response is

an easy method of determining the stability of the control loop.

Analyzing more complex feedback loops requires additional information.

The formula for AC gain at a frequency (f) is shown in Equation 1:

and where

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Feature Description (continued)

• Rf≈181 kΩ(1)

The resistor (Rf) in the formula is an internal resistor located on the die. Since this resistor value affects the

phase margin, the worst case maximum and minimum values are important when analyzing closed loop stability.

The minimum and maximum room temperature values of this resistor are specified in the LM3420 Electrical

Characteristics section of this data sheet, and a curve showing the temperature coefficient is shown in the curves

section. Minimum values of Rfresult in lower phase margins.

8.3.2 VREG External Voltage Trim

The regulation voltage (VREG) of the LM3420 can be externally trimmed by adding a single resistor from the

COMP pin to the +IN pin or from the COMP pin to the GND pin, depending on the desired trim direction. Trim

adjustments up to ±10% of VREG can be realized, with only a small increase in the temperature coefficient. (See

temperature coefficient curve shown in Figure 11.)

Figure 11. Normalized Temperature Drift With Output Externally Trimmed

Decreasing VREG

Figure 12. Increasing VREG Figure 13. Changing VREG

Formula for selecting trim resistor values is shown in Equation 2 and Equation 3, based on the percent of

increase (%incr) or percent of decrease (%decr) of the output voltage from the nominal voltage.

Rincrease = 26 × 105/%incr (2)

Rdecrease = (154 × 105/%decr) −181 × 103(3)

8.4 Device Functional Modes

8.4.1 Operation as Control Section

The LM3420 is monolithic integrated circuits, which is suitable for charging and end-of-charge control for Lithium-

Ion rechargeable batteries. In this application, LM3420 is the reference and control section in the overall

feedback loop. The regulated voltage is sensed between the IN pin and GND pin. If the voltage at the IN pin is

less than the regulating voltage (VREG), the OUT pin sources no current. As the voltage at the IN pin approaches

the VREG, the OUT pin begins sourcing current, which can drive a feedback device or a power device.

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9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

The LM3420 regulator/driver provides the reference and feedback drive functions for a Lithium-Ion battery

charger. It can be used in many different charger configurations using both linear and switching topologies to

provide the precision needed for charging lithium-ion batteries safely and efficiently. Output voltage tolerances

better than 0.5% are possible without using trim pots or precision resistors. The circuits shown are designed for

2-cell operation, but they can readily be changed for either 1-, 3-, or 4-cell charging applications.

One item to keep in mind when designing with the LM3420 is that there are parasitic diodes present. In some

designs, under special electrical conditions, unwanted currents may flow. Parasitic diodes exist from OUT to IN,

as well as from GROUND to IN. In both instances the diode arrow is pointed toward the IN pin.

9.2 Typical Application: Constant Current/Constant Voltage Li-Ion Battery Charger

The circuit shown in Figure 14 performs constant-current, constant-voltage charging of two Li-Ion cells. At the

beginning of the charge cycle, when the battery voltage is less than 8.4 V, the LM3420 sources no current from

the OUT pin, keeping Q2 off, thus allowing the LM317 Adjustable voltage regulator to operate as a constant-

current source. (The LM317 is rated for currents up to 1.5 A, and the LM350 and LM338 can be used for higher

currents.) The LM317 forces a constant 1.25 V across RLIM, thus generating a constant current of

ILIM = 1.25V/RLIM (4)

Transistor Q1 provides a disconnect between the battery and the LM3420 when the input voltage is removed.

This prevents the 85-μA quiescent current of the LM3420 from eventually discharging the battery. In this

application Q1 is used as a low offset saturated switch, with the majority of the base drive current flowing through

the collector and crossing over to the emitter as the battery becomes fully charged. It provides a very low

collector to emitter saturation voltage (approximately 5 mV). Diode D1 is also used to prevent the battery current

from flowing through the LM317 regulator from the output to the input when the DC input voltage is removed.

As the battery charges, its voltage begins to rise, and is sensed at the IN pin of the LM3420. Once the battery

voltage reaches 8.4 V, the LM3420 begins to regulate and starts sourcing current to the base of Q2. Transistor

Q2 begins controlling the ADJ pin of the LM317 which begins to regulate the voltage across the battery and the

constant voltage portion of the charging cycle starts. Once the charger is in the constant voltage mode, the

charger maintains a regulated 8.4 V across the battery and the charging current is dependent on the state of

charge of the battery. As the cells approach a fully charged condition, the charge current falls to a very low value.

Figure 14. Constant Current/Constant Voltage Li-Ion Battery Charger

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Typical Application: Constant Current/Constant Voltage Li-Ion Battery Charger (continued)

9.2.1 Design Requirements

DESIGN PARAMETER EXAMPLE VALUE

Input voltage 13 V - 20 V

Output voltage 8.4 V

Output current 1 A

9.2.2 Detailed Design Procedure

9.2.2.1 Compensation Capacitor

The capacitor between OUT pin and COMP pin can be increase or decreased depending on the desired loop

response. Functional Block Diagram can be referred as different capacitance selection. In this case, 0.01-µF

capacitor is used.

9.2.3 Application Curve

Figure 15. Regulation Voltage vs Output Voltage and Load Resistance

9.2.4 Other Application Circuits

NOTE

Although the application circuits shown here have been built and tested, they should be

thoroughly evaluated with the same type of battery the charger will eventually be used

with.

Different battery manufacturers may use a slightly different battery chemistry which may

require different charging characteristics. Always consult the battery manufacturer for

information on charging specifications and battery details, and always observe the

manufacturers precautions when using their batteries. Avoid overcharging or shorting

Lithium-Ion batteries.

9.2.4.1 Low Dropout Constant Current/Constant Voltage 2-Cell Charger

Figure 16 shows a Li-Ion battery charger that features a dropout voltage of less than one volt. This charger is a

constant-current, constant-voltage charger (it operates in constant-current mode at the beginning of the charge

cycle and switches over to a constant-voltage mode near the end of the charging cycle). The circuit consists of

two basic feedback loops. The first loop controls the constant charge current delivered to the battery, and the

second determines the final voltage across the battery.

With a discharged battery connected to the charger, (battery voltage is less than 8.4 V) the circuit begins the

charge cycle with a constant charge current. The value of this current is set by using the reference section of the

LM10C to force 200 mV across R7 thus causing approximately 100 μA of emitter current to flow through Q1, and

approximately 1 mA of emitter current to flow through Q2. The collector current of Q1 is also approximately 100

μA, and this current flows through R2 developing 50 mV across it. This 50 mV is used as a reference to develop

the constant charge current through the current sense resistor R1.

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The constant current feedback loop operates as follows. Initially, the emitter and collector current of Q2 are both

approximately 1 mA, thus providing gate drive to the MOSFET Q3, turning it on. The output of the LM301A op-

amp is low. As the Q3 current reaches 1 A, the voltage across R1 approaches 50 mV, thus canceling the 50-mV

drop across R2, and causing the op-amp's output to start going positive, and begin sourcing current into R8. As

more current is forced into R8 from the op-amp, the collector current of Q2 is reduced by the same amount,

which decreases the gate drive to Q3, to maintain a constant 50 mV across the 0.05-Ωcurrent sensing resistor,

thus maintaining a constant 1 A of charge current.

The current limit loop is stabilized by compensating the LM301A with C1 (the standard frequency compensation

used with this op-amp) and C2, which is additional compensation needed when D3 is forward biased. This helps

speed up the response time during the reverse bias of D3. When the LM301A output is low, diode D3 reverse

biases and prevents the op-amp from pulling more current through the emitter of Q2. This is important when the

battery voltage reaches 8.4 V, and the 1A charge current is no longer needed. Resistor R5 isolates the LM301A

feedback node at the emitter of Q2.

The battery voltage is sensed and buffered by the op-amp section of the LM10C, connected as a voltage follower

driving the LM3420. When the battery voltage reaches 8.4 V, the LM3420 begins regulating by sourcing current

into R8, which controls the collector current of Q2, which in turn reduces the gate voltage of Q3 and becomes a

constant voltage regulator for charging the battery. Resistor R6 isolates the LM3420 from the common feedback

node at the emitter of Q2. If R5 and R6 are omitted, oscillations could occur during the transition from the

constant-current to the constant-voltage mode. D2 and the PNP transistor input stage of the LM10C disconnects

the battery from the charger circuit when the input supply voltage is removed to prevent the battery from

discharging.

Figure 16. Low Dropout Constant Current/Constant Voltage 2-Cell Charger

9.2.4.2 High-Efficiency Switching Regulator Constant Current/Constant Voltage 2-Cell Charger

A switching regulator, constant-current, constant-voltage two-cell Li-Ion battery charging circuit is shown in

Figure 17. This circuit provides much better efficiency, especially over a wide input voltage range than the linear

topologies. For a 1-A charger an LM2575-ADJ. switching regulator IC is used in a standard buck topology. For

other currents, or other packages, other members of the SIMPLE SWITCHER®buck regulator family may be

used.

Circuit operation is as follows. With a discharged battery connected to the charger, the circuit operates as a

constant current source. The constant-current portion of the charger is formed by the loop consisting of one half

of the LM358 op amp along with gain setting resistors R3 and R4, current sensing resistor R5, and the feedback

reference voltage of 1.23 V. Initially the LM358 output is low causing the output of the LM2575-ADJ to rise thus

causing some charging current to flow into the battery. When the current reaches 1 A, it is sensed by resistor R5

(50 mΩ), and produces 50 mV. This 50 mV is amplified by the op-amps gain of 25 to produce 1.23V, which is

applied to the feedback pin of the LM2575-ADJ to satisfy the feedback loop.

Once the battery voltage reaches 8.4 V, the LM3420 takes over and begins to control the feedback pin of the

LM2575-ADJ. The LM3420 now regulates the voltage across the battery, and the charger becomes a constant-

voltage charger. Loop compensation network R6 and C3 ensure stable operation of the charger circuit under

both constant-current and constant-voltage conditions. If the input supply voltage is removed, diode D2 and the

PNP input stage of the LM358 become reversed biased and disconnects the battery to ensure that the battery is

not discharged. Diode D3 reverse biases to prevent the op-amp from sinking current when the charger changes

to constant voltage mode.

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The minimum supply voltage for this charger is approximately 11 V, and the maximum is around 30 V (limited by

the 32-V maximum operating voltage of the LM358). If another op-amp is substituted for the LM358, make sure

that the input common-mode range of the op-amp extends down to ground so that it can accurately sense 50

mV. R1 is included to provide a minimum load for the switching regulator to assure that switch leakage current

does not cause the output to rise when the battery is removed.

Figure 17. High-Efficiency Switching Regulator Constant Current/Constant Voltage 2-Cell Charger

9.2.4.3 Low Dropout Constant Current/Constant Voltage Li-Ion Battery Charger

The circuit in Figure 18 is very similar to Figure 17, except the switching regulator has been replaced with a low

dropout linear regulator, allowing the input voltage to be as low as 10 V. The constant current and constant

voltage control loops are the same as the previous circuit. Diode D2 has been changed to a Schottky diode to

provide a reduction in the overall dropout voltage of this circuit, but Schottky diodes typically have higher leakage

currents than a standard silicon diode. This leakage current could discharge the battery if the input voltage is

removed for an extended period of time.

Figure 18. Low Dropout Constant Current/Constant Voltage Li-Ion Battery Charger

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9.2.4.4 High-Efficiency Switching Charger With High Side Current Sensing

Another variation of a constant current/constant voltage switch mode charger is shown in Figure 19. The basic

feedback loops for current and voltage are similar to the previous circuits. This circuit has the current sensing

resistor, for the constant current part of the feedback loop, on the positive side of the battery, thus allowing a

common ground between the input supply and the battery. Also, the LMC7101 op-amp is available in a very

small SOT-23-5 package thus allowing a very compact PC board design. Diode D4 prevents the battery from

discharging through the charger circuitry if the input voltage is removed, although the quiescent current of the

LM3420 is still present (approximately 85 μA).

Figure 19. High Efficiency Switching Charger

With High Side Current Sensing

9.2.4.5 Fast-Pulsed Constant Current 2-Cell Charger

A rapid charge Lithium-Ion battery charging circuit is shown in Figure 20. This configuration uses a switching

regulator to deliver the charging current in a series of constant current pulses. At the beginning of the charge

cycle (constant-current mode), this circuit performs identically to the previous LM2575 charger by charging the

battery at a constant current of 1 A. As the battery voltage reaches 8.4 V, this charger changes from a constant

continuous current of 1 A to a 5-second pulsed 1 A. This allows the total battery charge time to be reduced

considerably. This is different from the other charging circuits that switch from a constant current charge to a

constant voltage charge once the battery voltage reaches 8.4 V. After charging the battery with 1 A for 5

seconds, the charge stops, and the battery voltage begins to drop. When it drops below 8.4 V, the LM555 timer

again starts the timing cycle and charges the battery with 1 A for another 5 seconds. This cycling continues with

a constant 5-second charge time, and a variable off time. In this manner, the battery is charged with 1 A for 5

seconds, followed by an off period (determined by the battery's state of charge), setting up a periodic 1-A charge

current. The off time is determined by how long it takes the battery voltage to decrease back down to 8.4 V.

When the battery first reaches 8.4 V, the off time is very short (1 ms or less), but when the battery approaches

full charge, the off time begins increasing to tens of seconds, then minutes, and eventually hours.

The constant-current loop for this charger and the method used for programming the 1-A constant current is

identical to the previous LM2575-ADJ charger. In this circuit, a second LM3420-8.4 has its VREG increased by

approximately 400 mV (via R2), and is used to limit the output voltage of the charger to 8.8V in the event of a

bad battery connection, or the battery is removed or possibly damaged.

The LM555 timer is connected as a one-shot, and is used to provide the 5-second charging pulses. As long as

the battery voltage is less than the 8.4 V, the output of IC3 is held low, and the LM555 one-shot never fires (the

output of the LM555 is held high) and the one-shot has no effect on the charger. Once the battery voltage

exceeds the 8.4-V regulation voltage of IC3, the trigger pin of the LM555 is pulled high, enabling the one shot to

begin timing. The charge current is now pulsed into the battery at a 5-second rate, with the off time determined

by the battery's state of charge. The LM555 output goes high for 5 seconds (pulling down the collector of Q1)

which allows the 1-A constant-current loop to control the circuit.

Product Folder Links: LM3420

LM3420

www.ti.com

SNVS116E –MAY 1998–REVISED DECEMBER 2014

Figure 20. (Fast) Pulsed Constant Current 2-Cell Charger

9.2.4.6 MOSFET Low Dropout Charger

Figure 21 shows a low dropout constant voltage charger using a MOSFET as the pass element, but this circuit

does not include current limiting. This circuit uses Q3 and a Schottky diode to isolate the battery from the

charging circuitry when the input voltage is removed, to prevent the battery from discharging. Q2 should be a

high-current (0.2-Ω) FET, while Q3 can be a low-current (2-Ω) device.

Figure 21. MOSFET Low Dropout Charger

10 Power Supply Recommendations

The LM3420 is designed to operated from up to 20-V input voltage supply. This input supply must be well

regulated. If the input supply is noisy, additional input capacitors with low ESR can help to improve the output

noise performance.

Product Folder Links: LM3420

4 (TAB)

ADJ

INPUT

OUTPUT

VOUT

VIN

GND

IN GND

OUT

5 4

COMP

LM3420

SNVS116E –MAY 1998–REVISED DECEMBER 2014

www.ti.com

11 Layout

11.1 Layout Guidelines

For best overall performance, place all the circuit components on the same side of the circuit board and as near

as practical to the respective pin connections. Place ground return connections to the input and output capacitor,

and to the regulator ground pin as close to each other as possible, connected by a wide, component-side, copper

surface. The use of vias and long traces to create circuit connections is strongly discouraged and negatively

affects system performance. This grounding and layout scheme minimizes inductive parasitic, and thereby

reduces load-current transients, minimizes noise, and increases circuit stability. A ground reference plane is also

recommended and is either embedded in the PCB itself or located on the bottom side of the PCB opposite the

components. This reference plane serves to assure accuracy of the output voltage, shield noise, and behaves

similar to a thermal plane to spread heat from the device. In most applications, this ground plane is necessary to

meet thermal requirements.

11.2 Layout Example

Figure 22. LM3420 Layout

12 Device and Documentation Support

12.1 Trademarks

SIMPLE SWITCHER is a registered trademark of Texas Instruments.

All other trademarks are the property of their respective owners.

12.2 Electrostatic Discharge Caution

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

12.3 Glossary

SLYZ022 —TI Glossary.

This glossary lists and explains terms, acronyms, and definitions.

Product Folder Links: LM3420

LM3420

www.ti.com

SNVS116E –MAY 1998–REVISED DECEMBER 2014

13 Mechanical, Packaging, and Orderable Information

The following pages include mechanical, packaging, and orderable information. This information is the most

current data available for the designated devices. This data is subject to change without notice and revision of

this document. For browser-based versions of this data sheet, refer to the left-hand navigation.

Product Folder Links: LM3420

PACKAGE OPTION ADDENDUM

www.ti.com 4-May-2017

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead/Ball Finish

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM3420AM5-8.4/NOPB NRND SOT-23 DBV 5 1000 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 D03A

LM3420M5X-8.4/NOPB NRND SOT-23 DBV 5 3000 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 D03B

(1) The marketing status values are defined as follows:

ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.

PREVIEW: Device has been announced but is not in production. Samples may or may not be available.

OBSOLETE: TI has discontinued the production of the device.

(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance

do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may

reference these types of products as "Pb-Free".

RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.

Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based

flame retardants must also meet the <=1000ppm threshold requirement.

(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation

of the previous line and the two combined represent the entire Device Marking for that device.

(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish

value exceeds the maximum column width.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information

provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and

continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.

TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

PACKAGE OPTION ADDENDUM

www.ti.com 4-May-2017

Addendum-Page 2

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

Type Package

Drawing Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

Quadrant

LM3420AM5-8.4/NOPB SOT-23 DBV 5 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3

LM3420M5X-8.4/NOPB SOT-23 DBV 5 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3

PACKAGE MATERIALS INFORMATION

www.ti.com 20-Dec-2016

Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

LM3420AM5-8.4/NOPB SOT-23 DBV 5 1000 210.0 185.0 35.0

LM3420M5X-8.4/NOPB SOT-23 DBV 5 3000 210.0 185.0 35.0

PACKAGE MATERIALS INFORMATION

www.ti.com 20-Dec-2016

Pack Materials-Page 2

www.ti.com

PACKAGE OUTLINE

TYP

0.22

0.08

0.25

3.0

2.6

2X 0.95

1.9

1.45 MAX

TYP

0.15

0.00

5X 0.5

0.3

TYP

0.6

0.3

TYP

1.9

3.05

2.75

1.75

1.45

(1.1)

SOT-23 - 1.45 mm max heightDBV0005A

SMALL OUTLINE TRANSISTOR

4214839/C 04/2017

NOTES:

1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing

per ASME Y14.5M.

2. This drawing is subject to change without notice.

3. Refernce JEDEC MO-178.

0.2 C A B

INDEX AREA

PIN 1

GAGE PLANE

SEATING PLANE

0.1 C

SCALE 4.000

www.ti.com

EXAMPLE BOARD LAYOUT

0.07 MAX

ARROUND 0.07 MIN

ARROUND

5X (1.1)

5X (0.6)

(2.6)

(1.9)

2X (0.95)

(R0.05) TYP

4214839/C 04/2017

SOT-23 - 1.45 mm max heightDBV0005A

SMALL OUTLINE TRANSISTOR

NOTES: (continued)

4. Publication IPC-7351 may have alternate designs.

5. Solder mask tolerances between and around signal pads can vary based on board fabrication site.

SYMM

LAND PATTERN EXAMPLE

EXPOSED METAL SHOWN

SCALE:15X

PKG

SOLDER MASK

OPENING

METAL UNDER

SOLDER MASK

DEFINED

EXPOSED METAL

METAL

SOLDER MASK

OPENING

NON SOLDER MASK

DEFINED

(PREFERRED)

SOLDER MASK DETAILS

EXPOSED METAL

www.ti.com

EXAMPLE STENCIL DESIGN

(2.6)

(1.9)

2X(0.95)

5X (1.1)

5X (0.6)

(R0.05) TYP

SOT-23 - 1.45 mm max heightDBV0005A

SMALL OUTLINE TRANSISTOR

4214839/C 04/2017

NOTES: (continued)

6. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate

design recommendations.

7. Board assembly site may have different recommendations for stencil design.

SOLDER PASTE EXAMPLE

BASED ON 0.125 mm THICK STENCIL

SCALE:15X

SYMM

PKG

www.ti.com

PACKAGE OUTLINE

TYP

0.22

0.08

0.25

3.0

2.6

2X 0.95

1.9

1.45 MAX

TYP

0.15

0.00

5X 0.5

0.3

TYP

0.6

0.3

TYP

1.9

3.05

2.75

1.75

1.45

(1.1)

SOT-23 - 1.45 mm max heightDBV0005A

SMALL OUTLINE TRANSISTOR

4214839/C 04/2017

NOTES:

1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing

per ASME Y14.5M.

2. This drawing is subject to change without notice.

3. Refernce JEDEC MO-178.

0.2 C A B

INDEX AREA

PIN 1

GAGE PLANE

SEATING PLANE

0.1 C

SCALE 4.000

www.ti.com

EXAMPLE BOARD LAYOUT

0.07 MAX

ARROUND 0.07 MIN

ARROUND

5X (1.1)

5X (0.6)

(2.6)

(1.9)

2X (0.95)

(R0.05) TYP

4214839/C 04/2017

SOT-23 - 1.45 mm max heightDBV0005A

SMALL OUTLINE TRANSISTOR

NOTES: (continued)

4. Publication IPC-7351 may have alternate designs.

5. Solder mask tolerances between and around signal pads can vary based on board fabrication site.

SYMM

LAND PATTERN EXAMPLE

EXPOSED METAL SHOWN

SCALE:15X

PKG

SOLDER MASK

OPENING

METAL UNDER

SOLDER MASK

DEFINED

EXPOSED METAL

METAL

SOLDER MASK

OPENING

NON SOLDER MASK

DEFINED

(PREFERRED)

SOLDER MASK DETAILS

EXPOSED METAL

www.ti.com

EXAMPLE STENCIL DESIGN

(2.6)

(1.9)

2X(0.95)

5X (1.1)

5X (0.6)

(R0.05) TYP

SOT-23 - 1.45 mm max heightDBV0005A

SMALL OUTLINE TRANSISTOR

4214839/C 04/2017

NOTES: (continued)

6. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate

design recommendations.

7. Board assembly site may have different recommendations for stencil design.

SOLDER PASTE EXAMPLE

BASED ON 0.125 mm THICK STENCIL

SCALE:15X

SYMM

PKG

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