Datasheet LM3621M, LM3621MX Datasheet (NSC)

LM3621
Single Cell Lithium-Ion Battery Charger Controller

General Description

The LM3621 is a full function constant voltage, constant cur­rent (CVCC) lithium-ion (Li+) battery charger controller. It
provides 1%regulation accuracy overthespecified tempera­ture range without requiring the use of external precision re­sistors. The IC controls five charge modes: conditioning,
fast, top-off, monitor and maintenance. In addition, the
LM3621 detects and flags defective batteries as well as over
current and over voltage fault events. The architecture of the
IC is based on high gain constant voltage and constant cur­rent control loops.

The LM3621 is designed to control a switching charger, a lin­ear charger or an off-line ac adapter charger.

The LM3621 consists of a logic controller, precision bandgap
reference, wide bandwidth transconductance error amplifi­ers, comparators, and an output buffer. The LM3621 is avail­able in a 16-pin SOIC package and is specified over the
range of 0˚C to 70˚C.

Key Specifications

n Tight output voltage accuracy (±0.5%at T

A

=

25˚C)

n Two selectable output voltages (4.2V or 4.1V)

n Less than 1 µA current drain from fully charged battery
n Preconditioning severely discharged cells (0V to 2.55V)

Features

n Automatic end-of-charge control
n Preset or user adjustable charge current regulation
n LED drivers for charging status and fault indication
n Battery self-discharge refresh (maintenance)
n Overvoltage/overcurrent fault detection and protection
n Defective battery pack detection
n Charge current boost control for cellular phone

applications

n Charge interruption control input

Applications

n Complete, full function, protected battery charger for

coke or graphite anode, single cell Lithium-Ion battery
packs

n Linear voltage regulator controlled chargers
n High efficiency switching regulator controlled chargers
n Cost effective wall adapter chargers

Typical Application

DS100107-7

1A, 4.1V CVCC Linear Charger for Graphite Anode Lithium-Ion Battery

March 1998

LM3621 Single Cell Lithium-Ion Battery Charger Controller

© 1998 National Semiconductor Corporation DS100107 www.national.com

Connection Diagram

Pin Description

Pin No. Symbol I/O Description

1V

BAT

+ I Battery pack high side sense input.

2V

BAT

− I Battery pack low side sense input.
3 CSR I Current Sense Resistor high side input.
4 PFD O Pass FET gate Drive output. (N-channel).
5I

COMP

I Compensation pin for current regulation loop.
6 MCO O Modulation Control Output- analog control signal output
7V

COMP

I Compensation pin for voltage regulation loop.
8I

SET

I Charge current adjust input pin (see application section).
9V

SET

I Charge termination voltage control input (V

SET

=

HI for 4.2V or

V

SET

=

LO for 4.1V).
10 LED1 O LED driver #1 output (open drain).
11 LED2 O LED driver #2 output (open drain).
12 ChgInt

I Charge current interrupt (active LO).
13 Enable I Enable charge cycle control.
14 Boost I Maximum output current boost control (max output current

increased by 80%).

15 V

SS

S IC common.

16 V

DD

S IC power supply.

16-Lead SOIC

DS100107-18

Top View

Order Number LM3621M or LM3621M-3.0

NSC Package Number M16A

www.national.com 2

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Supply Voltage, V

DD

6.0V

All pins −0.3 V ≤ V ≤ V

DD

+0.3V
Power Dissipation 100 mV
ESD Susceptibility (Note 2) 2kV
Junction Temperature 150˚C
Storage Temperature −65˚C to +150˚C

Lead Temperature,
soldering

Vapor Phase (60 sec) +215˚C
Infrared (15 sec) +220˚C

Operating Ratings

Ambient Temperature Range 0˚C ≤ TA≤ 70˚C
Supply Voltage Range (Note 3) 3.0V ≤ V

DD

≤ 5.5V

Electrical Characteristics

V

DD

=

4.2V unless otherwise specified. Specifications with standard type face are for T

A

=

25˚C, and those with boldface type

apply over full operating temperature range.

Symbol Parameter Conditions Min Typ Max Units

V

OUT

Battery Regulation Voltage (Note

4)

Charge termination voltage for
V

SET

=

HI

4.18 4.2 4.22 V

4.16 4.24 V

Charge termination voltage for
V

SET

=

LO

4.08 4.1 4.12 V

4.06 4.14 V

Battery conditioning (Hi-Z) charge
mode, LM3621M-3.0

2.95 3.1 3.25 V

Battery conditioning (Hi-Z) charge
mode, LM3621M

4.05 4.1 4.15 V

Monitor Mode float voltage for
V

SET

=

HI

4.05 4.09 4.13 V

Monitor Mode float voltage for
V

SET

=

LO

3.80 3.85 3.90 V

V

CSR

Charge Current Regulation
Voltage (Notes 5, 16)

Fast Charge Mode 0.475 0.5 0.525 V
Conditioning (Hi-Z) Charge Mode 0.04 0.05 0.06 V
Boost Mode 0.855 0.9 0.945 V

V

BAT

-Det Battery Voltage Detection
Threshold (Note 6)

Overvoltage Fault Threshold for
V

SET

=

HI

4.28 4.40 4.50 V

Overvoltage Fault Threshold for
V

SET

=

LO

4.18 4.30 4.40 V

Battery Resistance Free Voltage
Threshold

3.55 3.65 3.75 V

Conditioning (Hi-Z) Charge Mode
Threshold

2.45 2.55 2.65 V

2.40 2.70 V

V

CSR

-Det Charge Current Voltage Detection
Threshold (Notes 7, 16)

End of charge threshold 40 mV
Over Current Fault Threshold 0.95 1 1.05 V

IQ Quiescent Current Standby Mode with I

OUT

=

0mA 3 5 mA

I

OUT

MCO Output Source Current V

MCO

=

1.0V 20 mA

V

MCO

Maximum MCO Output Voltage I

OUT

=

1 mA, V

DD

=

5.5V 4.9 V

I

OUT

=

1 mA, V

DD

=

3.0V 2.9 V

GM-V V-Reg Loop Error Amp

Transconductance

0.1 mA/V

I

SLEW

-V V-Reg Loop Error Amp Slew
Current

100 µA

GM-I I-Reg Loop Error Amp

Transconductance

1 mA/V

I

SLEW

-I I-Reg Loop Error Amp Slew
Current

200 µA

T

HR

1 Hour Timer 55 60 65 min

3 www.national.com

Electrical Characteristics (Continued)

V

DD

=

4.2V unless otherwise specified. Specifications with standard type face are for T

A

=

25˚C, and those with boldface type

apply over full operating temperature range.

Symbol Parameter Conditions Min Typ Max Units

I

LKG

-0 Battery Load Current (Note 8) V

DD

=

0V 1 10 µA

I

LKG

-MM Battery Load Current (Note 9) Monitor Mode 1 10 µA

V

BSD

Maximum Allowed Battery Self­Discharge(Note 10)

V

SET

=

HI 70 110 150 mV

V

SET

=

LO 220 260 300 mV

G

CSR

Fast Charge Current Regulation
Adjustment Transfer Ratio (Notes
11, 12)

V

ISET

=

0.5V 0.90 0.93 0.96 V/V

I

LED

LED1 & LED2 Driver Sink Current V

LED1

=

V

LED2

=

1.5V 20 mA

V

SUV

Start Up Voltage (Note 13) 3.4 V

V

UVR

Under Voltage Reset (Note 14) 2.2 V

V

PFD

-MAX Maximum PFD Output Drive no DC load on PFD VDD−0.2 V

V

PFD

-MIN Minimum PFD Output Drive no DC load on PFD VSS+0.1 V

V

IL

Logic Input Low (Note 15) 0.5 V

V

IH

Logic Input High (Note 15) VDD−0.5 V

I

DIG

Digital Input Leakage Current
(Note 15)

−1 1 µA

Note 1: Absolute Maximum Ratings indicates limits beyond which damage to the device may occur. Operating ratings indicate conditions for which the device is in­tended to be functional, but device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions, see
the Electrical Characteristics.

Note 2: ESD rating is based on the human body model, 100 pF discharged through 1.5 kΩ.
Note 3: LM3621 requires a minimum V

DD

of 3.4V to start-up. After start-up, the operating range is 3.0V to 5.5V.

Note 4: V

OUT

is measured between V

BAT

+ and CSR.

Note 5: V

CSR

is measured between CSR and VSS(across the current sense resistor).

Note 6: V

BAT

-Det is measured between V

BAT

+ and V

BAT

−.

Note 7: V

CSR

-Det is measured between CSR and VSS(across the current sense resistor).

Note 8: This is the current drawn from the battery by the LM3621 when V

DD

=

0V.

Note 9: This is the current drawn from the battery by the LM3621 when the charger is in Monitor Mode.
Note 10: This is the maximum battery voltage droop that is allowed before the charger initiates a fast charge mode to refresh the battery to its full charge capacity.
Note 11: The current regulation and detection levels can be set by applying a dc voltage adjusting between 0.1V to 1V to the I

SET

pin without changing the value
of the current sense resistor. To ensure proper operation, if the default current regulation and detection values are desired, then a capacitor of at least 100 pF should
be connected from I

SET

to VSS(GND).

Note 12: Transfer ratio of V

CSR/VISET

to adjust the fast charge current regulation level. See application section.

Note 13: Minimum V

DD

supply voltage required at start-up.

Note 14: The LM3621 goes to a shutdown or reset state during “brown out” (i.e., when V

DD

<

V

UVR

)

Note 15: Digital inputs are Enable, Boost, Chgint and V

SET

. To ensure proper operation, never allow any unused input pin to be left open.

Note 16: No external voltage applied to I

set

pin; a 100 pF capacitor is connected across I

set

and VSS.

Definition of Terms

V

OUT

: Voltage measured between V

BAT

+ and CSR.

V

CSR

: Charging current sense voltage measured between

CSR and V

SS

(Gnd).

V

BATTERY

: Battery terminal voltage measured between

V

BAT

+ and V

BAT

−.

ESR: The equivalent series resistance of a battery.The ESR
is the purely resistive component of a battery’s impedance.
Its value is usually determined by the battery construction.

RFV:The RFV (resistance free voltage, often called the float
voltage) is the open circuit terminal voltage of a battery
which is free from the ESR voltage drop error.

VI

SET

: External voltage applied to I

SET

pin, measured be-

tween I

SET

and VSS, to override the default value of V

CSR

.

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Typical Performance Characteristics Unless otherwise specified, T

A

=

25˚C)

Charge Termination Voltage
Change vs V

DD

DS100107-10

Maximum MCO Output Voltage vs
V

DD

DS100107-17

Fast Charge Current Regulation
Voltage vs V

DD

DS100107-15

Charge Termination Voltage
Regulation vs LED1 or LED2 Sink
Current

DS100107-19

Fast Charge Current Regulation vs
LED1 or LED2 Sink Current

DS100107-20

Charge Termination Voltage
Regulation vs MCO Output Current,
I

OUT

DS100107-22

Fast Charge Current Regulation vs MCO Output
Current, I

OUT

DS100107-21

Charger Output Voltage Current Regulation Voltage vs
Battery Resistance Free Voltage

DS100107-14

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DS100107-2

FIGURE 1. LM3621 Simplified Block Diagram

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DS100107-3

Note 17: State 8 is not used.

FIGURE 2. LM3621 Charge State Diagram

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DS100107-1

FIGURE 3. Typical Charge Cycle Waveform (V

SET

=

HI)

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Note 18: Battery Voltage=V

BAT+−VBAT,VSET

=

HI

Note 19: Voltage across the current sense resistor connected between CSR and V

SS

.

TABLE 1. Truth Table for Operation of LED Drivers (LED1 and LED2)

Input Conditions LED Outputs

Charge Mode

Pack Present?

(Enable

=

HI?)

Defective Pack

Detected?

Boost Mode?

(Boost

=

HI?)

Battery Voltage

(Note 18)

Charge Current

Detect Voltage

(Note 19)

Timer

LED1

Output

LED2

Output

Standby No

X No X X X Open

Drain

Open

Drain

Conditioning (Hi-Z)

Yes NO X

<

2.55V 0.05V

<

1hour Low Open

Drain

Conditioning (Hi-Z)

Yes Yes, Shorted

Battery or No

Capacity

X

<

2.55V 0.05V ≥ 1hour Pulse at

0.8 Hz

Open

Drain

Fast Charge

Yes No No ≥ 2.55V

>

40mV X Low Open

Drain

Fast Charge

Yes Yes, Open

Battery or High

ESR

No RFV ≤ 3.65V ≤ 40mV X Pulse at

0.8 Hz

Open

Drain

Top-Off

Yes No No

=

4.2V

<

40 mV

<

1 hour Open

Drain

Low

Monitor

Yes No No

>

4.09V 0 ≥ 1 hour Open

Drain

Low

Boost X X Yes X X X Low Low

Fault

Yes X X ≥ 4.4V X X Pulse at

0.8 Hz

Pulse at

0.8 Hz

Fault

Yes X X X ≥ 1V X Pulse at

0.8 Hz

Pulse at

0.8 Hz

9 www.national.com

Application Information

Battery Charger Operation Information

Figure 4

shows a general battery charger configuration using
LM3621. The LM3621 provides all the necessary control
functions for charging Lithium-Ion batteries precisely and
safely. It features constant voltage and constant current
mode operation. The on chip timer provides all critical timing
functions to properly initialize the charging cycle, avoid over
charging the battery above its maximum capacity level, and
cut off charging to a defective battery.The LM3621 also pro­vides the high accuracy of output voltage regulation without
requiring a trim pot or precision resistors. A built-in power
down switch prevents the battery from discharging through
the LM3621.

Input Supply Voltage

The voltage supply to LM3621 must never exceed 6.0V or
catastrophic damage may occur to the IC. When power is
first applied to the battery charger, the LM3621 will remain in
a reset state until the voltage on the V

DD

pin exceeds 3.4V
for at least one second. This ensures that the power source
is stable before a charge cycle is initiated.

Figure 2

shows
the state diagram for the charge cycle operation. Once the
LM3621 emerges from the reset state after power up, it will
not go into the reset state again until the voltage on the V

DD

pin drops below approximately 2.2V. When the LM3621 is in

the reset state, the PFD (Pass FET Drive) pin is pulled low
so that current is not allowed to flow into the load (e.g., Li+
battery). The LM3621 transitions from the reset state to
standby mode when the conditions for a stable power source
are met.

Digital Control Inputs

The LM3621 has four digital input control pins: Enable,
Boost, V

SET

and ChgInt. To ensure proper operation, never
allow unused digital input pins to be left open circuited. En­able is used to initiate a charge cycle, Boost is used to in­crease the maximum regulation current output, V

SET

con­trols the maximum output voltage, and ChgInt is used to
instantaneously interrupt (and resume) a charge cycle in
progress.

Current Boost Mode

This mode is activated when the “Boost” pin is pulled high.
The charger increases the maximum output current equal to
aV

CSR

level of 0.9V.This mode of operation is overridden by

a charge interrupt signal.

Charge Interrupt Control

Charging is interrupted with the digital input “ChgInt” pulled
low. The PFD pin is pulled to ground turning off the series
low pass FET. This is useful to prevent charging a battery if,
for example, the ambient temperature is excessively high.

DS100107-4

FIGURE 4. General Application Circuit

www.national.com 10

Application Information (Continued)

Programmable Charge Termination Voltage

The charging status for battery of graphite or coke anode is
programmed with the digital input “V

SET

”. V

SET

=

LO for a
charge termination voltage of 4.1V, a float voltage of 3.84V
and over voltage detection threshold (V

BAT

-Det) of 4.3V.

V

SET

=

HI for a charge termination voltage of 4.2V, float volt-

age of 4.09V and V

BAT

-Det of 4.4V.

Defective Pack Detection

The LM3621 automatically checks for defective battery.
Whenever a defective pack is detected, the charging se­quence is suspended and LED1 driver is pulsed at a rate of

0.8 Hz. A defective battery is indicated under three condi­tions: (1) when a battery fails to charge up to 2.55V within
one hour, (2) when the battery ESR plus the contact resis­tance is excessive, and (3) when the pack is an open circuit.

Step by Step Description of a Typical Charging
Sequence. (Refer to

Figure 3

)

1. Standby Mode

The LM3621 will remain in standby while the digital inputs to
the Enable and Boost pins are low. Boost overrides Enable,
and Boost mode may be activated at any time with two ex­ceptions: (1) when a deeply discharged battery (i.e., V

BAT

-

TERY

≤ 2.5V) is attached to the charger or (2) when ChgInt
has been activated during a normal charge cycle. Both LED
drivers pull low during Boost mode. During standby, the
charger’s output voltage V

OUT

is regulated to either 4.2V or

4.1V depending on the state of the digital input to the V

SET

pin (V

OUT

=

4.2V when V

SET

=

high or V

OUT

=

4.1V when

V

SET

=

low). PFD is low so the low side pass FET is off. The

LED driver pins are high impedance (open drain).

Table 1

shows the state of the LED drivers during various modes of
operation.

2. Charging Sequence Initialization

The LM3621 determines the presence or absence of a bat­tery pack by the state of the “Enable” pin. Enable should be
pulled low when the pack is not present. When a pack is in­serted into the charger, Enable should go high to initiate the
charging sequence.

After Enable is asserted with a battery connected to the
charger,LED1 goes low and there is a one-second delay be­fore current is allowed to flow into the battery.During this de­lay,the LM3621 checks the charge condition of the battery to
determine if it is grossly overcharged or if it is deeply dis­charged. If the battery is grossly overcharged, PFD stays low
keeping the low side pass FET off, and both LED drivers
pulse at a frequency of 0.8 Hz to indicate a fault condition. If
the battery is less than 2.55V, the LM3621 goes to the Hi-Z
( battery conditioning) charge mode. During the Hi-Z charge
mode, V

OUT

is regulated to 4.1V, and the voltage (V

CSR

)

across the current sense resistor (R

CS

) is regulated to 50

mV. The LM3621 is capable of charging a battery that has

been discharged down to as low as 0V.This is accomplished
by the fact that the “ON” resistance of the low side N-channel
pass FET is modulated by the PFD output. This ensures that
V

CSR

stays constant at 50 mV regardless of what the battery
voltage is, and it prevents the charger’s regulation loop from
collapsing in the event that the charger’s output is shorted.
The LM3621 will remain in the Hi-Z Charge mode for a maxi­mum of one hour. If the battery voltage does not increase to
at least 2.55V by the end of the one-hour interval, then PFD
goes low to turn off the low side pass FET and LED1 will
pulse at 0.8 Hz to indicate a defective battery.

3. Fast Charge Mode

The LM3621 will transition to Fast Charge mode whenever
the battery voltage is above 2.55V. During Fast Charge
mode LED1 stays low and LED2 stays open drain, and the
LM3621 controls the charger to behave as a current limited,
constant output voltage source to the battery. If the battery
voltage is less than 4.2V (for V

SET

=

HI), the LM3621 con­trols the charger to behave as a constant current source.
V

CSR

is limited to 0.5V, so the maximum charge current de-

livered to the battery is equal to 0.5V / R

CS

. Once the battery
voltage reaches 4.2V, the LM3621 controls the charger to
behave as a constant voltage source, and V

OUT

is main­tained at 4.2V. As the battery continues to charge up, the
charge current will decrease. Correspondingly, V

CSR

will de-

crease as well.
The battery will continue to charge until V

CSR

has decreased
to 40 mV, at which time PFD pulls low to interrupt the charge
current for one second.At the end of the one second interval,
the LM3621 checks to see if the battery’s Resistance Free
Voltage(RFV) is greater than 3.65V or less than 3.65V.If the
battery’s RFV is less than 3.65V, then the ESR of the battery
is excessively high, PFD stays low to keep the charging se­quence suspended and LED1 pulses at 0.8 Hz to indicate a
defective battery. If the battery’s RFV is greater than 3.65V,
then the LM3621 transitions to Top-Off mode. At this transi­tion, LED1 becomes open drain and LED2 pulls low indicat­ing a fully charged battery.

4. Top-Off Mode

During Top-Off mode, the battery is trickle charged for one
hour. At the end of the one hour interval, PFD goes low to
terminate charging (i.e., the charge current is interrupted),
and the LM3621 transitions to Battery Monitor mode.

5. Monitor Mode

During Monitor mode, V

OUT

drops to 4.09V (if V

SET

is high)

or 3.84V (if V

SET

is low), and the battery is floating. The
LM3621 typically draws less than 1 µA from the battery dur­ing Monitor mode. If the battery self discharges so that its
voltage decreases to 4.09V (if V

SET

is high) or 3.84V (if V

SET

is low), then the LM3621 will transition back to Fast Charge
mode to refresh the battery and charge it back up to its full
capacity (

Figure 2&Figure 5

). This process will continue un-

til Enable goes low.

11 www.national.com

Application Information (Continued)

Fault Protection

LM3621 provides redundant fault protection for a Li-Ion bat­tery pack. If the charger’s control loop is accidentally
opened, the regulation voltage will begin to increase beyond
the level that are safe for the battery. In order to protect the
battery from a fault condition, PFD goes low to turn off the
series pass FET whenever the voltage across the battery ex­ceeds the over voltage detection threshold (V

BAT

-Det) or

whenever V

CSR

exceeds 1V. A fault condition also causes
both of the LED drivers to pulse at 0.8 Hz. Enable must go
low to cause the LM3621 to transition from the Fault State to
Standby mode.

Low Current Drain of Battery

If power is inadvertently removed from the battery charger,
the voltage at the V

DD

pin will collapse to the same potential

as the V

SS

pin.An internal switch will disconnect the circuitry

of the LM3621 from the V

BAT

+ pin so that no more than 1µA

(typical) of leakage current will be drawn from the battery.

Adjustable Charge Current

The current sense resistor (Rcs) converts the charging cur­rent to a voltage level, V

CSR

. Applying an external voltage

source (V

EXT

) to the I

SET

pin will adjust the value of V

CSR

for
Fast Charge current regulation. Simultaneously the regula­tion level for Boost mode, Hi-Z Charge mode, End-of-Charge
threshold and over current detect threshold will also be ad­justed accordingly. The voltage at I

SET

pin should be within

the range of 1V ≥ V

ISET

≥ 0.1V. The transfer functions of

V

CSR

to V

ISET

are:

Fast Charge Mode, V

CSR

=

0.933·V

ISET

Hi-Z Mode, V

CSR

=

0.083·V

ISET

Boost Mode, V

CSR

=

0.48·V

ISET

+0.65

Over Current Threshold, V

CSR

=

0.36·V

ISET

+0.79

End-Of-Charge, V

CSR

=

0.07·V

ISET

DS100107-5

FIGURE 5. Battery Refresh

DS100107-16

FIGURE 6. Adjusting V

CSR

by applying V

EXT

to I

SET

pin

www.national.com 12

Application Information (Continued)

DS100107-9

FIGURE 7. Charge Current Regulation (V

CSR

)vsI

SET

Voltage

DS100107-8

FIGURE 8. Charge Current Detection (V

CSR

)vsI

SET

Voltage

13 www.national.com

Physical Dimensions inches (millimeters) unless otherwise noted

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16-Lead SOIC Package

Order Number LM3621M or LM3621M-3.0

NSC Package Number M16A

LM3621 Single Cell Lithium-Ion Battery Charger Controller

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.