LM3420-42 Datasheet, PDF (10/17 Pages) National Semiconductor (TI) – Lithium-Ion Battery Charge Controller

Five Lead Surface Mount Package Information
The small SOT23-5 package allows only 4 alphanumeric characters to identify the product. The table below contains the field in-
formation marked on the package.
Voltage
Grade
4.2V
4.2V
4.2V
4.2V
8.2V
8.2V
8.2V
8.2V
8.4V
8.4V
8.4V
8.4V
12.6V
12.6V
12.6V
12.6V
16.8V
16.8V
16.8V
16.8V
A (Prime)
A (Prime)
B (Standard)
B (Standard)
A (Prime)
A (Prime)
B (Standard)
B (Standard)
A (Prime)
A (Prime)
B (Standard)
B (Standard)
A (Prime)
A (Prime)
B (Standard)
B (Standard)
A (Prime)
A (Prime)
B (Standard)
B (Standard)
Order
Information
LM3420AM5-4.2
LM3420AM5X-4.2
LM3420M5-4.2
LM3420M5X-4.2
LM3420AM5-8.2
LM3420AM5X-8.2
LM3420M5-8.2
LM3420M5X-8.2
LM3420AM5-8.4
LM3420AM5X-8.4
LM3420M5-8.4
LM3420M5X-8.4
LM3420AM5-12.6
LM3420AM5X-12.6
LM3420M5-12.6
LM3420M5X-12.6
LM3420AM5-16.8
LM3420AM5X-16.8
LM3420M5-16.8
LM3420M5X-16.8
Package
Marking
D02A
D02A
D02B
D02B
D07A
D07A
D07B
D07B
D03A
D03A
D03B
D03B
D04A
D04A
D04B
D04B
D05A
D05A
D05B
D05B
Supplied as
250 unit increments on tape and reel
3k unit increments on tape and reel
250 unit increments on tape and reel
3k unit increments on tape and reel
250 unit increments on tape and reel
3k unit increments on tape and reel
250 unit increments on tape and reel
3k unit increments on tape and reel
250 unit increments on tape and reel
3k unit increments on tape and reel
250 unit increments on tape and reel
3k unit increments on tape and reel
250 unit increments on tape and reel
3k unit increments on tape and reel
250 unit increments on tape and reel
3k unit increments on tape and reel
250 unit increments on tape and reel
3k unit increments on tape and reel
250 unit increments on tape and reel
3k unit increments on tape and reel
FIGURE 1. SOT23-5 Marking
The first letter “D” identifies the part as a Driver, the next two numbers indicate the voltage, “02” for a 4.2V part, “07” for an 8.2V
part, “03” for an 8.4V part, “04” for a 12.6V part, and “05” for a 16.8V part. The fourth letter indicates the grade, “B” for standard
grade, “A” for the prime grade.
The SOT23-5 surface mount package is only available on tape in quantity increments of 250 on tape and reel (indicated by the
letters “M5” in the part number), or in quantity increments of 3000 on tape and reel (indicated by the letters “M5X” in the part num-
ber).
Product Description
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 volt-
age 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 (V_REG), the OUT pin sources no current.
As the voltage at the IN pin approaches the V_REG 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 ser-
vos the output voltage to be the same value as V_REG.
In some applications, (even under normal operating condi-
tions) the voltage on the IN pin can be forced above the
V_REG voltage. In these instances, the maximum voltage ap-
plied to the IN pin should not exceed 20V. In addition, an ex-
ternal resistor may be required on the OUT pin to limit the
maximum current to 20 mA.
Compensation
The inverting input of the error amplifier is brought out to al-
low overall closed-loop compensation. In many of the appli-
cations circuits shown here, compensation is provided by a
single capacitor (C_C) 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 de-
sired 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 as follows;
where R_f ≈ 75 kΩ for the 4.2V part, R_f ≈ 181 kΩ for the 8.4V
part, R_f ≈ 287 kΩ for the 12.6V part, and R_f ≈ 392 kΩ for the
16.8V part.
The resistor (R_f) in the formula is an internal resistor located
on the die. Since this resistor value will affect the phase mar-
gin, the worst case maximum and minimum values are im-
www.national.com
10