LM3420AM5-4.2 National Semiconductor, LM3420AM5-4.2 Datasheet - Page 12

• Manufacturer Part Number: LM3420AM5-4.2
• Description: IC CTRLR LIION BAT CHRG SOT23-5
• Manufacturer: National Semiconductor
• Type: Battery Chargerr

Specifications of LM3420AM5-4.2

• Function: Charge Management
• Battery Type: Lithium-Ion (Li-Ion)
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SC-74A, SOT-753
• Output Current: 15mA
• Output Voltage: 4.2V
• Operating Supply Voltage (max): 20V
• Operating Temp Range: -40C to 85C
• Package Type: SOT-23
• Mounting: Surface Mount
• Pin Count: 5
• Operating Temperature Classification: Industrial
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM3420AM5-4.2TR; LM3420AM5-4.2; LM3420AM5-4.2TR

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V
Formulas for selecting trim resistor values are shown below,
based on the percent of increase (%incr) or percent of
decrease (%decr) of the output voltage from the nominal
voltage.
For LM3420-4.2
For LM3420-8.2
For LM3420-8.4
(Continued)
REG
External Voltage Trim
R
R
R
decrease
decrease
decrease
FIGURE 4. Changing V
R
R
R
increase
increase
increase
= (150x10
= (154x10
Decreasing V
= (53x10
Increasing V
FIGURE 5. Constant Current/Constant Voltage Li-Ion Battery Charger
= 22x10
= 26x10
= 26x10
5
5
5
/%decr) − 75x10
/%decr) − 176x10
/%decr) − 181x10
REG
5
5
5
REG
/%incr
/%incr
/%incr
01235909
01235910
REG
3
3
3
12
For LM3420-12.6
For LM3420-16.8
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 effi-
ciently. Output voltage tolerances better than 0.5% are pos-
sible without using trim pots or precision resistors. The cir-
cuits shown are designed for 2 cell operation, but they can
readily be changed for either 1, 3 or 4 cell charging applica-
tions.
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.
Application Circuits
The circuit shown in Figure 5 performs constant-current,
constant-voltage charging of two Li-Ion cells. At the begin-
ning of the charge cycle, when the battery voltage is less
than 8.4V, 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 1.5A, and the LM350 and
LM338 can be used for higher currents.) The LM317 forces
a constant 1.25V across R
current of
R
R
decrease
decrease
R
R
increase
increase
= (259x10
= (364x10
I
LIM
= 1.25V/R
01235901
= 28x10
= 29x10
LIM
5
5
, thus generating a constant
/%decr) − 287x10
/%decr) − 392x10
5
5
LIM
/%incr
/%incr
3
3