LM3420-12.6 National Semiconductor, LM3420-12.6 Datasheet - Page 11

• Manufacturer Part Number: LM3420-12.6
• Description: Lithium-Ion Battery Charge Controller
• Manufacturer: National Semiconductor

Compensation
portant when analyzing closed loop stability. The minimum
and maximum room temperature values of this resistor are
specified in the Electrical Characteristics section of this data
sheet, and a curve showing the temperature coefficient is
shown in the curves section. Minimum values of R
lower phase margins.
V
The regulation voltage (V
nally trimmed by adding a single resistor from the COMP pin
to the +IN pin or from the COMP pin to the GND pin, depend-
ing on the desired trim direction. Trim adjustments up to
the temperature coefficient. (See temperature coefficient
curve shown in Figure 3 below.)
±
10% of V
REG
External Voltage Trim
REG
Normalized Temperature Drift with
can be realized, with only a small increase in
Output Externally Trimmed
REG
(Continued)
) of the LM3420 can be exter-
DS012359-8
FIGURE 2. LM3420 Test Circuit
f
result in
11
Test Circuit
The test circuit shown in Figure 2 can be used to measure
and verify various LM3420 parameters. Test conditions are
set by forcing the appropriate voltage at the V
point and selecting the appropriate R
the Electrical Characteristics section. Use a DVM at the
“measure” test points to read the data.
Formulas for selecting trim resistor values are shown below,
based on the percent of increase (%incr) or percent of de-
crease (%decr) of the output voltage from the nominal volt-
age.
For LM3420-4.2
For LM3420-8.2
R
decrease
FIGURE 4. Changing V
R
increase
Decreasing V
= (53x10
Increasing V
= 22x10
5
/%decr) − 75x10
DS012359-7
REG
5
REG
/%incr
DS012359-10
L
DS012359-9
or I
REG
OUT
as specified in
OUT
3
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Set test