LM3420-4.2 NSC [National Semiconductor], LM3420-4.2 Datasheet - Page 11

• Manufacturer Part Number: LM3420-4.2
• Description: Lithium-Ion Battery Charge Controller
• Manufacturer: NSC [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
www.national.com
Set test