LTC4012-2 Linear Technology Corporation, LTC4012-2 Datasheet - Page 22

• Manufacturer Part Number: LTC4012-2
• Description: Multi-Chemistry Battery Charger
• Manufacturer: Linear Technology Corporation

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APPLICATIONS INFORMATION
LTC4012/
LTC4012-1/LTC4012-2
R
ues of R
programmed current accuracy. Use these equations and
guidelines, as represented in Table 6, to help select the cor-
rect inductor value. This table was developed to maintain
maximum ΔI
V
inductor value could also vary by 25% at I
Table 6. Minimum Typical Inductor Values
To guarantee that a chosen inductor is optimized in any
given application, use the design equations provided and
perform bench evaluation in the target application, par-
ticularly at duty cycles below 20% or above 80% where
PWM frequency can be much less than the nominal value
of 550kHz.
22
10V to 20V
10V to 20V
10V to 20V
10V to 20V
BAT
IN
<10V
>20V
<10V
>20V
<10V
>20V
<10V
>20V
V
should not be less than 2.37k or more than 6.04k. Val-
CLP
= 0.5 • V
IN
greater than 3.01k may cause some reduction in
CLP
L
≥5.1μH
≥3.4μH
≥6.8μH
≥9.5μH
≥2.5μH
≥5.1μH
≥7.1μH
≥10μH
≥20μH
≥28μH
≥10μH
≥14μH
(Typ)
near 0.6 • I
L1
(the point of maximum ΔI
I
MAX
1A
1A
1A
2A
2A
2A
3A
3A
3A
4A
4A
4A
MAX
100mΩ
100mΩ
100mΩ
R
50mΩ
50mΩ
50mΩ
33mΩ
33mΩ
33mΩ
25mΩ
25mΩ
25mΩ
with f
SENSE
PWM
MAX
L
3.01k
3.01k
3.01k
3.01k
3.01k
3.01k
3.01k
3.01k
3.01k
3.01k
3.01k
3.01k
), assuming that
R
at 550kHz and
IN
.
R
26.7k
26.7k
26.7k
26.7k
26.7k
26.7k
26.7k
26.7k
26.7k
26.7k
26.7k
26.7k
PROG
TGATE BOOST Supply
Use the external components shown in Figure 11 to de-
velop a bootstrapped BOOST supply for the TGATE FET
driver. A good set of equations governing selection of the
two capacitors is:
where Q
with V
then given by:
To improve effi ciency by increasing V
top FET, substitute a Schottky diode with low reverse
leakage for D1.
PWM jitter has been observed in some designs operating
at higher V
affect DC charge current accuracy. A series resistor with a
value of 5Ω to 20Ω can be inserted between the cathode
of D1 and the BOOST pin to remove this jitter, if present.
A resistor case size of 0603 or larger is recommended to
lower ESL and achieve the best results.
I
C
D
1
= Q
=
GS
G
20
G
= 4.5V. The maximum average diode current is
4 5
is the rated gate charge of the top external NFET
IN
• 665kHz
.
•
LTC4012
/V
Q
V
INTV
BOOST
G
OUT
Figure 11. TGATE Boost Supply
,
SW
DD
C
ratios. This jitter does not substantially
2 20
20
17
18
=
4012 F11
•
C
D1
1N4148
C2
2μF
1
C1
0.1μF
L1
GS
applied to the
TO
R
SENSE
4012f