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LTC4009IUF-2#TRPBF

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19
4009fd
LTC4009
LTC4009-1/LTC4009-2
applicaTions inForMaTion
If R
PROG
is greater than 26.7k, the actual level at which
low charge current is detected will be less than C/10. The
highest value of R
PROG
that can be used while reliably
indicating low charge current before reaching final V
BAT
is 30.1k. R
PROG
can safely be set to values higher than
this, but low current indication will be lost.
If R
PROG
is less than 26.7k, low charge current detection
occurs at a level higher than C/10. More importantly, the
LTC4009 becomes increasingly sensitive to reverse cur-
rent. The lowest value of R
PROG
that can be used without
the risk of erroneous boost operation detection at end of
charge is 26.1k. Values of R
PROG
less than this should not
be used. See the Operation section for more information
about reverse current.
The nominal fractional value of I
MAX
at which C/10 indica-
tion occurs is given by:
I
I
mV R µA
V R
C
MAX
PROG
PROG
10
400 11 67
1 2085
=
( )
– • .
. –
•• .11 67µA
( )
Direct digital monitoring of C/10 indication is possible with
an external application circuit like the one shown in Figure 9.
The LTC4009 initially indicates C/10 until the PWM has
started and the actual charge current can be determined
(PROG pin voltage). The 0.1µF capacitor from CHRG to
GND is used to filter this initial pulse, which is typically
less than 2ms when starting toward a final charge current
that is actually greater than C/10. If external circuitry is
insensitive to, or can ignore, this momentary C/10 indica-
tion at start-up, the capacitor can be omitted.
By using two different value pull-up resistors, a micro-
processor can detect three states from this pin (charging,
C/10 and not charging). See Figure 10. When a digital
output port (OUT) from the microprocessor drives one
of the resistors and a second digital input port polls the
network, the charge state can be determined as shown
in Table 5.
Figure 9. Digital C/10 Indicator
Figure 10. Microprocessor Status Interface
17
8
INTV
DD
CHRG
Q1
TP0610T
Q2
2N7002
100k
LTC4009
4009 F09
100k
V
LOGIC
100k
C/10
CHRG
100k
0.1µF
Q3
2N7002
33k
200k
4009 F10
V
DD
3.3V
µP
IN
OUT
LTC4009
CHRG
8
Table 5. Digital Read Back State (IN, Figure 10)
LTC4009
CHARGER STATE
OUT STATE
Hi-Z 1
Off 1 1
C/10 Charge 0 1
Bulk Charge 0 0
LTC4009
LTC4009-1/LTC4009-2
20
4009fd
Input and Output Capacitors
In addition to typical input supply bypassing (0.1µF) on
DCIN, the relatively high ESR of aluminum electrolytic
capacitors is helpful for reducing ringing when hot plug-
ging the charger to the AC adapter. Refer to LTC Application
Note 88 for more information.
The input capacitor between system power (drain of top
FET, Figure 1) and GND is required to absorb all input PWM
ripple current, therefore it must have adequate ripple current
rating. Maximum RMS ripple current is typically one-half
of the average battery charge current. Actual capacitance
value is not critical, but using the highest possible voltage
rating on PWM input capacitors will minimize problems.
Consult with the manufacturer before use.
The output capacitor shown across the battery and ground
must also absorb PWM output ripple current. The general
formula for this capacitor current is:
I
V
V
V
L f
RMS
BAT
BAT
CLP
PWM
=
0 29 1
1
. • • –
•
For example, I
RMS
= 0.22A with:
V
BAT
= 12.6V
V
CLP
= 19V
L1 = 10µH
f
PWM
= 550kHz
High capacity ceramic capacitors (20µF or more) available
from a variety of manufacturers can be used for input/out-
put capacitors. Other alternatives include OS-CON and
POSCAP capacitors from Sanyo.
Low ESR solid tantalum capacitors have high ripple cur-
rent rating in a relatively small surface mount package,
but exercise caution when using tantalum for input or
output bulk capacitors. High input surge current can be
created when the adapter is hot-plugged to the charger
or when a battery is connected to the charger. Solid tan-
talum capacitors have a known failure mechanism when
subjected to very high surge currents. Select tantalum
capacitors that have high surge current ratings or have
been surge tested.
EMI considerations usually make it desirable to minimize
ripple current in battery leads. Adding Ferrite beads or
inductors can increase battery impedance at the nominal
550KHz switching frequency. Switching ripple current splits
between the battery and the output capacitor in inverse
relation to capacitor ESR and the battery impedance. If
the ESR of the output capacitor is 0.2Ω and the battery
impedance is raised to 4Ω with a ferrite bead, only 5% of
the current ripple will flow to the battery.
Inductor Selection
Higher switching frequency generally results in lower
efficiency because of MOSFET gate charge losses, but it
allows smaller inductor and capacitor values to be used.
A primary effect of the inductor value L1 is the amplitude
of ripple current created. The inductor ripple current ∆I
L
decreases with higher inductance and PWM operating
frequency:
∆I
V
V
V
L f
L
BAT
BAT
CLP
PWM
=
• –
•
1
1
Accepting larger values of ∆I
L
allows the use of low in-
ductance, but results in higher output voltage ripple and
greater core losses. Lower charge currents generally call
for larger inductor values.
applicaTions inForMaTion
21
4009fd
LTC4009
LTC4009-1/LTC4009-2
The LTC4009 limits maximum instantaneous peak inductor
current during every PWM cycle. To avoid unstable switch
waveforms, the ripple current must satisfy:
∆I
mV
R
I
L
SENSE
MAX
<
2
150
• –
so choose:
L
V
f
mV
R
I
CLP
PWM
SENSE
MAX
1
0 125
150
>
. •
• –
For C-grade parts, a reasonable starting point for setting
ripple current is ΔI
L
= 0.4 • I
MAX
. For I-grade parts, use ΔI
L
= 0.2 • I
MAX
only if the IC will actually be used to charge
batteries over the wider I-grade temperature range. The
voltage compliance of internal LTC4009 circuits also im-
poses limits on ripple current. Select R
IN
(in Figure 1) to
avoid average current errors in high ripple designs. The
following equation can be used for guidance:
R I
µA
R
R I
µA
SENSE L
IN
SENSE L
• •∆ ∆
50 20
≤ ≤
R
IN
should not be less than 2.37k or more than 6.04k. Val-
ues of R
IN
greater than 3.01k may cause some reduction in
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 for C-grade
parts to maintain maximum ΔI
L
near 0.6 • I
MAX
with f
PWM
at
550kHz and V
BAT
= 0.5 • V
CLP
(the point of maximum ΔI
L
),
assuming that inductor value could also vary by 25% at
I
MAX
. For I-grade parts, reduce maximum ΔI
L
to less than
0.4 • I
MAX
, but only if the IC will actually be used to charge
batteries over the wider I-grade temperature range. In that
case, a good starting point can be found by multiplying
the inductor values shown in Table 6 by a factor of 1.6 and
rounding up to the nearest standard value.
Table 6. Minimum Typical Inductor Values
V
CLP
L1 (Typ)
I
MAX
R
SENSE
R
IN
R
PROG
<10V ≥10µH 1A
100mΩ
3.01k 26.7k
10V to 20V ≥20µH 1A
100mΩ
3.01k 26.7k
>20V ≥28µH 1A
100mΩ
3.01k 26.7k
<10V ≥5.1µH 2A
50mΩ
3.01k 26.7k
10V to 20V ≥10µH 2A
50mΩ
3.01k 26.7k
>20V ≥14µH 2A
50mΩ
3.01k 26.7k
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.
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:
C
Q
V
C C
G
1
20
4 5
2 20 1= =
•
.
, •
applicaTions inForMaTion
Figure 11. TGATE Boost Supply
20
17
BOOST
INTV
DD
18
SW
LTC4009
4009 F11
C2
2µF
C1
0.1µF
L1
TO
R
SENSE
D1
1N4148
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LTC4009IUF-2#TRPBF

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Manufacturer:
Analog Devices / Linear Technology
Description:
Battery Management High Efficiency, Multi-Chemistry QFN Battery Charger
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