LTC4012IUF-1#TRPBF Linear Technology, LTC4012IUF-1#TRPBF Datasheet - Page 21

• Manufacturer Part Number: LTC4012IUF-1#TRPBF
• Description: IC CTLR BATT CHARGER CC/CV 20QFN
• Manufacturer: Linear Technology

Specifications of LTC4012IUF-1#TRPBF

• Function: Charge Management
• Battery Type: Multi-Chemistry
• Voltage - Supply: 6 V ~ 28 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 20-WFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

applications inForMation
The output capacitor shown across the battery and ground
must also absorb PWM output ripple current. The general
formula for this capacitor current is:
For example, I
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.
V
V
L1 = 10µH
f
I
PWM
RMS
BAT
CLP
= 12.6V
= 19V
= 550kHz
=
0 29
.
RMS
•
V
L
BAT
= 0.22A with:
1
•
f
•
PWM

 
1
–
V
V
CLP
BAT

 
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
inductance and PWM operating frequency:
Accepting larger values of ∆I
ductance, but results in higher output voltage ripple and
greater core losses. Lower charge currents generally call
for larger inductor values.
The LTC4012 limits maximum instantaneous peak inductor
current during every PWM cycle. To avoid unstable switch
waveforms, the ripple current must satisfy:
so choose:
For C-grade parts, a reasonable starting point for setting
ripple current is ∆I
∆I
charge batteries over the wider I-grade temperature range.
The voltage compliance of internal LTC4012 circuits also
imposes limits on ripple current. Select R
to avoid average current errors in high ripple designs. The
following equation can be used for guidance:
L
L
∆I
∆I
R
= 0.2 • I
1
SENSE
L
L
>
=
<
50
f
PWM
2
V
µA
BAT
•
•



LTC4012-1/LTC4012-2
MAX
∆
L
R
150
0 125
•
I
1
• –
SENSE
L
.

 
•



R
150
1
≤
mV
f
only if the IC will actually be used to
PWM
SENSE
R
L
•
mV
IN
V
V
= 0.4 • I
–
V
BAT
CLP
CLP
≤
I
MAX
–
R



I
SENSE
MAX



20
MAX
L

 
allows the use of low in-
L
µA
. For I-grade parts, use
•
decreases with higher
∆
I
L
LTC4012/
IN
(in Figure 1)

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