MP2612 MPS, MP2612 Datasheet - Page 18

• Manufacturer Part Number: MP2612
• Description: 2a,24v Input, 600khz 2/3-cell Switching Li-ion Battery Charger
• Manufacturer: MPS

Also, any relationship between ∆I
can be realized by re-calculate equation (4),(5)
and (8).
Selecting the Inductor
A 1µH to 10µH inductor is recommended for
most applications. The inductance value can be
derived from the following equation.
Where ∆I
the 2/3 cell battery voltage.
Choose inductor current to be approximately
30% if the maximum charge current, 2A. The
maximum inductor peak current is:
Under light load conditions below 100mA, larger
inductance
efficiency.
For
resistance is recommended to be less than
200mΩ.
NTC Function
As Figure 9 shows, the low temperature
threshold and high temperature threshold are
preset internally via a resistive divider, which are
73%·VREF33 and 30%·VREF33. For a given
NTC thermistor, we can select appropriate R3
and R6 to set the NTC window.
In detail, for the thermistor (NCP18XH103) noted
in above electrical characteristic,
At 0ºC, R
At 50ºC, R
Assume that the NTC window is between 0ºC
and 50ºC, the following equations could be
derived:
MP2612 Rev. 0.92
11/23/2010
optimized
R3
R3
R6//R
R6//R
+
NTC_Cold
+
L
NTC_Hot
R6//R
R6//R
is the inductor ripple current. V
L
is
MP2612 – 2A, 24V INPUT, 600kHz 2-3CELL SWITCHING LI-ION BATTERY CHARGER
NTC_Cold
NTC_Hot
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
=
I
L(MAX)
NTC_Cold
= 27.445k;
NTC_Hot
= 4.1601k.
V
recommended
efficiency,
OUT
V
IN
=
×
× ∆ ×
I
=
(V
=
CHG
VREF33
I
VREF33
IN
V
L
V
TH_High
+
TH_Low
−
f
OSC
V
∆
the
2
OUT
I
L
)
for
=
SYS
=
inductor
30%
73%
and ∆I
© 2010 MPS. All Rights Reserved.
improved
www.MonolithicPower.com
OUT
(10)
(11)
(12)
(13)
BATT
DC
is
According to equation (12) and equation (13), we
can find that R3 = 9.63k and R6 = 505k.
To be simple in project, making R3=10k and R6
no
specification.
Selecting the Input Capacitor
The input capacitor reduces the surge current
drawn from the input and also the switching noise
from the device. The input capacitor impedance
at the switching frequency should be less than
the input source impedance to prevent high
frequency switching current passing to the input.
Ceramic capacitors with X5R or X7R dielectrics
are highly recommended because of their low
ESR and small temperature coefficients. For
most applications, a 4.7µF capacitor is sufficient.
Selecting the Output Capacitor
The output capacitor keeps output voltage ripple
small and ensures regulation loop stability. The
output capacitor impedance should be low at the
switching frequency. Ceramic capacitors with
X5R or X7R dielectrics are recommended.
PC Board Layout
The high frequency and high current paths (GND,
IN and SW) should be placed to the device with
short, direct and wide traces. The input capacitor
needs to be as close as possible to the IN and
GND pins. The external feedback resistors
should be placed next to the FB pin. Keep the
switching node SW short and away from the
feedback network.
R6
connect
Figure 9— NTC function block
R
R3
NTC
VREF33
will
NTC
approximately
Low Temp Threshold
High Temp Threshold
V
V
TH_Low
TH_High
meet
the
18