MP2618 MPS, MP2618 Datasheet - Page 17

• Manufacturer Part Number: MP2618
• Description: 2a, 24v Input, 600khz 2-3 Cell Switching Li-ion Battery Charger With System Power Path Management
• Manufacturer: MPS

APPLICATION INFORMATION
Setting the Charge Current
1. Standalone Switching Charger
The charge current of MP2618 is set by the
sense
programmable formula is as following:
2.
Management
Figure 7 shows the charge current sharing with
the system current.
The gain of the system current is set as:
The voltage of OUT1 pin, V
from:
When the system current increased ∆I
satisfy the charge current decreased ∆I
accordingly, the relationship should be:
Because ∆I
MP2618 Rev. 0.92
7/14/2010
V
OUT1
Switching
∆I
Figure 7— Charge current sharing with
=
BAT
I
resistor
SYS
=
SYS
×
∆V
MP2618 – 2A, 24V INPUT, 600kHz 2-3CELL SWITCHING LI-ION BATTERY CHARGER
RS2
RS1
=∆I
I
CHG
OUT1
System current
Charger
BAT
Gain =
RS2
RS1
RS1.
( )
×
A
Gain
=
, we can get:
=
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
=
∆I
RS1
RGS1
RGS1
200mV
RG1
SYS
RG1
=
The
RS1
I
(
OUT1
mΩ
SYS
×
with
RS2
×
×
)
can be calculated
RG1
RS2
charge
RG1
×
Power
RGS1
×
RGS1
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current
SYS
Path
, to
SYS
(1)
(2)
(3)
(4)
(5)
RGS1/2 causes the charge current sense error
as it changes the sense gain of A2, which can be
calculated from:
The charge current is set as:
Then the influence of R
is:
To decrease the power loss of the sensing circuit,
choose RS2 as small as possible, 20m is
recommended. Too small R
current sense error of the system current, 50Ω is
at least.
Substitute these two values into equation (5),
then the calibrated charge current set formula in
power path application is got from equation (8):
Following table is the calculated RS1 and RGS1
value for setting different charge current.
If choose different RS2 and RG1, re-calculated
from equation (5) and equation (8), then get the
different equation (9) and the table.
Also, any relationship between ∆I
can be realized by re-calculate equation (4), (5)
and (8).
Table2—I
I
CHG
(A)
1.5
0.8
0.5
I
2
1
CHG
CHG
I
( )
G
I
CHG
A
CHG
A2
=
Set in Power Path Application
( )
( )
A
=
A
2000
2
=
=
( )
kΩ
2000
RGS(Ω)
G
10
10
12.3
A2
+
280
402
665
909
2k
+
×
×
GS1
×
2.5
1230
RS1
RGS
RS1
RS1
+
( )
kΩ
RGS
to the charge current
×
G1
(
(
RS1
(
mΩ
mΩ
( )
mΩ
kΩ
results in too big
( )
Ω
)
)
(
)
mΩ
SYS
RS1(mΩ)
)
110
160
260
360
800
and ∆I
BATT
(6)
(7)
(8)
(9)
17