MP2612 MPS, MP2612 Datasheet - Page 17

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

APPLICATION INFORMATION
Setting the Charge Current
1. Standalone Switching Charger
The charge current of MP2612 is set by the
sense resistor RS1 (Figure1). The charge current
programmable formula is as following:
2.
Management
When MP2612 is applied together with MP8110,
the charge current setting should be calibrated
(Figure2).
Figure 8 shows MP8110 sensing the system
current and feeding back to the MP2612.
The gain of MP8110 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:
MP2612 Rev. 0.92
11/23/2010
Figure 8— System Current Sensing Circuit
V
OUT1
Switching
∆I
BAT
=
I
SYS
=
MP2612 – 2A, 24V INPUT, 600kHz 2-3CELL SWITCHING LI-ION BATTERY CHARGER
∆V
×
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
RS1
RS2
I
CHG
OUT1
Charger
Gain =
( )
A
×
=
Gain
=
∆I
RS1
RGS1
200mV
RG1
SYS
=
OUT1
RS1
(
with
I
mΩ
×
SYS
RS2
can be calculated
×
)
×
RG1
RS2
×
Power
RG1
RGS1
×
© 2010 MPS. All Rights Reserved.
RGS1
www.MonolithicPower.com
SYS
Path
, to
SYS
(1)
(2)
(4)
(3)
Because Δ I
R
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 MP8110, 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 R
value for setting different charge current.
If choose different RS2 and R
from equation (5) and equation (8), then get the
different equation (9) and the table.
GS1/2
Table2—I
I
1.5
0.8
0.5
CHG
causes charge current sense error as it
2
1
I
(A)
CHG
SYS
CHG
I
( )
G
I
CHG
A
CHG
= Δ I
A2
Set in Power Path Application
=
( )
( )
A
=
A
BATT
2000
RS2
RS1
2
=
=
R
( )
kΩ
2000
G
GS
280
402
665
909
, we can get:
10
10
2k
12.3
=
A2
(Ω)
GS1
+
RGS1
+
×
×
RG1
×
2.5
1230
RGS
RS1
RS1
RS1
+
( )
to the charge current
kΩ
RGS
G1
×
(
RS1
(
(
mΩ
mΩ
( )
mΩ
results in too big
kΩ
G1
( )
Ω
)
)
, re-calculated
(
)
mΩ
RS1(mΩ)
110
160
260
360
800
)
GS1
(5)
(6)
(7)
(8)
(9)
17