MP2619 – 2A, 24V INPUT, 600kHz 2-3CELL SWITCHING LI-ION BATTERY CHARGER
MP2619 Rev. 1.01 www.MonolithicPower.com 18
5/28/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2015 MPS. All Rights Reserved.
APPLICATION INFORMATION
Setting the Charge Current
1. Standalone Switching Charger
The charge current of MP2619 is set by the
sense resistor RS1. The charge current
programmable formula is as following:
mRS1
200mV
AI
CHG
(1)
2. Switching Charger with Power Path
Management
Figure 7 shows the charge current sharing with
the system current.
Figure 7— Charge current sharing with
System current
The gain of the system current is set as:
RG1
RGS1
Gain
(2)
The voltage of OUT1 pin, V
OUT1
can be calculated
from:
RG1
RGS1RS2I
GainRS2IV
SYS
SYSOUT1
(3)
When the system current increased I
SYS
, to
satisfy the charge current decreased I
SYS
accordingly. The relationship should be:
RG1RS1
RGS1RS2I
RS1
V
I
SYSOUT1
BAT
(4)
Because
ΔI
SYS
=ΔI
BATT
, we can get:
RGS1
RS1
(5)
RGS1/2 causes the charge current sense error
as it changes the sense gain of A2, which can be
calculated from:
kRGSk2
k12.3
G
A2
(6)
The charge current is set as:
mRS1G
1230
AI
A2
CHG
(7)
Then the influence of R
GS1
to the charge current
is:
mRS110
RGS2000
AI
CHG
(8)
To decrease the power loss of the sensing circuit,
choose RS2 as small as possible, 20m is
recommended. Too small R
G1
results in too big
current sense error of the system current, 50 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):
mRS110
mRS12.52000
AI
CHG
(9)
Following table is the calculated RS1 and R
GS1
value for setting different charge current.
Table2—I
CHG
Set in Power Path Application
I
CHG
(A) R
GS
() RS1(m)
2 280 110
1.5 402 160
1 665 260
0.8 909 360
0.5 2k 800
If choose different RS2 and R
G1
, re-calculated
from equation (5) and equation (8), then get the
different equation (9) and the table.
Also, any relationship between I
SYS
and I
BATT
can be realized by re-calculate equation (4), (5)
and (8).
