MP2619EV-LF-Z Datasheet, PDF (18/20 Pages) MPS Industries, Inc. – 2A, 24V Input, 600kHz 2-3 Cell Switching Li-Ion Battery Charger With System Power Path Management

MP2619 – 2A, 24V INPUT, 600kHz 2-3CELL SWITCHING LI-ION BATTERY CHARGER
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:
I_CHG
A


200mV
RS1mΩ
(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:
Gain

RGS1
RG1
(2)
The voltage of OUT1 pin, V_OUT1 can be calculated
from:
V_OUT1

I_SYS

RS2

Gain

I_SYS

RS2 
RG1
RGS1
(3)
When the system current increased ΔI_SYS, to
satisfy the charge current decreased ΔI_SYS
accordingly. The relationship should be:
ΔI_BAT

ΔV_OUT1
RS1

ΔI_SYS  RS2 RGS1
RS1 RG1
(4)
BecauseΔI_SYS=ΔI_BATT, we can get:
RRSS21 ^
RGS1
RG1
(5)
RGS1/2 causes the charge current sense error
as it changes the sense gain of A2, which can be
calculated from:
G_A2

12.3kΩ
2kΩ RGSkΩ
(6)
The charge current is set as:
I_CHG
A


G_A2
1230
 RS1mΩ
(7)
Then the influence of R_GS1 to the charge current
is:
I_CHG
A 

2000  RGSΩ
10  RS1mΩ
(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, 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):
I_CHG
A 

2000  2.5 RS1mΩ
10 RS1mΩ
(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)
2
1.5
1
0.8
0.5
R_GS(Ω)
280
402
665
909
2k
RS1(mΩ)
110
160
260
360
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 ΔI_SYS and ΔI_BATT
can be realized by re-calculate equation (4), (5)
and (8).
MP2619 Rev. 1.01
www.MonolithicPower.com
18
5/28/2015
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