Datasheet
18 Maxim Integrated
1.2A Switch-Mode Li+ Chargers with ±22V Input
Rating and JEITA Battery Temperature Monitoring
MAX8900A/MAX8900B/MAX8900C
Setting the Prequalification Current
and Done Threshold (DNI)
As shown in Figure 5, a resistor from DNI to ground
(R
DNI
) sets the prequalification current (I
PQ
) and done
current (I
DN
). The MAX8900_ supports values of R
DNI
from 1.19kI to 38.2kI. Select R
DNI
as follows:
I
DN
= 384V/R
DNI
I
PQ
= 415V/R
DNI
Determine the optimal I
PQ
and I
DN
for a given system by
considering the characteristics of the battery.
Depending on its mode of operation, the MAX8900_ controls
the voltage at DNI from 0 to 1.5V. Avoid adding capacitance
directly to the SETI pin that exceeds 10pF.
As shown in Figure 10, the prequalification current and
done threshold is set to 50% of programmed value when
T1 < THM < T2, and 100% of programmed value when
T2 < THM < T4.
As a protection feature, if the battery temperature is
between the T2 and T4 thresholds and DNI is shorted
to ground, then the MAX8900_ latches off the battery
charger and enters the timer fault state. This protection
feature is disabled inside of dead-battery mode and
thermal foldback. Furthermore, if DNI is unconnected,
then the prequalification and done current is 0A and the
charge timer prevents the MAX8900_ from indefinitely
operating in its done state.
Charge Enable Input (CEN)
CEN is a digital input. Driving CEN high disables the
battery charger. Pull CEN low or leave it unconnected
Figure 4. Fast-Charge Current vs. R
SETI
(www.maxim-ic.com/
tools/other/software/MAX8900-RSETI.XLS)
Figure 5. Prequalification Current and Done Threshold vs. R
DNI
(www.maxim-ic.com/tools/other/software/MAX8900-DNI.XLS)
FAST-CHARGE CURRENT
vs. R
SETI
R
SETI
(kI)
FAST-CHARGE CURRENT (A)
604020
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0
08
0
PREQUALIFICATION AND DONE CURRENT
vs. R
DNI
R
DNI
(kI)
CURRENT (mA)
10
50
100
150
200
250
0
0 100
I
PQ
I
DN
R
SETI
(kI)
I
FC
(A)
R
SETI
(kI)
I
FC
(A)
R
SETI
(kI)
I
FC
(A)
2.87 1.186 7.15 0.476 24.9 0.137
3.01 1.131 7.32 0.465 27.4 0.124
3.16 1.078 7.87 0.433 30.1 0.113
3.32 1.026 8.25 0.413 32.2 0.106
3.57 0.954 9.09 0.375 34.0 0.100
3.92 0.869 10.0 0.341 35.7 0.095
4.12 0.826 11.0 0.310 39.2 0.087
4.32 0.788 12.1 0.281 43.2 0.079
4.42 0.770 13.0 0.262 45.5 0.075
4.75 0.717 14.0 0.243 49.9 0.068
4.99 0.682 15.0 0.227 51.1 0.067
5.11 0.666 16.2 0.210 56.2 0.061
5.62 0.606 18.2 0.187 61.9 0.055
6.19 0.550 20.0 0.170 66.5 0.051
6.81 0.500 22.1 0.154 68.1 0.050
7.5 0.454 24.3 0.140
R
DNI
(kI)
I
PQ
(mA)
I
DN
(mA)
R
DNI
(kI)
I
PQ
(mA)
I
DN
(mA)
1.91 217.3 201.0 7.5 55.3 51.2
2.37 175.1 162.0 7.68 54.0 50.0
3.48 119.3 110.3 7.87 52.7 48.8
3.57 116.2 107.6 10.0 41.5 38.4
3.83 108.4 100.3 14.3 29.0 26.9
4.42 93.9 86.9 20.0 20.8 19.2
5.9 70.3 65.1 28.0 14.8 13.7
7.32 56.7 52.5 39.2 10.6 9.8