MAX8900BEWV+T Maxim Integrated Products, MAX8900BEWV+T Datasheet - Page 17

• Manufacturer Part Number: MAX8900BEWV+T
• Description: IC LI-ION/POLY BATT CHRGR 30WLP
• Manufacturer: Maxim Integrated Products

Specifications of MAX8900BEWV+T

• Function: Battery Monitor
• Battery Type: Lithium-Ion (Li-Ion), Lithium-Polymer (Li-Pol)
• Voltage - Supply: 3.4 V ~ 8.7 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 30-WLP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX8900_ is a full-featured, high-frequency switch-
mode charger for a 1-cell Li+ or Li-Poly battery. It
delivers up to 1.2A to the battery from 3.4V to 6.3V
(MAX8900A/MAX8900C) or 3.4V to 8.7V (MAX8900B).
Contact the factory for input operating voltage ranges
up to +20V. The 3.25MHz switch-mode charger is ide-
ally suited to small portable devices such as headsets
and ultra-portable media players because it minimizes
component size and heat.
Several features make the MAX8900_ ideal for high reli-
ability systems. The MAX8900_ is protected against input
voltages as high as +22V and as low as -22V. Battery
protection features include low voltage prequalification,
charge fault timer, die temperature monitoring, and bat-
tery temperature monitoring. The battery temperature
monitoring adjusts the charge current and termination
voltage as described in the JEITA (Japan Electronics and
Information Technology Industries Association) speci-
fication for safe use of secondary Li+ batteries. The
full title of the standard is A Guide to the Safe Use
of Secondary Lithium Ion Batteries in Notebook-Type
Personal Computers, April 20, 2007.
Charge parameters are easily adjustable with external
components. An external resistance adjusts the charge
current from 50mA to 1200mA. Another external resis-
tance adjusts the prequalification and done current
thresholds from 10mA to 200mA. The done current thresh-
old is very accurate achieving Q1mA at the 10mA level.
The charge timer is adjustable with an external capacitor.
A proprietary hysteretic current PWM control scheme
ensures high efficiency, fast switching, and physically tiny
external components. Inductor ripple current is internally
set to provide 3.25MHz. At very high duty factors, when
the input voltage is lowered close to the output volt-
age, the steady-state duty ratio does not allow 3.25MHz
operation because of the minimum off-time. The controller
then provides minimum off-time, peak current regula-
tion. Similarly, when the input voltage is too high to allow
3.25MHz operation due to the minimum on-time, the con-
troller becomes a minimum on-time, valley current regula-
tor. In this way, the ripple current in the inductor is always
as small as possible to reduce the output ripple voltage.
The inductor ripple current is made to vary with input and
output voltage in a way that reduces frequency variation.
Rating and JEITA Battery Temperature Monitoring
1.2A Switch-Mode Li+ Chargers with ±22V Input
Detailed Description
Control Scheme
To prevent input current transients, the rate of change
of the input current (di/dt) and charge current is limited.
When the input is valid, the charge current ramps from
0mA to the fast-charge current value in 1.5ms. Charge
current also soft-starts when transitioning from the
prequalification state to the fast-charge state. There is
no di/dt limiting when transitioning from the done state
to the fast-charge state (Figures 7 and 8). Similarly, if
R
able resistor at SETI as shown in Figure 2 there is no di/
dt current limiting.
As shown in Figure 4, a resistor from SETI to ground
(R
supports values of I
R
Determine the optimal I
ering the characteristics of the battery and the capabili-
ties of the charge source.
Depending on its mode of operation, the MAX8900_
controls the voltage at SETI to be between 0V and 1.5V.
Avoid adding capacitance directly to the SETI pin that
exceeds 10pF.
As a protection feature, if the battery temperature is
between the T2 and T4 thresholds and SETI is shorted
to ground, then the MAX8900_ latches off the battery
charger and enters the timer fault state. This protection
feature is disabled outside of fast-charge, top-off, done
mode and inside thermal foldback. Furthermore, if SETI is
unconnected, then the battery fast-charge current is 0A.
SETI
SETI
SETI
Example 1: If you are using a 5V Q5% 1A charge
source along with an 800mAh battery that has a 1C
fast-charge rating, then choose R
Q1%. This value provides a typical charge current
of 770mA. Given the Q2% six sigma limit on the
MAX8900_ fast-charge current accuracy along with
the Q1% accuracy of the resistor, we can reasonably
expect that the 770mA typical value has an accuracy
of Q2.2% (2.2 ≈ sqrt(2
since the MAX8900_ charger uses a step-down con-
verter topology, we can guarantee that the input cur-
rent is less than or equal to the output current so we
do not violate the 1A rating of the charge source.
is changed suddenly when using a switch or vari-
as follows:
) sets the fast-charge current (I
Setting the Fast-Charge Current (SETI)
I
FC
FC
= 3405V/R
FC
from 50mA to 1200mA. Select
2
+ 1
for a given system by consid-
2
)) or Q17mA. Furthermore,
SETI
FC
SETI
). The MAX8900_
to be 4.42kI
Soft-Start
17