MAX1612 Datasheet, PDF (11/12 Pages) Maxim Integrated Products – Bridge-Battery Backup Controllers for Notebooks

Bridge-Battery Backup Controllers
for Notebooks
Table 5. Surface-Mount Inductor Information
MANUFACTURER
AND PART
Sumida CD43-8R2
Sumida CD43-150
Sumida CD54-100
Sumida CD54-150
Sumida CD54-220
INDUCTANCE
(µH)
8.2
15
10
15
22
RESISTANCE
(Ω)
0.132
0.235
0.100
0.140
0.180
RATED CURRENT
(A)
1.26
0.92
1.44
1.30
1.11
HEIGHT
(mm)
3.2
3.2
4.5
4.5
4.5
where V_OUT is the DC-DC converter’s output voltage
and V_TRIP is the voltage level the main battery must fall
below to trip the low-battery comparator. For example,
for a +5V boost DC-DC output, a 4.75V main battery
trip level is feasible. For this case, R1 = 750kΩ, R2 =
26kΩ, and R3 = 474kΩ.
Step 6: Select a resistor value to set the charging cur-
rent. The resistor value at ISET limits the current
through the switch for bridge-battery charging. There is
a voltage drop across the high-voltage switch (see
Electrical Characteristics) with a typical value of 1V.
The maximum charge current through the internal high-
voltage switch is 10mA.
R_ISET = (V_CHARGE - V_SWITCH - V_BBATT) / I_CHARGE
where V_CHARGE is the charging supply voltage,
V_SWITCH is the drop across the high-voltage internal
switch, V_BBATT is the bridge battery voltage, and
I_CHARGE is the charge current (in amperes).
Stand-Alone Application
To reduce cost and save space, the MAX1612/
MAX1613 can be operated in a stand-alone configura-
tion, which eliminates the need for a microcontroller. A
stand-alone configuration could also reduce the work-
load of an existing microcontroller in the system, thus
allowing these unused I/Os to be used for other appli-
cations.
Figure 3 shows the MAX1612/MAX1613 operating with-
out the microcontroller by using the low-battery detec-
tor to monitor the main battery. If the main battery is too
low, LBO pulls BBON and DCMD low to start the DC-
DC step-up converter and allow the bridge battery to
discharge. If the bridge battery requires charging,
FULL pulls CCMD low to start the battery charging
process. If both CCMD and DCMD are low, discharg-
ing takes precedence and the bridge battery keeps the
boost DC-DC converter active.
Microcontroller-Based Application
The MAX1612/MAX1613 are also suited to operate in a
microcontroller-based system. A microcontroller-based
application provides more flexibility by allowing for sep-
arate, independent control of the charging process, the
DC-DC converter, and the counter. Independent con-
trol can be beneficial in situations where other subsys-
tems are operating, so that automatic switchover of
power might create some timing issues. If necessary, a
microcontroller can be used to reset the counter by tak-
ing ISET low. Another advantage of a microcontroller-
based system is the ability to stop charging the bridge
battery during a fault condition.
Figure 4 shows an example of how the MAX1612/
MAX1613 can be interfaced to a MAX1630 to deliver
the input voltage to the main DC-DC converter. In this
example, the microcontroller monitors the main bat-
tery’s status and switches over to the bridge battery
when V_MAIN falls below a specified trip level (see
Design Procedure). When V_MAIN falls below the LBI
threshold, LBO goes low. This signals the microcon-
troller, via an I/O, to switch over to the bridge battery as
the input source to the system main DC-DC converter.
In this application, the microcontroller also initiates the
bridge-battery charging process. When CCMD goes
low with DCMD high, the battery is charged through the
internal switch. The counter increments until it overflows
and FULL goes high, indicating a full charge. The
microcontroller I/O can read and write the appropriate
states to control the execution and timing of the entire
process.
If the main DC-DC is supplied by the main source, the
MAX1612/MAX1613’s step-up converter turns off, mini-
mizing power consumption. The device typically draws
only 18µA of quiescent current under this condition.
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