MAX8939_11 Datasheet, PDF (21/44 Pages) Maxim Integrated Products – System Power Management for Mobile Handset

System Power Management
for Mobile Handset
To qualify charge as done, the current has to be below top-
off current threshold or a timeout has occurred. To main-
tain the battery voltage, the charger can be programmed
to restart once the battery voltage drops below a program-
mable threshold. When restart is enabled and the battery
voltage drops below the restart threshold, the charger
starts a new charging cycle by entering fast-charge.
If restart is disabled, the charger stops charging when
done and does not maintain the battery voltage. When
charge done occurs, an IRQ is sent to the host and a
flag is set in register 0x03. Reading the register disables
the charger. The charger can be enabled by writing to
register 0x09 bit 0 (CHG_EN). If one of the safety timers
(fast-charge or top-off) expires, an interrupt is sent to
the host and a flag is set in register 0x03. The charger is
disabled 5s after the safety times out.
If, at any point while charging the battery, the die tem-
perature approaches the thermal regulation threshold
(+100°C default), the ICs reduce the charging current
so that the die temperature does not this temperature.
This feature not only protects the ICs from overheating,
but also allows the higher charge current without risking
damage to the system.
Note all charger registers are reset to their default set-
tings by power-on reset (POR) or RESET.
Charger Disable (CHG)
CHG is a logic input used to enable or disable the char-
ger. Connect CHG high to disable the charger, or low to
enable the charger. CHG operates when BATT is below
its operating range and when BATT is valid, but prior
to accessing the CHG_CONTROL_A register. Once the
CHG_CONTROL_A resister is accessed, either by reading
or writing, the register CHG_CONTROL_A. CHG_EN bit
controls the charger status and the state of CHG is ignored
(although it still triggers an interrupt unless masked).
SAFE_OUT
SAFE_OUT is an LDO powered from the CHG_IN input.
SAFE_OUT is enabled when a charger is detected (4.1V
< VCHG_IN < 10V (MAX8939) or 6.25V (MAX8939A)) and
provides a protected output regulated to 4.9V (5V max).
Typically, SAFE_OUT is used to power low-voltage USB
systems and the precharge indicator.
Indicator LED
The LED3 output sinks 3mA (typ) to drive an indica-
tor LED. LED3 is on by default and can be controlled
by the host by I²C (bit 7 of the REG_CONTROL
register). Typically, this LED indicates charge status
and SAFE_OUT powers the LED as shown in Figure 1.
WATCHDOG_EN
CHG_EN/DET
RESET TIMER
CHARGER
DISABLED
WATHCDOG
TIMER
IRQ
HOST READ
OR WRITE
CHARGE
REGISTERS
THE WATCHDOG
TIMER EXPIRES
t < 5s
t = 5s
Figure 4. Watchdog Timing Diagram
Charge Current Monitor (CHG_MON)
CHG_MON is an analog output used to monitor the
charge current. CHG_MON outputs a voltage propor-
tional to the charge current with 1.2V corresponding to
the programmed fast-charge current.
The CHG_MON output includes ripple from loads on the
battery. If this is not desired, connect a small 0.01FF to
0.1FF capacitor at the input of the ADC to filter the ripple.
Charger Watchdog Timer
During battery fast-charge, a watchdog monitoring func-
tion can be activated to ensure that the host processor
has control of the charge algorithm. The watchdog timer
is enabled through register REG_CONTROL bit WD_EN.
When the charger is enabled by CHG_EN or CHG_IN, the
watchdog timer starts counting. Within 5s of enabling the
charger, the host must read or write register 0x09 or 0x0A
to indicate it is alive. This resets the watchdog timer and
the host must continue to read or write register 0x09 or
0x0A in intervals of under 5s. If the host takes more than
5s for reading or writing these registers, the watchdog
timer expires, generates an interrupt, flags the watchdog
timeout in register 0x03, and disables the charger.
Linear Regulators
The ICs include four low-dropout linear regulators
(LDOs). All LDOs are designed for low dropout, low
noise, high PSRR, and low quiescent current to maximize
battery life. When the battery voltage is above the UVLO
upper threshold, the ICs’ LDOs are ready to be turned on
through the I²C interface. The guaranteed current drive
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