MAX8939EWVT datasheet(21/43 Pages) MAXIM

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______________________________________________________________________________________ 21

System Power Management

for Mobile Handset

turned on through the I2C interface. The guaranteed cur-

rent drive capabilities for the LDOs are 400mA for LDO1,

200mA for LDO2 and LDO3, and 100mA for LDO4. The

output voltage for each LDO is programmable through

the I2C interface from 1.7V to 3.2V in 0.1V steps.

LDO1 can be enabled through a hardware pin

LDO1_EN. By connecting this pin to a logic-high level,

the LDO enables automatically when the UVLO upper

threshold is reached. The LDO can also be controlled

by the LDO1_EN bit of the REG_CONTROL. When the

LDO1_EN bit is written to, the LDO1 enable state reflects

the value written, overriding the state of the LDO1_EN

pin. When the state of the LDO1_EN pin changes, the

LDO1 enable state is determined by the new state of the

LDO1_EN pin, overriding the LDO1_EN bit value. This

allows the system software to reduce quiescent power

consumption by turning off LDO1 without impacting

other logic that may utilize the same hardware control

used for the LDO1_EN pin.

Interrupt Request (IRQ)

IRQ is an active-low, open-drain output signal (requires

an external pullup resistor) that indicates that an interrupt

event has occurred and that the event and status infor-

mation are available in the event/status registers. Such

information includes temperature and voltages inside

the MAX8939, fault conditions, etc. The event registers

hold information about events that have occurred in the

MAX8939. Events are triggered by a status change in

the monitored signals. When an event bit is set in the

event register, the IRQ signal is asserted (unless IRQ is

masked by a bit in the IRQ mask register). The IRQ is

also masked during power-up and is not released until

the event registers have been read. Each event register

is reset to its initial condition after being read. The IRQ is

not released until all the event registers have been read.

New events that occur during read-out of the event reg-

isters are held until all the event registers have been read

to, ensuring that the host processor does not miss them.

PWR_ON_CMP

PWR_ON_CMP is an open-drain output used to wake-up

a sleeping baseband. PWR_ON_CMP is activated when

a charger is detected (VCHG_IN is between 4.1V and

10V) and the battery voltage is above the UVLO thresh-

old. If the battery has already reached the UVLO upper

threshold, the charger is detected by a rising edge.

When such an event is detected, the MAX8939 starts

pulsing the PWR_ON_CMP output every 50ms, with a

duty cycle of 98%. See Figure 5.

The event is also signaled by IRQ, which is asserted

when the UVLO upper threshold is reached and the

CHG_DET bit is set in register 0x04 (bit 6). The MAX8939

continues pulsing PWR_ON_CMP until the EVENT

registers are read, then the register is cleared and

PWR_ON_CMP and IRQ return to high impedance.

The events causing the PWR_ON_CMP activation are

triggered by a rising edge signal that must remain valid

for the duration of a 10ms debounce filter.

RESET_IN

RESET_IN is an active-low input signal to the MAX8939 and

is used to provide a full system reset inside the MAX8939.

As long as RESET_IN is asserted, the MAX8939 is not

able to do anything (except the charger), until RESET_IN

is released. All registers are cleared except the STATUS

and EVENT registers. When RESET_IN is asserted, the

EVENT_B bit RESET is set. If the CHG_IN voltage is valid

and RESET_IN is asserted, the charger operates in its

default state.

OUT1 Step-Up DC-DC Converter

OUT1 is a fixed-frequency PWM step-up converter.

The converter switches an internal power MOSFET and

synchronous rectifier at a constant 2MHz frequency with

varying duty cycle up to 75% to maintain constant out-

put voltage as the input voltage and load current vary.

Figure 5. Wake-Up Sequence

1ms

50ms

UVLO

UPPER THRESHOLD

UVLO AND CHARGER

DETECTION EVENT

ALL EVENT REGISTERS

ARE READ. PWR_ON_CMP

AND IRQ ARE CLEARED

CHARGER

REMOVAL

EVENT

ALL EVENT

REGISTERS

ARE READ.

IRQ IS CLEARED.

VCHG_IN

VBATT

IRQ

PWR_ON_CMP

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