DS2792 datasheet(13/40 Pages) MAXIM

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DS2792 Programmable Fuel Gauge with UART Interface

13 of 40

DS2792 POWER MODES

When power is first applied to the DS2792, a power-on-reset (POR) circuit transitions the IC to brownout state

where cell voltage is monitored. If VDD voltage is above the brownout threshold VBO, the DS2792 enters CPU mode

and begins code execution. Firmware determines if the IC switches to ANALOG mode or low-power SLEEP mode

when a STOP halts CPU operation.

The DS2792 enters SLEEP mode after a CPU STOP if the ADC and all internal timers are disabled and the

suspend timer is off. In SLEEP mode, all IC operation becomes inactive except for external activity interrupts.

Brownout detection does not occur in SLEEP mode. Any interrupt generated by UART communication or external

input on ports P0.0 or P0.1 will transition the DS2792 from SLEEP to brownout to verify cell voltage before

returning to CPU mode. If the suspend timer is enabled, the IC will transition from SLEEP to ANALOG mode if a

suspend timeout occurs.

The DS2792 enters ANALOG mode after a CPU STOP if any one of the following is active: the ADC, the interval

timer, or the watchdog timer. An external interrupt or an interrupt from any active internal circuit causes the DS2792

to transition back to CPU mode to service the condition.

If the DS2792 is in ANALOG or CPU mode, and VDD falls below VBO, a brownout condition occurs and the DS2792

enters the brownout state. In brownout state, the processor is halted without changing the instruction pointer. If VDD

voltage rises above VBO within a time of tSU:OSCI, the DS2792 returns to CPU mode and generates a brown-out

interrupt (if enabled). Otherwise, if VDD remains below VBO for tSU:OSCI, the DS2792 again enters SLEEP mode and

waits to receive an interrupt.

Note that the supply rise time at initial power up of the IC must be faster than tSU:OSCI to prevent the DS2792 from

entering SLEEP mode prior to software enabling external interrupts. If this situation occurs, the DS2792 remains in

SLEEP until power cycled.

Figure 5. DS2792 State Diagram

Code Execution

CPU Disabled.

ADC Active

External Interrupts

Monitored

Brown-Out

Timeout

t > tSU:OSCI

Brown-Out

VDD < VBO

External

Interrupt

CPU STOP

Analog Circuits Inactive

Brown-Out Recovery

VDD > VBO for tSU:OSCI

Brown-Out

VDD < VBO

Interrupt

Power On Reset

CPU STOP

Analog Circuits Active

Suspend Timeout

Suspend Timer Enabled

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