MAX77751 datasheet(26/40 Pages) MAXIM

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MAX77751

3.15A USB-C Autonomous Charger

for 1-Cell Li+ Batteries

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Top-Off State

As shown in Figure 6, the top-off state can only be entered from the fast-charge CV state when the charger current

decreases below ITO for tTERM. In the top-off state, the battery charger tries to maintain VBATTREG across the battery,

and typically, the charge current is less than or equal to ITO.

The smart power selector control circuitry might reduce the charge current lower than the battery can otherwise consume

for any of the following reasons:

• The charger input current is lower than the input current limit

• The charger input voltage is low

• The charger is in thermal foldback

• The system load is consuming adapter current. Note that the system load always gets priority over the battery charge

current.

The following events cause the state machine to exit this state:

• After being in this state for the top-off time (tTO), the charger enters the next state in the charging cycle, done state.

• If VBATT < VBATTREG – VRSTRT, the charger goes back to the fast-charge CC state

Done State

As shown in Figure 6, the battery charger enters its done state after the charger has been in the top-off state for tTO.

The state machine exits this state if VBATT < VBATTREG – VRSTRT and the charger goes back to the fast-charge CC

state

In the done state, the charge current into the battery (ICHG) is 0A, and the charger presents a very low quiescent current

to the battery. If the system load presented to the battery is low (<<100μA), then a typical system can remain in the done

state for many days. If left in the done state long enough, the battery voltage decays below the restart threshold (VRSTRT)

and the charger state machine transitions back into the fast-charge CC state. There is no soft-start (di/dt limiting) during

the done state to fast-charge state transition.

Timer Fault State

The battery charger provides a charge timer to ensure safe charging. As shown in Figure 6, the charge timer prevents

the battery from charging indefinitely. The time that the charger is allowed to remain in each of its prequalification states

is tPQ. The time that the charger is allowed to remain in the fast-charge CC and fast-charge CV states is tFC. Finally, the

time that the charger is in the top-off state is tTO. Upon entering the timer fault state, STAT becomes Hi-Z.

In the timer fault state, the charger is off. The charger input can be removed and re-inserted to exit the timer fault state

(see the “any state” bubble in the lower left of Figure 6).

Thermal Shutdown State

As shown in Figure 6, the thermal shutdown state occurs when the battery charger is in any state and the junction

temperature (TJ) exceeds the device’s thermal shutdown threshold (TSHDN). When TJ is close to TREG, the charger

folds back the charge current to 0A so that the charger is effectively off (see the Thermal Foldback section).

In the thermal shutdown state, the charger is off.

MAX77751 Datasheet(PDF) 26 Page - Maxim Integrated Products