Detailed Description
The MAX4880 provides up to 28V overvoltage protection 
for low-voltage systems. When the input voltage at IN 
exceeds the overvoltage trip level (OVLO), the MAX4880 
turns off a low-cost, external n-channel MOSFET to prevent damage to the protected components and issues 
an overvoltage fault flag.
When the correct adapter is plugged in, the n-channel 
MOSFET is turned on. The output of the MOSFET is 
then connected to the internal current-limit switch that 
provides the charge-current path to the battery. When 
the battery reaches the trip voltage (4.2V), the internal 
switch turns off and BAT_OK asserts low, indicating 
that the battery has reached its full charged state. The 
internal switch turns back on only when the battery voltage drops by more than 200mV.
IN Overvoltage Lockout (OVLO)
The MAX4880 has a 5.6V typical overvoltage threshold 
(OVLO). When VINis higher than V
OVLO
, GATE goes
low to turn off the external n-channel MOSFET. An overvoltage FLAGV is asserted low to notify the processor 
of the fault condition.
IN Undervoltage Lockout (UVLO)
The MAX4880 includes a fixed 4.35V typical undervoltage-lockout level (UVLO). When VINis below the V
UVLO
(1.2V ≤ VIN≤ 4.35V), GATE goes low to turn off the 
external n-channel MOSFET. In addition, the driver for 
the internal switch (BTA-BTB) is also turned off; therefore, this switch is open. This ensures the reverse current, drained from the battery, is less than 1µA when 
the adapter is not present.
Fault Flag Output (
FLAGV
)
The FLAGV output signals the host system that there is 
a fault with the input voltage. FLAGV asserts low in 
response to either an overvoltage or an undervoltage 
fault. FLAGV stays low for 50ms after GATE turns on, 
before deasserting high.
FLAGV is an open-drain, active-low output. Connect a 
pullup resistor from FLAGV to the logic I/O voltage of 
the host system or to any voltage source up to 6V. 
FLAGV is invalid when driving EN high.
Battery-Voltage-Limit Flag Output
(
BAT_OK
)
The MAX4880 includes a battery-voltage-limit flag output (BAT_OK). BAT_OK asserts low to indicate the voltage on BTB exceeds the BTB trip level of 4.2V. 
BAT_OK deasserts high when the voltage on BTB falls 
by the BTB hysteresis voltage of more than 200mV.
BAT_OK is an open-drain, active-low output. Connect a 
pullup resistor from BAT_OK to the logic I/O voltage of 
the host system, or to any voltage source up to 6V. 
BAT_OK is invalid when driving EN high.
EN
Input
The MAX4880 features an active-low enable input (EN). 
Drive EN low or connect to ground for normal operation. Drive EN high to force the external n-channel 
MOSFET off, disabling FLAGV and BAT_OK.
Internal Current Limit (BTA to BTB)
The internal switch from BTA to BTB has a preset current-limit of 525mA (typ). If the load current from BTA to 
BTB reaches this current limit, the switch operates in 
the continuous mode, limiting the load current to the 
preset value.
The switch remains in the current-limit condition until the 
battery voltage on BTB exceeds 4.2V, or until the control 
bit CB is driven low to open the switch.
Internal Switch Control Input (CB)
The CB input controls the internal switch. When CB is 
high, the on/off state of the internal switch depends on 
the battery voltage level. The internal switch turns off 
when the battery voltage reaches the BTB trip level,
MAX4880
Overvoltage-Protection Controller with
Internal Disconnect Switch
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