MAX20303 datasheet(54/152 Pages) MAXIM

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Current Sink

In addition to several voltage regulators, the MAX20303

also includes three low-dropout linear current regulators

from LED_ to GND. The sink current of each current

regulator is independently programmable through its

respective LED_ISet[4:0] bits in direct registers LED_

Direct (0x2D–0x2F). The current regulators can be

programmed to sink 0.6mA to 30mA with configurable step

sizes and are ideal for sinking current from external LEDs.

The LEDIStep[1:0] bits in direct register LEDStepDirect

(0x2C) control the size of the current steps for all current

sinks. This step size also sets an effective limit on the

sinking current as the number of steps remains constant

while the step size varies. Current sinks are enabled

through an I2C command, by an internal charger status

signal, or by an external MPC pin allowing for LED status

indicators. Note that the current sinks always draw

quiescent current when tied to an MPC_ control or status

signal regardless of the MPC_ or status state.

System Load Switch

An internal 80mΩ (typ) MOSFET connects BAT to SYS

when no voltage source is available on CHGIN. When an

external source is detected at CHGIN, this switch opens

and SYS is powered from the input source through the

input current limiter. The SYS-to-BAT switch also prevents

VSYS from falling below VBAT when the system load

exceeds the input current limit. If VSYS drops to VBAT

due to the current limit, the BAT-SYS switch turns on so

the load is supported by the battery. If the system load

continuously exceeds the input current limit, the battery

is not charged. This is useful for handling loads that are

nominally below the input current limit but have high

current peaks exceeding the input current limit. During

these peaks, battery energy is used, but at all other times

the battery charges.

Smart Power Selector

The smart power selector seamlessly distributes power

from the external CHGIN input to the BAT and SYS

nodes. With both an external adapter and battery

connected, the smart power selector basic functions are:

● When the system load requirements are less than

the input current limit, the battery is charged with

residual power from the input.

● When the system load requirements exceed the

input current limit, the battery supplies supplemental

current to the load.

● When the battery is connected and there is no external

power input, the system is powered from the battery.

Input Limiter

The input limiter distributes power from the external

adapter to the system load and battery charger. In

addition to the input limiter’s primary function of passing

power to the system load and charger, it performs several

additional functions to optimize use of available power.

Invalid CHGIN Voltage Protection: If CHGIN is above

the overvoltage threshold, the device enters overvoltage

lockout (OVL). OVL protects the MAX20303 and down-

stream circuitry from high-voltage stress up to +28V and

down to -5.5V. During positive OVL, the internal circuit

remains powered and an interrupt is sent to the host.

The negative voltage protection disconnects CHGIN and

the device is powered only by BAT. The charger turns off

and the system load switch closes, allowing the battery to

power SYS. CHGIN is also invalid if it is less than VBAT,

or less than the USB undervoltage threshold. With an

invalid input voltage, the BAT-SYS load switch closes and

allows the battery to power SYS.

CHGIN Input Current Limit: The CHGIN input current

is limited to prevent input overload. The input current

limit is controlled by I2C. To accommodate systems with

a high in-rush current, the limiter includes a program-

mable blanking time during which the input current limit

increases to ILIM_MAX.

Thermal Limiting: In case the die temperature exceeds

the normal limit (TCHG_LIM), the MAX20303 attempts

to limit temperature increase by reducing the input

current from CHGIN. In this condition, the system load has

priority over the charger current, so the input current is

first reduced by lowering the charge current. If the junction

temperature continues to rise and reaches the maximum

operating limit (TCHGIN_SHDN), no input current is drawn

from CHGIN and the battery powers the entire system load.

Adaptive Battery Charging: While the system is powered

from CHGIN, the charger draws power from SYS to

charge the battery. If the total load exceeds the input

current limit, an adaptive charger control loop reduces

charge current to prevent VSYS from collapsing. When

the charge current is reduced below 50% due to ILIM or

TCHG_LIM limits, the timer clock operates at half speed.

When the charge current is reduced below 20% due to

ILIM or TCHG_LIM limits, the timer clock is paused.

Fast-Charge Current Setting: The MAX20303 uses an

external resistor connected from SET to GND to set the

fast-charge current. The precharge and charge-termina-

tion currents are programmed as a percentage of this

value by opcode 0x14. The fast-charge current resistor

can be calculated as:

RSET = KSET x VSET/IFChg

MAX20303

Wearable Power Management Solution

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