MAX77751 datasheet(27/40 Pages) MAXIM

27 / 40 page

MAX77751

3.15A USB-C Autonomous Charger

for 1-Cell Li+ Batteries

www.maximintegrated.com

Maxim Integrated | 27

Reverse Boost Mode

The DC-DC converter topology of the MAX77751 allows it to operate as a buck converter or as a reverse boost converter.

The modes of the DC-DC converter are controlled by ENBST. When ENBST = high, the DC-DC converter operates in

reverse boost mode allowing it to source current to BYP and CHGIN. It is commonly referred to as OTG mode or a source

role.

The current through the BYP to CHGIN switch is limited to 1.5A minimum. When the reverse boost mode is enabled, the

unipolar CHGIN transfer function measures current going out of CHGIN.

The BYP to CHGIN switch automatically tries to retry after 300ms if CHGIN loading exceeds the 1.5A current limit. If the

overload at CHGIN persists, then the CHGIN switch toggles ON and OFF with approximately 60ms ON and approximately

300ms OFF.

Battery Overcurrent Protection During System Power-Up

The battery overcurrent protection during system power-up feature limits the battery to system current to ISYSPU if VSYS

is less than VSYSPU. This feature limits the surge current that typically flows from the battery to the device’s low-

impedance system to bypass capacitors during a system power-up. System power-up is anytime that energy from the

battery is supplied to SYS when VSYS < VSYSPU. This system power-up condition typically occurs when a battery is hot

inserted into an otherwise unpowered device.

When system power-up occurs due to hot-insertion into an otherwise unpowered device, a small delay is required for this

feature’s control circuits to activate. A current spike over ISYSPU might occur during this time.

Battery Overcurrent Protection Due to Fault

The MAX77751 protects itself, the battery, and the system from potential damage due to excessive battery discharge

current. Excessive battery discharge current can occur for several reasons such as exposure to moisture, a software

problem, an IC failure, a component failure, or a mechanical failure that causes a short circuit.

When the battery (BATT)-to-system (SYS) discharge current (IBATT) exceeds 6A for at least tBOVRC, then the MAX77751

disables the BATT-to-SYS discharge path (QBAT switch) and turns off buck.

Under the OCP fault condition, when SYS is low (VSYS < VSYSUP) for tOCP_RETRY, the MAX77751 restarts on its own

and attempts to pull up SYS again. If the fault condition remains, the whole cycle repeats until this fault condition is

removed.

Thermal Foldback

Thermal foldback maximizes the battery charge current while regulating the MAX77751 junction temperature. As shown

in Figure 7, when the die temperature exceeds the REGTEMP (TREG), a thermal limiting circuit reduces the battery

charger’s target current by 5% of the fast charge current per 1°C (ATJREG), which corresponds to 157.5mA/°C when the

fast charge current is 3.15A. The target charge current reduction is achieved with an analog control loop (i.e., not a digital

reduction in the input current).

MAX77751 Datasheet(PDF) 27 Page - Maxim Integrated Products