CDH2D09 datasheet(25/44 Pages) MAXIM

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PMIC with Integrated Charger and

Smart Power Selector for Handheld Devices

______________________________________________________________________________________

with a single power input to operate from either an AC-

to-DC adapter or USB host (see Table 1).

A thermal-limiting circuit reduces the battery charger

rate and external power-source current to prevent the

MAX8671X from overheating.

System Load Switch

An internal 80m

Ω (RBS) MOSFET connects SYS to BAT

when no voltage source is available at DC or USB.

When an external source is detected at DC or USB, this

switch is opened and SYS is powered from the valid

input source through the Smart Power Selector.

When the system load requirements exceed the input

current limit, the battery supplies supplemental current

to the load through the internal system load switch. If

the system load continuously exceeds the input current

limit, the battery does not charge, even though external

power is connected. This is not expected to occur in

most cases because high loads usually occur only in

short peaks. During these peaks, battery energy is

used, but at all other times the battery charges.

USB Power Input (USB)

USB is a current-limited power input that supplies the

system (SYS) up to 500mA. The USB to SYS switch is a

linear regulator designed to operate in dropout. This lin-

ear regulator prevents the SYS voltage from exceeding

5.3V. USB is typically connected to the VBUS line of the

universal serial bus (USB) interface. As shown in Table

1, USB supports three different current limits that are

set with the PEN2 and USUS digital inputs. These cur-

rent limits are ideally suited for use with USB power.

The operating voltage range for USB is 4.1V to 6.6V,

but it can tolerate up to 14V without damage. When the

USB input voltage is below the undervoltage threshold

(VUSBL, 4V typ) it is considered invalid. Similarly, if the

USB voltage is above the overvoltage threshold

(VUSBH, 6.9V typ) it is considered invalid. When the

USB voltage is below the battery voltage, it is consid-

ered invalid. The USB power input is disconnected

when the USB voltage is invalid. As shown in Table 1,

when power is available at the DC input, it has priority

over the USB input. Bypass USB to ground with at least

a 4.7µF capacitor.

To support USB power sources at the USB input drive

PEN2 and USUS to select between three internally set

USB-related current limits as shown in Table 1. Choose

100mA for low-power USB mode. Choose 500mA for

high-power USB mode. Choose suspend to reduce the

USB current to 0.11mA (typ) for both USB suspend

mode and unconfigured OTG mode. To comply with

the USB 2.0 specification, each device must be initially

configured for low power. After USB enumeration, the

device can switch from low power to high power if

given permission from the USB host. The MAX8671X

does not perform enumeration. It is expected that the

system communicates with the USB host and com-

mands the MAX8671X through its PEN1, PEN2, and

USUS inputs. When the load exceeds the input current

limit, SYS drops to 82mV below BAT and the battery

supplies supplemental load current.

The MAX8671X reduces the USB current limit by 5%/°C

when the die temperature exceeds +100°C. The sys-

tem load (ISYS) has priority over the charger current, so

input current is first reduced by lowering charge cur-

rent. If the junction temperature still reaches +120°C in

spite of charge current reduction, no input current is

drawn from USB; the battery supplies the entire load

and SYS is regulated below BAT by VBSREG. Note that

this on-chip thermal-limiting circuit is not related to and

operates independently from the thermistor input.

If the USB power input is not required, connect USB to

ground or leave it unconnected. When both DC and

USB inputs are powered, the DC input has priority.

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