MAX8730 Просмотр технического описания (PDF) - Maxim Integrated

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MAX8730

Low-Cost Battery Charger

Maxim Integrated 

Low-Cost Battery Charger

reaches 100% depth of discharge, it is then recharged.

Connect MODE to GND to place the MAX8730 in

relearn mode. In relearn mode, charging stops, PDS

turns off, and PDL turns on.

To utilize relearn mode, there must be two source-con-

nected MOSFETs to prevent the AC adapter from sup-

plying current to the system through the P1’s body

diode. Connect SRC to the common source node of

two MOSFETs.

The system must alert the user before performing a

relearn cycle. If the user removes the battery during

relearn mode, the MAX8730 detects battery removal

and reconnects the AC adapter (PDS turns on and PDL

turns off). Battery removal is detected when the battery

falls below 5xRELTH.

LDO Regulator, REF, and SWREF

An integrated linear regulator (LDO) provides a 5.35V

supply derived from SRC, and delivers over 10mA of

load current. LDO biases the 4.2V reference (REF) and

most of the control circuitry. Bypass LDO to GND with a

1µF ceramic capacitor. An additional standalone 1%,

3.3V linear regulator (SWREF) provides 20mA and can

remain on when the adapter is absent. Set REFON low

to disable SWREF. Set REFON high for normal opera-

tion. SWREF must be enabled to allow charging.

Operating Conditions

• Adapter present: The adapter is considered to be

present when:

VSRC > 8V (max)

VASNS > VBATT - 300mV (max)

• Charging: The MAX8730 allows charging when:

VSRC - VCSIN > 100mV (typ)

3 or 4 cells selected (MODE float or high condition)

ICTL > 110mV (max)

INPON is high

• Relearn mode: The MAX8730 enables relearn mode

when:

VBATT / 5 > VRELTH

MODE is grounded

DC-DC Converter

The MAX8730 employs a step-down DC-DC converter

with a p-channel MOSFET switch and an external

Schottky diode. The MAX8730 features a constant-cur-

rent-ripple, current-mode control scheme with cycle-by-

cycle current limit. For light loads, the MAX8730

operates in discontinuous conduction mode for

improved efficiency. The operation of the DC-DC con-

troller is determined by the following four comparators

as shown in the functional block diagram in Figure 3:

• The IMIN comparator sets the peak inductor current

in discontinuous mode. IMIN compares the control

signal (LVC) against 100mV (corresponding to

222mA when RS2 = 30mΩ). The comparator termi-

nates the switch on-time when IMIN exceeds the

threshold.

• The CCMP comparator is used for current-mode reg-

ulation in continuous conduction mode. CCMP com-

pares LVC against the charging-current feedback

signal (CSI). The comparator output is high and the

MOSFET on-time is terminated when the CSI voltage

is higher than LVC.

• The IMAX comparator provides a cycle-by-cycle cur-

rent limit. IMAX compares CSI to 2.95V (correspond-

ing to 6.56A when RS2 = 30mΩ). The comparator

output is high and the MOSFET on-time is terminated

when the current-sense signal exceeds 6.56A. A new

cycle cannot start until the IMAX comparator output

goes low.

• The OVP comparator is used to prevent overvoltage

at the output due to battery removal. OVP compares

BATT against the set voltage; see the Setting Charge

Voltage section. When BATT is 20mV x CELLS above

the set value, OVP goes high and the MOSFET on-

time is terminated.

BATT/CELLS

VCTLSETPOINT + 20mV

CSI

2.95V

LVC

OVP

IMAX

CCMP

R

Q

DH

DRIVER

IMIN

100mV

BATT

OFF-TIME

COMPUTE

S

Q

OFF-TIME

ONE-SHOT

Figure 3. DC-DC Converter Block Diagram

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