MAX1873S Просмотр технического описания (PDF) - Maxim Integrated

Номер в каталоге

Компоненты Описание

производитель

MAX1873S

Simple Current-Limited Switch-Mode Li+ Charger Controller

Maxim Integrated 

Simple Current-Limited Switch-Mode

Li+ Charger Controller

CSSN

CSSP

CCS

CCV

CCI

ICHG

/EN

IOUT

VADJ

5.4

REGULATOR

VL

UNDERVOLTAGE

COMPARATOR

SHUTDOWN

BATT

FOR ALL

BLOCKS

DCIN

VH

CONTROL

LOGIC

EXT

DRIVER

VH

VOLTAGE

GND

ERROR AMP

CSB

CURRENT

ERROR AMP

BATT

9R

A=1

GND

R

R

REF

4.2V

REFERENCE

Figure 2. Functional Block Diagram

Charging-Current Regulator

The charging-current regulator limits the battery charg-

ing current. Current is sensed by the current-sense

resistor (RCSB in Figure 1) connected between BATT

and CSB. The voltage on ICHG/EN can also adjust the

charging current. Full-scale charging current (ICHG =

0.2V / RCSB) is achieved by connecting ICHG/EN to

REF. See Setting the Charging-Current Limit section for

more details.

The charging-current error amplifier is compensated at

CCI (Figure 1). A 47nF capacitor from CCI to GND pro-

vides suitable performance for most applications.

Input-Current Regulator

The input-current regulator limits the source current by

reducing charging current when the input current

reaches the set input-current limit. In a typical portable

design, system load current will normally fluctuate as

portions of the system are powered up or put to sleep.

Without the benefit of input-current regulation, the input

source would have to be able to supply the maximum

system current plus the maximum charger-input cur-

rent. The MAX1873 input-current loop ensures that the

system always gets adequate power by reducing

charging current as needed. By using the input-current

limiter, the size and cost of the AC adapter can be

reduced. See Setting the Input-Current Limit section for

design details.

Input current is measured through an external sense

resistor, RCSS, between CSSP and CSSN. The input-

current limit feature may be bypassed by connecting

CSSP to CSSN.

The input-current error amplifier is compensated at

CCS. A 47nF capacitor from CCS to GND provides suit-

able performance for most applications.

PWM Controller

The pulse-width modulation (PWM) controller drives the

external MOSFET at a constant 300kHz to regulate the

charging current and voltage while maintaining low

noise. The controller accepts inputs from the CCI, CCV,

and CCS error amplifiers. The lowest signal of these

three drives the PWM controller. An internal clamp limits

the noncontrolling signals to within 200mV of the con-

trolling signal to prevent delay when switching between

the battery-voltage control, charging-current control,

and input-current regulation loops.

Shutdown

The MAX1873 stops charging when ICHG/EN is pulled

low (below 0.5V) and shuts down when the voltage at

DCIN falls below the voltage at BATT. In shutdown, the

internal resistive voltage-divider is disconnected from

BATT to reduce the battery drain. When AC-adapter

power is removed, or when the part is shut down, the

MAX1873 typically draws 1.5µA from the battery.

Source Undervoltage Shutdown (Dropout)

The DCIN voltage is compared to the voltage at BATT.

When the voltage at DCIN drops below BATT + 50mV,

the charger turns off, preventing drain on the battery

when the input source is not present or is below the

battery voltage.

A diode is typically connected between the input

source and the charger input. This diode prevents the

battery from discharging through the body diode of the

high-side MOSFET should the input be shorted to GND.

It also protects the charger, battery, and systems from

reversed polarity adapters and negative input voltages.

10 ______________________________________________________________________________________

Share Link: