LTC4101 Просмотр технического описания (PDF) - Linear Technology

Номер в каталоге

Компоненты Описание

производитель

LTC4101

Smart Battery Charger Controller

Linear Technology 

LTC4101

OPERATION

to set the bottom MOSFET on time. The result is quasi-

constant frequency operation: the converter frequency

remains nearly constant over a wide range of output

voltages. This activity is diagrammed in Figure 3.

OFF

TGATE

ON

ON

BGATE

OFF

INDUCTOR

CURRENT

tOFF

Figure 3.

TRIP POINT SET

BY ITH VOLTAGE

4101 F01

The peak inductor current, at which ICMP resets the SR

latch, is controlled by the voltage on ITH. ITH is in turn

controlled by several loops, depending upon the situation

at hand. The average current control loop converts the

voltage between CSP and BAT to a representative current.

Error amp CA2 compares this current against the desired

current programmed by the IDAC at the IDC pin and adjusts

ITH for the desired voltage across RSENSE.

The voltage at BAT is divided down by an internal resis-

tor divider set by the VDAC and is used by error amp EA

to decrease ITH if the divider voltage is above the 1.19V

reference.

The amplifier CL1 monitors and limits the input current,

normally from the AC adapter, to a preset level (100mV/RCL).

At input current limit, CL1 will decrease the ITH voltage to

reduce charging current.

An overvoltage comparator, OV, guards against transient

overshoots (>7%). In this case, the top MOSFET is turned

off until the overvoltage condition is cleared. This feature

is useful for batteries that “load dump” themselves by

opening their protection switch to perform functions such

as calibration or pulse mode charging.

PWM Watchdog Timer

There is a watchdog timer that observes the activity on the

TGATE pin. If TGATE stops switching for more than 40μs,

the watchdog activates and turns off the top MOSFET for

about 400ns. The watchdog engages to prevent very low

frequency operation in dropout – a potential source of audible

noise when using ceramic input and output capacitors.

Charger Start-Up

When the charger is enabled, it will not begin switching

until the ITH voltage exceeds a threshold that assures initial

current will be positive. This threshold is 5% to 15% of the

maximum programmed current. After the charger begins

switching, the various loops will control the current at a

level that is higher or lower than the initial current. The

duration of this transient condition depends upon the loop

compensation, but is typically less than 1ms.

SMBus Interface

All communications over the SMBus are interpreted by the

SMBus interface block. The SMBus interface is a SMBus

slave device at address 0x12. All internal LTC4101 reg-

isters may be updated and accessed through the SMBus

interface, and charger controller as required. The SMBus

protocol is a derivative of the I2C bus (Reference “I2C-

Bus and How to Use It, V1.0” by Philips, and “System

Management Bus Specification,” Version 1.1, from the

SBS Implementers Forum, for a complete description of

the bus protocol requirements.)

All data is clocked into the shift register on the rising edge

of SCL. All data is clocked out of the shift register on the

falling edge of SCL. Detection of an SMBus Stop condi-

tion, or power-on reset via the VDD power-fail, will reset

the SMBus interface to an initial state at any time.

The LTC4101 command set is interpreted by the SMBus

interface and passed onto the charger controller block as

control signals or updates to internal registers.

Description of Supported Battery Charger Functions

The functions are described as follows (see Table 1 also):

FunctionName() 'hnn (command code)

Description: A brief description of the function.

Purpose: The purpose of the function, and an example

where appropriate.

• SMBus Protocol: Refer to Section 5 of the Smart

Battery Charger specification for more details.

*http://www.SBS-FORUM.org

4101fa

11

Share Link: