LTC4101 Просмотр технического описания (PDF) - Linear Technology

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LTC4101

Smart Battery Charger Controller

Linear Technology 

LTC4101

TEST CIRCUIT

1.19V +

–

EA

–

+

21 22

18

CSP

BAT VSET

VDAC

BAT

LT1055

LTC4101

19

ITH

0.7V

4101 TC01

VTOL

=

VBAT – VVDAC

VVDAC

• 100

FOR VVDAC = 4.176V(0 x 1050)

DCIN = 21V

CLN = CLP = 20V

VDD = 3.3V

OPERATION

Overview (Refer to Block Diagram)

The LTC4101 is composed of a battery charger section, a

charger controller, a 10-bit DAC to control charger current,

an 11-bit DAC to control charger voltage, a SafetySignal

decoder, limit decoder and an SMBus controller block. If

no battery is present, the SafetySignal decoder indicates

a RES_OR condition and charging is disabled by the

charger controller (CHGEN = Low). Charging will also be

disabled if DCDIV is low, or the SafetySignal is decoded

as RES_HOT. If a battery is inserted and AC power is

connected, the battery will be charged with an 80mA

“wake-up” current. The wake-up current is discontinued

after tTIMEOUT if the SafetySignal is decoded as RES_UR

or RES_C0LD, and the battery or host doesn’t transmit

charging commands.

The SMBus interface and control block receives Charg-

ingCurrent() and ChargingVoltage() commands via the

SMBus. If ChargingCurrent() and ChargingVoltage()

command pairs are received within a tTIMEOUT interval, the

values are stored in the current and voltage DACs and the

charger controller asserts the CHGEN line if the decoded

SafetySignal value will allow charging to commence. Charg-

ingCurrent() and ChargingVoltage() values are compared

against limits programmed by the limit decoder block; if

the commands exceed the programmed limits these limits

are substituted and overrange flags are set.

The charger controller will assert SMBALERT whenever

a status change is detected, namely: AC_PRESENT, BAT-

TERY_PRESENT, ALARM_INHIBITED, or VDD power-fail.

The host may query the charger, via the SMBus, to obtain

ChargerStatus() information. SMBALERT will be deasserted

upon a successful read of ChargerStatus() or a successful

Alert Response Address (ARA) request.

Battery Charger Controller

The LTC4101 charger controller uses a constant off-time,

current mode step-down architecture. During normal

operation, the top MOSFET is turned on each cycle when

the oscillator sets the SR latch and turned off when the

main current comparator ICMP resets the SR latch. While

the top MOSFET is off, the bottom MOSFET is turned

on until either the inductor current trips the current

comparator IREV, or the beginning of the next cycle.

The oscillator uses the equation,

tOFF

=

(VDCIN –

(VDCIN •

VBAT )

fOSC )

4101fa

10

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