LTC4090(RevA) 데이터 시트보기 (PDF) - Linear Technology

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LTC4090
(Rev.:RevA)

USB Power Manager with 2A High Voltage Bat-Track Buck Regulator

Linear Technology 

LTC4090/LTC4090-5

OPERATION

Suspend Mode

When SUSP is pulled above VIH the LTC4090/LTC4090-5

enter suspend mode to comply with the USB specification.

In this mode, the power path between IN and OUT is put

in a high impedance state to reduce the IN input current to

50μA. If no other power source is available to drive HVIN,

the system load connected to OUT is supplied through the

ideal diodes connected to BAT.

Battery Charger

The battery charger circuits of the LTC4090/LTC4090-5

are designed for charging single cell lithium-ion batteries.

Featuring an internal P-channel power MOSFET, the charger

uses a constant current / constant voltage charge algorithm

with programmable charge current and a programmable

timer for charge termination. Charge current can be

programmed up to 1.5A. The final float voltage accuracy

is ±0.8% typical. No blocking diode or sense resistor is

required when powering either the IN or the HVIN pins.

The ⎯C⎯H⎯R⎯G open-drain status output provides information

regarding the charging status of the LTC4090/LTC4090-5

at all times. An NTC input provides the option of charge

qualification using battery temperature.

The charge cycle begins when the voltage at the OUT

pin rises above the battery voltage and the battery volt-

age is below the recharge threshold. No charge current

actually flows until the OUT voltage is 100mV above

the BAT voltage. At the beginning of the charge cycle, if

the battery voltage is below 2.9V, the charger goes into

LTC4090/LTC4090-5

IMAX

CONSTANT

I0N

SLOPE: 1/RDIO(ON)

CONSTANT

R0N

IFWD

SLOPE: 1/RFWD

SCHOTTKY

DIODE

CONSTANT

V0N

0

FORWARD VOLTAGE (V)

VFWD

4090 F03

Figure 3. LTC4090/LTC4090-5 Versus Schottky Diode Forward

Voltage Drop

trickle charge mode to bring the cell voltage up to a safe

level for charging. The charger goes into the fast charge

constant current mode once the voltage on the BAT pin

rises above 2.9V. In constant current mode, the charge

current is set by RPROG. When the battery approaches the

final float voltage, the charge current begins to decrease

as the LTC4090/LTC4090-5 switch to constant voltage

mode. When the charge current drops below 10% of the

programmed value while in constant voltage mode the

⎯C⎯H⎯R⎯G pin assumes a high impedance state.

An external capacitor on the TIMER pin sets the total

minimum charge time. When this time elapses, the

charge cycle terminates and the ⎯C⎯H⎯R⎯G pin assumes a

high impedance state, if it has not already done so. While

charging in constant current mode, if the charge current

is decreased by thermal regulation or in order to maintain

the programmed input current limit, the charge time is

automatically increased. In other words, the charge time is

extended inversely proportional to the actual charge current

delivered to the battery. For Li-Ion and similar batteries that

require accurate final float potential, the internal bandgap

reference, voltage amplifier and the resistor divider provide

regulation with ±0.8% accuracy.

Trickle Charge and Defective Battery Detection

At the beginning of a charge cycle, if the battery voltage

is below 2.9V, the charger goes into trickle charge reduc-

ing the charge current to 10% of the full-scale current.

If the low battery voltage persists for one quarter of the

programmed total charge time, the battery is assumed

to be defective, the charge cycle is terminated and the

⎯C⎯H⎯R⎯G pin output assumes a high impedance state. If

for any reason the battery voltage rises above ~2.9V the

charge cycle will be restarted. To restart the charge cycle

(i.e., when the dead battery is replaced with a discharged

battery), simply remove the input voltage and reapply it

or cycle the TIMER pin to 0V.

Programming Charge Current

The formula for the battery charge current is:

ICHG

= IPROG

•

50,000

=

VPROG

RPROG

•

50,000

4090fa

15

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