LTC4089EDJC-5#TRPBF Datasheet LTC4089EDJC#PBF, LTC4089EDJC-5#PBF, LTC4089EDJC#TRPBF | P13-P15

LTC4089/LTC4089-5

40895fc

High Voltage Step Down Regulator

The power delivered from HVIN to HVOUT is controlled

by a 750kHz constant frequency, current mode step down

regulator. An external P-channel MOSFET directs this

power to OUT and prevents reverse conduction from OUT

to HVOUT (and ultimately HVIN).

A 750kHz oscillator enables an RS ﬂ ip-ﬂ op, turning on the

internal 1.95A power switch Q1. An ampliﬁ er and compara-

tor monitor the current ﬂ owing between the HVIN and SW

pins, turning the switch off when this current reaches a

level determined by the voltage at V

. An error ampliﬁ er

servos the V

node to maintain approximately 300mV

between OUT and BAT (LTC4089). By keeping the voltage

across the battery charger low, efﬁ ciency is optimized

because power lost to the battery charger is minimized

and power available to the external load is maximized. If

the BAT pin voltage is less than approximately 3.3V, then

the error ampliﬁ er will servo the V

node to provide a

constant HVOUT output voltage of about 3.6V. An active

clamp on the V

node provides current limit. The V

node

is also clamped to the voltage on the HVEN pin; soft-start

is implemented by a voltage ramp at the HVEN pin using

an external resistor and capacitor.

An internal regulator provides power to the control circuitry.

This regulator includes an undervoltage lockout to prevent

switching when HVIN is less than about 4.7V. The HVEN

pin is used to disable the high voltage regulator. HVIN

input current is reduced to less than 2μA and the external

P-channel MOSFET disconnects HVOUT from OUT when

the high voltage regulator is disabled.

The switch driver operates from either the high voltage

input or from the BOOST pin. An external capacitor and

diode are used to generate a voltage at the BOOST pin that

is higher than the input supply. This allows the driver to

fully saturate the internal bipolar NPN power switch for

efﬁ cient operation.

When HVOUT is below 3.95V the operating frequency

is reduced. This frequency foldback helps to control the

regulator output current during start-up and overload.

Ideal Diode from BAT to OUT

The LTC4089/LTC4089-5 has an internal ideal diode as

well as a controller for an optional external ideal diode. If

a battery is the only power supply available, or if the load

current exceeds the programmed input current limit, then

the battery will automatically deliver power to the load via

an ideal diode circuit between the BAT and OUT pins. The

ideal diode circuit (along with the recommended 4.7μF

capacitor on the OUT pin) allows the LTC4089/LTC4089-5

to handle large transient loads and wall adapter or USB

BUS

connect/disconnect scenarios without the need for

large bulk capacitors. The ideal diode responds within

a few microseconds and prevents the OUT pin voltage

from dropping signiﬁ cantly below the BAT pin voltage.

A comparison of the I-V curve of the ideal diode and a

Schottky diode can be seen in Figure 3.

If the input current increases beyond the programmed

input current limit additional current will be drawn from the

battery via the internal ideal diode. Furthermore, if power

to IN (USB V

BUS

) or HVIN (high voltage input) is removed,

then all of the application power will be provided by the

battery via the ideal diode. A 4.7μF capacitor at OUT is

sufﬁ cient to keep a transition from input power to battery

power from causing signiﬁ cant output voltage droop. The

ideal diode consists of a precision ampliﬁ er that enables a

large P-channel MOSFET transistor whenever the voltage

at OUT is approximately 20mV (V

FWD

) below the voltage

at BAT. The resistance of the internal ideal diode is ap-

proximately 200m . If this is sufﬁ cient for the application

Figure 3. LTC4089/LTC4089-5 Versus

Schottky Diode Forward Voltage Drop

CONSTANT

FWD

MAX

FORWARD VOLTAGE (V)

4089 F03

FWD

CURRENT (A)

SLOPE: 1/R

DIO(ON)

SLOPE: 1/R

FWD

SCHOTTKY

DIODE

LTC4089

OPERATION

LTC4089/LTC4089-5

40895fc

then no external components are necessary. However,

if more conductance is needed, an external P-channel

MOSFET can be added from BAT to OUT. The GATE pin of

the LTC4089/LTC4089-5 drives the gate of the PFET for

automatic ideal diode control. The source of the external

MOSFET should be connected to OUT and the drain should

be connected to BAT. In order to help protect the external

MOSFET in over-current situations, it should be placed in

close thermal contact to the LTC4089/LTC4089-5.

Battery Charger

The battery charger circuits of the LTC4089/LTC4089-5

are designed for charging single cell lithium-ion batter-

ies. Featuring an internal P-channel power MOSFET, the

charger uses a constant-current/constant-voltage charge

algorithm with programmable current and a program-

mable timer for charge termination. Charge current can be

programmed up to 1.2A. The ﬁ nal ﬂ oat voltage accuracy

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

required when powering either the IN or the HVIN pins.

The CHRG open-drain status output provides information

regarding the charging status of the LTC4089/LTC4089-5

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

qualiﬁ cation using battery temperature.

An internal thermal limit reduces the programmed charge

current if the die temperature attempts to rise above a

preset value of approximately 105°C. This feature protects

the LTC4089/LTC4089-5 from excessive temperature, and

allows the user to push the limits of the power handling

capability of a given circuit board without risk of dam-

aging the LTC4089/LTC4089-5. Another beneﬁ t of the

LTC4089/LTC4089-5 thermal limit is that charge current

can be set according to typical, not worst-case, ambient

temperatures for a given application with the assurance

that the charger will automatically reduce the current in

worst-case conditions.

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 ﬂ ows until the OUT voltage is 100mV above

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

the battery voltage is below 2.8V, the charger goes into

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 2.8V. In constant current mode, the charge

current is set by R

PROG

. When the battery approaches the

ﬁ nal ﬂ oat voltage, the charge current begins to decrease

as the LTC4089/LTC4089-5 switches to constant-voltage

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

programmed charge current while in constant-voltage

mode the CHRG 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 CHRG 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 ﬁ nal ﬂ oat potential, the internal bandgap

reference, voltage ampliﬁ er 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 volt-

age is low (below 2.8V) the charger goes into trickle

charge reducing the charge current to 10% of the full-

scale current. If the low battery voltage persists for one

quarter of the total charge time, the battery is assumed

to be defective, the charge cycle is terminated and the

CHRG pin output assumes a high impedance state. If

for any reason the battery voltage rises above ~2.8V 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:

CHG PROG

PROG

==•, •,50 000 50 000

where V

PROG

is the PROG pin voltage and R

PROG

is the total

resistance from the PROG pin to ground. Keep in mind that

OPERATION

LTC4089/LTC4089-5

40895fc

when the LTC4089/LTC4089-5 is powered from the IN pin,

the programmed input current limit takes precedent over

the charge current. In such a scenario, the charge current

cannot exceed the programmed input current limit.

For example, if typical 500mA charge current is required,

calculate:

PROG

500

50 000 100•,

For best stability over temperature and time, 1% metal ﬁ lm

resistors are recommended. Under trickle charge conditions,

this current is reduced to 10% of the full-scale value.

The Charge Timer

The programmable charge timer is used to terminate the

charge cycle. The timer duration is programmed by an

external capacitor at the TIMER pin. The charge time is

typically:

t hours

C R hours

μF k

TIMER

TIMER PROG

()

••

.•

0 1 100

The timer starts when an input voltage greater than the

undervoltage lockout threshold level is applied or when

leaving shutdown and the voltage on the battery is less than

the recharge threshold. At power-up or exiting shutdown

with the battery voltage less than the recharge threshold

the charge time is a full cycle. If the battery is greater than

the recharge threshold the timer will not start and charging

is prevented. If after power-up the battery voltage drops

below the recharge threshold, or if after a charge cycle

the battery voltage is still below the recharge threshold,

the charge time is set to one-half of a full cycle.

The LTC4089/LTC4089-5 has a feature that extends charge

time automatically. Charge time is extended if the charge

current in constant current mode is reduced due to load

current or thermal regulation. This change in charge time

is inversely proportional to the change in charge current.

As the LTC4089/LTC4089-5 approaches constant voltage

mode the charge current begins to drop. This change in

charge current is due to normal charging operation and

does not affect the timer duration.

Consider, for example, a USB charge condition where

CLPROG

= 2k, R

PROG

= 100k and C

TIMER

= 0.1μF. This

corresponds to a three hour charge cycle. However, if the

HPWR input is set to a logic low, then the input current

limit will be reduced from 500mA to 100mA. With no ad-

ditional system load, this means the charge current will

be reduced to 100mA. Therefore, the termination timer

will automatically slow down by a factor of ﬁ ve until the

charger reaches constant voltage mode (i.e. V

BAT

= 4.2V)

or HPWR is returned to a logic high. The charge cycle is

automatically lengthened to account for the reduced charge

current. The exact time of the charge cycle will depend on

how long the charger remains in constant-current mode

and/or how long the HPWR pin remains a logic low.

Once a time-out occurs and the voltage on the battery is

greater than the recharge threshold, the charge current

stops, and the CHRG output assumes a high impedance

state if it has not already done so.

Connecting the TIMER pin to ground disables the battery

charger.

CHRG Status Output Pin

When the charge cycle starts, the CHRG pin is pulled to

ground by an internal N-channel MOSFET capable of driv-

ing an LED. When the charge current drops below 10%

of the programmed full charge current while in constant

voltage mode, the pin assumes a high impedance state,

but charge current continues to ﬂ ow until the charge

time elapses. If this state is not reached before the end

of the programmable charge time, the pin will assume a

high impedance state when a time-out occurs. The CHRG

current detection threshold can be calculated by the fol-

lowing equation:

DETECT

PROG PROG

50 000

5000.

•,

For example, if the full charge current is programmed

to 500mA with a 100k PROG resistor the CHRG pin will

change state at a battery charge current of 50mA.

Note: The end-of-charge (EOC) comparator that moni-

tors the charge current latches its decision. Therefore,

the ﬁ rst time the charge current drops below 10% of the

programmed full charge current while in constant volt-

age mode, it will toggle CHRG to a high impedance state.

OPERATION

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24

LTC4089EDJC-5#TRPBF

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Manufacturer:

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Description:

Battery Management 5V Out, High Voltage USB Power Manager w/ High Voltage Switching Charger

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