LT3652HVIMSE View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LT3652HVIMSE

Power Tracking 2A Battery Charger

Linear Technology 

LT3652HV

APPLICATIONS INFORMATION

stant-current (CC) mode, which corresponds to 100mV

across RSENSE. The ITH voltage is pulled down to reduce

this maximum charge current should the voltage on the

VIN_REG pin falls below 2.7V (VIN_REG(TH)) or the die tem-

perature approaches 125°C.

If the voltage on the VFB pin is below 2.3V (VFB(PRE)),

the LT3652HV engages precondition mode. During the

precondition interval, the charger continues to operate in

constant-current mode, but the maximum charge current

is reduced to 15% of the maximum programmed value

as set by RSENSE.

When the charger output voltage approaches the float volt-

age, or the voltage on the VFB pin approaches 3.3V (VFB(FLT)),

the charger transitions into constant-voltage (CV) mode

and charge current is reduced from the maximum value.

As this occurs, the ITH voltage falls from the limit clamp

and servos to lower voltages. The IC monitors the ITH volt-

age as it is reduced, and detection of C/10 charge current

is achieved when ITH = 0.1V. If the charger is configured

for C/10 termination, this threshold is used to terminate

the charge cycle. Once the charge cycle is terminated,

the CHRG status pin becomes high-impedance and the

charger enters low-current standby mode.

The LT3652HV contains an internal charge cycle timer that

terminates a successful charge cycle after a programmed

amount of time. This timer is typically programmed to

achieve end-of-cycle (EOC) in 3 hours, but can be con-

figured for any amount of time by setting an appropriate

timing capacitor value (CTIMER). When timer termination

is used, the charge cycle does not terminate when C/10

is achieved. Because the CHRG status pin responds to

the C/10 current level, the IC will indicate a fully-charged

battery status, but the charger continues to source low

currents into the battery until the programmed EOC time

has elapsed, at which time the charge cycle will terminate.

At EOC when the charging cycle terminates, if the battery did

not achieve at least 97.5% of the full float voltage, charging

is deemed unsuccessful, the LT3652HV re-initiates, and

charging continues for another full timer cycle.

Use of the timer function also enables bad-battery detec-

tion. This fault condition is achieved if the battery does

not respond to preconditioning, such that the charger

remains in (or enters) precondition mode after 1/8th of

the programmed charge cycle time. A bad battery fault

halts the charging cycle, the CHRG status pin goes high-

impedance, and the FAULT pin is pulled low.

When the LT3652HV terminates a charging cycle, whether

through C/10 detection or by reaching timer EOC, the

average current mode analog loop remains active, but

the internal float voltage reference is reduced by 2.5%.

Because the voltage on a successfully charged battery is

at the full float voltage, the voltage error amp detects an

over-voltage condition and ITH is pulled low. When the

voltage error amp output drops below 0.3V, the IC enters

standby mode, where most of the internal circuitry is dis-

abled, and the VIN bias current is reduced to 85μA. When

the voltage on the VFB pin drops below the reduced float

reference level, the output of the voltage error amp will

climb, at which point the IC comes out of standby mode

and a new charging cycle is initiated.

VIN Input Supply

The LT3652HV is biased through a reverse-current block-

ing element from the charger input supply to the VIN pin.

This supply provides large switched currents, so a high-

quality, low ESR decoupling capacitor is recommended

to minimize voltage glitches on VIN. The VIN decoupling

capacitor (CVIN) absorbs all input switching ripple current

in the charger, so it must have an adequate ripple current

rating. RMS ripple current (ICVIN(RMS)) is:

ICVIN(RMS) ≅ ICHG(MAX) • (VBAT / VIN)•([VIN / VBAT] – 1)1/2,

where ICHG(MAX) is the maximum average charge current

(100mV/RSENSE). The above relation has a maximum at

VIN = 2 • VBAT, where:

ICVIN(RMS) = ICHG(MAX)/2.

The simple worst-case of ½ • ICHG(MAX) is commonly

used for design.

3652hvf

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