LTC4098EUDC-3.6 View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LTC4098EUDC-3.6

USB Compatible Switching Power Manager/LiFePO4 Charger with Overvoltage Protection

Linear Technology 

LTC4098-3.6

OPERATION

For very low battery voltages, the battery charger acts like

a load and, due to limited input power, its current will tend

to pull VOUT below the 3.5V instant-on voltage. To prevent

VOUT from falling below this level, an undervoltage circuit

automatically detects that VOUT is falling and reduces the

battery charge current as needed. This reduction ensures

that load current and voltage are always prioritized while

allowing as much battery charge current as possible. Refer

to Overprogramming the Battery Charger in the Applica-

tions Information section.

The voltage regulation loop compensation is controlled by

the capacitance on VOUT. An MLCC capacitor of 10µF is

required for loop stability. Additional capacitance beyond

this value will improve transient response.

An internal undervoltage lockout circuit monitors VBUS and

keeps the switching regulator off until VBUS rises above

the rising UVLO threshold (4.3V). If VBUS falls below the

falling UVLO threshold (4V), system power at VOUT will

be drawn from the battery via the ideal diodes.

Bat-Track High Voltage External Switching Regulator

Control

The WALL, ACPR and VC pins can be used in conjunction

with an external high voltage step-down switching regulator

such as the LT3653 or LT3480 to minimize heat production

when operating from higher voltage sources, as shown in

Figures 3 and 4. Bat-Track control circuitry regulates the

external switching regulator’s output voltage to the larger

of BAT + 400mV or 3.6V. This maximizes battery charger

efficiency while still allowing instant-on operation when

the battery is deeply discharged.

When using the LT3480, the feedback network should be

set to generate an output voltage between 4.5V and 5.5V.

When high voltage is applied to the external regulator, WALL

will rise toward this programmed output voltage. When

WALL exceeds approximately 4.3V,  ACPR is brought low

and the Bat-Track control of the LTC4098-3.6 overdrives

the local VC control of the external high voltage step-down

switching regulator. Therefore, once the Bat-Track control

is enabled, the output voltage is set independent of the

switching regulator feedback network.

Bat-Track control provides a significant efficiency advantage

over the simple use of a 5V switching regulator output to

drive the battery charger. With a 5V output driving VOUT,

battery charger efficiency is approximately:

ηTOTAL

=

ηBUCK

•

VBAT

5V

where hBUCK is the efficiency of the high voltage switching

regulator and 5V is the output voltage of the switching

regulator. With a typical switching regulator efficiency of

87% and a typical battery voltage of 3.4V, the total battery

charger efficiency is approximately 59%. Assuming a 1A

charge current, well over 2W of power is dissipated just

to charge the battery!

With Bat-Track, battery charger efficiency is approximately:

ηTOTAL

=

ηBUCK

•

BAT

BAT + 0.4V

SW

LT3653

ISENSE

VC

HVOK

VOUT

VC

WALL

LTC4098-3.6

ACPR

VOUT

409836 F03

SYSTEM

LOAD

Figure 3. LT3653 Typical Interface

SW

LT3480

VC

FB

VC

WALL

LTC4098-3.6

ACPR

VOUT

409836 F04

SYSTEM

LOAD

Figure 4. LT3480 Typical Interface

409836f

15

Share Link: