DESCRIPTION

The LTC4000 is a high voltage, high performance controller that converts many externally compensated DC/DC power supplies into full-featured battery chargers.Features of the LTC4000’s battery charger include: accurate(±0.25%) programmable float voltage, selectable timer or current termination, temperature qualified charging using an NTC thermistor, automatic recharge, C/10 trickle charge for deeply discharged cells, bad battery detection and status indicator outputs. The battery charger also includes precision current sensing that allows lower sense voltages for high current applications.

The LTC4000 supports intelligent PowerPath control. An external PFET provides low loss reverse current protection. Another external PFET provides low loss charging or discharging of the battery. This second PFET also facilitates an instant-on feature that provides immediate downstream system power even when connected to a heavily discharged or short faulted battery.

The LTC4000 is available in a low profile 28-lead 4mm ×5mm QFN and SSOP packages.

 

CARACTÉRISTIQUES

Complete High Performance Battery Charger When Paired with a DC/DC Converter

Wide Input and Output Voltage Range: 3V to 60V

Input Ideal Diode for Low Loss Reverse Blocking and Load Sharing

Output Ideal Diode for Low Loss PowerPath™ and Load Sharing with the Battery

Instant-On Operation with Heavily Discharged Battery

Programmable Input and Charge Current:  ±1% Accuracy

±0.25% Accurate Programmable Float Voltage

Programmable C/X or Timer Based Charge Termination

NTC Input for Temperature Qualified Charging

28-Lead 4mm × 5mm QFN or SSOP Packages

 

CANDIDATURES

High Power Battery Charger Systems

High Performance Portable Instruments

Industrial Battery Equipped Devices

Notebook/Subnotebook Computers

 

FONCTIONNEMENT

The LTC4000 is designed to simplify the conversion of any externally compensated DC/DC converter into a high performance battery charger with PowerPath control. It only requires the DC/DC converter to have a control or external-compensation pin (usually named VC or ITH) whose voltage level varies in a positive monotonic way with its output. The output variable can be either output voltage or output current.

The LTC4000 includes four different regulation loops: input current, charge current, battery float voltage and output voltage. Whichever loop requires the lowest voltage on the ITH pin for its regulation controls the external DC/DC converter.

The input current regulation loop ensures that the programmed input current limit (using a resistor at IL) is not exceeded at steady state. The charge current regulation loop ensures that the programmed battery charge current limit (using a resistor at CL) is not exceeded. The float voltage regulation loop ensures that the programmed battery stack voltage (using a resistor divider from BAT to FBG via BFB) is not exceeded. The output voltage regulation loop ensures that the programmed system output voltage (using a resistor divider from CSP to FBG via OFB) is not exceeded. The LTC4000 also provides monitoring pins for the input current and charge current at the IIMON and IBMON pins respectively.

The LTC4000 features an ideal diode controller at the input from the IID pin to the CSP pin and a PowerPath controller at the output from the BAT pin to the CSN pin. The output PowerPath controller behaves as an ideal diode controller when not charging. When charging, the output PowerPath controller has two modes of operation. If VOFB is greater than VOUT(INST_ON), BGATE is driven low. When VOFB is less than VOUT(INST_ON), a linear regulator implements the instant-on feature. This feature provides regulation of the BGATE pin so that a valid voltage level is immediately available at the output when the LTC4000 is charging an over-discharged, dead or short faulted battery.

 

Compensation

In order for the LTC4000 to control the external DC/DC converter, it has to be able to overcome the sourcing bias current of the ITH or VC pin of the DC/DC converter. The typical sinking capability of the LTC4000 at the ITH pin is 1mA at 0.4V with a maximum voltage range of 0V to 6V.

It is imperative that the local feedback of the DC/DC converter be set up such that during regulation of any of the LTC4000 loops this local loop is out of regulation and sources as much current as possible from its ITH/VC pin. For example for a DC/DC converter regulating its output voltage, it is recommended that the converter feedback divider is programmed to be greater than 110% of the output voltage regulation level programmed at the OFB pin.