BESCHREIBUNG

The LTC7804 is a high performance synchronous boost DC/DC switching regulator controller that drives an all N-channel power MOSFET stage. Synchronous rectification increases efficiency, reduces power losses and eases thermal requirements. A constant frequency current mode architecture allows a phase-lockable switching frequency of up to 3MHz. The LTC7804 operates from a wide 4.5V to 40V input supply range. When biased from the boost converter output , the LTC7804 can operate from an input supply as low as 1V after startup.

The very low no-load quiescent current extends operating runtime in battery powered systems. OPTI-LOOP compensation allows the transient response to be optimized over a wide range of output capacitance and ESR values. The MODE pin selects among Burst Mode operation, pulse-skipping mode, or continuous inductor current mode at light loads.

The LTC7804 additionally features spread spectrum operation which significantly reduces the peak radiated and conducted noise on both the input and output supplies, making it easier to comply with electromagnetic interference (EMI) standards.

 

FEATURES

Synchronous Operation for Highest Efficiency and Reduced Heat Dissipation

Wide VIN Range: 4.5V to 40V and Operates Down to 1V After Start-Up

Output Voltage Up to 40V

Low Operating IQ: 14μA

Spread Spectrum Operation

Pass-Thru™/100% Duty Cycle Capability for Synchronous MOSFET

RSENSE or Inductor DCR Current Sensing

Programmable Fixed Frequency (100kHz to 3MHz)

Phase-Lockable Frequency (100kHz to 3MHz)

Selectable Continuous, Pulse-Skipping, or Low Ripple Burst Mode® Operation at Light Loads

Low Shutdown IQ: 1.2μA

Thermally Enhanced 16-Pin 3mm × 3mm QFN and MSOP Packages

AEC-Q100 qualifiziert für Automobilanwendungen

 

ANWENDUNGEN

Automotive and Transportation

Industriell

Military/Avionics

Telekommunikation

 

OPERATION

Hauptkontrollschleife

The LTC7804 uses a constant frequency, peak current mode step-up architecture. During normal operation, the external bottom MOSFET is turned on when the clock sets the RS latch, and is turned off when the main current comparator, ICMP, resets the RS latch. The peak inductor current at which ICMP trips and resets the latch is controlled by the voltage on the ITH pin, which is the output of the error amplifier, EA. The error amplifier compares the output voltage feedback signal at the VFB pin (which is generated with an external resistor divider connected across the output voltage, VOUT, to ground) to the internal 1.200V reference voltage. When the load current increases, it causes a slight decrease in VFB relative to the reference, which causes the EA to increase the ITH voltage until the average inductor current matches the new load current.

After the bottom MOSFET is turned off each cycle, the top MOSFET is turned on until either the inductor current starts to reverse, as indicated by the current comparator IR, or the beginning of the next clock cycle.

Shutdown and Start-Up (RUN, SS Pins)

The LTC7804 can be shut down using the RUN pin. Pulling this pin below 1.1V shuts down the main control loop. Pulling the RUN pin below 0.7V disables the controller and most internal circuits, including the INTVCC LDOs. In this state, the LTC7804 draws only 1.2μA of quiescent current.

NOTE: Do not apply a heavy load for an extended time while the chip is in shutdown. The top MOSFETs are turned off during shutdown and the output load may cause excessive dissipation in the body diodes.

Light Load Current Operation: Burst Mode Operation, Pulse-Skipping or Forced Continuous Mode (MODE Pin)

The LTC7804 can be enabled to enter high efficiency Burst Mode operation, constant frequency pulse-skipping mode, or forced continuous conduction mode at low load currents.

To select Burst Mode operation, tie the MODE pin to GND. To select forced continuous operation, tie the MODE pin to INTVCC. To select pulse-skipping mode, tie the MODE pin to a DC voltage greater than 1.2V and less than INTVCC – 1.3V. An internal 100k resistor to GND invokes Burst Mode operation when the MODE pin is floating and pulse-skipping mode when the MODE pin is tied to INTVCC through an external 100k resistor.