ISL6520B

Features:

* Operates from +5V Input
* 0.8V to V_IN Output Range
- 0.8V Internal Reference
- ±1.5% Over Line Voltage and Temperature
* Drives N-Channel MOSFETs
* Simple Single-Loop Control Design
- Voltage-Mode PWM Control
* Fast Transient Response
- High-Bandwidth Error Amplifier
- Full 0% to 100% Duty Cycle
* Small Converter Size
- 300kHz Fixed Frequency Oscillator
- Internal Soft Start
- 8 Ld SOIC or 16Ld 4x4mm QFN
* QFN Package:
- Compliant to JEDEC PUB95 MO-220 QFN - Quad Flat
No Leads - Package Outline
- Near Chip Scale Package footprint, which improves PCB efficiency and has a thinner profile
* Pb-Free Available (RoHS Compliant)




Application

* Power Supplies for Microprocessors
-PCs
- Embedded Controllers
* Subsystem Power Supplies
- PCI/AGP/GTL+ Buses
- ACPI Power Control
- SSTL-2 and DDR SDRAM Bus Termination Supply
* Cable Modems, Set Top Boxes, and DSL Modems
* DSP and Core Communications Processor Supplies
* Memory Supplies
* Personal Computer Peripherals
* Industrial Power Supplies
* 5V-Input DC-DC Regulators
* Low-Voltage Distributed Power Supplies




Pinout






Specifications

Supply Voltage, V_CC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6.0V
Absolute Boot Voltage, V_BOOT . . . . . . . . . . . . . . . . . . . . . . . +15.0V
Upper Driver Supply Voltage, V_BOOT - V_PHASE . . . . . . . . . . . +6.0V
Input, Output or I/O Voltage. . . . . . . . . . . GND -0.3V to VCC +0.3V
ESD Classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Class 2




Description

Functional Pin Description
VCC
This pin provides the bias supply for the ISL6520B, as well as the lower MOSFET's gate. Connect a well-decoupled 5V supply to this pin.
FB
This pin is the inverting input of the internal error amplifier. Use this pin, in combination with the COMP/SD pin, to
compensate the voltage-control feedback loop of the converter.
GND
This pin represents the signal and power ground for the IC. Tie this pin to the ground island/plane through the lowest impedance connection available.
PHASE
Connect this pin to the upper MOSFET's source.
UGATE
Connect this pin to the upper MOSFET's gate. This pin provides the PWM-controlled gate drive for the upper
MOSFET. This pin is also monitored by the adaptive shootthrough protection circuitry to determine when the upper
MOSFET has turned off.
BOOT
This pin provides ground referenced bias voltage to the upper MOSFET driver. A bootstrap circuit is used to create a
voltage suitable to drive a logic-level N-channel MOSFET.
COMP/SD
This pin is the output of the error amplifier. Use this pin, in combination with the FB pin, to compensate the voltage-
control feedback loop of the converter.Pulling COMP/SD to a level below 0.8V disables the controller. Disabling the ISL6520B causes the oscillator to stop, the LGATE and UGATE outputs to be held low, and the softstart circuitry to re-arm. The COMP/SD pin must be pulled above 0.8V to terminate shutdown. This may be donethrough a pullup resistor tied between VCC and COMP/SD. The recommended range of resistor values to use as the pullup resistor is between 50k? and 100k?.
LGATE
Connect this pin to the lower MOSFET's gate. This pin provides the PWM-controlled gate drive for the lower
MOSFET. This pin is also monitored by the adaptive shootthrough protection circuitry to determine when the lower
MOSFET has turned off.
Functional Description
Initialization
The ISL6520B automatically initializes upon receipt of power. The Power-On Reset (POR) function continually onitors the bias voltage at the VCC pin. The POR function initiates the soft start operation.
Soft Start
The ISL6520B is held in reset with both UGATE and LGATE driven to ground until the POR threshold on VCC has been
reached and the COMP/SD pin has been pulled above 0.8V. If COMP is not actively pulled high following POR the internal 20A current sink will hold COMP/SD low and the device will remain in reset. COMP/SD can either be statically tied to VCC through a pullup resistor or driven high through a resistor to terminate reset. The recommended range of resistor values to use as the pullup resistor is between 50k? and 100k?
Following reset the ISL6520B provides a 1024 clock cycle settling period (~3.4ms) prior to initiating softstart. At the conclusion of the settling period the COMP/SD pin is driven to 0.8V for 24 clock cycles (~75s) to discharge the compensation network. Soft start of the regulated output is generated by imposing an internal offset on the FB pin which ramps down from 0.8V to 0V over the next 2048 clock cycles (~6.8ms). Total time from end of reset to completion of soft start is 10.2ms.
Pulling COMP/SD below.8V or VCC dropping below minimum POR initiates another reset.

Current Sinking
The ISL6520B incorporates a MOSFET shoot-through protection method which allows a converter to sink current
as well as source current. Care should be exercised when designing a converter with the ISL6520B when it is known that the converter may sink current.When the converter is sinking current, it is behaving as a boost converter that is regulating it's input voltage. This means that the converter is boosting current into the V_CC rail, which supplies the bias voltage to the ISL6520B. If there is nowhere for this current to go, such as to other distributed loads on the V_CC rail, through a voltage limiting protection device, or other methods, the capacitance on the V_CC bus will absorb the current. This situation will allow voltage level of the V_CC rail to increase. If the voltage level of the rail is boosted to a level that exceeds the maximum voltage rating of the ISL6520B, then the IC will experience an irreversible
failure and the converter will no longer be operational. Ensuring that there is a path for the current to follow other
than the capacitance on the rail will prevent this failure mode.

The ISL6520B makes simple work out of implementing a complete control scheme for a DC/DC stepdown converter. Designed to drive N-channel MOSFETs in a synchronous buck topology, the ISL6520B integrates the control, output adjustment and monitoring functions into a single 8 Lead package. The ISL6520B provides simple, single feedback loop, voltage-mode control with fast transient response. The output voltage can be precisely regulated to as low as 0.8V, with a maximum tolerance of 1.5% over-temperature and line voltage variations. A fixed frequency oscillator reduces design complexity, while balancing typical application cost and efficiency. The error amplifier features a 15MHz gain-bandwidth product and 8V/s slew rate which enables high converter bandwidth for fast transient performance. The resulting PWM duty cycles range from 0% to 100%.