ISL6341ACRZ-T Datasheet, PDF(13/17 Page) Intersil Corporation – 5V or 12V Single Synchronous Buck Pulse-Width Modulation (PWM) Controller

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ISL6341ACRZ-T Datasheet, PDF (13/17 Pages) Intersil Corporation – 5V or 12V Single Synchronous Buck Pulse-Width Modulation (PWM) Controller

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ISL6341, ISL6341A, ISL6341B, ISL6341C

VIN

ISL6341x

UGATE

PHASE

LGATE/OCSET

VOUT

CIN

RETURN

FIGURE 11. PRINTED CIRCUIT BOARD POWER AND

GROUND PLANES OR ISLANDS

Figure 11 shows the critical power components of the

converter. To minimize the voltage overshoot, the

interconnecting wires indicated by heavy lines should be part of

a ground or power plane in a printed circuit board. The

components shown should be located as close together as

possible. Please note that the capacitors CIN and CO may each

represent numerous physical capacitors. For best results,

locate the ISL6341x within 1 inch of the MOSFETs, Q1 and Q2.

The circuit traces for the MOSFET gate and source

connections from the ISL6341x must be sized to handle up to

2A peak current.

+VGD

VOUT

VOS

COMP/EN

+VCC

VCC

ISL6341x

BOOT

CBOOT

PHASE

LGATE/OCSET

CVCC

GND

ROCSET

+VIN

Q1 LO

VOUT

Q2 CO

FIGURE 12. PRINTED CIRCUIT BOARD SMALL SIGNAL

LAYOUT GUIDELINES

Figure 12 shows the circuit traces that require additional

layout consideration. Use single point and ground plane

construction for the circuits shown. Provide local VCC

decoupling between VCC and GND pins. Locate the

capacitor, CBOOT as close as practical to the BOOT and

PHASE pins. Locate the resistor, ROSCET close to the

LGATE/OCSET pin because the internal current source is

only 10ÂµA. Minimize any leakage current paths on the

COMP/EN pin. All components used for feedback

compensation and VOS resistor divider (inside the dotted

box) should be located as close to the IC as practical. Near

the load, pick a point VOUT that will be the regulation center;

run a single unloaded narrow trace from there to the

compensation components. The same trace can also be

used for VOS divider.

Feedback Compensation

This section highlights the design consideration for a

voltage-mode controller requiring external compensation. To

address a broad range of applications, a type-3 feedback

network is recommended, as shown in the top part of

Figure 13.

Figure 13 also highlights the voltage-mode control loop for a

synchronous-rectified buck converter, applicable to the

ISL6341x circuit. The output voltage (VOUT) is regulated to

the reference voltage, VREF. The error amplifier output

(COMP pin voltage) is compared with the oscillator (OSC)

modified sawtooth wave to provide a pulse-width modulated

wave with an amplitude of VIN at the PHASE node. The

PWM wave is smoothed by the output filter (L and C). The

output filter capacitor bankâs equivalent series resistance is

represented by the series resistor E.

The modulator transfer function is the small-signal transfer

function of VOUT/VCOMP. This function is dominated by a DC

gain, given by dMAXVIN/VOSC, and shaped by the output

filter, with a double pole break frequency at FLC and a zero at

FCE. For the purpose of this analysis, L and D represent the

channel inductance and its DCR, while C and E represent the

total output capacitance and its equivalent series resistance.

FLC=

-------------1--------------

2Ï â L â C

FCE= 2----Ï-----â--1-C------â---E--

(EQ. 3)

COMP

R2 C1

R3 C3

E/A +

VREF

OSCILLATOR

PWM

CIRCUIT

VOSC

HALF-BRIDGE

DRIVE

VIN

UGATE

PHASE

LGATE

VOUT

ISL6341x

EXTERNAL CIRCUIT

FIGURE 13. VOLTAGE-MODE BUCK CONVERTER

COMPENSATION DESIGN

FN6538.2

December 2, 2008

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