SP6120EYSLASHTR datasheet(10/22 Pages) SIPEX

10 / 22 page

Date: 5/25/04

SP6120 Low Voltage, AnyFETTM, Synchronous, Buck Controller

TIME

3% Low

Enable Voltage

V(VCC)

SWN

Voltage

V(VCC)

FAULT

Reset Voltage

V(VCC)

Inductor Current

ILOAD

Error Amplifier

Reference

Voltage

1.25V

VOUT = V(Eamp REF)* (1+RF/RI)

SS Voltage

0.25V

0.7V

2.0V

2.4V

dVSS/dt = 50µA/CSS

V(ISP) - V(ISN)

250mV

V(VCC)

2.0V

SS Voltage

FAULT Voltage

2.4V

43mV

finite propagation delay of the controller. When

the SS voltage reaches 2.0V, the secondary loop

including the 3% window comparator is en-

abled. Lastly, the SS voltage is clamped at 2.4V,

ending the soft start charge cycle.

Hiccup Mode

When the converter enters a fault mode, the

driver holds the high side and low side MOSFETs

off for a finite period of time. Provided the part

is enabled, this time is set by the discharge of the

SS capacitor. The discharge time is roughly 10

times the charge interval thereby giving the

power supply plenty of time to cool during an

over current fault. The driver off-time is pre-

dominantly determined by the discharge time.

Restart will occur just like a normal soft start

cycle.

However, if a fault occurs during the soft start

charge cycle, the FAULT latch is immediately

set, turning off the high side and low side

MOSFETs. The MOSFETs remain off during

the remainder of the charge cycle and subse-

quent discharge cycle of the SS capacitor. Again,

provided there are no external fault conditions,

the FAULT latch will be reset when the SS

voltage reaches 250 mV.

Over Current Protection

The SP6120 over current protection scheme is

designed to take advantage of three popular

detection schemes: Sense Resistor, Trace Resis-

tor or Inductor Sense. Because the detection

threshold is only 43mV, both trace resistor and

inductor sense become attractive protection

schemes. The inductor sense scheme adds no

additional dc loss to the converter and is an

excellent alternative to Rdson based schemes;

providing continuous current sensing and flex-

ible MOSFET selection. An internal, 10

µs filter

conditions the over current signal from tran-

sients generated during load steps. In addition,

because the over current inputs, ISP and ISN,

are capable of rail to rail operation, the SP6120

provides excellent over current protection dur-

ing conditions where V

IN approaches VOUT.

THEORY OF OPERATIONS: Continued

SP6120EY/TR Datasheet(PDF) 10 Page - Sipex Corporation

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