SP6128A Datasheet, PDF(7/10 Page) Sipex Corporation – Low Voltage, Synchronous Step Down PWM Controller Ideal for 2A to 10A, Small Footprint, DC-DC Power Converters

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SP6128A Datasheet, PDF (7/10 Pages) Sipex Corporation – Low Voltage, Synchronous Step Down PWM Controller Ideal for 2A to 10A, Small Footprint, DC-DC Power Converters

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A more detailed description of the waveform is shown below.

OPERATION: continued

SP6128A OVER CURRENT (HICCUP MODE)

Test Conditions

VFB = 0.7V

VCC = PVCC = 5.0V

BST = 5.0V

SWN - tied to GND through 1k Resistor

COMP â released from GND

Overcurrent Detected

GH Turns Off

Fault Mode Enabled

Internal SSTART rises until

~ VCC-1V, then gives command

to attempt RESTART

COMP

ENABLE

Part

COMP Clamps

~ 3V

After pop, COMP

retains internal

SSTART slope

Attempt

RESTART

5ÂµA PULLUP slope to 0.3V;

35ÂµA PULLUP to 0.7V

Internal SSTART

passes V(VFB), COMP

pops to ~ internal

SSTART voltage +0.7V

Over Current Protection

Over current protection on the SP6128A is imple-

mented through detection of an excess voltage

condition across the high side NMOS switch

during conduction. This is typically referred to

as high side RDS(ON) detection and eliminates the

need of an external sense resistor. The over

current comparator charges an internal sam-

pling capacitor each time VSWN is lower than

(VISET - 140mV) and the GH voltage is high. The

discharge/charge current ratio on the sampling

capacitor is about 2%. Therefore, provided that

the over current condition persists, the capacitor

voltage will be pumped up during each time GH

switches high. This voltage will trigger an over

current condition upon reaching a CMOS in-

verter threshold. There are many advantages to

this approach. First, the filtering action of the

gated scheme protects against false and undesir-

able triggering that could occur during a minor

transient overload condition or supply line noise.

Furthermore, the total amount of time to trigger

the fault depends on the on-time of the high side

NMOS switch. Fifteen, 1Âµs pulses are equiva-

lent to thirty, 500ns pulses or one, 15Âµs pulse,

however, depending on the period, each sce-

nario takes a different amount of total time to

trigger a fault. Therefore, the fault becomes an

indicator of average power in the high side

Rev. 05/25/04

SP6128A Low Voltage, Synchronous Step Down PWM Controller

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