DAP018A/B/C/D/F

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21

When the input voltage is low, below VBO(on), the BO

comparator output is low and the current source is activated,

drawing 10

mA from the BO pin (pin 11) to ground. The

controller is silent, and no driving pulses are delivered to the

power MOSFET. When the input is sufficiently high, the BO

comparator toggles high and shuts down the current source,

providing the necessary hysteresis to the circuit. When

toggling high, the BO signal also resets ALL the internal

logic circuits including an eventual latch state triggered by

an OVP for instance (or a latched OCP for this particular

version). When the BO comparator has given the

authorization to work, the controller resets its hiccup mode

on the VCC (if any) and waits for the next VCC(on) event to

start pulsing again (via soft−start sequence). A 20

ms RC

time−constant has been added in series with the brown−out

comparator to further avoid false trigger of the controller.

Figure 44 shows typical signals in presence of a

brown−out suddenly occuring and coming back again:

BO

signal

Drv

1

restart

BO acknowledged

here: hiccup reset

General

internal reset

(latch...)

Double hiccup

Mains

Figure 44. A Brown−out Event Immediately Stops the Driving Pulses

VBO(off)

VBO(on)

Interruption

Controller waits for

the next VCC(on) event

Vbulk

VCCreset

VCClatch

VCC(min)

VCC(on)

VCC

When the bulk comes back to its normal level, the controller waits for the next VCC(on) event to re−start pulsing. If the

controller was in a double−hiccup mode, the logic circuit is reset to accelerate the restart to the next VCC(on) event.