ZXLB1600X10TC(2003) データシートの表示（PDF） - Zetex => Diodes
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ZXLB1600X10TC Datasheet PDF : 16 Pages
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BLOCK DIAGRAM
ZXLB1600
Device description
The device is a flyback boost converter, working in
discontinuous mode.
With reference to the chip block diagram and typical
application circuit, the operation of the device is as
follows:
Control loop
When 'EN' is high, the control circuits become active. The
high side of the coil is connected to the input via a large
PMOS isolating switch (MP) and the low side to ground via
NDMOS transistor (MN). The current in the coil is allowed
to build up to an internally defined level (nominally 200 to
300mA) before MN is turned off. The energy stored in the
coil is then transferred to the output capacitor (C2) via
diode (D1). The output voltage is sensed at pin 'SENSE' by
internal resistors R1 and R2 (which may be shunted
externally at pin 'FB') and compared to a reference voltage
(1.23V nominal). A comparator senses when the output
voltage is above that set by the reference and its output is
used to control the 'off' time of the output switch. The
control loop is self-oscillating, producing pulses of 10s
maximum duration (switch 'on'), at a frequency that varies
in proportion to the output load current. The minimum
'off' time of the output switch is fixed at 1.25s nominal, to
allow time for the coil's energy to be dissipated before the
switch is turned on again. This maintains stable and
efficient operation.
Setting output voltage
With external voltage
The output voltage is equal to the voltage present on
the 'ADJ' pin of the device multiplied by the internal
resistor network factor (R1+R2)/R1. The ADJ pin is
connected to the internal reference voltage of value
VADJ(nom) and by default will give a nominal output of
28V. However, if required, the ADJ pin may be
overdriven with an external dc voltage VADJ, in order to
adjust the output voltage to a value lower than the
default value.
ISSUE 3 - SEPTEMBER 2003
5
SEMICONDUCTORS
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