tea1521t-n2 NXP Semiconductors, tea1521t-n2 Datasheet - Page 6

• Manufacturer Part Number: tea1521t-n2
• Description: Tea152x Family Smps Ics For Low-power Systems
• Manufacturer: NXP Semiconductors

Philips Semiconductors
TEA152X_FAM_2
Product data sheet
8.4 Valley switching
A new cycle is started when the primary switch is switched on (see
certain time (determined by the oscillator voltage RC and the internal regulation level), the
switch is turned off and the secondary stroke starts. The internal regulation level is
determined by the voltage on pin REG.
After the secondary stroke, the drain voltage shows an oscillation with a frequency of
approximately:
where:
As soon as the oscillator voltage is high again and the secondary stroke has ended, the
circuit waits for a low drain voltage before starting a new primary stroke.
Figure 4
secondary stroke and the RC voltage.
The primary stroke starts some time before the actual valley at low ringing frequencies,
and some time after the actual valley at high ringing frequencies.
---------------------------------------------- -
2
Fig 4. Signals for valley switching
L
C
p
p
= primary self inductance
= parasitic capacitance on drain node
1
A: Start of new cycle with valley switching.
B: Start of new cycle in a classical PWM system.
shows the drain voltage together with the valley signal, the signal indicating the
L
p
C
secondary
p
oscillator
stroke
valley
drain
RC
Rev. 02 — 25 January 2006
primary
stroke
regulation level
secondary
stroke
SMPS ICs for low-power systems
TEA152x family
secondary
ringing
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
B
Figure
mgt423
A
4). After a
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