TEA1520T NXP [NXP Semiconductors], TEA1520T Datasheet - Page 6

• Manufacturer Part Number: TEA1520T
• Description: SMPS ICs for low-power systems
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
TEA152X_3
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.
L
C
p
p
= primary self inductance
= parasitic capacitance on drain node
1
shows the drain voltage together with the valley signal, the signal indicating the
A: Start of new cycle with valley switching.
B: Start of new cycle in a classical PWM system.
Signals for valley switching
L
p
C
secondary
p
oscillator
stroke
valley
drain
RC
Rev. 03 — 23 March 2009
primary
stroke
regulation level
secondary
stroke
SMPS ICs for low-power systems
secondary
ringing
B
Figure
mgt423
A
TEA152x
© NXP B.V. 2009. All rights reserved.
4). After a
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