TEA1532
Philips Semiconductors
GreenChip II SMPS control IC
When pin DEM is grounded (CCM), the brown-out protection is disabled. In this case the
duty cycle is limited to 0.7, so at low mains voltage the on-time is limited and therefore the
dissipation in the FET is limited.
7.15 OverTemperature Protection (OTP)
The IC provides accurate temperature protection. The IC will stop switching when the
junction temperature exceeds the thermal shutdown temperature. When VCC drops to
VUVLO, capacitor CVCC will be recharged to the Vstart level, however switching will not
restart. Subsequently, VCC will drop again to VUVLO, etc..
Operation only recommences when VCC drops below a level of about 4.5 V (typically,
when Vmains is disconnected for a short period).
7.16 Soft start-up (pin SENSE)
To prevent transformer rattle at start-up or during hiccup, the transformer peak current is
slowly increased by the soft start function. This can be achieved by inserting a resistor
and a capacitor between pin SENSE (pin 6) and sense resistor Rsense. An internal current
source charges the capacitor to Vsense = Iss × Rss (about 0.5 V maximum).
The start level and the time constant of the increasing primary current level can be
adjusted externally by changing the values of Rss and Css.
V
– (I × R )
ss ss
ocp
I
=
------------------------------------------
primary(max)
R
sense
τ = R × C
ss
ss
The charging current ISS will flow as long as the voltage on pin SENSE is
below approximately 0.5 V. If the voltage on pin SENSE exceeds 0.5 V, the soft start
current source will start limiting current Iss. At Vstart, the Iss current source is completely
switched off; see Figure 9.
Since the soft start current Iss is supplied from pin DRAIN, the Rss value will not affect VCC
current during start-up.
I
ss
0.5 V
start-up
R
C
ss
6
SENSE
R
sense
ss
V
ocp
mgu237
Fig 9. Soft start-up.
9397 750 13113
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
Preliminary data sheet
Rev. 01 — 28 May 2004
11 of 27
NXP [ NXP ]
