TEA1532
Philips Semiconductors
GreenChip II SMPS control IC
value of Rslopecomp. Slope compensation prevents modulation of the on-time (duty cycle)
while operating in FF CCM. A possible drawback of sub-harmonic oscillation can be
output voltage ripple.
TEA1532
Slope compensation
current
R
slopecomp
CTRL
4
−1
5.6 V
R
CTRL
control
detect
0.63 V
001aaa830
Fig 7. Slope compensation.
7.11 Minimum and maximum on-time
The minimum on-time of the SMPS is determined by the LEB time. The IC limits the
on-time to a maximum time which is dependent on the mode of operation:
QR mode: When the system requires an ‘on-time’ of more than 25 µs, a fault condition is
assumed (e.g. CVCC removed), the IC stops switching and enters the safe restart mode.
CCM: The driver duty cycle is limited to 70 %. So the maximum on-time is correlated to
the oscillator time which results in an accurate limit of the minimum input voltage of the
flyback converter.
7.12 PROTECT and timing input
The PROTECT input (pin 3) is a multi-purpose (high-impedance) input, which can be used
to switch off the IC and create a relatively long timing function. As soon as the voltage on
this pin rises above 2.5 V, switching stops immediately. For the timing function, a current of
typically 50 µA flows out of pin PROTECT and charges an external capacitor until the
activation level of 2.5 V is reached. This current source however, is only activated when
the converter is not in regulation, which is detected by the voltage on pin CTRL
(VCTRL < 0.63 V). A (small) discharge current is also implemented to ensure that the
capacitor is not charged, for example, by spikes, and a MOSFET switch is added to
ensure a defined start situation. The voltage on pin CTRL determines whether the IC
enters latched protection mode, or safe restart protection mode:
9397 750 13113
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
Preliminary data sheet
Rev. 01 — 28 May 2004
8 of 27
NXP [ NXP ]
