TEA1507 Philips Semiconductors, TEA1507 Datasheet - Page 9

• Manufacturer Part Number: TEA1507
• Description: GreenChipII SMPS control IC
• Manufacturer: Philips Semiconductors

Philips Semiconductors
Burst mode standby
Pin CTRL (pin 3) is also used to implement the burst mode
standby. In burst mode standby, the power supply enters
a special low dissipation state, where it typically consumes
less than 1 W of input power (P
able to supply a microprocessor, for example. Figure 12
shows a flyback converter using the burst mode standby
function. The system enters burst mode standby when the
microprocessor closes switches S2 and S3 on the
secondary side. Switch S2 connects the high voltage
output secondary winding to the low voltage
microprocessor capacitor (C
When the voltage on C
opto-coupler is activated, sending a large current signal to
CTRL. In response to this signal, the IC stops switching
and enters a ‘hiccup’ mode. This burst activation signal
should be present for longer than the ‘burst blank’ period
(typically 30 s): the blanking time prevents false burst
triggering due to spikes. Figure 11 shows the burst-mode
standby signals. The hiccup mode during burst mode
standby operation does not differ from the hiccup mode in
safe-restart mode during a system fault condition (e.g.
OVP or output short circuit). The power is reduced
during soft-restart mode.
Burst mode standby operation continues until the
microcontroller opens switches S2 and S3. The system
then enters the start-up sequence and begins normal
switching behaviour.
(For burst mode specification, see Figs 11 and 12.)
Soft start-up (pin I
To prevent transformer rattle 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 I
resistor. An internal current source charges the capacitor
to V = I
The start level and the time constant of the increasing
primary current level can be adjusted externally by
changing the values of R
2000 Dec 05
I
burstmode
GreenChip II SMPS control IC
ss
=
R
ss
---------------- -
R
, with a maximum of about 0.5 V.
V
CTRL
th
sense
+
I
th on
C
)
ss
exceeds the Zener voltage, the
and C
C
sense
), bypassing C
o
< 100 mW), but is still
ss
(pin 5) and the sense
.
o
.
9
The charging current I
pin I
pin I
will start limiting the current I
current source is completely switched off (see Fig.9).
Since the soft start current I
charging current, the R
current level by a maximum of 60 A (typical value).
Driver
The driver circuit to the gate of the power MOSFET has a
current sourcing capability of typically 125 mA and a
current sink capability of typical 540 mA. This permits fast
turn-on and turn-off of the power MOSFET for efficient
operation.
A low driver source current has been chosen to limit the
Interference (EMI) and also limits the current spikes
across R
I
handbook, halfpage
primary(max)
V/ t at switch-on. This reduces Electro Magnetic
=
sense
sense
R
ss
sense
0.5 V
is below approximately 0.5 V. If the voltage on
exceeds the 0.5 V, the soft start current source
C
=
ss
.
V
------------------------------------------- -
ocp
Fig.9 Soft start-up.
–
R
sense
ss
I
start-up
V ocp
ss
ss
I sense
I SS
will flow as long as the voltage on
pin 5
value will affect the V
R
ss
ss
ss
. At the V
is subtracted from pin V
R SS
C SS
Preliminary specification
CC(start)
TEA1507
R sense
MGU237
level, the I
CC
charging
CC
ss