
2002 Aug 27
5
Philips Semiconductors
Product specification
GreenChip
II SMPS control IC
TEA1552
PINNING
FUNCTIONAL DESCRIPTION
The TEA1552 is the controller of a compact flyback
converter, with the IC situated at the primary side.
An auxiliary winding of the transformer provides
demagnetization detection and powers the IC after
start-up.
The TEA1552 operates in multi modes (see Fig.4).
The next converter stroke is started only after
demagnetization of the transformer current (zero current
switching), while the drain voltage has reached the lowest
voltage to prevent switching losses (green function). The
primary resonant circuit of primary inductance and drain
capacitor ensures this quasi-resonant operation. The
design can be optimized in such a way that zero voltage
switching can be reached over almost the complete
universal mains range.
To prevent very high frequency operation at lower loads,
the quasi-resonant operation changes smoothly in fixed
frequency PWM control.
At very low power (standby) levels, the frequency is
controlled down, via the VCO, to a minimum frequency of
approximately 25 kHz.
Start-up, mains enabling operation level and
undervoltage lock-out
(see Figs 11 and 12)
Initially, the IC is self supplying from the rectified mains
voltage via pin DRAIN. Supply capacitor C
VCC
is charged
by the internal start-up current source to a level of
approximately 4 V or higher, depending on the drain
voltage. Once the drain voltage exceeds the M-level
(mains-dependent operation-enabling level), the start-up
current source will continue charging capacitor C
VCC
(switch S1 will be opened); see Fig.2. The IC will activate
the power converter as soon as the voltage on pin V
CC
passes the level V
CC(start)
. The IC supply is taken over by
the auxiliary winding as soon as the output voltage
reaches its intended level and the IC supply from the
mains voltage is subsequently stopped for high efficiency
operation (green function).
The moment the voltage on pin V
CC
drops below the
undervoltage lock-out level V
UVLO
, the IC stops switching
and enters a safe restart from the rectified mains voltage.
Inhibiting the auxiliary supply by external means causes
the converter to operate in a stable, well defined burst
mode.
Supply management
All (internal) reference voltages are derived from a
temperature compensated, on-chip band gap circuit.
SYMBOL PIN
VCOadj
I
sense
STDBY
DRIVER
HVS
DESCRIPTION
1
2
3
4
5
VCO adjustment input
programmable current sense input
standby indication or control output
gate driver output
high voltage safety spacer, not
connected
high voltage safety spacer, not
connected
drain of external MOS switch, input for
start-up current and valley sensing
supply voltage
not connected
ground
5 V output
lock input
control input
input from auxiliary winding for
demagnetization timing, OVP and OPP
HVS
6
DRAIN
7
V
CC
n.c.
GND
V
CC(5V)
LOCK
CTRL
DEM
8
9
10
11
12
13
14
handbook, halfpage
TEA1552T
MBL497
1
2
3
4
5
6
7
VCOadj
Isense
STDBY
DRIVER
HVS
HVS
DRAIN
DEM
CTRL
LOCK
VCC(5V)
GND
n.c.
VCC
14
13
12
11
10
9
8
Fig.3 Pin configuration.