Philips TEA1552 User Manual

TEA1552

INTEGRATED CIRCUITS

DATA SHEET

TEA1552

GreenChipäII SMPS control IC

Product specification			2002 Aug 27
Supersedes data of 2002 Jul 03

Philips Semiconductors	Product specification
GreenChipäII SMPS control IC	TEA1552

FEATURES

Distinctive features

·Universal mains supply operation (70 to 276 V AC)

·High level of integration, giving a very low external component count.

Green features

·Valley or zero voltage switching for minimum switching losses

·Efficient quasi-resonant operation at high power levels

·Frequency reduction at low power standby for improved system efficiency (<3 W)

·Cycle skipping mode at very low loads. Pi < 300 mW at no-load operation for a typical adapter application

·On-chip start-up current source

·Standby indication pin to indicate low output power consumption.

Protection features

·Safe restart mode for system fault conditions

·Continuous mode protection by means of demagnetization detection (zero switch-on current)

·Accurate and adjustable overvoltage protection (latched)

·Short winding protection

·Undervoltage protection (foldback during overload)

·Overtemperature protection (latched)

·Low and adjustable overcurrent protection trip level

·Soft (re)start

·Mains voltage-dependent operation-enabling level

·General purpose input for lock protection.

APPLICATIONS

Typical application areas are adapters and chargers (e.g. for laptops, camcorders and printers) and all applications that demand an efficient and cost-effective solution up to 250 W.

GENERAL DESCRIPTION

The GreenChipä(1)II is the second generation of green Switched Mode Power Supply (SMPS) control ICs operating directly from the rectified universal mains. A high level of integration leads to a cost effective power supply with a very low number of external components.

The special built-in green functions allow the efficiency to be optimum at all power levels. This holds for quasi-resonant operation at high power levels, as well as fixed frequency operation with valley switching at medium power levels. At low power (standby) levels, the system operates at reduced frequency and with valley detection.

The proprietary high voltage BCD800 process makes direct start-up possible from the rectified mains voltage in an effective and green way. A second low voltage BICMOS IC is used for accurate, high speed protection functions and control.

Highly efficient, reliable supplies can easily be designed using the GreenChipII control IC.

(1)GreenChip is a trademark of Koninklijke Philips Electronics N.V.

2002 Aug 27

2

Philips Semiconductors	Product specification
GreenChipäII SMPS control IC	TEA1552

VCOadj	1	14	DEM
Isense	2	13	CTRL
STDBY	3	12	LOCK
DRIVER	4	TEA1552T 11	VCC(5V)
HVS	5	10	GND
HVS	6	9	n.c.
DRAIN	7	8	VCC

MBL498

Fig.1 Basic application.

ORDERING INFORMATION

TYPE		PACKAGE
NUMBER	NAME	DESCRIPTION	VERSION
TEA1552T	SO14	plastic small outline package; 14 leads; body width 3.9 mm	SOT108-1

2002 Aug 27

3

Philips Semiconductors	Product specification
GreenChipäII SMPS control IC	TEA1552

BLOCK DIAGRAM

8		SUPPLY					START-UP			7	DRAIN
VCC		MANAGEMENT					CURRENT SOURCE
									clamp
		internal UVLO start					VALLEY			5, 6	HVS
		supply
S1	M-level									14
		VOLTAGE									DEM
10					LOGIC
GND		CONTROLLED
		OSCILLATOR
							100 mV
3	FREQUENCY							OVER-
								VOLTAGE
STDBY
	CONTROL						PROTECTION
1										4
VCOadj					LOGIC			DRIVER			DRIVER
									Iss
		POWER-ON			S	Q		LEB	soft	0.5 V
		RESET
13
	−1								start
CTRL								blank
									S2
			UVLO		R	Q				2
											Isense
								OCP
TEA1552				MAXIMUM
				ON-TIME
			PROTECTION
12
LOCK					S	Q	short
300 Ω								0.88 V
							winding
2.5 V
	lock	OVER-
5.6 V		TEMPERATURE			R	Q				11
	detect		VCC < 4.5 V								VCC(5V)
		PROTECTION
							OVER-POWER		5 V/1 mA
							PROTECTION		(max)
										MBL499
			Fig.2	Block diagram.
2002 Aug 27					4

Philips Semiconductors	Product specification
GreenChipäII SMPS control IC	TEA1552

PINNING

SYMBOL	PIN				DESCRIPTION
VCOadj	1	VCO adjustment input
Isense	2	programmable current sense input
STDBY	3	standby indication or control output
DRIVER	4	gate driver output
HVS	5	high voltage safety spacer, not
		connected
HVS	6	high voltage safety spacer, not
		connected
DRAIN	7	drain of external MOS switch, input for
		start-up current and valley sensing
VCC	8	supply voltage
n.c.	9	not connected
GND	10	ground
VCC(5V)	11	5 V output
LOCK	12	lock input
CTRL	13	control input
DEM	14	input from auxiliary winding for
		demagnetization timing, OVP and OPP
handbook, halfpage
	VCOadj		1			14	DEM
	Isense		2			13	CTRL
	STDBY		3			12	LOCK
	DRIVER		4	TEA1552T		11	VCC(5V)
	HVS		5			10	GND
	HVS		6			9	n.c.
	DRAIN		7			8	VCC
					MBL497
		Fig.3		Pin configuration.

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 CVCC 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 CVCC (switch S1 will be opened); see Fig.2. The IC will activate the power converter as soon as the voltage on pin VCC

passes the level VCC(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 VCC drops below the undervoltage lock-out level VUVLO, 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.

2002 Aug 27

5

Philips Semiconductors	Product specification
GreenChipäII SMPS control IC	TEA1552

f		MBL500
handbook, halfpage(kHz)
VCO	fixed	quasi resonant
125

25

P (W)

Fig.4 Multi mode operation.

Current mode control

Current mode control is used for its good line regulation behaviour.

The ‘on-time’ is controlled by the internally inverted control pin voltage, which is compared with the primary current information. The primary current is sensed across an external resistor. The driver output is latched in the logic, preventing multiple switch-on.

The internal control voltage is inversely proportional to the external control pin voltage, with an offset of 1.5 V. This means that a voltage range from 1 to 1.5 V on pin CTRL will result in an internal control voltage range from

0.5 to 0 V (a high external control voltage results in a low duty cycle).

Oscillator

MGU233

Vsense(max) handbook, halfpage

0.52 V

1 V	1.5 V		VCTRL
(typ)	(typ)

Fig.5 Vsense(max) as a function of VCTRL.

The maximum fixed frequency of the oscillator is set by an internal current source and capacitor. The maximum frequency is reduced once the control voltage enters the VCO control window. Then, the maximum frequency changes linearly with the control voltage until the minimum frequency is reached (see Figs 5 and 6).

MBL501

f

handbook, halfpage

(kHz)

125 kHz

125

25

VCO2	VCO1 Vsense(max) (V)
level	level

Fig.6 VCO frequency as a function of Vsense(max).

VCO adjustment

The VCOadj pin can be used to set the VCO operation point. As soon as the peak voltage on the sense resistor is controlled below half the voltage on the VCOadj pin (VCO1 level), frequency reduction will start. The actual peak voltage on sense will be somewhat higher due to switch-off delay (see Fig.7). The frequency reduction will stop approximately 25 mV lower (VCO2 level), when the minimum frequency is reached.

Cycle skipping

At very low power levels, a cycle skipping mode will be activated. A high control voltage will reduce the switching frequency to a minimum of 25 kHz. If the voltage on the control pin has raised even more, switch-on of the external power MOSFET will be inhibited until the voltage on the control pin has dropped to a lower value again (see Fig.7).

For system accuracy, it is not the absolute voltage on the control pin that will trigger the cycle skipping mode, but a signal derived from the internal VCO will be used.

Remark: If the no-load requirement of the system is such that the output voltage can be regulated to its intended level at a switching frequency of 25 kHz or above, the cycle skipping mode will not be activated.

2002 Aug 27

6

Philips Semiconductors	Product specification
GreenChipäII SMPS control IC	TEA1552

					fosc
1.5 V − VCTRL		current			dV2	dV1
					fmax
CTRL		comparator
				DRIVER
			DRIVER
				Isense	fmin
VCC(5V)	X2
5 V	Vx				VSTDBY	dV3	V	x	(mV)
							dV4
					(V)
		V
VCOadj			OSCILLATOR				VCOadj
		I
					5
					0
					cycle		Vx (mV)
					skipping
					1
				MBL502	0
							Vx (mV)

The voltage levels dV1, dV2, dV3 and dV4 are fixed in the IC to typically 50 mV, 18 mV, 40 mV and 15 mV respectively.

The level at which VCO mode of operation starts or ends can be externally controlled with the VCOadj pin.

Fig.7 A functional implementation of the standby and cycle skipping circuitry.

Standby output

The STDBY output pin (VSTDBY = 5 V) can be used to drive an external NPN transistor or FET in order to e.g.

switch-off a PFC circuit. The STDBY output is activated by the internal VCO: as soon as the VCO has reduced the switching frequency to (almost) the minimum frequency of 25 kHz, the STDBY output will be activated (see Fig.7). The STDBY output will go low again as soon as the VCO allows a switching frequency close to the maximum frequency of 125 kHz.

Demagnetization

The system will be in discontinuous conduction mode all the time. The oscillator will not start a new primary stroke until the secondary stroke has ended.

Demagnetization features a cycle-by-cycle output short-circuit protection by immediately lowering the frequency (longer off-time), thereby reducing the power level.

Demagnetization recognition is suppressed during the first

time (tsuppr). This suppression may be necessary in applications where the transformer has a large leakage

inductance and at low output voltages/start-up.

OverVoltage Protection (OVP)

An OVP mode is implemented in the GreenChip series. For the TEA1552, this works by sensing the auxiliary voltage via the current flowing into pin DEM during the secondary stroke. The auxiliary winding voltage is a well-defined replica of the output voltage. Any voltage spikes are averaged by an internal filter.

If the output voltage exceeds the OVP trip level, the OVP circuit switches off the power MOSFET. The controller then waits until the UVLO level is reached on pin VCC. When VCC drops to UVLO, capacitor CVCC will be

recharged to the Vstart level, however the IC will not start switching again. Subsequently, VCC will drop again to the

UVLO level, etc.

2002 Aug 27

7

Philips Semiconductors	Product specification
GreenChipäII SMPS control IC	TEA1552

Operation only recommences when the VCC voltage drops below a level of approximately 4.5 V (practically when the Vmains has been disconnected for a short period).

The output voltage (VOVP) at which the OVP function trips, can be set by the demagnetization resistor RDEM:

VOVP	Ns	× [IOVP(DEM) × RDEM + Vclamp(DEM)(pos) ]
	= -----------
	Naux

where Ns is the number of secondary turns and Naux is the number of auxiliary turns of the transformer.

Current IOVP(DEM) is internally trimmed.

The value of the demagnetization resistor (RDEM) can be adjusted to the turns ratio of the transformer, thus making an accurate OVP possible.

Valley switching (see Fig.8)

A new cycle starts when the power switch is switched on. After the ‘on-time’ (which is determined by the ‘sense’ voltage and the internal control voltage), the switch is opened and the secondary stroke starts.

After the secondary stroke, the drain voltage shows an oscillation with a frequency of approximately

1

----------------------------------------------------

(2 × π × (Lp × Cd))

where Lp is the primary self inductance of the transformer and Cd is the capacitance on the drain node.

handbook, full pagewidth	primary	secondary	secondary
	stroke	stroke	ringing
	drain
	valley
	secondary
	stroke
			B	A
	oscillator
				MGU235

A:Start of new cycle at lowest drain voltage.

B:Start of new cycle in a classical PWM system at high drain voltage.

Fig.8 Signals for valley switching.

2002 Aug 27

8