Philips TEA1620 Service Manual

INTEGRATED CIRCUITS

DATA SHEET

TEA1620P

STARplugTM

Preliminary specification			2003 June 18
File under Integrated Circuits, IC11

Philips Semiconductors	Preliminary specification
STARplugTM	TEA1620P

FEATURES

∙Designed for general purpose supplies up to 50 W

∙Integrated power switch:

– TEA1620: 48 Ω; 650 V

∙Operates from universal AC mains supplies (80 to 276 V)

∙Adjustable frequency for flexible design

∙RC oscillator for load insensitive regulation loop constant

∙Valley switching for minimum switch-on loss

∙Frequency reduction at low power output makes low standby power possible (<100 mW)

∙Adjustable overcurrent protection

∙Under voltage protection

∙Temperature protection

∙Short circuit winding protection

∙Simple application with both primary and secondary (opto) feedback

∙Available in 8-pin DIP package.

GENERAL DESCRIPTION

The TEA1620P is a Switched Mode Power

Supply (SMPS) controller IC that operates directly from the rectified universal mains. It is implemented in the high voltage EZ-HV SOI process, combined with a low voltage BICMOS process. The device includes a high voltage power switch and a circuit for start-up directly from the rectified mains voltage.

A dedicated circuit for valley switching is built in, which makes a very efficient slim-line electronic powerplug concept possible.

In its most basic version of application, the TEA1620P acts as a voltage source. Here, no additional secondary electronics are required. A combined voltage and current source can be realized with minimum costs for external components. Implementation of the TEA1620P renders an efficient and low cost power supply system.

APPLICATIONS

Typical application areas for the STARplugTM are:

∙Chargers

∙Adapters

∙STB (Set Top Box)

∙DVD

∙CD(R)

∙TV/monitor standby supplies

∙PC peripherals

∙PC Silverbox standby SMPS

∙Microcontroller supplies in home applications and small portable equipment, etc.

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Philips Semiconductors					Preliminary specification
STARplugTM					TEA1620P
QUICK REFERENCE DATA
SYMBOL	PARAMETER		CONDITIONS	MIN.	TYP.	MAX.	UNIT
Vdrain(max)	maximum voltage at the DRAIN		Tj > 0 °C	−	−	650	V
	pin
RDS(on)	drain-source on-state resistance		Tj = 25 °C; Isource = −0.06 A	−	48	55.2	Ω
	of TEA1620		Tj = 100 °C; Isource = −0.06 A	−	68	78.2	Ω
VCC(max)	maximum supply voltage			−	−	40	V
fosc	frequency range of oscillator			10	−	200	kHz
Idrain	supply current drawn from DRAIN		no auxiliary supply	−	0.5	−	mA
	pin
Tamb	ambient temperature			−20	−	+85	°C
ORDERING INFORMATION
TYPE			PACKAGE
NUMBER	NAME		DESCRIPTION			VERSION
TEA1620P	DIP8	plastic dual in-line package; 8 leads (300 mil)				SOT97-1

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Philips Semiconductors	Preliminary specification
STARplugTM	TEA1620P
BLOCK DIAGRAM

VCC	1		SUPPLY	8
				DRAIN
			TEA15 x	VALLEY
			TEA1620P
	2		LOGIC	7
GND
				n.c.
				100 mV
			PWM
	stop			6
RC	3		THERMAL
	OSCILLATOR			SOURCE
	low freq		SHUTDOWN
			PROTECTION
			LOGIC	blank
	F		POWER-UP
			RESET
	1.8	U
			overcurrent
	2.5 V			0.5 V
REG	4			5
	10x			AUX
			short circuit winding
				0.75 V
				MGT419

Fig.1 Block diagram.

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Philips Semiconductors			Preliminary specification
STARplugTM			TEA1620P
PINNING
SYMBOL	PIN	DESCRIPTION
	TEA1620P
VCC	1	supply voltage
GND	2	ground
RC	3	frequency setting
REG	4	regulation input
AUX	5	input for voltage from auxiliary winding for timing
		(demagnetization)
SOURCE	6	source of internal MOS switch
n.c.	7	not connected
DRAIN	8	drain of internal MOS switch; input for start-up current
		and valley sensing

handbook, halfpage

VCC	1	8		DRAIN
GND	2	7		n.c.
		52xP
RC	3	TEA1620P		SOURCE
		6
REG	4	5		AUX
		MGT420

Fig.2 Pin configuration of TEA1620P.

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Philips Semiconductors	Preliminary specification
STARplugTM	TEA1620P

FUNCTIONAL DESCRIPTION

The TEA1620P is the heart of a compact flyback converter, with the IC placed at the primary side. The auxiliary winding of the transformer can be used for indirect feedback to control the isolated output. This additional winding also powers the IC. A more accurate control of the output voltage and/or current can be implemented with an additional secondary sensing circuit and optocoupler feedback.

The TEA1620P uses voltage mode control. The frequency is determined by the maximum transformer demagnetizing time and the time of the oscillator. In the first case, the converter operates in the Self Oscillating Power Supply (SOPS) mode. In the latter case, it operates at a constant frequency, which can be adjusted with external components RRC and CRC. This mode is called Pulse Width Modulation (PWM). Furthermore, a primary stroke is started only in a valley of the secondary ringing. This valley switching principle minimizes capacitive switch-on losses.

Start-up and under voltage lock-out

Initially, the IC is self supplying from the rectified mains voltage. The IC starts switching as soon as the voltage on

pin VCC passes the VCC(start) level. The supply is taken over by the auxiliary winding of the transformer as soon as

VCC is high enough and the supply from the line is stopped for high efficiency operation.

As soon as the voltage on pin VCC drops below the

VCC(stop) level, the IC stops switching and restarts from the rectified mains voltage.

Oscillator

The frequency of the oscillator is set by the external resistor and capacitor on pin RC. The external capacitor is

charged rapidly to the VRC(max) level and, starting from a new primary stroke, it discharges to the VRC(min) level. Because the discharge is exponential, the relative

sensitivity of the duty factor to the regulation voltage at low duty factor is almost equal to the sensitivity at high duty factors. This results in a more constant gain over the duty factor range compared to PWM systems with a linear sawtooth oscillator. Stable operation at low duty factors is easily realized. For high efficiency, the frequency is reduced as soon as the duty factor drops below a certain value. This is accomplished by increasing the oscillator charge time.

Duty factor control

The duty factor is controlled by the internal regulation voltage and the oscillator signal on pin RC. The internal

regulation voltage is equal to the external regulation voltage (minus 2.5 V) multiplied by the gain of the error amplifier (typical 20 dB (10 ×)).

Valley switching

A new cycle is started when the primary switch is switched on (see Fig.3). After a certain time (determined by the oscillator voltage RC and the internal regulation level), the switch is turned off and the secondary stroke starts. The internal regulation level is determined by the voltage on pin REG. After the secondary stroke, the drain voltage shows an oscillation with a frequency of approximately

1

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

(2 × π × (Lp × Cp))

where Lp is the primary self inductance and Cp is the parasitic capacitance on the drain node.

As soon as the oscillator voltage is high again and the secondary stroke has ended, the circuit waits for a low drain voltage before starting a new primary stroke.

Figure 3 shows the drain voltage together with the valley signal, the signal indicating the secondary stroke and the RC voltage.

The primary stroke starts some time before the actual valley at low ringing frequencies, and some time after the actual valley at high ringing frequencies. Figure 4 shows a typical curve for a reflected output voltage N × Vo of 80 V. This voltage is the output voltage Vo (see Fig.5) transferred to the primary side of the transformer with the factor N (determined by the turns ratio of the transformer). Figure 4 shows that the system switches exactly at minimum drain voltage for ringing frequencies of 480 kHz, thus reducing the switch-on losses to a minimum.

At 200 kHz, the next primary stroke is started at 33° before the valley. The switch-on losses are still reduced significantly.

Demagnetization

The system operates in discontinuous conduction mode all the time. As long as the secondary stroke has not ended, the oscillator will not start a new primary stroke. During the first tsuppr seconds, demagnetization recognition is suppressed. This suppression may be necessary in applications where the transformer has a large leakage inductance and at low output voltages.

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