Philips TEA1566 Technical data

TEA1566

INTEGRATED CIRCUITS

DATA SHEET

TEA1566

GreenChipä; SMPS module

Preliminary specification			1999 Apr 20
File under Integrated Circuits, IC11

Philips Semiconductors	Preliminary specification
GreenChipä; SMPS module	TEA1566

FEATURES

Distinctive features

·High level of integration results in 20 to 50 fewer components compared to a power supply with discrete components

·On-chip 600 V MOSFET

·On/off function replaces expensive mains switch with functional switch

·Direct off-line operation (90 to 276 VAC)

·On-chip 5% accurate oscillator.

Green features

·Low power consumption in off-mode (<100 mW)

·On-chip efficient start-up current source giving fast start-up

·Burst mode stand-by (<2 W) for overall improved system efficiency

·Low power operation mode with lower frequency to reduce switching losses.

Protection features

·Demagnetization protection

·Cycle by cycle current limitation with programmable current trip level

·Over voltage protection

·Over temperature protection

·Safe-restart mode with reduced power for system fault conditions.

Highly versatile

·Usable in Buck and flyback topology

·Interfaces both primary and secondary side feedback.

APPLICATIONS

mains

output

9 Vin

8 NC

7 OOB

6 Dem

TEA1566 5 Gnd

4 Vctrl

3 Iref

2 Vaux

1 Isense

MGR691

Fig.1 Typical flyback application.

GENERAL DESCRIPTION

The GreenChipä, intended for off-line 90 to 276 VAC power supply applications, is a monolithic high voltage family of ICs that combines analog and digital circuits to implement all necessary control functions for a switched mode power supply. The functions include integrated high voltage start-up current source, voltage mode PWM control, 5% accurate trimmed oscillator, band gap derived reference voltages, comprehensive fault protection, and leading edge blanking. High level of integration leads to cost effective power supplies that are compact, weigh less, and at the same time give higher efficiency, are more reliable and simple to design. Efficient green features lead to very low power operation modes and a novel on/off function helps replace the expensive mains switch with a low cost functional switch.

1999 Apr 20

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Philips Semiconductors			Preliminary specification
GreenChipä; SMPS module				TEA1566
ORDERING INFORMATION
TYPE NUMBER		PACKAGE
	NAME	DESCRIPTION			VERSION
TEA1566S	SIL9P	plastic single in-line power package; 9 leads			SOT131-2
TEA1566J	DBS9P	plastic DIL-bent-SIL power package; 9 leads (lead length12 mm)			SOT157-2

BLOCK DIAGRAM

	Iref	Vaux					Vin
	3	2					9
	VAUX		START-UP
	MANAGEMENT		CURRENT SOURCE
	ON/OFF
7	1 kΩ				TEA1566
OOB
	5.5 V
	burst mode
	stand-by
		OVER		R	driver	power
					stage	MOSFET
		TEMPERATURE			Q
4		PROTECTION		S		6 Ω
Vctrl
	SAMPLE	SAMPLE			OVER CURRENT
	AND	AND
					PROTECTION
	HOLD1	HOLD2
			error		LEADING EDGE
				PWM
6			amplifier	comparator	BLANKING
Dem	DEMAGNETIZATION
			OSCILLATOR		FREQUENCY
	MANAGEMENT
					CONTROL
	NEGATIVE
	CLAMP
			5	8			1
			Gnd	NC		MGR692	Isense

Fig.2 Block diagram.

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Philips Semiconductors	Preliminary specification
GreenChipä; SMPS module	TEA1566

PINNING

SYMBOL		PIN		DESCRIPTION
Isense		1	programmable current sense
			resistor
Vaux		2	IC supply capacitor
Iref		3	reference resistor for setting
			internal reference currents
Vctrl		4	feedback voltage for duty cycle
			control
Gnd		5	ground
Dem		6	demagnetization input signal from
			primary side auxiliary winding
OOB		7	on/off/burst mode input signal
NC		8	not connected
Vin		9	MOSFET drain connection
handbook, halfpage		Isense	1
		Vaux	2
		Iref	3
		Vctrl	4
		Gnd	5	TEA1566
		Dem	6
		OOB	7
		NC	8
		Vin	9
				MGR693

Fig.3 Pin configuration.

FUNCTIONAL DESCRIPTION

The GreenChipä family of ICs are highly integrated, with most common PWM functions like error amplifier, oscillator, bias current generator, and band gap based reference voltage circuits fully integrated in the ICs. High level of integration leads to easy and cost effective

design of power supplies.The ICs have been fabricated in a Philips proprietary high voltage BCDMOS process that enables devices of up to 720 V to be fabricated on the same chip with low voltage circuitry.

An efficient on-chip start-up circuit enables fast start-up and dissipates negligible power after start up. On-chip accurate oscillator generates a saw tooth waveform which is used by the voltage mode feedback control circuitry to generate a pulse width modulated signal for driving the gate of the power MOSFET. A novel regulation scheme is used to implement both primary and secondary side regulation to minimize external component count. Protection features like over voltage, over current, over temperature, and demagnetization protection, give comprehensive safety against system fault conditions. The GreenChipä offers some advanced features that greatly enhance the efficiency of the overall system. Off-mode reduces the power consumption of the IC below 100 mW. Burst mode stand-by reduces the power consumption of the system to below 2 W. Low power operation mode reduces the operating frequency of the system, when the system is working under low load conditions, to reduce the switching losses.

Start-up current source and Vaux management

A versatile on-chip start-up current source makes an external, highly dissipating, trickle-charge circuit unnecessary. See Fig.2 for the block diagram of the IC.

The start-up current source derives power from the mains via pin Vin (drain). It supplies current (see symbols ‘Istart-low’ and ‘Istart-high’ of Chapter “Characteristics”) to charge the Vaux (IC supply) capacitor and at the same time provides current to the control circuitry of the IC. Once the Vaux capacitor is charged to its start-up voltage level (11 V), the on-chip oscillator starts oscillating and the IC starts switching the power MOSFET. Power is then supplied to the load capacitor via the secondary winding.

Figure 1 shows a typical flyback application diagram. The Vaux capacitor is also supplied by an auxiliary winding on the primary side. This winding is coupled to the secondary side winding supplying the output capacitor. As the output capacitor voltage increases and approaches its nominal value, the re-supply of the Vaux capacitor is done by the auxiliary winding. Figure 4 shows relevant waveforms at start-up. For successful take over of supply of Vaux capacitor by the auxiliary winding, it is important that the re-supply of Vaux capacitor starts before its voltage drops to its Under Voltage Lockout (UVLO) level of 8.05 V of the system and stops delivering power to the output.

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Philips Semiconductors

Preliminary specification

GreenChipä; SMPS module

TEA1566

In case of output short circuit, the Vaux capacitor is no

longer supplied by the auxiliary winding and its voltage

drops till it reaches the UVLO level. If the output is an open

Vaux

11 V

circuit, the output voltage will rise till it reaches the Over

(2)

Voltage Protection (OVP) level. The IC will detect this state

8.05 V

and stop switching.

In absence of switching of the power device, the Vaux

(1)

capacitor will not be re-supplied and its voltage will drop till

it reaches UVLO level. Once the Vaux voltage drops to

UVLO level, the start-up current source is re-activated and

t

it charges the Vaux capacitor to its start level and the

system goes through a cycle similar to the start-up cycle.

Vout

Figure 5 shows the relevant waveforms during safe-restart

mode. The charging current (see symbol ‘Irestart-prot’ in

Chapter “Characteristics”) from the start-up circuit during

the safe-restart mode is lower than the normal start-up

t

current (see symbol ‘Istart-high’ in

Chapter “Characteristics”) in order to implement a low

Vgate

“hiccup” duty cycle. This helps insure devices on the

output secondary winding do not get destroyed during

output short circuit, violating safety conditions.

off

switching

t MGR694

The start-up current source also plays a key role in

implementation of burst mode stand-by (see symbol

(1) Start-up current charges capacitor Vaux.

‘Irestart-stby’ in Chapter “Characteristics”), which will be

(2) Charging of capacitor Vaux is taken-over by the auxiliary winding.

explained later.

Fig.4 Normal start-up waveforms.

Vaux	MGR695
	fault condition
	normal operation
	(1)
	t
Vgate

switching

off

t

(1) Start-up current source charges capacitor Vaux.

Fig.5 Safe-start mode waveforms.

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Philips Semiconductors	Preliminary specification
GreenChipä; SMPS module	TEA1566

Reference

All reference voltages are derived from a temperature compensated, on-chip, band gap. The band gap reference voltage is also used, together with an external resistor connected at pin Iref, to generate accurate, temperature independent, bias currents in the chip:

VREF

IREF = ------------- [A]

RREF

The frequency of the controller is also set by the reference resistor Rref (also see Section “Oscillator”).

Sample and hold

GreenChipä ICs employ voltage mode feedback for regulating the output voltage. In primary feedback mode, a novel sample and hold circuit is used. The sample and hold circuit works by sampling the current into pin Dem, which is related to the output voltage via Rdem, during the time that the secondary current is flowing:

a ´ Vout = Iref ´ Rdem + Vdem+ where:

Vdem+ is specified in chapter “Characteristics”

a = a constant determined by turn ratio of the transformer.

This sampled current information is stored on the external capacitor connected to pin Vctrl. The pulse width modulator uses this voltage information to set the duty cycle of operation for the power MOSFET. In secondary feedback, the feedback voltage is provided by an opto-coupler.

Pulse width modulator

The pulse width modulator, which is made up of an inverting error amplifier and a comparator (see Fig.2), drives the power MOSFET with a duty cycle which is inversely proportional to the voltage on pin Vctrl.

In primary feedback mode, this is the voltage on the sample and hold capacitor and in secondary feedback mode, this voltage is provided by an opto-coupler. A signal from the oscillator sets a latch that turns on the power MOSFET. The latch is reset by the signal from the pulse width modulator or by the duty cycle limiting circuit.

The latching PWM mode of operation prevents multiple switching of the power switch. The maximum duty cycle is set internally at 80%.

Figure 7 shows the normal switching operation of the IC.

Oscillator

The oscillator is used to set the switching duty cycle by comparing the oscillator ramp to the output of the error amplifier in the pulse width modulator circuit.The oscillator is fully integrated and works by charging and discharging an internal capacitor between two voltage levels to create a sawtooth waveform with a rising edge which is 80% of the oscillator cycle. This ratio is used to set a maximum switching duty cycle of 80% for the IC. The oscillator is internally trimmed to 5% accuracy. The oscillator frequency can be adjusted between 50 to 100 kHz

(see symbol fosc-h-range in Chapter “Characteristics”) by changing the external reference resistor (see symbol Rref in Chapter “Characteristics”) that sets the chip bias currents. This gives additional flexibility to the power supply designer in the choice of his system components.The frequency is correlated with the value of the reference resistor Rref (see Fig.6).

In Chapter “Characteristics” fosc-typical, fosc-l and fosc-h and the Rref operating resistor range are specified.

			MGR936
110			55
handbook, halfpage			low
high
frequency			frequency
(kHz)			(kHz)
90			45
70			35
		(1)
		(2)
50			25
30			15
10	20	30	40
			RREF (kΩ)

(1)High frequency mode.

(2)Low frequency mode.

Fig.6 Frequency as function of the RREF value.

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(protection) current is therefore: Iprot

Philips Semiconductors	Preliminary specification
GreenChipä; SMPS module	TEA1566

Multi frequency control

The oscillator is also capable of working at a lower frequency (see fosc-l in Chapter “Characteristics”). A ratio of 1 : 2.5 is maintained between high and low frequency of the oscillator. Low frequency operation is invoked if the power supply is working at or below one ninth of its peak power. By working at a lower frequency, the switching losses in the power supply are reduced. A novel scheme is used to ensure that the transfer of high to low frequency and vice versa has no effect on the regulation of the output voltage.

Gate driver

The gate driver has a totem-pole output stage that has current sourcing capability of 120 mA and a current sink capability of 550 mA. This is to enable fast turn on and turn off of the power device for efficient operation.

A lower driver source current has been chosen in order to limit the DV/Dt at switch-on. This is advantageous for EMI (ElectroMagnetic Interference) and reduces the current spike across Rsense.

Demagnetization protection

This feature guarantees discontinuous conduction mode operation for the power supply which simplifies the design of feedback control and gives faster transient response.

Demagnetization protection is an additional protection feature that protects against saturation of the transformer/inductor. Demagnetization protection also protects the power supply components against excessive stresses at start-up, when all energy storage components are completely discharged. The converter is cycle by cycle protected during shorted output system fault condition due to the demagnetization protection. The value of the demagnetization resistor (Rdem) can be calculated with the formula given in Section “Sample and hold”.

Negative clamp

The negative clamp circuit does not let the voltage on pin Dem go below -0.4 V, when the auxiliary winding voltage goes negative during the time that the power device is turned on, to ensure correct operation of the IC.

Over voltage protection

An Over Voltage Protection (OVP) mode has been implemented in the GreenChipä series. This circuit works by sensing the Vaux voltage. If the output voltage exceeds the preset voltage limit, the OVP circuit turns off the power MOSFET. With no switching of the power device, the Vaux capacitor is not re-supplied and discharges to UVLO level and the system goes into the low dissipation safe-restart mode described earlier. The system recovers from the safe-restart mode only if the OVP condition is removed.

Over current protection

Cycle by cycle Over Current Protection (OCP) is provided by sensing the voltage on an external resistor which is connected to the source of the power MOSFET.

The voltage on the current sense resistor, which reflects the amplitude of the primary current, is compared internally with a reference voltage using a high speed comparator. This threshold voltage is specified as Vth(Imax) in the chapter “Characteristics”. The maximum primary

Vth ( Imax)

= ------------------------ [A]

Rsense

If the power device current exceeds the current limit, the comparator trips and turns off the power device.

The power device is typically turned off in 210 ns (see tD in Chapter “Characteristics”).

The availability of the current sense resistor off-chip for programming the OCP trip level increases design flexibility for the power supply designer. An off-chip current sense resistor also reduces the risk of an OCP condition being sensed incorrectly. At power MOSFET turn-on the

DV/Dt limiters capacitance discharge current does not have to flow through the sense resistor, because this capacitor can be connected between drain and source of the power MOSFET directly.

The Leading Edge Blanking (LEB) circuit works together with the OCP circuit and inhibits the operation of the OCP comparator for a short duration (see tLEB in

Chapter “Characteristics”) when the power device is turned on. This ensures that the power device is not turned off prematurely due to false sensing of an OCP condition because of current spikes caused by discharge of primary-side snubber and parasitic capacitances.

LEB time is not fixed and it tracks the oscillator frequency.

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Philips Semiconductors	Preliminary specification
GreenChipä; SMPS module	TEA1566

Over temperature protection

Protection against excessive temperature is provided by an analog temperature sensing circuit that turns off the power device when the temperature exceeds typically 140 °C.

On/off mode

The expensive mains switch can be replaced by an in-expensive functional switch by using the on/off mode. Figure 13 shows a flyback converter configured to use the on/off mode. Depending upon the position of switch S1, either voltage close to ground or a voltage of greater than typical 2.5 V exists on pin OOB.

The difference between these voltages is detected internally by the IC. The IC goes into the off-mode if the voltage is low, where it consumes a current of typical 350 μA (see Iin-off in Chapter “Characteristics”). If the voltage on pin OOB is typically 2.5 V (see Von/off in Chapter “Characteristics”), the IC goes through the start-up sequence and commences normal operation.

In Fig.14 a Mains Under Voltage Lock Out (MUVLO) function has been created using 3 resistors. Assuming that R3 is chosen very high ohmic, the GreenChip™ starts

operating if: V		R1	× V		( R1 » R2)
	MAINS	≈ -------		OOB
		R2

In this way it is assured that the power supply only starts working above a Vmains of e.g. 80 V. The bleeder current through R1 should be low (e.g. 30 μA at 300 V).

Burst mode stand-by

Pin OOB is also used to implement the burst mode stand-by. In burst mode stand-by, the power supply goes into a special low dissipation state where it typically consumes less than 2 W of power. Figure 14 shows a flyback converter using the burst mode stand-by feature. The system enters burst mode when the microcontroller closes switches S2 and S3 on the secondary side. Switch S2 shorts the output capacitor to the voltage level of the microcontroller capacitor. The output secondary winding now supplies the microcontroller capacitor. When the voltage on the microcontroller capacitor exceeds the zener voltage (Vz) the opto-coupler is activated which sends a signal to pin OOB. In response to this signal, the IC stops switching and goes into a “hiccup” mode.

Figure 7 shows the burst-mode operation graphically. The hiccup mode during burst mode operation differs from the hiccup in safe-restart mode during system fault. For safe restart mode, the power has to be reduced. For burst mode, sufficient power to supply the microcontroller has to be delivered. To prevent transformer rattle, the transformer peak current is reduced by a factor of 3. Burst mode stand-by operation continues till the microcontroller opens switches S2 and S3. The system then goes through the start-up sequence and commences normal switching behaviour.

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