Philips TEA1504 Datasheet

INTEGRATED CIRCUITS

DATA SH EET

TEA1504

GreenChip; SMPS control IC

Preliminary speciﬁcation File under Integrated Circuits, IC11

1998 Mar 17

Philips Semiconductors Preliminary speciﬁcation

GreenChip; SMPS control IC TEA1504

PRODUCT HIGHLIGHTS Distinctive features

• High level of integration leads to 20 to 50 fewer components compared to power supply with discrete components

• On-chip efficient startup current source giving fast startup

• 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)

• 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

• Accurate over voltage protection which tracks the output voltage

• 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.

Output

OOB

Dem

Gnd

Vctrl

Iref

Vin

Driver

Isense

Vaux

Fig.1 Typical Flyback Application.

GENERAL DESCRIPTION

The GreenChip, 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 startup current source, voltage mode PWM control, 5% accurate trimmed oscillator, bandgap 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.

ORDERING INFORMATION

PACKAGE

TYPE NUMBER

NAME DESCRIPTION VERSION

TEA1504 DIP14 plastic dual in-line package; 14 leads (300 mil) SOT27-1

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Philips Semiconductors Preliminary speciﬁcation

GreenChip; SMPS control IC TEA1504

FUNCTIONAL BLOCK DIAGRAM

OOB

5.5V

Vctrl

Dem

On/Off

Iref

Burst mode stand-by

Sample & Hold 1

Demag Mgmnt

Vaux

Vaux management

Over temp protection

Sample & Hold 2

Error Amp.

Oscillator

PWM Comp.

Vin

Startup current source

* Over current protection * Leading Edge blanking

Frequency control

TEA1504

Driver

Isense

Negative Clamp

Gnd

Fig.2 Functional Block Diagram.

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NC pins: 2, 3, 10 & 12

Philips Semiconductors Preliminary speciﬁcation

GreenChip; SMPS control IC TEA1504

PINNING

SYMBOL PIN DESCRIPTION

Vin 1 MOSFET Drain connection HVS 2 High voltage safety spacer NC 3 Not connected Driver 4 MOSFET gate driver output Isense 5 Programmable current

sense resistor Vaux 6 IC supply capacitor DS 7 Supply for driver circuit Iref 8 Reference resistor for

setting internal reference

currents Vctrl 9 Feedback voltage for duty

cycle control NC 10 Not connected Gnd 11 Ground NC 12 Not connected Dem 13 Demagnetization input

signal from primary side

auxiliary winding OOB 14 On/Off/Burst Mode input

signal

Vin

HVS

Driver

Isense

Vaux

TEA1504

Fig.3 Pin assignment.

OOB

Dem

Gnd

Vctrl

Iref

FUNCTIONAL DESCRIPTION

The GreenChip 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 650 V to be fabricated on the same chip with low voltage circuitry.

An efficient on-chip startup circuit enables fast startup 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 GreenChip 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.

Startup current source and vaux management

A versatile on-chip startup current source makes an external, highly dissipative, trickle-charge circuit unnecessary. Refer to Fig.2 for a block diagram of the IC. The startup current source derives power from the mains via the Vin (drain) pin. It supplies current (see Istart-low and Istart-high in 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 startup 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 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

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Philips Semiconductors Preliminary speciﬁcation

GreenChip; SMPS control IC TEA1504

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 startup. 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 8.15 V.

Vaux

11V

8.15V

Istartup charging Vaux cap

charging of Vaux cap taken over by Auxiliary Winding

circuit, the output voltage will rise till it reaches the OVP level. The IC will detect this state and stop switching. In absence of switching of the power device, the Vaux 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 startup current source is re-activated and it charges the Vaux capacitor to its start level and the system goes through a cycle similar to the startup cycle. Figure 5 shows the relevant waveforms during safe-restart mode. The charging current (see Irestart-prot in Chapter “Characteristics”) from the startup circuit during the safe-restart mode is lower than the normal startup current (see Istart-high in Chapter “Characteristics”) in order to implement a low “hiccup” duty cycle. This helps insure devices on the output secondary winding do not get destroyed during output short circuit, violating safety conditions.

Vaux

Normal operation

Fault condition

Vout

Vgate

Off

Fig.4 Normal startup waveforms.

The startup current source also helps implement the safe-restart or “hiccup” mode during system fault conditions like output short circuit, output open circuit, and Over Voltage Protection (OVP). In all the above fault situations, the IC reacts by inhibiting the normal operation of the system and stops delivering power to the output. 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

Switching

Startup current source charging Vaux capacitor

Vgate

Switching

Off

Fig.5 Safe-restart mode waveforms.

The startup current source also plays a key role in implementation of burst mode stand-by (see Irestart-stdby in Chapter “Characteristics”), which will be explained later.

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

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Philips Semiconductors Preliminary speciﬁcation

GreenChip; SMPS control IC TEA1504

Sample and Hold

GreenChip 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 the demag pin, which is related to the output voltage via Rdem, during the time that the secondary current is flowing: V

out=Iref

× R

dem+Vdem+

This sampled current information is stored on the external capacitor connected to the Vctrl pin. 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 (Fig.2), drives the power MOSFET with a duty cycle which is inversely proportional to the voltage at the Vctrl pin. In primary feedback, this is the voltage on the Sample and Hold capacitor and in secondary feedback, 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 6 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 49 to 91 kHz (see f

osc-h-range

in Chapter “Characteristics”) by changing the external reference resistor (see 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 Rref

resistor:

oscfosc typical–

osc-typical

and f

osc-h

is specified in Chapter “Characteristics”, f

. The operating Rref resistor range is specified in

24.900

× Hz[]=

-----------------Rref

osc-l

Chapter “Characteristics”, Rref.

Multi Frequency Control

The oscillator is also capable of working at a lower frequency (see f

in Chapter “Characteristics”). A ratio

osc-l

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 500 mA. This is to enable fast turn on and turn off of the power device for efficient operation. In the DIL14 controller version, the driver supply and driver output pins are available separately to the power supply designer. In this way the power supply designer can control the source and sink currents of the gate driver circuit with a minimum of external components.

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 startup, when all energy storage components are completely discharged, and during shorted output system fault condition.

Negative Clamp

The negative clamp circuit does not let the voltage at the demag pin 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.

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