TEA1507 查看數據表（PDF） - Philips Electronics

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TEA1507

GreenChipII SMPS control IC

Philips Electronics 

Philips Semiconductors

GreenChip™II SMPS control IC

Preliminary specification

TEA1507

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 (the maximum external control voltage results in

a minimum duty cycle).

Oscillator

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).

Valley switching (see Fig.7)

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.

As soon as the oscillator voltage is high again and the

secondary stroke has ended, the circuit waits for the

lowest drain voltage before starting a new primary stroke.

This method is called valley detection. Figure 7 shows the

drain voltage together with the valley signal, the signal

indicating the secondary stroke and the oscillator signal.

In an optimum design, the reflected secondary voltage on

the primary side will force the drain voltage to zero. Thus,

zero voltage switching is very possible, preventing large

capacitive switching losses P = 12-- × C × V2 × f , and

allowing high frequency operation, which results in small

and cost effective inductors.

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

tsuppr time. This suppression may be necessary in

applications where the transformer has a large leakage

inductance and at low output voltages/start-up.

Minimum and maximum ‘on-time’

The minimum ‘on-time’ of the SMPS is determined by the

Leading Edge Blanking (LEB) time. The IC limits the

‘on-time’ to 50 µs. When the system desires an ‘on-time’

longer than 50 µs, a fault condition is assumed (e.g.

removed Ci), the IC will stop switching and enter the safe

restart mode.

handbook, halVfpsaegnese(max)

0.5 V

MGU233

handbook, halfpage f

MGU234

175 kHz

1V

(typ)

1.5 V

(typ)

VCTRL

Fig.5 The Vsense(max) voltage as function of VCTRL.

6 kHz

50 mV 75 mV Vsense(max)

(typ) (typ)

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

2000 Dec 05

6

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