TEA1522T View Datasheet(PDF) - NXP Semiconductors.

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TEA1522T

SMPS ICs for low-power systems

NXP Semiconductors. 

NXP Semiconductors

TEA152x

SMPS ICs for low-power systems

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.

8.1 Start-up and Underoltage lockout

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(startup) 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.

When for some reason the auxiliary supply is not sufficient, the high-voltage supply also

supplies the IC. 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.

8.2 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.

To ensure that the capacitor can be charged within the charge time, the value of the

oscillator capacitor should be limited to approximately 1 nF.

8.3 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 (−2.5 V)

multiplied by the gain of the error amplifier (typically 20 dB which is 10×).

8.4 Valley switching

A new cycle is started when the primary switch is switched on (see Figure 4). 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-----------------------

(1)

2 × π × (Lp × Cp)

where:

Lp = primary self-inductance

Cp = parasitic capacitance on drain node

TEA152X

Product data sheet

All information provided in this document is subject to legal disclaimers.

Rev. 04 — 14 September 2010

© NXP B.V. 2010. All rights reserved.

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