TEA1553T_1

© NXP B.V. 2007. All rights reserved.

Product data sheet

Rev. 01 — 3 July 2007

7 of 27

NXP Semiconductors

TEA1553T

GreenChip II SMPS control IC

7.3 Current mode control

Current mode control is used for its good line regulation behavior.

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 V to 0 V (a high external control voltage

results in a small duty cycle).

7.4 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. It then changes linearly with the control voltage until the minimum

frequency is reached (see Figure 5 and Figure 6).

Fig 5.

Fig 6.

014aaa003

0.52 V

1 V

(TYP)

1.5 V

(TYP)

014aaa005

f

25 kHz

125 kHz

LEVEL

LEVEL