TEA1733T_TEA1733LT_1

© NXP B.V. 2009. All rights reserved.

Objective data sheet

Rev. 01 — 26 October 2009

8 of 17

NXP Semiconductors

TEA1733T; TEA1733LT

GreenChip SMPS control IC

7.11 Soft start-up (ISENSE pin)

To prevent audible noise during start-up or restart, a soft start is made. Before the

converter (re)starts, the soft start capacitor on the ISENSE pin is charged. When the

converter (re)starts switching, the primary peak current increases slowly when the soft

start capacitor discharges through the soft start resistor. (see also Figure 4)

The time constant of the soft start can be chosen by setting the soft start capacitor. The

soft start resistor must also be taken into account, but this value is typically defined by the

overpower compensation. (see Section 7.10)

7.12 Low power operation

In low power operation the switching losses are reduced by lowering the switching

frequency. The switching frequency of the converter is reduced while the peak current is

set to 25 % of the maximum peak current. (see Figure 6 and Figure 9)

7.13 Driver (pin DRIVER)

The driver circuit to the gate of the power MOSFET has a current sourcing capability of

typically

−250 mA and a current sink capability of typically 750 mA. This permits fast

turn-on and turn-off of the power MOSFET for efficient operation.

Fig 8.

Overpower compensation

2

1.7

0.68

1234

014aaa933

(

µA)

Fig 9.

Frequency control

12

switching

frequency

014aaa934

(kHz)