TEA1738FT

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Preliminary data sheet

Rev. 1 — 30 December 2010

9 of 20

NXP Semiconductors

TEA1738FT

GreenChip SMPS control IC

7.11 Overpower or high/low line compensation

(VINSENSE and ISENSE pins)

The overpower compensation function can be used to realize a maximum output power

which is nearly constant over the full input mains.

The overpower compensation circuit measures the input voltage on the VINSENSE pin

and outputs a proportionally dependent current on the ISENSE pin. The DC voltage

across the soft start resistor limits the maximum peak current on the current sense resistor

(see Figure 8).

At low output power levels the overpower compensation circuit is switched off.

7.12 Soft start-up (ISENSE pin)

A soft start is performed to prevent audible noise during start-up or a restart condition.

Before the converter (re)starts, the soft start capacitor C6 (see Figure 3) on the ISENSE

pin is charged. When the converter (re)starts switching, the primary peak current slowly

increases as the soft start capacitor discharges through the soft start resistor (R6, see

Figure 3).

The soft start time constant is set by the soft start capacitor value chosen. The soft start

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

overpower compensation (see Section 7.11).

Fig 7.

Leading edge blanking

t

014aaa932

Fig 8.

Overpower compensation

2

1.7

0.68

1234

014aaa933

(

μA)