tea1738t NXP Semiconductors, tea1738t Datasheet - Page 10

• Manufacturer Part Number: tea1738t
• Description: Tea1738t; Tea1738lt Greenchip Smps Control Ic
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TEA1738T_TEA1738LT
Product data sheet
7.12 Soft start-up (ISENSE pin)
7.13 Peak power, medium power and low power operation
A soft start is performed to prevent audible noise during start-up or a restart condition.
Before the converter (re)starts, soft start capacitor C6 (see
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
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
The switching frequency is increased for peak power operation. In medium power
operation the switching losses are reduced by lowering the switching frequency. A second
frequency reduction step is made when the output power is reduced to low power. In low
power operation the converter switching frequency is reduced while the peak current is
set to 25 % of the maximum peak current (see
Fig 9.
Fig 10. Frequency control
3).
Overpower compensation
f
osc
All information provided in this document is subject to legal disclaimers.
28 kHz
80 kHz
66 kHz
Rev. 2 — 14 January 2011
I
ISENSE
(μA)
1.7
2
Section
0.68
1
1
low power
7.11).
TEA1738T; TEA1738LT
Figure 7
medium
2
2
power
V
V
VINSENSE
CTRL
and
3
power
Figure
high
014aaa933
3
GreenChip SMPS control IC
Figure
(V)
4
3) on the ISENSE pin is
peak power
10).
014aab294
© NXP B.V. 2011. All rights reserved.
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