TEA1703T

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© NXP B.V. 2011. All rights reserved.

Product data sheet

Rev. 2.3 — 28 April 2011

7 of 15

NXP Semiconductors

TEA1703T

GreenChip SMPS standby control IC

7.4 Power sensing (pin PSENSE)

Output power sensing is implemented using an external filter network on pin PSENSE.

The PSENSE input is not latched internally. If, during standby mode, pin PSENSE is

7.5 Switching detection (pin SWDET)

A switching detection pin is provided to prevent applications resetting a latched protection

of the primary-side converter, such as the TEA1753. The standby mode can only be

The SWDET signal is latched internally. As soon as the OPTO output is activated, the

SWDET signal is ignored.

If the SWDET input is not needed, it can be connected to pin VCC via a series resistor.

power supply is in normal operation.

7.6 Optocoupler output (pin OPTO)

The optocoupler output is an open-drain output with an integrated diode connected to

The optocoupler diode current can be set by choosing the value of the series inductor.

The current is not limited internally.

7.7 Optocoupler CTR

The CTR of a typical optocoupler falls significantly when small opto-diode currents are

used. With low optocoupler output currents, a significantly higher diode current is needed

for a typical low-cost optocoupler.

In low standby power operation of the switched-mode power supply it is necessary to

keep all currents low. To maintain a high CTR, the optocoupler diode can be driven with a

high current and a small duty cycle. The average driving current will still be low.

Figure 6 shows a typical optocoupler CTR plotted for a DC-driven opto-diode and a

pulse-driven opto-diode. The pulse-driven diode is driven with a 2 mA duty cycle

modulated current. The CTR remains high even for a very small average diode current

(low duty cycle) when the diode is pulse-driven, while the CTR for a DC-driven

optocoupler falls to a few percent.