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TEA1541

SMPS control IC with synchronization function

Philips Electronics 

Philips Semiconductors

SMPS control IC with

synchronization function

Product specification

TEA1541

handbfook, halfpage

(kHz)

50

25

synchronized operation

6

VCO

variable

unsynchronized operation

VCO

fixed

P(W)

MDB085

Fig.4 Multi mode operation.

handbook, halfpage

M-level

VIN

VCC(start)

VCC(trip)(VIN)

VCC

IVIN(max)

IVIN(min)

IVIN

ICC

6.1 Start-up, mains voltage-dependent

operation-enabling level and undervoltage

lock-out

Initially, the IC is supplied by the rectified mains voltage at

pin VIN. When the voltage at pin VCC is below the VCC

voltage for VIN current trip level VCC(trip)(VIN), the supply

current drawn from pin VIN, (IVIN) is at the low value

IVIN(min). When VCC rises to the VCC(trip)(VIN) level, the

current at pin VIN changes to the high value IVIN(max).

When the voltage at pin VIN is below the mains

voltage-dependent operation-enabling level (M-level), the

IC supply capacitor CVCC is charged by the internal

start-up current source to approximately 5 V. When the

voltage at pin VIN exceeds the M-level, the start-up

current source continues to charge CVCC (switch S1 open;

see Fig.2).

When VCC reaches the start-up voltage level VCC(start), the

IC switches to high efficiency (green function) operation by

no longer drawing current from pin VIN (see Fig.5).

At VCC(start) the IC activates the external MOSFET. When

the voltage across the auxiliary winding rises above the

voltage across CVCC, the IC supply current will be supplied

by the auxiliary winding via pin VCC.

If the voltage on pin VCC falls below the VCC undervoltage

lock-out level VCC(UVLO), the IC stops switching and enters

a safe restart mode in which current to the IC is supplied

by the rectified mains voltage via pin VIN, and CVCC is

re-charged by the internal start-up current source to

VCC(start).

Fig.5 Start-up sequence.

MDB087

Inhibiting the auxiliary supply by external means causes

the converter to operate in a stable, well-defined burst

mode. This is a burst standby mode that is less efficient

than the normal burst standby mode described in

section 6.12.

If the voltage at pin VIN falls below the mains undervoltage

lock-out level MUVLO, a safe restart mode is activated, and

the IC stops switching.

During normal operation (non-burst standby mode), the

duty cycle of the IC, and thus the output power of the

supply, is regulated by a control voltage at pin CTRL.

If pin VCC is connected to ground, the IC switches to low

power standby operation and the start-up current drawn

via pin VIN reduces to 400 µA (typical). When the voltage

on pin VCC rises above 700 mV (typical), the start-up

current increases to 1 mA (typical).

6.2 Supply management

All internal reference voltages are derived from a

temperature compensated, on-chip bandgap.

2003 Aug 11

7

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