TEA1552 View Datasheet(PDF) - Philips Electronics

Part Name

Description

Manufacturer

TEA1552

GreenChip™II SMPS control IC

Philips Electronics 

Philips Semiconductors

GreenChip™II SMPS control IC

Product specification

TEA1552

LOCK input

Pin LOCK is a general purpose (high-impedance) input

pin, which can be used to switch off the IC. As soon as the

voltage on this pin is raised above 2.5 V, switching will stop

immediately. The voltage on the VCC pin will cycle between

VCC(start) and VCC(UVLO), but the IC will not start switching

again until the latch function is reset. The latch is reset as

soon as the VCC drops below 4.5 V (typical value). The

internal OVP and OTP will also trigger this latch (see

Fig.2).

The detection level of this input is related to the VCC(5V) pin

voltage in the following way: 0.5 × VCC(5V) ± 4%.

An internal Zener diode clamp of 5.6 V will protect this pin

from excessive voltages. No internal filtering is done on

this input.

Since the soft start current ISS is subtracted from pin VCC

charging current, the RSS value will affect the VCC charging

current level by a maximum of 60 µA (typical value).

handbook, halfpage

0.5 V

ISS

start-up

2 Isense RSS

Vocp

CSS

Rsense

OverTemperature Protection (OTP)

An accurate temperature protection is provided in the

circuit. When the junction temperature exceeds the

thermal shutdown temperature, the IC will stop switching.

When VCC drops to UVLO, capacitor CVCC will be

recharged to the Vstart level, however the IC will not start

switching again. Subsequently, VCC will drop again to the

UVLO level, etc.

Operation only recommences when the VCC voltage drops

below a level of approximately 4.5 V (practically when the

Vmains has been disconnected for a short period).

Soft start-up

To prevent transformer rattle during hiccup, the

transformer peak current is slowly increased by the soft

start function. This can be achieved by inserting a resistor

and a capacitor between pin Isense and the sense resistor

(see Fig.10). An internal current source charges the

capacitor to V = ISS × RSS, with a maximum of

approximately 0.5 V.

The start level and the time constant of the increasing

primary current level can be adjusted externally by

changing the values of RSS and CSS.

Iprimary(max) = V-----o--c---p----–--R--(--sI--S-e--nS---s--×e-----R----S---S----)

τ = RSS × CSS

The charging current ISS will flow as long as the voltage on

pin Isense is below approximately 0.5 V. If the voltage on

pin Isense exceeds 0.5 V, the soft start current source will

start limiting the current ISS. At the VCC(start) level, the ISS

current source is completely switched off.

Fig.10 Soft start-up.

MBL503

5 V output

Pin VCC(5V) can be used for supplying external circuitry.

The maximum output current must be limited to 1 mA.

If higher peak currents are required, an external RC

combination should limit the current drawn from this pin to

1 mA maximum.

The 5 V output voltage will be available as soon as the

start-up voltage is reached. As the high voltage supply can

not supply the 5 V pin during start-up and/or shutdown,

during latched shutdown (via pin LOCK or other latched

protection such as OVP or OTP), the voltage is switched

to zero.

Driver

The driver circuit to the gate of the power MOSFET has a

current sourcing capability of typically 170 mA and a

current sink capability of typically 700 mA. This permits

fast turn-on and turn-off of the power MOSFET for efficient

operation. A low driver source current has been chosen to

limit the ∆V/∆t at switch-on. This reduces Electro Magnetic

Interference (EMI) and also limits the current spikes

across Rsense.

2002 Aug 27

10

Share Link: