FA5590 Ver la hoja de datos (PDF) - Fuji Electric

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componentes Descripción

Fabricante

FA5590

Power Supply Control IC(Power Factor Correction)

Fuji Electric 

FA5590N,FA5591N

MOSFET turn on.

(6-2) Overcurrent detection protective circuit

The overcurrent detection protective circuit detects the inductor

current and protects MOSFET by turning off the OUT output when it

becomes higher than a set current level. With the overcurrent detection,

the voltage across the current detection resistance Rs connected to the

GND is fed to the IS terminal, and when the IS terminal voltage

compared by the overcurrent detection comparator becomes lower than

-0.6V, it is regarded as overcurrent state.

When the overcurrent is detected, the F/F for OUT output is reset to

make MOSFET turn off.

(7) Zero cross delay time setting circuit

Vds between the drain and the sources of the MOSFET starts

oscillating through resonance of L1 and the parasitic capacitor

component on the circuit just before the MOSFET turns on.

inductor

イcンurダreクnタt電流

MOVSdFEsT の Vds

Tzcd

T＜ 1/Fmax

Fig.11 when the switching frequency is

lower than the maximum frequency Fmax

When the proper value of Rtzc, the turn on timing of MOSFET can be

adjusted at the bottom of the voltage oscillation. This makes it possible

to minimize the switching loss and the surge current generated at the

turn-on. (Fig. 13)

When the Rtzc is smaller, the turn-on timing becomes earlier, and

vice versa. (Fig. 14)

Since the optimum value of this Rtzc changes depending on the

circuit and input/output conditions, tuning up is required so as to achieve

an optimum state while evaluating the operation with actual circuit.

(8) Restart timer

This IC utilizes self oscillation instead of the oscillator with fixed

frequency, and in the steady operation, it turns on MOSFET with a signal

from the zero current detector.

But in start up or light load condition, a trigger signal is required for

starting up or stable operation.

This IC is provided with a restart timer, and when the output of IC

continues turn off for 20μs or more, the trigger signal is automatically

generated.

This signal can realize stable operation even when starting up or the

load is light.

inductor

イcンuダrrクeタn電t 流

MOVSdFsET の Vds

Tzcd

T= 1/Fmax

Fig.12 when the switching frequency is

limited to the maximum frequency Fmax

MVdOsSFET

のVds

(9) Under Voltage Lock out (UVLO)

UVLO is equipped to prevent circuit malfunction when supply voltage

drops.

When the supply voltage rises from zero, the operation starts at 9.6V

(typ.) for FA5590 and 13V (typ.) for FA5591.

When the supply voltage decreases after the operation starts, either part

number stops the operation at 9V (typ.).

When UVLO is on and IC stops operation the OUT terminal becomes

LOW and cuts off the output. The current consumption of the IC

decreases to 80μA or less.

Tzcd(RTtzcd最適）

(with adequate Rtzc)

Fig.13 Vds waveform at turn on

(with adequate Rtzc)

(10) Output circuit portion

MOSFET

The output portion is of push-pull circuit and can directly drive the

Vds

のVds

MOSFET. The peak current of the output portion is 1.0A maximum for

sink and 0.5A maximum for source.

Tzcd（TRztczdcが小さい）

(Rtzc is too small)

Tzcd(RtTzzccがd 大きい）

(Rtzc is too large)

Fig.14 Vds waveform at turn on

(with inadequate Rtzc)

Fuji Electric Co., Ltd.

AN-016E Rev.1.2

April-2011

15

http://www.fujielectric.co.jp/products/semiconductor/

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