IR2520D 데이터 시트보기 (PDF) - International Rectifier

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IR2520D

ADAPTIVE BALLAST CONTROL IC

International Rectifier 

IR2520D(S) & (PbF)

Functional Description

Under-voltage Lock-Out Mode

The under-voltage lock-out mode (UVLO) is defined as the

state the IR2520D is in when VCC is below the turn-on

threshold of the IC. The IR2520D UVLO is designed to main-

tain an ultra-low supply current (IQCCUV<80uA), and to

guarantee that the IR2520D is fully functional before the

high- and low-side output gate drivers are activated. The

VCC capacitor, CVCC, is charged by current through sup-

ply resistor, RSUPPLY, minus the start-up current drawn by

the IR2520D (Figure 1). This resistor is chosen to provide

sufficient current to supply the IR2520D from the DC bus.

Once the capacitor voltage on VCC reaches the start-up

threshold, VCCUV+, the IR2520D turns on and HO and LO

start oscillating. Capacitor CVCC should be large enough to

hold the voltage at VCC above the VCCUV+ threshold for

one half-cycle of the line voltage or until the external auxil-

iary supply can maintain the required supply voltage and

current to the IC.

DCBUS(+)

RSUPPLY

DCP2

CVCC

VCC

1

COM

2

FMIN

3

RFMIN

VCO

4

CVCO

Bootstrap

FET

Driver

15.6V

CLAMP

VCC

High-

and

Low-

side

Driver

UVLO

VB

8

HO

7

VS

6

LO

5

MHS

CBS

MLS

CSNUB

TO LOAD

high-side driver is enabled. During UVLO mode, the high- and

low-side gate driver outputs, HO and LO, are both low and

pin VCO is pulled down to COM for resetting the starting

frequency to the maximum.

Frequency Sweep Mode

When VCC exceeds VCCUV+ threshold, the IR2520D enters

frequency sweep mode. An internal current source (Figure

2) charges the external capacitor on pin VCO, CVCO, and

the voltage on pin VCO starts ramping up linearly. An addi-

tional quick-start current (IVCOQS) is also connected to the

VCO pin and charges the VCO pin initially to 0.85V. When the

VCO voltage exceeds 0.85V, the quick-start current is then

disconnected internally and the VCO voltage continues to

charge up with the normal frequency sweep current source

(IVCOFS) (Figure 3). This quick-start brings the VCO voltage

quickly to the internal range of the VCO. The frequency ramps

down towards the resonance frequency of the high-Q bal-

last output stage causing the lamp voltage and load current to

increase. The voltage on pin VCO continues to increase and

the frequency keeps decreasing until the lamp ignites. If the

lamp ignites successfully, the voltage on pin VCO continues

to increase until it internally limits at 6V (VVCO_MAX). The

frequency stops decreasing and stays at the minimum fre-

quency as programmed by an external resistor, RFMIN, on

pin FMIN. The minimum frequency should be set below the

high-Q resonance frequency of the ballast output stage to

ensure that the frequency ramps through resonance for lamp

ignition (Figure 4). The desired preheat time can be set by

adjusting the slope of the VCO ramp with the external capaci-

tor CVCO.

DCBUS(+)

DCP1

DCBUS(-)

LOAD RETURN

Fig. 1 Start-up circuitry

An internal bootstrap MOSFET between VCC and VB and

external supply capacitor, CBS, determine the supply volt-

age for the high-side driver circuitry. An external charge

pump circuit consisting of capacitor CSNUB and diodes DCP1

and DCP2, comprises the auxiliary supply voltage for the

low-side driver circuitry. To guarantee that the high-side

supply is charged up before the first pulse on pin HO, the

first pulse from the output drivers comes from the LO pin.

LO may oscillate several times until VB-VS exceeds the

high-side UVLO rising threshold, VBSUV+ (9 Volts), and the

RSUPPLY

DCP2

CVCC

VCC

1

COM

2

FMIN

3

RFMIN

VCO

4

CVCO

Bootstrap

FET

Driver

15.6V

CLAMP

VCO

High-

and

Low-

side

Driver

VB

8

HO

7

VS

6

LO

5

MHS

CBS

MLS

CSNUB

TO LOAD

DCP1

DCBUS(-)

LOAD RETURN

Fig. 2 Frequency sweep circuitry mode circuitry

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