IR22141 datasheet(21/28 Pages) IRF

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IR2214/IR22141(SS)

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ADVANCE DATA

Sizing tips

Bootstrap supply

The V

BS voltage provides the supply to the high

side driver circuitry of the IR2214. This supply

sits on top of the V

S voltage and so it must be

floating.

The bootstrap method to generate V

BS supply

can be used with IR2214. The bootstrap supply

is formed by a diode and a capacitor connected

as in figure 19.

Figure 19:

bootstrap supply schematic

This method has the advantage of being simple

and low cost but may force some limitations on

duty-cycle and on-time since they are limited by

the requirement to refresh the charge in the boot-

strap capacitor.

Proper capacitor choice can reduce drastically

these limitations.

Bootstrap capacitor sizing

To size the bootstrap capacitor, the first step is

to establish the minimum voltage drop (

∆V

BS)

that we have to guarantee when the high side

IGBT is on.

bootstrap

diode

bootstrap

capacitor

VCC

HOP

HON

SSDH

DC+

bootstrap

resistor

COM

VCC

VBS

VGE

VCEon

VFP

ILOAD

motor

Rboot

If V

GEmin is the minimum gate emitter voltage we

want to maintain, the voltage drop must be:

under the condition:

where V

CC is the IC voltage supply, VF is boot-

strap diode forward voltage, V

CEon is emitter-col-

lector voltage of low side IGBT and V

BSUV- is the

high-side supply undervoltage negative going

threshold.

Now we must consider the influencing factors

contributing V

BS to decrease:

- IGBT turn on required Gate charge (Q

G);

- IGBT gate-source leakage current (I

LK_GE);

- Floating section quiescent current (I

QBS);

- Floating section leakage current (I

LK)

- Bootstrap diode leakage current (I

LK_DIODE);

- Desat diode bias when on (I

DS- )

- Charge required by the internal level shifters

LS); typical 20nC

- Bootstrap capacitor leakage current (I

LK_CAP);

- High side on time (T

HON).

LK_CAP is only relevant when using an electrolytic

capacitor and can be ignored if other types of

capacitors are used. It is strongly recommend

using at least one low ESR ceramic capacitor

(paralleling electrolytic and low ESR ceramic

may result in an efficient solution).

Then we have:

CEon

−

≤

∆

min

−

BSUV

min

QBS

TOT

(

HON

CAP

DIODE

⋅

− )

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