HIP6301VCB datasheet(17/20 Pages) RENESAS

17 / 20 page

HIP6301V, HIP6302V

FN9034 Rev 3.00

Page 17 of 20

May 5, 2008

single channel’s ripple current is approximtely calculated in

Equation 8:

The current from multiple channels tend to cancel each other

and reduce the total ripple current. Figure 14 gives the total

ripple current as a function of duty cycle, normalized to the

parameter

at zero duty cycle. To determine

the total ripple current from the number of channels and the

duty cycle, multiply the y-axis value by

Small values of output inductance can cause excessive

power dissipation. The HIP6301V and HIP6302V are

designed for stable operation for ripple currents up to twice

the load current. However, for this condition, the RMS

current is 115% above the value shown in “MOSFET

Selection and Considerations” on page 17. With all else

fixed, decreasing the inductance could increase the power

dissipated in the MOSFETs by 30%.

Input Capacitor Selection

The important parameters for the bulk input capacitors are

the voltage rating and the RMS current rating. For reliable

operation, select bulk input capacitors with voltage and

current ratings above the maximum input voltage and

largest RMS current required by the circuit. The capacitor

voltage rating should be at least 1.25x greater than the

maximum input voltage and a voltage rating of 1.5x is a

conservative guideline. The RMS current required for a

multi-phase converter can be approximated with the aid of

Figure 15.

First determine the operating duty ratio as the ratio of the

output voltage divided by the input voltage. Find the current

multiplier from the curve with the appropriate power

channels. Multiply the current multiplier by the full load

output current. The resulting value is the RMS current rating

required by the input capacitor.

Use a mix of input bypass capacitors to control the voltage

overshoot across the MOSFETs. Use ceramic capacitance for

the high frequency decoupling and bulk capacitors to supply

the RMS current. Small ceramic capacitors should be placed

very close to the drain of the upper MOSFET to suppress the

voltage induced in the parasitic circuit impedances.

For bulk capacitance, several electrolytic capacitors

(Panasonic HFQ series or Nichicon PL series or Sanyo

MV-GX or equivalent) may be needed. For surface mount

designs, solid tantalum capacitors can be used, but caution

must be exercised with regard to the capacitor surge current

rating. These capacitors must be capable of handling the

surge-current at power-up. The TPS series available from

AVX, and the 593D series from Sprague are both surge

current tested.

MOSFET Selection and Considerations

In high-current PWM applications, the MOSFET power

dissipation, package selection and heatsink are the

dominant design factors. The power dissipation includes two

loss components; conduction loss and switching loss. These

losses are distributed between the upper and lower

MOSFETs according to duty factor (see Equation 9). The

conduction losses are the main component of power

dissipation for the lower MOSFETs, Q2 and Q4 of Figure 1.

Only the upper MOSFETs, Q1 and Q3 have significant

switching losses, since the lower device turns on and off into

near zero voltage.

The equations assume linear voltage-current transitions and

do not model power loss due to the reverse-recovery of the

lower MOSFETs body diode. The gate-charge losses are

dissipated by the Driver IC and don't heat the MOSFETs.

I

VIN VOUT

–

FSW L



--------------------------------

VOUT

VIN

----------------



(EQ. 8)

 LxF





 LxF





1.0

0.8

0.6

0.4

0.2

0.1

0.2

0.3

0.4

0.5

DUTY CYCLE (VO/VIN)

SINGLE

CHANNEL

2-CHANNEL

3-CHANNEL

4-CHANNEL

FIGURE 14. RIPPLE CURRENT vs DUTY CYCLE

0.5

0.4

0.3

0.2

0.1

0.2

0.3

0.4

0.5

DUTY CYCLE (VO/VIN)

SINGLE

CHANNEL

3 CHANNEL

4 CHANNEL

2 CHANNEL

FIGURE 15. CURRENT MULTIPLIER vs DUTY CYCLE

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