2-170

operation, select the bulk capacitor 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 1.25 times greater than the maximum

input voltage and a voltage rating of 1.5 times is a

conservative guideline. The RMS current rating requirement

for the input capacitor of a buck regulator is approximately

1/2 the DC load current.

For a through hole design, 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/Considerations

The HIP6013 requires an N-Channel power MOSFET. It

requirements, and thermal management requirements.

In high-current 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.

The conduction losses are the largest component of power

dissipation for the MOSFET. Switching losses also

contribute to the overall MOSFET power loss (see the

equations below). These equations assume linear voltage-

current transitions and are approximations. The gate-

charge losses are dissipated by the HIP6013 and don't

heat the MOSFET. However, large gate-charge increases

MOSFET switching losses. Ensure that the MOSFET is

within its maximum junction temperature at high ambient

temperature by calculating the temperature rise according

to package thermal-resistance specifications. A separate

heatsink may be necessary depending upon MOSFET

power, package type, ambient temperature and air flow.

Standard-gate MOSFETs are normally recommended for

use with the HIP6013. However, logic-level gate MOSFETs

can be used under special circumstances. The input voltage,

upper gate drive level, and the MOSFET’s absolute gate-to-

source voltage rating determine whether logic-level

MOSFETs are appropriate.

Figure 9 shows the upper gate drive (BOOT pin) supplied by

develops a floating supply voltage referenced to the PHASE

turns on. A logic-level MOSFET can only be used for Q1 if

the MOSFET’s absolute gate-to-source voltage rating

Figure 10 shows the upper gate drive supplied by a direct

connection to VCC. This option should only be used in

converter systems where the main input voltage is +5VDC

or less. The peak upper gate-to-source voltage is

power and +12VDC for the bias, the gate-to-source voltage

of Q1 is 7V. A logic-level MOSFET is a good choice for Q1

and a logic-level MOSFET is a good choice for Q1 under

these conditions.

1

2

Fs is the switching frequency.

FIGURE 9. UPPER GATE DRIVE - BOOTSTRAP OPTION

+12V

HIP6013

GND

UGATE

PHASE

BOOT

VCC

+5V OR +12V

Q1

D2

NOTE:

+

-

HIP6013