10

DACOUT setting. Be sure to check both of these equations

at the minimum and maximum output levels for the worst

case response time. With a +12V input, and output voltage

Input Capacitor Selection

Use a mix of input bypass capacitors to control the voltage

overshoot across the MOSFETs. Use small ceramic

capacitors for high frequency decoupling and bulk capacitors

the small ceramic capacitors physically close to the

The important parameters for the bulk input capacitor are the

voltage rating and the RMS current rating. For reliable

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 HIP6004A requires 2 N-Channel power MOSFETs.

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 both the upper and the lower MOSFETs.

These losses are distributed between the two MOSFETs

according to duty factor (see the equations below). Only the

upper MOSFET has switching losses, since the Schottky

rectifier clamps the switching node before the synchronous

rectifier turns on. These equations assume linear voltage-

current transitions and do not adequately model power loss

due the reverse-recovery of the lower MOSFET’s body

diode. The gate-charge losses are dissipated by the

HIP6004A and don't heat the MOSFETs. However, large

increases the upper MOSFET switching losses. Ensure that

both MOSFETs are within their 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 HIP6004A. 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

pin. This supply is refreshed each cycle to a voltage of VCC

turns on. Logic-level MOSFETs can only be used if the

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

the maximum voltage applied to VCC.

Figure 10 shows the upper gate drive supplied by a direct

connection to VCC . This option should only be used in

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

approximately VCC less the input supply. For +5V main

absolute gate-to-source voltage rating exceeds the

maximum voltage applied to VCC .

1

2

+12V

PGND

HIP6004A

GND

LGATE

UGATE

PHASE

BOOT

VCC

+5V OR +12V

NOTE:

NOTE:

Q1

Q2

+

-

FIGURE 9. UPPER GATE DRIVE - BOOTSTRAP OPTION

D2

HIP6004A