HIP6006CB データシートの表示（PDF） - Renesas Electronics
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HIP6006CB Datasheet PDF : 12 Pages
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HIP6006
careful not to add inductance in the circuit board wiring that
could cancel the usefulness of these low inductance
components. Consult with the manufacturer of the load on
specific decoupling requirements. For example, Intel
recommends that the high frequency decoupling for the
Pentium Pro be composed of at least forty (40) 1.0F ceramic
capacitors in the 1206 surface-mount package.
Use only specialized low-ESR capacitors intended for
switching-regulator applications for the bulk capacitors. The
bulk capacitor’s ESR will determine the output ripple voltage
and the initial voltage drop after a high slew-rate transient. An
aluminum electrolytic capacitor's ESR value is related to the
case size with lower ESR available in larger case sizes.
However, the equivalent series inductance (ESL) of these
capacitors increases with case size and can reduce the
usefulness of the capacitor to high slew-rate transient
loading. Unfortunately, ESL is not a specified parameter.
Work with your capacitor supplier and measure the
capacitor’s impedance with frequency to select a suitable
component. In most cases, multiple electrolytic capacitors of
small case size perform better than a single large case
capacitor.
Output Inductor Selection
The output inductor is selected to meet the output voltage
ripple requirements and minimize the converter’s response
time to the load transient. The inductor value determines the
converter’s ripple current and the ripple voltage is a function of
the ripple current. The ripple voltage and current are
approximated by the following equations:
I = V-----I--N-F----s------Vx----O-L---U-----T- V----V-O---I-U-N---T--
VOUT= I x ESR
Increasing the value of inductance reduces the ripple current
and voltage. However, the large inductance values reduce the
converter’s response time to a load transient.
One of the parameters limiting the converter’s response to a
load transient is the time required to change the inductor
current. Given a sufficiently fast control loop design, the
HIP6006 will provide either 0% or 100% duty cycle in response
to a load transient. The response time is the time required to
slew the inductor current from an initial current value to the
transient current level. During this interval the difference
between the inductor current and the transient current level
must be supplied by the output capacitor. Minimizing the
response time can minimize the output capacitance required.
The response time to a transient is different for the application
of load and the removal of load. The following equations give
the approximate response time interval for application and
removal of a transient load:
tRISE = -VL---O-I--N-----–---I-V-T---R-O---A-U---N-T--
tFALL = L----O----V----O--I--T-U---R-T---A----N--
where: ITRAN is the transient load current step, tRISE is the
response time to the application of load, and tFALL is the
response time to the removal of load. With a +5V input source,
the worst case response time can be either at the application
or removal of load and dependent upon the output voltage
setting. Be sure to check both of these equations at the
minimum and maximum output levels for the worst case
response time.
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 to supply the
current needed each time Q1 turns on. Place the small ceramic
capacitors physically close to the MOSFETs and between the
drain of Q1 and the source of Q2.
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 HIP6006 requires 2 N-Channel power MOSFETs. These
should be selected based upon rDS(ON), gate supply
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 MOSFETs body diode. The gate-charge losses are
dissipated by the HIP6006 and don't heat the MOSFETs.
However, large gate-charge increases the switching interval,
FN4306 Rev.3.00
April 1, 2005
Page 8 of 12
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