HIP6005BCB Intersil Corporation, HIP6005BCB Datasheet - Page 9

• Manufacturer Part Number: HIP6005BCB
• Description: Buck Pulse-Width Modulator (PWM) Controller and Output Voltage Monitor
• Manufacturer: Intersil Corporation

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
HIP6005B 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:
where: I
response time to the application of load, and t
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
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
level equal to DACOUT, t
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 Q
capacitors physically close to the MOSFETs and between the
drain of Q
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.
t
RISE
=
TRAN
------------------------------- -
V
L x I
1
IN
and the anode of Schottky diode D
–
TRAN
V
is the transient load current step, t
OUT
FALL
2-118
1
turns on. Place the small ceramic
t
FALL
is the longest response time.
=
L x I
--------------------------- -
V
OUT
TRAN
2
.
FALL
RISE
is the
is the
HIP6005B
MOSFET Selection/Considerations
The HIP6005B requires an N-Channel power MOSFET. It
should be selected based upon r
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 HIP6005B and do not heat
the MOSFET. However, large gate-charge increases the
switching interval, t
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.
Where: D is the duty cycle = V
Standard-gate MOSFETs are normally recommended for
use with the HIP6005B. However, logic-level gate MOSFETs
can be used under special circumstances. The input voltage,
upper gate drive level, and the MOSFETs absolute
gate-to-source voltage rating determine whether logic-level
MOSFETs are appropriate.
Figure 9 shows the upper gate drive (BOOT pin) supplied by
a bootstrap circuit from V
develops a floating supply voltage referenced to the PHASE
pin. This supply is refreshed each cycle to a voltage of V
less the boot diode drop (V
conducts. Logic-level MOSFETs can only be used if the
MOSFETs absolute gate-to-source voltage rating exceeds
the maximum voltage applied to V
Figure 10 shows the upper gate drive supplied by a direct
connection to V
converter systems where the main input voltage is +5V
less. The peak upper gate-to-source voltage is approximately
V
the bias, the gate-to-source voltage of Q
MOSFET is a good choice for Q
P
P
CC
COND
SW
t
F
SW
S
less the input supply. For +5V main power and +12V
= 1/2 I
is the switching frequency
is the switching interval, and
= I
O
O
2 x r
x V
CC
DS(ON)
IN
. This option should only be used in
SW
x t
, which increases the upper MOSFET
SW
x D
x F
CC
D
S
. The boot capacitor, C
) when the Schottky diode, D2,
OUT
1
under these conditions.
DS(ON)
CC
/V
IN
.
1
,
, gate supply
is 7V. A logic-level
BOOT
DC
DC
or
CC
,
for