hip6020 Intersil Corporation, hip6020 Datasheet - Page 13

• Manufacturer Part Number: hip6020
• Description: Advanced Dual Pwm And Dual Linear Power Controller
• Manufacturer: Intersil Corporation

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. Be sure to check both
of these equations at the minimum and maximum output
levels for the worst case response time.
Input Capacitor Selection
The important parameters for the bulk input capacitor 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 1.25 times greater than the
maximum input voltage. The RMS current rating requirement
for the input capacitors of a buck regulator is approximately
1/2 of the summation of the DC output load current.
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 can be
placed very close to the upper MOSFET to suppress the
voltage induced in the parasitic circuit impedances.
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 HIP6020 requires 5 external transistors. Three
N-channel MOSFETs are employed by the PWM converters.
The GTL and memory linear controllers can each drive a
MOSFET or a NPN bipolar as a pass transistor. All these
transistors should be selected based upon r
gain, saturation voltages, gate supply requirements, and
thermal management considerations.
PWM1 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 the duty factor. The conduction losses are the
t
RISE
=
TRAN
------------------------------- -
V
L
O
IN
–
I
TRAN
V
is the transient load current step, t
OUT
2-293
t
FALL
=
L
------------------------------ -
O
V
OUT
I
TRAN
DS(ON)
FALL
RISE
is the
, current
is the
HIP6020
main component of power dissipation for the lower MOSFETs.
Only the upper MOSFET has significant switching losses, since
the lower device turns on and off into near zero voltage.
The equations presented assume linear voltage-current
transitions and do not model power loss due to the reverse
recovery of the lower MOSFET’s body diode. The gate
charge losses are dissipated by the HIP6020 and don't heat
the MOSFETs. However, large gate-charge increases the
switching time, t
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.
The r
the same device is used for both. This is because the gate
drive applied to the upper MOSFET is different than the
lower MOSFET. Figure 13 shows the gate drive where the
upper MOSFET’s gate-to-source voltage is approximately
V
for the bias, the gate-to-source voltage of Q1 is 7V. The lower
gate drive voltage is +12VDC. A logic-level MOSFET is a
good choice for Q1 and a logic-level MOSFET can be used for
Q2 if its absolute gate-to-source voltage rating exceeds the
maximum voltage applied to V
Rectifier CR1 is a clamp that catches the negative inductor
swing during the dead time between the turn off of the lower
MOSFET and the turn on of the upper MOSFET. The diode
must be a Schottky type to prevent the lossy parasitic
MOSFET body diode from conducting. It is acceptable to omit
the diode and let the body diode of the lower MOSFET clamp
the negative inductor swing, but efficiency could drop, in some
P
P
CC
UPPER
LOWER
HIP6020
FIGURE 10. UPPER GATE DRIVE - DIRECT V
-
+
less the input supply. For +5V main power and +12VDC
DS(ON)
+12V
=
=
I
----------------------------------------------------------- -
I
-------------------------------------------------------------------------------- -
O
O
is different for the two equations above even if
2
2
VCC
SW
r
r
GND
DS ON
DS ON
, which increases the upper MOSFET
UGATE
PHASE
LGATE
PGND
V
IN
V
IN
V
V
OUT
IN
CC
–
.
+
V
I
----------------------------------------------------
OUT
Q1
Q2
O
+5V OR LESS
V
IN
CR1
2
t
NOTE:
V
SW
NOTE:
V
GS
GS
CC
F
DRIVE
V
S
V
CC
CC
-5V