hip6018cb Intersil Corporation, hip6018cb Datasheet - Page 10

• Manufacturer Part Number: hip6018cb
• Description: Advanced Pwm And Dual Linear Power Control
• Manufacturer: Intersil Corporation

The soft-start function controls the output voltage rate of rise
to limit the current surge at start-up. The soft-start interval is
programmed by the soft-start capacitor, C
a faster soft-start interval increases the peak surge current.
The peak surge current occurs during the initial output
voltage rise to 80% of the set value.
Shutdown
The PWM output does not switch until the soft-start voltage
(V
the reference on each linear’s amplifier is clamped to the
soft-start voltage. Holding the SS pin low with an open drain
or collector signal turns off all three regulators.
The VID codes resulting in an INHIBIT as shown in Table 1
also shuts down the IC.
Layout Considerations
MOSFETs switch very fast and efficiently. The speed with
which the current transitions from one device to another
causes voltage spikes across the interconnecting
impedances and parasitic circuit elements. The voltage
spikes can degrade efficiency, radiate noise into the circuit,
and lead to device over-voltage stress. Careful component
layout and printed circuit design minimizes the voltage
spikes in the converter. Consider, as an example, the turn-
off transition of the upper PWM MOSFET. Prior to turn-off,
the upper MOSFET was carrying the full load current. During
the turn-off, current stops flowing in the upper MOSFET and
is picked up by the lower MOSFET (and/or parallel Schottky
diode). Any inductance in the switched current path
generates a large voltage spike during the switching interval.
Careful component selection, tight layout of the critical
components, and short, wide circuit traces minimize the
magnitude of voltage spikes. Contact Intersil for evaluation
board drawings of the component placement and printed
circuit board.
There are two sets of critical components in a DC-DC
converter using a HIP6018 controller. The power
components are the most critical because they switch large
amounts of energy. The critical small signal components
connect to sensitive nodes or supply critical bypassing
current.
The power components should be placed first. Locate the
input capacitors close to the power switches. Minimize the
length of the connections between the input capacitors and
the power switches. Locate the output inductor and output
capacitors between the MOSFETs and the load. Locate the
PWM controller close to the MOSFETs.
The critical small signal components include the bypass
capacitor for VCC and the soft-start capacitor, C
these components close to their connecting pins on the
control IC. Minimize any leakage current paths from SS
node because the internal current source is only 11µA.
SS
) exceeds the oscillator’s valley voltage. Additionally,
233
SS
. Programming
SS
. Locate
HIP6018
A multi-layer printed circuit board is recommended. Figure 10
shows the connections of the critical components in the
converter. Note that capacitors C
represent numerous physical capacitors. Dedicate one solid
layer for a ground plane and make all critical component
ground connections with vias to this layer. Dedicate another
solid layer as a power plane and break this plane into
smaller islands of common voltage levels. The power plane
should support the input power and output power nodes.
Use copper filled polygons on the top and bottom circuit
layers for the phase nodes. Use the remaining printed circuit
layers for small signal wiring. The wiring traces from the
control IC to the MOSFET gate and source should be sized
to carry 1A currents. The traces for OUT2 need only be
sized for 0.2A. Locate C
PWM Controller Feedback Compensation
Both PWM controllers use voltage-mode control for output
regulation. This section highlights the design consideration
for a voltage-mode controller. Apply the methods and
considerations to both PWM controllers.
Figure 11 highlights the voltage-mode control loop for a
synchronous-rectified buck converter. The output voltage is
regulated to the reference voltage level. The reference
voltage level is the DAC output voltage for the PWM
controller. The error amplifier output (V
the oscillator (OSC) triangular wave to provide a pulse-width
modulated wave with an amplitude of V
The PWM wave is smoothed by the output filter (L
The modulator transfer function is the small-signal transfer
function of V
gain and the output filter, with a double pole break frequency
at F
simply the input voltage, V
oscillator voltage, ∆V
+5V
+3.3V
V
FIGURE 10. PRINTED CIRCUIT BOARD POWER PLANES AND
OUT2
IN
V
LC
OUT3
IN
and a zero at F
Q3
OUT
ISLANDS
C
C
IN
OUT2
/V
E/A
+12V
OSC
. This function is dominated by a DC
ESR
KEY
OUT2
VIN2
GATE3
VOUT2
C
.
SS
VCC
IN
. The DC gain of the modulator is
ISLAND ON POWER PLANE LAYER
ISLAND ON CIRCUIT PLANE LAYER
VIA CONNECTION TO GROUND PLANE
HIP6018
, divided by the peak-to-peak
C
SS PGND
VCC
close to the HIP6018 IC.
OCSET1
UGATE1
PHASE1
LGATE1
GND
IN
and C
IN
E/A
Q1
Q2
C
OCSET1
at the PHASE node.
) is compared with
OUT
R
L
CR1
could each
OCSET1
C
OUT1
OUT1
O
and C
V
OUT1
O
).