NCP5314 ON Semiconductor, NCP5314 Datasheet - Page 13

• Manufacturer Part Number: NCP5314
• Description: Two/Three/Four-Phase Buck CPU Controller
• Manufacturer: ON Semiconductor

Overview
was developed using the Enhanced V
V
current−mode control for fast transient response and current
sensing capability. The addition of an internal PWM ramp
and implementation of fast−feedback directly from Vcore
has improved transient response and simplified design. This
controller can be adjusted to operate as a two−, three− or
four−phase controller. Differential current sensing provides
improved current sharing and easier layout. The NCP5314
includes Power Good (PWRGD), providing a highly
integrated solution to simplify design, minimize circuit
board area, and reduce overall system cost.
single−phase converter are current sharing and increased
effective output frequency. Current sharing allows the designer
to use less inductance in each phase than would be required in
a single−phase converter. The smaller inductor will produce
larger ripple currents but the total per−phase power dissipation
is reduced because the RMS current is lower. Transient
response is improved because the control loop will measure
and adjust the current faster with a smaller output inductor.
Increased effective output frequency is desirable because
the off−time and the ripple voltage of the multi−phase
converter will be less than that of a single−phase converter.
output current in each phase. An additional differential input
(CSxN and CSxP) for inductor current information has been
added to the V
The triangular inductor current is measured differentially
across RS, amplified by CSA and summed with the channel
startup offset, the internal ramp and the output voltage at the
non−inverting input of the PWM comparator. The purpose
of the internal ramp is to compensate for propagation delays
in the NCP5314. This provides greater design flexibility by
allowing smaller external ramps, lower minimum pulse
2
The NCP5314 DC/DC controller from ON Semiconductor
Two advantages of a multi−phase converter over a
The Enhanced V
combines the original V
(V
Figure 17. Enhanced V
SWNODE
2
CORE
loop for each phase as shown in Figure 17.
V
OUT
2
)
architecture measures and adjusts the
+
Lx
2
+
topology with peak
2
RLx
2
topology. Enhanced
Control Employing Resistive Current Sensing and Internal Ramp
RSx
THEORY OF OPERATION
x = 1, 2, 3 or 4
CSxP
CSxN
V
COMP
FB
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NCP5314
DAC
Out
V
“Fast−Feedback”
13
FFB
+
−
CSA
Connection
Internal Ramp
Fixed Frequency Multi−Phase Control
connected in parallel and are switched on at different times.
This reduces output current from the individual converters
and increases the ripple frequency. Because several
converters are connected in parallel, output current can ramp
up or down faster than a single converter (with the same
value output inductor) and heat is spread among multiple
components.
Enhanced V
individual phases. In four phase mode, each phase is
delayed 90 from the previous phase (120 in three−phase
mode). Normally, GATEx transitions to a high voltage at
the beginning of each oscillator cycle. Inductor current
ramps up until the combination of the amplified current
sense signal, the internal ramp and the output voltage ripple
trip the PWM comparator and bring GATEx low. Once
GATEx goes low, it will remain low until the beginning of
the next oscillator cycle. While GATEx is high, the
Enhanced V
On the other hand, once GATEx is low, the loop cannot
respond until the beginning of the next PWM cycle.
Therefore, constant frequency Enhanced V
respond to disturbances within the off−time of the
converter.
widths, higher frequency operation and PWM duty cycles
above 50% without external slope compensation. As the
sum of the inductor current and the internal ramp increase,
the voltage on the positive pin of the PWM comparator rises
and terminates the PWM cycle. If the inductor starts a cycle
with higher current, the PWM cycle will terminate earlier
providing negative feedback. The NCP5314 provides a
differential current sense input (CSxN and CSxP) for each
phase. Current sharing is accomplished by referencing all
phases to the same COMP pin, so that a phase with a larger
−
+
E.A.
In a multi−phase converter, multiple converters are
The NCP5314 controller uses four−phase, fixed−frequency,
COx
2
2
Channel
Startup
architecture to measure and control currents in
Offset
loop will respond to line and load variations.
+
−
COMP
PWM
To F/F
Reset
2
will typically