ncp5215 ON Semiconductor, ncp5215 Datasheet - Page 13

• Manufacturer Part Number: ncp5215
• Description: Dual Synchronous Buck Controller For Notebook
• Manufacturer: ON Semiconductor

General
fast-transient-response dual-channel buck controller,
provides a multifunctional power solution for notebook
power system. 180° interleaved operation function
between the two channels has capabilities of reducing the
common input capacitor requirement and improving noise
immunity. Adaptive-Voltage-Positioning (AVP) control
reduces the requirement of output filter capacitors.
Programmable power-saving operation ensures high
efficiency over entire load range. Input feedforward
voltage-mode control is employed to deal with wide input
voltage range. Transient-Response-Enhancement (TRE)
control for the both channels enables fast transient
response.
PWM Operation
operation
300 kHz, or 400 kHz. As shown in Table 1, the connection
of the pin FSET determines normal operation frequency in
continuous-conduction-mode (CCM).
rate, an internal high-frequency clock is employed, which
frequency is four times of the selected normal operating
frequency. As an instance, if the FSET pin is connected to
V
internal high-frequency clock is 1.2 MHz. Figure 28
shows internal clocks of the NCP5215 in this case. The
1.2MHz high-frequency clock with 50% duty-ratio
introduced to the two PWM channels. A digital circuitry
generates two interleaved 300 kHz clocks using the
1.2 MHz clock and output them to the two PWM channels
as normal operation clocks in CCM, respectively.
Forced-PWM Operation (FPWM Mode)
under forced-PWM operation and thus always in CCM.
The two channels always run in selected fixed frequency
and 180° interleaved operation. In this mode, the low-side
gate-drive signal is forced to be the complement of the
high-side gate-drive signal. This mode allows reverse
inductor current, in such a way that it provides more
accurate voltage regulation and fast transient response.
runs in FPWM mode regardless of the FPWM# pin's setting
to guarantee smooth powerup.
Table 1. SWITCHING FREQUENCY SELECTION
CC
FSET Pin
Fsw (kHz)
The
The NCP5215 operates at a pin-selectable normal
To speed up transient response and increase sampling
If the FPWM# pin is pulled low, the NCP5215 works
During soft-start operation, the NCP5215 automatically
, the normal switching frequency is set to 300 kHz. The
NCP5215,
switching
frequency, allowing 200 kHz,
Float
200
a
high-efficiency
VCC
300
OPERATION DESCRIPTION
GND
400
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and
NCP5215
13
Light-Load Pulse-Skipping Operation (Skip Mode)
the NCP5215 works in pulse-skipping enabled operation
(PS).
in CCM, and the switching frequency is fixed as the
selected frequency. If both channels run in CCM, they
operate interleaved.
negative inductor current appears continuously. In the skip
mode, the bottom MOSFET will be turned off when the
inductor current is going negative. The top MOSFET's
on-time is fixed to around 1.5 times as the on-time in
CCM. The NCP5215 continuously monitors the voltage at
FB pin and comparing to the voltage at VDRP Pin. When
the FB voltage drops below the VDRP voltage, a fixed
on-time will be initiated at the time of the next coming
high-frequency clock edge, which can be either rising edge
or falling edge. The minimum off-time is half
high-frequency cycle.
becomes continuous, the controller will automatically
return to fixed-frequency operation and be synchronized to
the normal operation clock.
Transient Response Enhancement (TRE)
to constant on-time scheme. The response time of the
controller is between half to one cycle of the
high-frequency clock. However, for a conventional
trailing-edge PWM controller in CCM, the fastest
response time is one switching cycle in the worst case. To
further improve transient response in CCM, a transient
Figure 28. Internal Clocks in the NCP5215 as F
If the skip mode is enabled by pulling high FPWM# pin,
In medium and high load range, the converter still runs
In light load range, the converter will enter skip mode if
When the load increases and the inductor current
In the skip mode, the operation of the NCP5215 is similar
High Sampling
Response
(4*F
Fast
OSC
Rate
SW
)
1.2MHz
Digital Counter & 180°
CLK1
CLK2
Phase Shift
300 kHz
1.2MHz
300kHz
300kHz
1.2MHz
Interleaved in CCM
PWM1
PWM2
SW
=