NCP5212A, NCP5212T
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DETAILED OPERATING DESCRIPTION
General
The NCP5212A/NCP5212T synchronous stepdown
power controller contains a PWM controller for wide
battery/adaptor voltage range applications
The NCP5212A/NCP5212T includes power good voltage
monitor, soft−start, overcurrent protection, undervoltage
protection, overvoltage protection and thermal shutdown.
The NCP5212A/NCP5212T features power saving function
which can increase the efficiency at light load. It is ideal for
battery operated systems. The IC is packaged in QFN16.
Control Logic
The internal control logic is powered by V
CC
. The device
is controlled by an EN pin. The EN pin serves two functions.
When voltage of EN is below VEN_Disable, it shuts down
the device. When the voltage of EN is at the level of
VEN_Master, the device is operating as Master mode. When
voltage level of EN is at VEN_Slave, the device is operating
as Slave mode. It should be noted that no matter the device
is operating either at Master or Slave mode, the device is
operating in the manner of auto power saving condition such
that it operates as skip mode automatically at light load.
When EN is above VEN_Disable, the internal V
ref
is
activated and power−on reset occurs which resets all the
protection faults. Once V
ref
reaches its regulation voltage, an
internal signal will wake up the supply undervoltage
monitor which will assert a “GOOD” condition. In addition,
the NCP5212A/NCP5212T continuously monitors V
CC
and
V
IN
levels with undervoltage lockout (UVLO) function.
Single Device Operation
The device is operating as single device operation when
the SYNC pin is pull to ground. Under this configuration, the
device will use the internal clock for normal PWM
operation.
Dual Device Operation (Master/Salve Mode)
The device is operating as Master/Slave mode if two
devices are tied up together. (Detail configuration please see
the application schematic) One device is served as Master
and another one is served as Slave. Once they already, they
are synchronized to each other and they are operating as
“interleaved” mode such that the phase shift of their
switching clocks is 180°. It has the benefit that the amount
of ripple current at the V
IN
will be lower and hence lesser
bulk capacitors at V
IN
to save the confined PCB space and
material cost. Figure 15 and Figure 16 show the difference
when the devices are operating independently
(unsynchronized) and operating at interleaved mode
(Synchronized). It can be seen that at the unsynchronized
condition, the system is obviously noisy because of high
ripple voltage at V
IN
(ripple voltage directly reflects the
amount of ripple current at V
IN
). Once the devices are
operating at interleaving mode, the overall V
IN
ripple
current is significantly reduced.
Top to Bottom: VIN AC Voltage, SWN_Slave, SWN_Master
Figure 15. Two Devices are Unsynchronized
Top to Bottom: VIN AC Voltage, SWN_Slave, SWN_Master
Figure 16. Two Devices are in Interleaved Operation
Transient Response Enhancement (TRE)
For the conventional 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
response enhancement circuitry is implemented inside the
NCP5212A/NCP5212T. In CCM operation, the controller is
continuously monitoring the COMP pin output voltage of
the error amplifier to detect the load transient events. The
functional block diagram of TRE is shown below.
+
R
+
C
internal TRE_TH
COMP
TRE
Figure 17. Block Diagram of TRE Circuit
