NCP1573D ONSEMI [ON Semiconductor], NCP1573D Datasheet - Page 14

• Manufacturer Part Number: NCP1573D
• Description: Low Voltage Synchronous Buck Controller
• Manufacturer: ONSEMI [ON Semiconductor]

where:
where:
System Considerations for the NCP1573
designs where the power supply for the controller IC has
very short turn−on and turn−off times. Such systems can be
found providing power to graphics cards or memory where
standby power is also provided. The key features of the
NCP1573 are that undervoltage lockout and soft start
resetting are not included. These features must be absent to
allow the NCP1573 to interface in a glitch−free manner with
back−up power supplies.
using the NCP1573 is included in Figure 23. Note that an
PWRGD
D = Duty cycle.
For switching power losses:
n = number of switch FETs (either top or bottom),
C = FET gate capacitance,
V = maximum gate drive voltage (usually V
f
The NCP1573 controller is optimized for converter
A schematic showing a possible system implementation
OSC
I PEAK + I LOAD )
= switching frequency.
10 k
R11
5 V
I RIPPLE +
Q5
MGSF1N02ELT1
R3
10
0.01 μF
P D + nCV 2 (f OSC )
12 V
C12
Q3
NTMS10P02R2
(V IN * V OUT )(V OUT )
0.1 μF
47 k
I RIPPLE
R1
C13
(f OSC )(L)(V IN )
2
1
2
3
4
+
U1
V
PWRGD
PGDELAY
COMP
I OUT
CC
3
NCP1573
)
0.1 μF
C4
I RIPPLE
GATEH
1N5817
GATEL
CC
2
D1
GND
),
V
FB
http://onsemi.com
LDO_ON_3.3
8
7
6
5
GND
Figure 23.
C6
100 pF
V
FB
14
R5
16.9 k
R7
16.2 k
external p−channel FET gates the 12 V supply to the IC. The
signal also controls an alternate supply that drives a linear
regulator. The linear regulator provides back−up power for
the load during low−power operation.
that the controller does not charge or discharge the output
capacitance significantly during the transition intervals.
This minimizes glitching during the transitions. Also, note
that a resistor divider and a diode connect the logic signal to
the COMP pin of the NCP1573. The divider and diode
network serve to hold the COMP voltage up when the IC is
powered down. When the power management state changes
and the IC powers back up, having the COMP voltage at its
correct level further reduces glitching. The correct COMP
level is determined to be the IC reference voltage (0.98 V)
plus the channel start−up offset of the controller (0.525 V),
plus about 10 mV to account for artificial ramp amplitude
(total of 1.615 V). The divider voltage must be about 100 mV
higher to allow for the diode forward voltage. Note that very
little current is assumed to flow through the diode since only
capacitor leakage current should be present.
during transitions due to manufacturing tolerances. Having
the COMP voltage slightly low will result in a temporary sag
in the output voltage as the linear regulator turns off and the
switching supply turns on. Similarly, a positive change in
V
1800 μF
OUT
In this case, the 12 V supply turn−on and turn−off is so fast
There will always be some small voltage adjustment
C1
will occur if the COMP voltage is slightly too high.
5 V
+
Q1
MTB1306
SWN
Q2
MTB1306
Rubycon MBZ
1800 μF
3.3 k
R6
L1 2.7 μH
C2
5.1 k
+
R4
Q6
MGSF1N02ELT1
+
R10
10 k
C8
1800 μF
Rubycon MBZ
Q4
NTMS10P02R2
+
3
2
V
V
C9
1800 μF
1.25 k
IN
OUT
R8
U2
CS5201
1.25 k
2.5 V
ADJUST
R9
1