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NCP6334BMT26TBG

P1-P3P4-P6P7-P9P10-P12P13-P14
NCP6334B, NCP6334C
http://onsemi.com
10
hysteresis is required on power good comparator before
signal going high again.
Soft−Start
A soft start limits inrush current when the converter is
enabled. After a minimum 300 ms delay time following the
enable signal, the output voltage starts to ramp up in 100 ms
(for external adjustable voltage devices) or with a typical
10 V/ms slew rate (for fixed voltage devices).
Active Output Discharge
An output discharge operation is active in when EN is low.
A discharge resistor (500 W typical) is enabled in this
condition to discharge the output capacitor through SW pin.
Cycle−by−Cycle Current Limitation
The NCP6334B/C protects the device from over current
with a fixed−value cycle−by−cycle current limitation. The
typical peak current limit ILMT is 2.8 A. If inductor current
exceeds the current limit threshold, the P−MOSFET will be
turned off cycle−by−cycle. The maximum output current
can be calculated by
I
MAX
+ I
LMT
*
V
OUT
@
ǒ
V
IN
* V
OUT
Ǔ
2 @ V
IN
@ f
SW
@ L
(eq. 1)
where VIN is input supply voltage, VOUT is output voltage,
L is inductance of the filter inductor, and f
SW
is 3 MHz
normal switching frequency.
Thermal Shutdown
The NCP6334B/C has a thermal shutdown protection to
protect the device from overheating when the die
temperature exceeds 150°C. After the thermal protection is
triggered, the fault state can be ended by re−applying VIN
and/or EN when the temperature drops down below 125°C.
NCP6334B, NCP6334C
http://onsemi.com
11
APPLICATION INFORMATION
Output Filter Design Considerations
The output filter introduces a double pole in the system at
a frequency of
f
LC
+
1
2 @ p @ L @ C
Ǹ
(eq. 2)
The internal compensation network design of the
NCP6334B/C is optimized for the typical output filter
comprised of a 1.0 mH inductor and a 10 mF ceramic output
capacitor, which has a double pole frequency at about
50 kHz. Other possible output filter combinations may have
a double pole around 50 kHz to have optimum operation
with the typical feedback network. Normal selection range
of the inductor is from 0.47 mH to 4.7 mH, and normal
selection range of the output capacitor is from 4.7 mF to
22 mF.
Inductor Selection
The inductance of the inductor is determined by given
peak−to−peak ripple current IL_PP of approximately 20%
to 50% of the maximum output current IOUT_MAX for a
trade−off between transient response and output ripple. The
inductance corresponding to the given current ripple is
L +
ǒ
V
IN
* V
OUT
Ǔ
@ V
OUT
V
IN
@ f
SW
@ I
L_PP
(eq. 3)
The selected inductor must have high enough saturation
current rating to be higher than the maximum peak current
that is
I
L_MAX
+ I
OUT_MAX
)
I
L_PP
2
(eq. 4)
The inductor also needs to have high enough current
rating based on temperature rise concern. Low DCR is good
for efficiency improvement and temperature rise reduction.
Table 1 shows some recommended inductors for high power
applications and Table 2 shows some recommended
inductors for low power applications.
Table 1. LIST OF RECOMMENDED INDUCTORS FOR HIGH POWER APPLICATIONS
Manufacturer Part Number
Case Size
(mm)
L (mH)
Rated Current (mA)
(Inductance Drop)
Structure
MURATA LQH44PN2R2MP0 4.0 x 4.0 x 1.8 2.2 2500 (−30%) Wire Wound
MURATA LQH44PN1R0NP0 4.0 x 4.0 x 1.8 1.0 2950 (−30%) Wire Wound
MURATA LQH32PNR47NNP0 3.0 x 2.5 x 1.7 0.47 3400 (−30%) Wire Wound
Table 2. LIST OF RECOMMENDED INDUCTORS FOR LOW POWER APPLICATIONS
Manufacturer Part Number
Case Size
(mm)
L (mH)
Rated Current (mA)
(Inductance Drop)
Structure
MURATA LQH44PN2R2MJ0 4.0 x 4.0 x 1.1 2.2 1320 (−30%) Wire Wound
MURATA LQH44PN1R0NJ0 4.0 x 4.0 x 1.1 1.0 2000 (−30%) Wire Wound
TDK VLS201612ET−2R2 2.0 x 1.6 x 1.2 2.2 1150 (−30%) Wire Wound
TDK VLS201612ET−1R0 2.0 x 1.6 x 1.2 1.0 1650 (−30%) Wire Wound
Output Capacitor Selection
The output capacitor selection is determined by output
voltage ripple and load transient response requirement. For
a given peak−to−peak ripple current IL_PP in the inductor
of the output filter, the output voltage ripple across the
output capacitor is the sum of three ripple components as
below.
V
OUT_PP
[ V
OUT_PP(C)
) V
OUT_PP(ESR)
) V
OUT_PP(ESL)
(eq. 5)
where VOUT_PP(C) is a ripple component by an equivalent
total capacitance of the output capacitors, VOUT_PP(ESR)
is a ripple component by an equivalent ESR of the output
capacitors, and VOUT_PP(ESL) is a ripple component by
an equivalent ESL of the output capacitors. In PWM
operation mode, the three ripple components can be
obtained by
V
OUT_PP(C)
+
I
L_PP
8 @ C @ f
SW
(eq. 6)
V
OUT_PP(ESR)
+ I
L_PP
@ ESR
(eq. 7)
V
OUT_PP(ESL)
+
ESL
ESL ) L
@ V
IN
(eq. 8)
and the peak−to−peak ripple current is
I
L_PP
+
ǒ
V
IN
* V
OUT
Ǔ
@ V
OUT
V
IN
@ f
SW
@ L
(eq. 9)
NCP6334B, NCP6334C
http://onsemi.com
12
In applications with all ceramic output capacitors, the
main ripple component of the output ripple is
VOUT_PP(C). So that the minimum output capacitance can
be calculated regarding to a given output ripple requirement
VOUT_PP in PWM operation mode.
C
MIN
+
I
L_PP
8 @ V
OUT_PP
@ f
SW
(eq. 10)
Input Capacitor Selection
One of the input capacitor selection guides is the input
voltage ripple requirement. To minimize the input voltage
ripple and get better decoupling in the input power supply
rail, ceramic capacitor is recommended due to low ESR and
ESL. The minimum input capacitance regarding to the input
ripple voltage VIN_PP is
C
IN_MIN
+
I
OUT_MAX
@
ǒ
D * D
2
Ǔ
V
IN_PP
@ f
SW
(eq. 11)
where
D +
V
OUT
V
IN
(eq. 12)
In addition, the input capacitor needs to be able to absorb
the input current, which has a RMS value of
I
IN_RMS
+ I
OUT_MAX
@ D * D
2
Ǹ
(eq. 13)
The input capacitor also needs to be sufficient to protect
the device from over voltage spike, and normally at least a
4.7 mF capacitor is required. The input capacitor should be
located as close as possible to the IC on PCB.
Table 3. LIST OF RECOMMENDED INPUT CAPACITORS AND OUTPUT CAPACITORS
Manufacturer Part Number
Case
Size
Height
Max (mm)
C (mF)
Rated
Voltage
(V)
Structure
MURATA GRM21BR60J226ME39, X5R 0805 1.4 22 6.3 MLCC
TDK C2012X5R0J226M, X5R 0805 1.25 22 6.3 MLCC
MURATA GRM21BR61A106KE19, X5R 0805 1.35 10 10 MLCC
TDK C2012X5R1A106M, X5R 0805 1.25 10 10 MLCC
MURATA GRM188R60J106ME47, X5R 0603 0.9 10 6.3 MLCC
TDK C1608X5R0J106M, X5R 0603 0.8 10 6.3 MLCC
MURATA GRM188R60J475KE19, X5R 0603 0.87 4.7 6.3 MLCC
Design of Feedback Network
For NCP6334B/C devices with an external adjustable
output voltage, the output voltage is programmed by an
external resistor divider connected from V
OUT
to FB and
then to AGND, as shown in the typical application
schematic Figure 1(a). The programmed output voltage is
V
OUT
+ V
FB
@
ǒ
1 )
R
1
R
2
Ǔ
(eq. 14)
where V
FB
is equal to the internal reference voltage 0.6 V,
R1 is the resistance from V
OUT
to FB, which has a normal
value range from 50 kW to 1 MW and a typical value of
220 kW for applications with the typical output filter. R2 is
the resistance from FB to AGND, which is used to program
the output voltage according to equation (14) once the value
of R1 has been selected. A capacitor Cfb needs to be
employed between the V
OUT
and FB in order to provide
feedforward function to achieve optimum transient
response. Normal value range of Cfb is from 0 to 100 pF, and
a typical value is 15 pF for applications with the typical
output filter and R1 = 220 kW.
Table 4 provides reference values of R1 and Cfb in case
of different output filter combinations. The final design may
need to be fine tuned regarding to application specifications.
Table 4. Reference Values of Feedback Networks (R1 and Cfb) for Output Filter Combinations (L and C)
R1 (kW) L (mH)
Cfb (pF) 0.47 0.68 1 2.2 3.3 4.7
C (mF)
4.7
220 220 220 220 330 330
3 5 8 15 15 22
10
220 220 220 220 330 330
8 10 15 27 27 39
22
220 220 220 220 330 330
15 22 27 39 47 56
P1-P3P4-P6P7-P9P10-P12P13-P14

NCP6334BMT26TBG

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Manufacturer:
ON Semiconductor
Description:
Switching Voltage Regulators USR BUCK CONVERTER
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