NCP5331_05 ONSEMI [ON Semiconductor], NCP5331_05 Datasheet - Page 34

• Manufacturer Part Number: NCP5331_05
• Description: Two-Phase PWM Controller with Integrated Gate Drivers
• Manufacturer: ONSEMI [ON Semiconductor]

impedances necessary to maintain less than the specified
maximum junction temperatures at 55 C ambient.
q CNTRL SA t (120 * 55°C) 1.48 W * 1.65°C W
q SYNCH SA t (120 * 55°C) 0.85 W * 1.65°C W
formed by using a TO−263 mounting pad of at least 2.0 in
(1282 mm
single−sided, 1 oz copper PCB. The total required pad area
would be slightly less if the area were divided evenly
between top and bottom layers with multiple thermal vias
joining the two areas. To conserve board space, AAVID
offers clip−on heatsinks for TO−220 thru−hole packages.
Examples of these heatsinks include #577002 (1
0.25 , 33 C/W at 2 W) and #591302 (0.75
29 C/W at 2 W).
6. Adaptive Voltage Positioning
Figure 5 to determine that a 51 kW resistor is needed for
R
corresponding value of R
R
7.0 mA. Knowing the V
required values for R
Equation 31.
the inductor’s resistance (R
resistance added by the circuit board (R
inductor’s nominal resistance in Section 2 (0.965 mW). In
this example, we assume 0.2 mW for the circuit board
resistance (R
be used to calculate the increase at the V
R DRP +
OSC
OSC
Equation 28 is used to calculate the heat sink thermal
If board area permits, a cost effective heatsink could be
First, to achieve the 200 kHz switching frequency, use
The no−load position is easily set using Equation 29.
For inductive current sensing, the designer must calculate
R
DRP
DV DRP + I O,MAX @ (R L ) R PCB ) @ G VDRP
+ 42.3°C W
+ 74.8°C W per MOSFET
. Then, use Figure 6 to find the V
resistor results in a V
+ 254 mV (7.0 mA ) 37 mV 3.6 kW)
+ 14.7 kW
or 37.4°C W per phase for two MOSFETs phase
can then be calculated from Equation 31.
(IBIAS VFB ) DV CORE,FULL−LOAD R F1 )
2
R VFBK + DV NO−LOAD IBIAS VFB
) for the upper and lower MOSFETs on a
+ 52 A @ (0.965 mW ) 0.2 mW) @ 4.2 V V
+ 0.254 mV
PCB
). With this information, Equation 30 can
+ +25 mV 7.0 mA
+ 3.6 kW
F1
FB
and R
OSC
bias current, one can calculate the
FB
DV DRP
DRP
. In this example, the 51 kW
bias current of approximately
L
) and approximate any
using Equation 29 through
FB
PCB
DRP
bias current at the
). We found the
pin at full load.
0.5
0.75
http://onsemi.com
0.5 ,
(29)
(30)
(31)
NCP5331
2
34
7. Current Sensing
satisfy
core material (such as the −8 from Micrometals). This
material is very consistent with dc current and frequency.
Less expensive core materials (such as the −52 from
Micrometals) change their characteristics with dc current,
ac flux density, and frequency. This material will yield
acceptable converter performance if the current sense time
constant is set lower (longer) than anticipated. As a rule of
thumb, start with approximately twice the resistance (R
or twice the capacitance (C
core material.
R
value for C
C
pin with minimal overshoot and fast rise time due to a step
change in load current as shown in Figure 35, Figure 36 and
Figure 37. This testing has shown that for a 3 to 25 A
transient, a value of 10.0 kW will produce the desired square
wave at V
8. Error Amplifier Tuning
an acceptable full−load transient response as shown in
Figure 38, Figure 39 and Figure 40. After a value for C
chosen, the peak−to−peak voltage ripple on the COMP pin
is examined under full−load to insure less than 20 mVpp as
shown in Figure 41.
9. Current Limit Setting
resistance, and the maximum current−sense gain determine
the current limit as shown in Equation 34. The maximum
current, I
requirements. The maximum inductor resistance occurs at
full load and the highest ambient temperature. This value
was found in the “Output Inductor Section” (1.28 mW). This
analysis assumes the PCB resistance only increases due to
the change in ambient temperature. Component heating will
also increase the PCB temperature but quantifying this
effect is difficult. Lab testing should be used to “fine tune”
the overcurrent threshold.
L
Sx
Choose the current sense network (R
Equation 32 will be most accurate for better iron powder
The component values determined thus far are L
After the circuit is constructed, the values of R
The error amplifier is tuned by adjusting C
The maximum inductor resistance, the maximum PCB
= 0.965 mW, and R
should be tuned to provide a “square−wave” at the V
R Sn + 828 nH (0.965 mW ) 0.2 mW) @ 0.1 mF
R PCB,MAX + 0.2 mW @ {1 ) 0.39% °C
+ 7.10 kW
DRP.
OUT,LIMIT
S1
R Sx @ C Sx + Lo (R L ) R PCB )
(0.1 mF) and solve for R
+ 0.26 mW
, was specified in the design
PCB
@ (100°C * 25°C)}
= 0.2 mW. We choose a convenient
Sx
) when using the less expensive
Sx
Sx
.
, C
Sx
, x = 1 or 2) to
A1
o
to provide
= 828 nH,
Sx
and/or
A1
DRP
(32)
Sx
is
)