ON Semiconductor NCP4305 User manual

©Semiconductor Components Industries, LLC, 2016
January, 2016 − Rev. 1 1Publication Order Number:
EVBUM2350/D
NCP4305DGEVB
NCP4305 Synchronous
Rectification Evaluation
Board User's Manual
Table 1. GENERAL PARAMETERS
SMPS Type Supply
Voltage Reverse Voltage Effective Resistance
LLC 5−35 V 40 V 0.9 mW
Description
This evaluation board user’s manual describes a high efficiency
synchronous rectification evaluation board that can easily replace
a secondary side rectification diode in an SMPS.
The NCP4305 is used as synchronous rectification controller.
The evaluation board has very few external components and illustrates
how small and effective such a design can be.
The NCP4305 features a very precise 0 mV turn-off comparator that
supports even very low current flowing through the MOSFET even
when very low RDSON synchronous MOSFETs is used.
Key Features
•Precise Turn-off Comparator
•Wide Input Voltage Range
•High Operation Frequency
•Strong MOSFET Driver
•High Efficiency
•Adjustable Minimum On and Off Times
•Light Load Detection Feature
•Capable to Operate in Positive and Negative Branch
•Small size
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EVAL BOARD USER’S MANUAL
Figure 1. NCP4305 Evaluation Board

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Connection Diagram
Figure 2. Possible Connections in to Circuit
VCC
A) B)
+
VCC
+
The evaluation board can be connected in circuit where
the rectification diode is in the positive or negative branch.
When connection to a positive branch is used, it is necessary
to use an external power supply (or auxiliary winding with
rectification) to provide power to the evaluation board. VCC
should be referenced to A1 or A2 points. When LLD
function is used it is needed to connect LLD1 pin with
opposite side rectifier cathode.

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Evaluation Board Schematic
Figure 3. Schematic of the NCP4305
D4
BAS20
D1
BAS20
MIN_TOFF
VCC
DRV
A2
A1
C
TRIG/DIS
LLD1
GND
GND
GND
GND GND
GNDGND
GND GND
1
2
3
4
8
7
6
5
VCC
MIN_TOFF
MIN_TON
LLD
DRV
GND
CS
TRIG/DIS
IC1
NCP4305S08
RLLDD_PD
10 kW
LLD
RLLD2
NU RLLD3 NU
RLLD1
NU
CLLD2
NU
CLLD1
NU
RMIN_TOFF
22 kW
RMIN_TON
4.7 kW
RTRIG_PD
1 kW
RTRIG
1 kW
RCS
0 W
RG
0 W
RG_PD
10 kW
C2
1 mF/35 V
C1
100 nF
RMIN_TOFFM
NU
CSNB
3.9 nF
RSNB1
15 kW
RSNB2
NU
M1
NVMFS5830 M2
The evaluation board was designed to support a minimal
external component count implementation. C1 and C2 are
decoupling capacitors. They should be placed as close as
possible to the VCC and GND pins. Resistors RMIN_TON and
RMIN_TOFF are used to set the protection interval when the
synchronous MOSFET is turned on and off. Resistor
RMIN_TOFFM is placed there to support a situation when an
external circuit provides control for minimum off-time
modulation. This is needed only in situations when the
minimum off-time cannot be set across the whole range of
power supply operation. Resistor RTRIG_PD is only pull
down for TRIG pin and RTRIG is only protection resistor.
A position for a gate resistor RGis provided in case there is
a need to slow down the MOSFET switching process. The
turn-off (and also the turn-on) threshold can be lowed when
resistor RCS is used. Components CSNB, RSNB1 and RSNB2
form a snubber circuit.
LLD circuit consists of CLLD1, CLLD2, RLLD1, RLLD2,
RLLD3 and D4. Purpose of circuit is to estimate output
power. This can be done in two ways. The first is to measure
duty cycle of skip burst. LLD circuit time constant is high
and it filters and averages duty cycle ratio. This is good for
systems which transfer low energy during skip each switch
cycle. When duty cycle of skip bursts is low NCP4305 enters
disable mode to save energy, when it is higher SR controller
starts to operate and SR transistor gate voltage is modulated
according to skip duty cycle. The second option is for system
which transfers lot of energy in few first pulses in skip and
then transferred energy is minimal. In this case LLD circuit
time constant is low and RLLD3 resistance is close to 0. LLD
pin voltage drops down in first switching pulse in skip mode
and NCP4305 wakes up fast and allows using fully open SR
transistor. When skip burst ends, LLD voltage goes high and
if time between skip bursts is long enough NCP4305 enters
disable mode to save energy.
Circuit Layout
The PCB consists of a 2 layer FR4 board with 35 mm
copper cladding. All components are surface mount and
most of the components that may require adjustment are on
the same side and use 1206 values for easy rework. Critical
component such as blocking capacitors C1 and C2 have to
be placed carefully near the IC. The synchronous driver path
to the MOSFETs was done with very low resistance and
parasitic inductance to minimize emissions and minimize
turn-on and turn-off times. The same is true for the CS pin.
For the CS pin, a kelvin contact was done to be able to sense
the voltage directly at the drain. Improper connection of the
GND and CS connects can impact the turn-off process
especially when a very low RDSON MOSFETs are used.

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Figure 4. Top Layer
Figure 5. Bottom Layer
Figure 6. Top Side Components

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Figure 7. Bottom Side Components
Figure 8. Evaluation Board Photo − Top Side
Figure 9. Evaluation Board Photo − Bottom Side

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Table 2. BILL OF MATERIALS FOR NCP4305 PUT-IN BOARD SO-8FL (Note 1)
Parts Qty Description Value Tolerance Footprint Manufacturer Manufacturer
Part Number Substitution Allowed
C1 1 Ceramic Capacitor 100 nF 10% 1206 Kemet C1206X104K5RACTU Yes
C2 1 Ceramic Capacitor 1mF/50 V 10% 1206 Kemet C1206X105K5RACTU Yes
CLLD1, CLLD2 2 − NU − 1206 − − Yes
CSNB 1Ceramic Capacitor 3.9 nF − 1206 Kemet C1206C392K5RACTU Yes
D1, D4 2Switching Diode BAS20HT1G − SOD−323 ON Semiconductor BAS20HT1G Yes
IC1 1 Secondary Side
Synchronous
Rectification Controller
NCP4305D − SOIC−08 ON Semiconductor NCP4305DDR2G No
M1, M2 2N-Channel Power
MOSFET NVMFS5830NL − SO−8FL ON Semiconductor NVMFS5830NLT1G Yes
RCS, RG2Resistor SMD 0W5% 1206 Yageo RC1206JR−070RL Yes
RG_PD 1Resistor SMD 10 kW1% 1206 Yageo RC1206FR−0710KL Yes
RLLD_PD,
RTRIG,
RTRIG_PD
3Resistor SMD 1kW1% 1206 Yageo RC1206FR−071KL Yes
RLLD1, RLLD2,
RLLD3,
RSNB2,
RMIN_TOFFML
5Resistor SMD NU − 1206 − − Yes
RMIN_TOFF 1Resistor SMD 22 kW1% 1206 Yageo RC1206FR−0722KL Yes
RMIN_TON 1Resistor SMD 4.7 kW1% 1206 Yageo RC1206FR−074K7L Yes
RSNB1 1Resistor SMD 15 W1% 1206 Yageo RC1206FR−0715RL Yes
1. All parts are Pb-Free
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and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each
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