Datasheet

UCC28700, UCC28701
UCC28702, UCC28703
SLUSB41 – JULY 2012 www.ti.com
DESIGN PROCEDURE
This procedure outlines the steps to design a constant-voltage, constant-current flyback converter using the
UCC28700 family of controllers. Refer to the Figure 19 for component names and network locations. The design
procedure equations use terms that are defined below.
Figure 19. Design Procedure Application Example
Definition of Terms
Capacitance Terms in Farads
• C
BULK
: total input capacitance of C
B1
and C
B2
.
• C
DD
: minimum required capacitance on the VDD pin.
• C
OUT
: minimum output capacitance required.
Duty Cycle Terms
• D
MAGCC
: secondary diode conduction duty cycle in CC, 0.425.
• D
MAX
: MOSFET on-time duty cycle.
Frequency Terms in Hertz
• f
LINE
: minimum line frequency.
• f
MAX
: target full-load maximum switching frequency of the converter.
• f
MIN
: minimum switching frequency of the converter, add 15% margin over the f
SW(min)
limit of the device.
• f
SW(min)
: minimum switching frequency (see ELECTRICAL CHARACTERISTICS).
Current Terms in Amperes
• I
OCC
: converter output constant-current target.
• I
PP(max)
: maximum transformer primary current.
• I
START
: start-up bias supply current (see ELECTRICAL CHARACTERISTICS).
• I
TRAN
: required positive load-step current.
• I
VSL(run)
: VS pin run current (see ELECTRICAL CHARACTERISTICS).
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