UPS703 Unisonic Technologies, UPS703 Datasheet - Page 7

• Manufacturer Part Number: UPS703
• Description: High Performance Current Mode Power Switch
• Manufacturer: Unisonic Technologies

UPS703
(2) Switch Frequency Set
operating. At no load or light load condition, most of the power dissipation in a switching mode power supply is from
switching loss on the MOSFET transistor, the core loss of the transformer and the loss on the subber circuit. The
magnitude of power loss is in proportion to the number of switching events within a fixed period of time. So lower
switch frequency at lower load, which more and more improve IC’s efficiency at light load. At from no load to light
load condition, The IC will operate at from Burst mode to Reducing Frequency Mode. The relation curve between f
and P
(3) Internal Synchronized Slope Compensation
generation, this greatly improves the close loop stability at CCM and prevents the sub-harmonic oscillation and thus
reduces the output ripple voltage.
(4) Frequency Hopping For EMI Improvement
is to set the normal switching frequency; the switching frequency is modulated with a period signal generated by the
2nd oscillator. The relation between the first oscillator and the 2nd oscillator as followed FIG.5. So the tone energy is
evenly spread out, the spread spectrum minimizes the conduction band EMI and therefore eases the system design
in meeting stringent EMI requirement.
FUNCTIONAL DESCRIPTION(Cont.)
The maximum switch frequency is set to 68kHz. Switch frequency is modulated by output power P
OUT
Built-in slope compensation circuit adds voltage ramp onto the current sense input voltage for PWM
The Frequency hopping is implemented in the IC; there are two oscillators built-in the IC. The first oscillator
/P
OUT (MAX)
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
FIG.4 The relation curve between f
as followed FIG.4.
F
F
F
SW_MAX
SW_TYP
SW_MIN
Fosc
(kHz)
FIG.5 Frequency Hopping
SW
and relative output power P
T
Hopping
LINEAR INTEGRATED CIRCUIT
OUT
/ P
t(ms)
OUT (MAX)
OUT
QW-R119-015.A
during IC
7 of 12
SW