UPS3652 Datasheet, PDF (6/9 Pages) Unisonic Technologies – HIGH PERFORMANCE CURRENT MODE POWER SWITCH

UPS3652
LINEAR INTEGRATED CIRCUIT
 FUNCTIONAL DESCRIPTION(Cont.)
(3) Internal Synchronized Slope Compensation
Built-in slope compensation circuit adds voltage ramp onto the current sense input voltage for PWM
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
The Frequency Hopping is implemented in the IC; there are two oscillators built-in the IC. The first oscillator
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.
FIG.5 Frequency Hopping
(5) Constant Output Power Limit
When the primary current, across the primary wind of transfer, reaches the limit current, around 1.2A, the output
GATE drive will be turned off after a small propagation delay t_D. This propagation delay will introduce an additional
current proportional to t_D×V_IN/Lp. Since the propagation delay is nearly constant regardless of the input line voltage
V_IN. Higher input line voltage will result in a larger additional current and hence the output power limit is also higher
than that under low input line voltage. To compensate for this output power limit variation across a wide AC input
range, the threshold voltage is adjusted by adding a positive ramp. This ramp signal rises from 0.75V to 0.95V, and
then flattens out at 0.95V. A smaller threshold voltage forces the output GATE drive to terminate earlier. This
reduces the total PWM turn-on time and makes the output power equal to that of low line input. This proprietary
internal compensation ensures a constant output power limit for a wide AC input voltage range (90VAC to 264VAC).
(6) Protection section
The IC takes on more protection functions such as OLP, OVP and OTP etc. In case of those failure modes for
continual blanking time, the driver is shut down. At the same time, IC enters auto-restart, V_CC power on and driver is
reset after V_CC power on again.
OLP
After power on, IC will shutdown driver if over load state occurs for continual T_D-OLP. OLP case as followed FIG.6.
The test circuit as followed FIG.8. T_D-OLP≈2C_FB/1.4_.
OVP
OVP will shutdown the switching of the power MOSFET whenever V_CC>V_OVP. The OVP case as followed FIG.7.
the test circuit as followed FIG.9.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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QW-R119-021.B