FSEZ1307 Fairchild Semiconductor, FSEZ1307 Datasheet - Page 11

• Manufacturer Part Number: FSEZ1307
• Description: This third-generation Primary Side Regulation (PSR) PWM controller combination power MOSFET, FSEZ1307, provides several features to enhance the performance of low-power flyback converters
• Manufacturer: Fairchild Semiconductor

© 2010 Fairchild Semiconductor Corporation
FSEZ1307 • Rev. 1.0.2
Cable Voltage Drop Compensation
In cellular phone charger applications, the battery is
located at the end of cable, which typically causes
several percentage points of voltage drop on the battery
voltage. FSEZ1307 has a built-in cable voltage drop
compensation that provides a constant output voltage at
the end of the cable over the entire load range in CV
mode. As load increases, the voltage drop across the
cable is compensated by increasing the reference
voltage of the voltage regulation error amplifier.
Operating Current
The FSEZ1307 operating current is as small as 2.5mA,
which results in higher efficiency and reduces the V
hold-up capacitance requirement. Once FSEZ1307
enters “deep” green mode, the operating current is
reduced to 0.95mA, assisting the power supply in
meeting power conservation requirements.
Green-Mode Operation
The FSEZ1307 uses voltage regulation error amplifier
output (V
modulates the PWM frequency, as shown in Figure 26.
The switching frequency decreases as the load
decreases. In heavy load conditions, the switching
frequency is fixed at 50kHz. Once V
below 2.5V, the PWM frequency linearly decreases from
50kHz. When FSEZ1307 enters deep green mode, the
PWM frequency is reduced to a minimum frequency of
370Hz, gaining power saving to meet international
power conservation requirements.
Frequency Hopping
EMI reduction is accomplished by frequency hopping,
which spreads the energy over a wider frequency range
than the bandwidth measured by the EMI test
equipment. FSEZ1307 has an internal frequency
hopping circuit that changes the switching frequency
between 47kHz and 53kHz over the period shown in
Figure 27.
Figure 26. Switching Frequency in Green Mode
COMV
) as an indicator of the output load and
COMV
decreases
DD
11
High-Voltage Startup
Figure 28 shows the HV-startup circuit for FSEZ1307
applications. The HV pin is connected to the line input or
bulk capacitor through a resistor, R
recommended). During startup, the internal startup
circuit is enabled. Meanwhile, line input supplies the
current, I
through R
V
I
on, C
consumption current before the PWM starts to switch.
Therefore, C
from dropping down to V
delivered from the auxiliary winding.
STARTUP
DD-ON
DD
, the internal startup circuit is disabled, blocking
from flowing into the HV pin. Once the IC turns
STARTUP
is the only energy source to supply the IC
Figure 27. Frequency Hopping
START
Figure 28. HV Startup Circuit
DD
, to charge the hold-up capacitor, C
must be large enough to prevent V
. When the V
DD-OFF
before the power can be
DD
voltage reaches
START
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(100kΩ
DD
DD
,