ZLR964222L
Line Module User Guide
16
Microsemi Corporation Confidential and Proprietary
The CSW1 input capacitor for this design is a 220uF 25V low impedance electrolytic. In a customer system design,
this capacitor could be reduced to a 10uF 25V X5R ceramic if there is additional bulk capacitance already in the
system near the supply.
Capacitor, CREF1, must be 10uF 6.3V X5R/X7R. This should have a minimum package size of 0603.
4.5.3 High Voltage PNP
The BBABS power supply uses a 100V PNP power transistor as the main power switch. This transistor is designed
for applications where low Vce saturation voltage is important. When the transistor is turned on the current can be
as high as 1.5A. The thermal tab (collector tab) of the transistor should have a thermal pad of at least 1cm
2
. The
PNP transistor requirements for the buck-boost switcher are shown below:
• Type: PNP,Low Vce sat, Diodes/Zetex ZXTP2013 or equivalent.
• Collector (Vce) Voltage Rating: Vce=100V for up to 85Vpk ringing
• Suitable Packages: SOT-223, SOT89, or equivalent
• 100V Sources: Diodes/Zetex ZXTP2013/ZX5T953/FZT953, Central Semiconductor CZT953
• 140V Sources: Diodes/Zetex ZXTP2014/ZX5T955/FZT955, Central Semiconductor CZT955.
4.5.4 Inductor Requirements
The BBABS power supply has been designed to make use of low cost unshielded/semi-shielded inductors. The
inductor should not be placed in close proximity to noise sensitive circuits. See the next section on xDSL
compatibility. The ZLR964222L line module has been designed to support 8mm to 10mm size 47uH inductors.
47uH inductors with saturation current rating of 1.5A and greater are acceptable. Inductance should not be
degraded more than 30% at rated current.
4.5.5 Switching Diode Requirements
The BBABS uses three diodes in its output stage. DSW1 is the VBATL rectifier and is specified. The VBATH diodes,
DSW3 and DSW4, are BAV70
dual parallel diodes. To minimize cost, the diodes being used are small signal
diodes. The BAV70 was chosen specifically for its cost and suitable peak pulse rating. Because peak currents can
still be high in switch power supplies, resistors RS1 and RS2 are used to limit the peak current in the diodes. The
reverse voltage rating of the diodes should be greater than 70V. The diodes should have at least a 600mA repetitive
peak current rating for a pair. Observe supplier data sheet specifications. Consult with Microsemi Applications
concerning suitable parts for this application.
Alternately, DSW3 and DSW4, could be replaced with a single BAV23S. This was used in the previous revision of
the BBABS design and is still a valid choice. The BAV23S is a dual series diode with higher current rating compared
to BAV70 allowing for a single device to be used.
4.5.6 Compatibility with xDSL
Switching power supplies are inherently noisy and the buck-boost switching regulator is no exception. The collector
node of the PNP will have high dv/dt signals with a voltage swing of 50 V or more at a frequency of up to 128kHz.
Placing the switcher in close proximity of a DSL AFE can and most likely will cause degraded performance of the
DSL interface. It is therefore extremely important that the PNP, inductor, and associated circuitry be placed at least
one inch (2.5 cm) away from any DSL AFE signals.
4.5.7 Other Design Options
In addition to the design in this guide, Microsemi has other two channel switcher design options available that are
optimized for various cost, input supplies, and maximum ringing drive requirements. Please consult with Microsemi
CMPG Customer Applications for details or about specific requirements.
