FEATURES
Fixed +5-V or +3.3-V Output
Integrated Floating Feedback Amplifier
On-Chip 70-V, 1.5- N-Channel
MOSFET Switch
Integrated High Voltage Start-Up Circuit,
with VCC Regulator
−10-V to −60-V Input Voltage Range
95-kHz PWM Operation
Integrated Soft-Start and Oscillator
High Efficiency Over Full Load Range
Under Voltage Lockout
Current Mode Control
Hiccup Mode Short Circuit
Protection
Thermal Shutdown
SOIC-8 Narrow-Body Package
DESCRIPTION
The Si9121 simplifies the −48-V to +5-V or +3.3-V converter
design for ISDN application by integrating the floating
feedback error amplifier providing direct output voltage
regulation. This approach eliminates the need for an external
shunt regulator. The Si9121 also integrates a high voltage
depletion mode MOSFET which allows the converter to be
powered directly from the high input bus voltage without
requiring an external start-up circuit. Combined with simple
magnetic design due to its non-isolated topology, the Si9121
provides a one-chip solution for complete ISDN power supply.
In order to reduce external component count, the Si9121 has
a fully integrated 95-kHz oscillator and soft-start circuit.
The Si9121 is available in both standard and lead (Pb)-free
SOIC-8 pin packages, and is offered in either +5-V or +3.3-V
fixed output options (Si9121DY-5 or Si9121DY-3,
respectively). In order to satisfy the stringent ambient
temperature requirements in many applications, the Si9121 is
rated to the industrial temperature range of −40 C to 85 C.