Features: ` On-board high-voltage, 1- Switching FET
` Switching Frequencies of Up to 1 MHz
` Synchronization Capability
` Easily Compensated Current-Mode Operation
` Operates with Input Voltages Up to 200 V
` 1.8-MHz Error Amplifier
` Soft-Start
` Latched SHUTDOWNPinout
SpecificationsVoltages Referenced to −VIN
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 V
+VIN (Note: VCC < +VIN + 0.3 V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 V
Logic Input (SHUTDOWN, SYNC) . . . . . . . . . . . . . . . . −0.3 V to VCC + 0.3 V
Linear Inputs (FEEDBACK, SENSE,
SOFT-START) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −0.3 V to VCC + 0.3 V
HV Pre-Regulator Input Current (continuous) . . . . . . . . . . . . . . . . . . . . . 5 mA
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −65 to 150
Operating Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . −40 to 85
Junction Temperature (TJ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Drain-Source Voltage (TA = 250) (VDS)a . . . . . . . . . . . . . . . . . . . . . . . . . 200 V
Continuous Drain Current (TA = 250) (ID)a . . . . . . . . . . . . . . . . . . . . . . . 1.0 A
Power Dissipation (Package)a
16-Pin SOIC (Y Suffix)b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 900 mW
Thermal Impedance JA)
16-Pin SOIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140/W
Notes
a. Device mounted with all leads soldered or welded to PC board, t 2
sec.
b. Derate 7.2 mW/ above 25. DescriptionSi9117 datasheet
The Si9117 high-efficiency converter for telecom systems running off 48 V is ideal for emerging applications such as interactive video (IV) set-top boxes and microcell base stations, such as those used for Personal Communications Systems (PCS). IV set-top boxes and microcell base stations typically require less than 15 W of power and have access to the analog telephone line power. Both IV set-top boxes and microcell base stations process extremely low-level, modulated analog signals (on the order of Vs), making the frequency and energy content of radiated and conducted noise a major issue. These application circuits are also constrained in terms of available board space and place a premium on minimal footprint.
The combination of an on-board, high-voltage, 1-switch and a PWM IC with operational input voltage of 200 V allows operation off of the analog telephone line, even with the worst case battery voltage and ringing voltage. Once the converter has started up, a simple bootstrap circuit can provide power to the IC by raising the source voltage of the n-channel, depletion mode, start-up FET above its gate voltage of 9.2 V. This technique lowers system costs, reduces the area required for circuit implementation, and minimizes circuit power consumption.
Processing high-frequency, modulated analog signals for video or RF requires receivers with sensitivities in the range of 0.5 to 25 V. At these levels, noise generated by switchmode power conversion can impair the signal recovery process. Controlling radiated noise is a matter of proper layout and shielding. Controlling conducted noise is a matter of limiting its energy and isolating the conducted energy's fundamental and harmonic frequencies to bands which will not affect the frequencies of interest. The high-frequency, synchronized switching of the Si9117 enables this design requirement. First, for a given output current, high-frequency switching attenuates output ripple, minimizing conducted energy. Second, synchronizing the high switching frequency to an external frequency allows the fundamental and its harmonics to be moved out of range of the frequency bands of interest. An additional benefit of high-frequency switching is reduced size and cost of the inductor and the output filter capacitance.
In addition to these mandatory design considerations, the Si9117 is easy to design with and compensate, and takes a minimum of board area to implement: an important benefit in high-volume/small-package applications such as set-top boxes and microcell base stations.
The Si9117 is available in both standard and lead (Pb)-free packages.
Si9117 Data Sheet
