PSB2120 데이터 시트보기 (PDF) - Siemens AG

부품명

상세내역

제조사

PSB2120

ISDN Remote Power Controller (IRPC)

Siemens AG 

PSB 2120

Functional Description

The reference provides a 4.0 V voltage for the regulation loop. A high gain error amplifier compares

the reference voltage with the switch mode supply output voltage. The output of the error amplifier

is compared with a periodic linear ramp, which is generated by the sawtooth-oscillator circuit. The

comparator output is a fixed-frequency, variable pulse width logic signal, which passes through

logic circuits to the high voltage power-switching-FET.

A digital current limiting device suppresses the PWM logic signal when the voltage difference at the

current limit sense input reaches 100 mV. In this case the control logic inhibits double pulses during

one oscillator period.

Start-Up Procedure

Before the switched-mode DC/DC-converter starts, a sequence of several conditions has to be

passed in order to avoid any system malfunction.

The primary undervoltage detection inhibits the converter function. This insures that all control

functions have stabilized in the proper state when the turn on voltage (ca. 10 V) is reached, and it

prevents start-up glitches.

In case of connecting the TE to powered lines or if a line is powered up, the charge current of the

primary buffer capacitor is limited by an external resistor (figure 2).

This resistor is short-circuited by the PSB 2120 when the voltage drop across it falls below

approximately 2.0 V. The residual resistance of this short-circuit is about 3 Ω. In case of a primary

undervoltage detection the short-circuit will be always deactivated. So, the DC/DC-converter does

not start until the charging of the primary buffer capacitor is completed, and the maximum line input

voltage is reached. If this feature is not desired, CIN has to be connected to GND. In this case the

primary current measuring circuit turns off, to reduce chip-power dissipation from 9 mW to 6 mW.

In order to avoid high current peaks during the charging of the secondary capacitors or line

capacitors in case of supplying an S-interface, a soft start circuit is implemented in the PSB 2120.

This circuit requires an external capacitor, connected between CSS and GND.

In addition, the enable input (ENA) allows an external switch-on/switch-off control. If the DC/DC-

converter is disabled via ENA, the soft-start-capacitor at pin CSS is discharged. This input can also

be used for several other functions, e.g. secondary overvoltage protection.

Semiconductor Group

6

Share Link: