PEB2023 Datasheet, PDF (18/25 Pages) Siemens Semiconductor Group – ISDN DC Converter Circuit IDCC

PEB 2023
PEF 2023
Functional Description
Voltage Reference
The reference regulator of the PEB/F 2023 is based on a temperature compensated
bandgap. This circuitry is fully active at supply voltages (pin V_EXT) above 6 volts and
provides up to 0.5mA of load current to external circuitry at 4 volts. This reference has to
be buffered by an external capacitor (C_min = 1µF).
Sawtooth Oscillator
The oscilator frequency is programmed by the two components R₁ and C₁ (see figure 4,
5 or 6). The oscillator timing capacitor C₁ is charged by V_REF through R₁ and discharged
by an internal 10kΩ discharge-resistor. The rise-time of the sawtooth oscillator can be
programmed with R₁ and C₁. The internal discharge-resistor and C₁ define the fall-time.
At the beginning of the discharge period a positive synchronization pulse is generated at
pin SYNC. Otherwise the PEB/F 2023 can be synchronized via pin SYNC to an external
logic clock by programming the oscillator to free run at a frequency 10% lower than the
synchronization frequency. The PEB/F 2023 is synchronized by the rising edge of the
sync. signal. So multiple devices can be synchronized together by programming one
master unit for the desired frequency (only one possible interfering frequency).
Note that the frequency of the output driver is half the oscillator frequency. The switching
frequency as a function of R₁ and C₁ is shown in figure 9.
350
10 pF
300
250
22 pF
200
150
68 pF
100 pF
100
220 pF
50
470 pF
1 nF
0
10
20
30
40
50
60
70
80
90
100
R [ kOHM ]
Figure 9
Switching Frequency
Semiconductor Group
18
08.97