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PWM5031-7 View Datasheet(PDF) - Aeroflex Corporation

Part Name
Description
Manufacturer
PWM5031-7
Aeroflex
Aeroflex Corporation Aeroflex
PWM5031-7 Datasheet PDF : 17 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
OSCILLATOR
The chip uses two precision current mirrors that alternately charge and discharge an external capacitor to generate an
extremely linear sawtooth oscillator waveform. At the start of each cycle, the charging current, set by the choice of
resistor at the Rset pin, is 1:1 mirrored over to the Cset pin where it charges an external capacitor. When the capacitor
voltage reaches the comparator’s upper threshold (nominally VREF), the comparator switches current mirrors and begins
to discharge the external capacitor. The discharge current is set at roughly five times the charging current to result in fast
discharge and minimal Dead Time. When the voltage reaches the comparator’s lower threshold (0.9V), the comparator
switches back to the charging mirror, powers down the discharge mirror, and the whole process repeats.
The frequency is set by choosing Rset and Cset such that:
FOSC
-----------------------1-------------------------
0.84 × RSET × CSET
20KHz FOSC 1MHz
Suggested Ranges for Cset and Rset are:
y 50K ohms < Rset < 300K
r 10pf < Cset < 600pF
Rset 6
Cset 7
GND 12
limina 320K
300K
e280K
Pr260K
240K
390pF 220000ppFF 100pF 47pF
20pF
220K
RSET 200K
Ω
180K
160K
140K
120K
100K
80K
60K
40K
10K
100K
Frequency Hz
Ct Rt
10pF
1M
FIGURE 3 – Timing Resistance vs Frequency
SCD5031 Rev B
8
 

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