Motore di ricerca datesheet componenti elettronici
  Italian  ▼
ALLDATASHEETIT.COM

X  

UC2842BNG Scheda tecnica(PDF) 8 Page - ON Semiconductor

Il numero della parte UC2842BNG
Spiegazioni elettronici  High Performance Current Mode Controllers
Download  22 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
Produttore elettronici  ONSEMI [ON Semiconductor]
Homepage  http://www.onsemi.com
Logo ONSEMI - ON Semiconductor

UC2842BNG Scheda tecnica(HTML) 8 Page - ON Semiconductor

Back Button UC2842BNG Datasheet HTML 4Page - ON Semiconductor UC2842BNG Datasheet HTML 5Page - ON Semiconductor UC2842BNG Datasheet HTML 6Page - ON Semiconductor UC2842BNG Datasheet HTML 7Page - ON Semiconductor UC2842BNG Datasheet HTML 8Page - ON Semiconductor UC2842BNG Datasheet HTML 9Page - ON Semiconductor UC2842BNG Datasheet HTML 10Page - ON Semiconductor UC2842BNG Datasheet HTML 11Page - ON Semiconductor UC2842BNG Datasheet HTML 12Page - ON Semiconductor Next Button
Zoom Inzoom in Zoom Outzoom out
 8 / 22 page
background image
UC3842B, UC3843B, UC2842B, UC2843B
http://onsemi.com
8
OPERATING DESCRIPTION
The UC3842B, UC3843B series are high performance,
fixed frequency, current mode controllers. They are
specifically designed for Off−Line and DC−to−DC
converter applications offering the designer a cost−effective
solution
with
minimal
external
components.
A
representative block diagram is shown in Figure 19.
Oscillator
The oscillator frequency is programmed by the values
chosen for the timing components RT and CT. It must also be
noted that the value of RT uniquely determines the
maximum duty ratio of UC384xx. The oscillator
configuration depicting the connection of the timing
components to the RT/CT pin of the controller is shown in
Figure 18. Capacitor CT gets charged from the Vref source,
through resistor RT to its peak threshold VRT/CT(peak),
typically 2.8 V. Upon reaching this peak threshold volage, an
internal 8.3 mA current source, Idischg, is enabled and the
voltage across CT begins to decrease. Once the voltage
across CT reaches its valley threshold, VRT/CT(valley),
typically 1.2 V, Idischg turns off. This allows capacitor CT to
charge up again from Vref. This entire cycle repeats, and the
resulting waveform on the RT/CT pin has a sawtooth shape.
Typical waveforms are shown in Figure 20.
The oscillator thresholds are temperature compensated to
within
±6% at 50 kHz
. Considering the general industry
trend of operating switching controllers at higher
frequencies, the UC384xx is guaranteed to operate within
±10% at 250 kHz. These internal circuit refinements
minimize variations of oscillator frequency and maximum
duty ratio.
The charging and discharging times of the timing
capacitor CT are calculated using Equations 1 and 2. These
equations do not take into account the propagation delays of
the internal comparator. Hence, at higher frequencies, the
calculated value of the oscillator frequency differs from the
actual value.
t
RT CT(chg) + RTCT ln
VRT CT(valley) * Vref
V
RT CT(peak) * Vref
(eq. 1)
t
RT CT(dischg) + RTCT ln
RTIdischg ) VRT CT(peak) * Vref
RTIdischg ) VRT CT(valley) * Vref
(eq. 2)
The maximum duty ratio, Dmax is given by Equation 3.
Dmax +
t
RT CT(chg)
t
RT CT(chg) ) tRT CT(dischg)
(eq. 3)
Substituting Equations 1 and 2 into Equation 3, and after
algebraic simplification, we obtain
Dmax +
ln
VRT CT(valley)*Vref
VRT CT(peak)*Vref
ln
VRT CT(valley)*Vref
VRT CT(peak)*Vref @
RTIdischg)VRT CT(peak)*Vref
RTIdischg)VRT CT(valley)*Vref
(eq. 4)
Clearly, the maximum duty ratio is determined by the
timing resistor RT. Therefore, RT is chosen such as to
achieve a desired maximum duty ratio. Once RT has been
selected, CT can now be chosen to obtain the desired
switching frequency as per Equation 5.
f +
1
RTCT ln
VRT CT(valley)*Vref
VRT CT(peak)*Vref @
RTIdischg)VRT CT(peak)*Vref
RTIdischg)VRT CT(valley)*Vref
(eq. 5)
Figure 2 shows the frequency and maximum duty ratio
variation versus RT for given values of CT. Care should be
taken to ensure that the absolute minimum value of RT
should not be less than 542
W. However, considering a 10%
tolerance for the timing resistor, the nearest available
standard resistor of 680
W is the absolute minimum that can
be used to guarantee normal oscillator operation. If a timing
resistor smaller than this value is used, then the charging
current through the RT, CT path will exceed the pulldown
(discharge) current and the oscillator will get permanently
locked/latched to an undefined state.
In many noise-sensitive applications it may be desirable
to frequency-lock the converter to an external system clock.
This can be accomplished by applying a clock signal to
the
circuit shown in Figure 22. For reliable synchronization, the
free-running oscillator frequency should be set about 10%
less than the clock frequency. A method for multi-unit
synchronization is shown in Figure 23. By tailoring the
clock waveform, accurate Output duty ratio clamping can be
achieved.
Enable
Idischg
Vref
RT/CT
RT
CT
2.8 V
1.2 V
Figure 18. Oscillator Configuration


Codice articolo simile - UC2842BNG

Produttore elettroniciIl numero della parteScheda tecnicaSpiegazioni elettronici
logo
ON Semiconductor
UC2842BNG ONSEMI-UC2842BNG Datasheet
370Kb / 21P
   High Performance Current Mode Controllers
February, 2007 ??Rev. 9
UC2842BNG ONSEMI-UC2842BNG Datasheet
743Kb / 25P
   High Performance Current Mode Controllers
August, 2021 - Rev. 18
More results

Descrizione simile - UC2842BNG

Produttore elettroniciIl numero della parteScheda tecnicaSpiegazioni elettronici
logo
Motorola, Inc
UC3842B MOTOROLA-UC3842B Datasheet
401Kb / 16P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
logo
Freescale Semiconductor...
MC34129EF FREESCALE-MC34129EF Datasheet
444Kb / 16P
   high performance current mode controllers
logo
ON Semiconductor
UC3844BNG ONSEMI-UC3844BNG Datasheet
399Kb / 19P
   High Performance Current Mode Controllers
August, 2013 ??Rev. 11
UC3845BDR2G ONSEMI-UC3845BDR2G Datasheet
387Kb / 19P
   High Performance Current Mode Controllers
December, 2012 ??Rev. 11
UC3845BVDG ONSEMI-UC3845BVDG Datasheet
399Kb / 19P
   High Performance Current Mode Controllers
August, 2013 ??Rev. 11
UC3845BVDR2G ONSEMI-UC3845BVDR2G Datasheet
399Kb / 19P
   High Performance Current Mode Controllers
August, 2013 ??Rev. 11
UC3844BVDG ONSEMI-UC3844BVDG Datasheet
399Kb / 19P
   High Performance Current Mode Controllers
August, 2013 ??Rev. 11
logo
Unisonic Technologies
UC3842B UTC-UC3842B_08 Datasheet
518Kb / 11P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
logo
Motorola, Inc
UC3844 MOTOROLA-UC3844 Datasheet
376Kb / 14P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
logo
ON Semiconductor
UC3842A ONSEMI-UC3842A Datasheet
399Kb / 14P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
1996 REV 1
UC3844 ONSEMI-UC3844 Datasheet
376Kb / 14P
   HIGH PERFORMANCE CURRENT MODE CONTROLLERS
1996 REV 1
More results


Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22


Scheda tecnica Scarica

Go To PDF Page


Link URL




Privacy Policy
ALLDATASHEETIT.COM
Lei ha avuto il aiuto da alldatasheet?  [ DONATE ] 

Di alldatasheet   |   Richest di pubblicita   |   contatti   |   Privacy Policy   |   scambio Link   |   Ricerca produttore
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com