Zakładka z wyszukiwarką danych komponentów
  Polish  ▼
ALLDATASHEET.PL

X  

LM34919 Arkusz danych(PDF) 10 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor. Click here to check the latest version.
Numer części LM34919
Szczegółowy opis  Ultra Small 40V, 600 mA Constant On-Time Buck Switching Regulator
Download  18 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
Producent  NSC [National Semiconductor (TI)]
Strona internetowa  http://www.national.com
Logo NSC - National Semiconductor (TI)

LM34919 Arkusz danych(HTML) 10 Page - National Semiconductor (TI)

Back Button LM34919 Datasheet HTML 6Page - National Semiconductor (TI) LM34919 Datasheet HTML 7Page - National Semiconductor (TI) LM34919 Datasheet HTML 8Page - National Semiconductor (TI) LM34919 Datasheet HTML 9Page - National Semiconductor (TI) LM34919 Datasheet HTML 10Page - National Semiconductor (TI) LM34919 Datasheet HTML 11Page - National Semiconductor (TI) LM34919 Datasheet HTML 12Page - National Semiconductor (TI) LM34919 Datasheet HTML 13Page - National Semiconductor (TI) LM34919 Datasheet HTML 14Page - National Semiconductor (TI) Next Button
Zoom Inzoom in Zoom Outzoom out
 10 / 18 page
background image
Regulation Comparator
The feedback voltage at FB is compared to the voltage at the
Softstart pin (2.5V). In normal operation (the output voltage is
regulated), an on-time period is initiated when the voltage at
FB falls below 2.5V. The buck switch stays on for the pro-
grammed on-time, causing the FB voltage to rise above 2.5V.
After the on-time period, the buck switch stays off until the FB
voltage falls below 2.5V. Input bias current at the FB pin is
less than 100 nA over temperature.
Over-Voltage Comparator
The voltage at FB is compared to an internal 2.9V reference.
If the voltage at FB rises above 2.9V the on-time pulse is im-
mediately terminated. This condition can occur if the input
voltage or the output load changes suddenly, or if the inductor
(L1) saturates. The buck switch remains off until the voltage
at FB falls below 2.5V.
ON-Time Timer, and Shutdown
The on-time is determined by the R
ON resistor and the input
voltage (V
IN), and is calculated from:
(4)
The inverse relationship with V
IN results in a nearly constant
frequency as V
IN is varied. To set a specific continuous con-
duction mode switching frequency (F
S), the RON resistor is
determined from the following:
(5)
In high frequency applicatons the minimum value for t
ON is
limited by the maximum duty cycle required for regulation and
the minimum off-time of (155 ns, ±15%). The minimum off-
time limits the maximum duty cycle achievable with a low
voltage at V
IN. At high values of VIN, the minimum on-time is
limited to
120 ns.
The LM34919 can be remotely shut down by taking the RON/
SD pin below 0.8V. See Figure 3. In this mode the SS pin is
internally grounded, the on-timer is disabled, and bias cur-
rents are reduced. Releasing the RON/SD pin allows normal
operation to resume. The voltage at the RON/SD pin is be-
tween 1.4V and 4.0V, depending on V
IN and the RON resistor.
30004413
FIGURE 3. Shutdown Implementation
Current Limit
Current limit detection occurs during the off-time by monitor-
ing the recirculating current through the free-wheeling diode
(D1). Referring to the Block Diagram, when the buck switch
is turned off the inductor current flows through the load, into
SGND, through the sense resistor, out of ISEN and through
D1. If that current exceeds 0.64A the current limit comparator
output switches to delay the start of the next on-time period.
The next on-time starts when the current out of ISEN is below
0.64A and the voltage at FB is below 2.5V. If the overload
condition persists causing the inductor current to exceed
0.64A during each on-time, that is detected at the beginning
of each off-time. The operating frequency is lower due to
longer-than-normal off-times.
Figure 4 illustrates the inductor current waveform. During nor-
mal operation the load current is Io, the average of the ripple
waveform. When the load resistance decreases the current
ratchets up until the lower peak reaches 0.64A. During the
Current Limited portion of Figure 4, the current ramps down
to 0.64A during each off-time, initiating the next on-time (as-
suming the voltage at FB is <2.5V). During each on-time the
current ramps up an amount equal to:
ΔI = (V
IN - VOUT) x tON / L1
During this time the LM34919 is in a constant current mode,
with an average load current (I
OCL) equal to 0.64A + ΔI/2.
Generally, in applications where the switching frequency is
higher than
300 kHz and uses a small value inductor, the
higher dl/dt of the inductor's ripple current results in an effec-
tively lower valley current limit threshold due to the response
time of the current limit detection circuit. However, since the
small value inductor results in a relatively high ripple current
amplitude (
ΔI in Figure 4), the load current (I
OCL) at current
limit is typically in excess of 640 mA.
www.national.com
10


Podobny numer części - LM34919

ProducentNumer częściArkusz danychSzczegółowy opis
logo
National Semiconductor ...
LM34919 NSC-LM34919 Datasheet
369Kb / 18P
   40V, 600 mA Step Down COT Switching Regulator
logo
Texas Instruments
LM34919 TI1-LM34919 Datasheet
1Mb / 21P
[Old version datasheet]   Ultra-Small 40-V 600-mA Constant On-Time Buck Switching Regulator
LM34919 TI1-LM34919 Datasheet
1Mb / 21P
[Old version datasheet]   Ultra-Small 40-V 600-mA Constant On-Time Buck Switching Regulator
logo
National Semiconductor ...
LM34919B NSC-LM34919B Datasheet
497Kb / 20P
   Ultra Small 40V, 600 mA Constant On-Time Buck Switching Regulator
LM34919B NSC-LM34919B Datasheet
647Kb / 12P
   Evaluation Board provides the design engineer with a fully functional
More results

Podobny opis - LM34919

ProducentNumer częściArkusz danychSzczegółowy opis
logo
National Semiconductor ...
LM34919B NSC-LM34919B Datasheet
497Kb / 20P
   Ultra Small 40V, 600 mA Constant On-Time Buck Switching Regulator
logo
Texas Instruments
LM34919 TI1-LM34919_14 Datasheet
1Mb / 21P
[Old version datasheet]   Ultra-Small 40-V 600-mA Constant On-Time Buck Switching Regulator
LM34919B TI-LM34919B_15 Datasheet
1Mb / 27P
[Old version datasheet]   Ultra-Small 40-V 600-mA Constant On-Time Buck Switching Regulator
LM34919 TI1-LM34919_15 Datasheet
1Mb / 21P
[Old version datasheet]   Ultra-Small 40-V 600-mA Constant On-Time Buck Switching Regulator
LM34919C-Q1 TI1-LM34919C-Q1 Datasheet
1Mb / 29P
[Old version datasheet]   LM34919C-Q1 Ultra Small 50V, 600 mA Constant On-Time Buck Switching Regulator
LM34923 TI1-LM34923_14 Datasheet
1Mb / 26P
[Old version datasheet]   80V, 600 mA Constant On-Time Buck Switching Regulator
LM5006 TI1-LM5006_14 Datasheet
850Kb / 25P
[Old version datasheet]   80V, 600 mA Constant On-Time Buck Switching Regulator
LM5006 TI-LM5006_15 Datasheet
1Mb / 27P
[Old version datasheet]   LM5006 80V, 600 mA Constant On-Time Buck Switching Regulator
LM34923 TI1-LM34923 Datasheet
1Mb / 26P
[Old version datasheet]   80-V 600-mA Constant On-Time Buck Switching Regulator
LM5008A TI1-LM5008A_14 Datasheet
1Mb / 22P
[Old version datasheet]   350 mA Constant On-Time Buck Switching Regulator
More results


Html Pages

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


Arkusz danych Pobierz

Go To PDF Page


Link URL




Polityka prywatności
ALLDATASHEET.PL
Czy Alldatasheet okazała się pomocna?  [ DONATE ] 

O Alldatasheet   |   Reklama   |   Kontakt   |   Polityka prywatności   |   Linki   |   Lista producentów
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