參數(shù)資料
型號(hào)： SC4808B-1
廠商： Semtech Corporation
英文描述： High Performance Dual Ended PWM Controller
中文描述： 高性能雙端PWM控制器
文件頁數(shù)： 11/28頁
文件大?。?/td> 453K
代理商： SC4808B-1
11
2006 Semtech Corp.
www.semtech.com
SC4808B-1
POWER MANAGEMENT
Application Information (Cont.)
VCC UNDER VOLTAGE LOCK OUT
Depending on the application and the voltages available,
the SC4808B-1 (UVLO = 4.4V) can be used to provide the
VCC undervoltage lock out function to ensure the convert-
ers controlled start up.
Before the VCC UVLO has been reached, the internal refer-
ence, oscillator, OUTA/OUTB drivers, and logic are disabled.
LINE UNDER VOLTAGE LOCK OUT
The SC4808B-1 also provides a line undervoltage (LUVLO
= Vref) function. The LUVLO pin is programmed via an ex-
ternal resistor divider connected as shown below. The ac-
tual start-up voltage can be calculated by using the equa-
tion below:
(
)
33
R
33
R
23
R
V
V
REF
Startup
+
×
=
R27
15k
R24 10k
200p
VCC
R26
2.2k
R28
10
2.2u,16V
C26
82p
C29
15
REF
0.1u,25V
C33
R25 18
R33
10k
SYNC
U4
SC4808
4
5
3
2
10
1
6
7
8
9
FB
REF
CS
RC
LUVLO
SYNC
GND
OUTB
OUTA
VCC
R23
56.2k
Vin
REFERENCE
A 3.125V(SC4808B-1) reference voltage is available that
can be used to source a typical current of 5mA to the ex-
ternal circuitry. The Vref can be used to provide the oscilla-
tor RC network with a regulated bias.
OSCILLATOR
The oscillator frequency is set by connecting a RC network
as shown below.
0
R27
15k
0
200p
VCC
R28
10
2.2u,16V
C26
REF
0.1u,25V
C33
R33
10k
SYNC
U4
SC4808
4
5
3
2
10
1
6
7
8
9
FB
REF
CS
RC
LUVLO
SYNC
GND
OUTB
OUTA
VCC
R23
56.2k
Vin
The oscillator has a ramp voltage of about Vref/2. The os-
cillator frequency is twice the frequency of the OUTA and
OUTB gate drive controls.
The oscillator capacitor C31 is charged by a current sourced
from the Vref through R27. Once the RC pin reaches about
Vref/2, the capacitor is discharged internally by the
SC4808B-1. It should be noted that larger capacitor val-
ues will result in a longer dead time during the down slope
of the ramp.
The following equation can be used as an approximation
of the oscillator frequency and the Dead time:
8
×
1
_
TOT
OSC
A
OSC
F
C
R
9
×
1
_
TOT
OSC
B
OSC
F
C
R
where:
Circuit
SC
OSC
TOT
C
C
C
C
+
+
=
4808
pF
C
SC
22
4808
3
10
3
5
×
×
REF
OSC
deadtime
T
V
C
The recommended range of timing resistors is between 10
kohm and 200kohm, range of timing capacitors is between
100pF and 1000pF. Timing resistors less than 10 kohm
should be avoided.
相關(guān)PDF資料
PDF描述
SC4808B-1MSTRT High Performance Dual Ended PWM Controller
SC4808B-2 High Performance Dual Ended PWM Controller
SC4808B-2MSTRT High Performance Dual Ended PWM Controller
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SC4808CMSTRT High Performance Dual Ended PWM Controller
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
SC4808B-1MSTRT 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Dual Ended PWM Controller
SC4808B-2 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Dual Ended PWM Controller
SC4808B-2_09 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Dual Ended PWM Controller
SC4808B-2MSTRT 制造商:Semtech Corporation 功能描述:Current Mode PWM Controller -0.5V to 18V 250mA 10-Pin MSOP T/R 制造商:Semtech 功能描述:Current Mode PWM Controller -0.5V to 18V 250mA 10-Pin MSOP T/R
SC4808BIMS.TR 制造商:Semtech Corporation 功能描述:
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