參數(shù)資料
型號(hào)： SC4808CMSTRT
廠(chǎng)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(yè)數(shù)： 7/24頁(yè)
文件大?。?/td> 395K
代理商： SC4808CMSTRT
7
2006 Semtech Corp.
www.semtech.com
SC4808C
POWER MANAGEMENT
Application Information (Cont.)
VCC UNDER VOLTAGE LOCK OUT
Depending on the application and the voltages available,
the SC4808C can be used to provide the VCC undervoltage
lock out function to ensure the converters 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 SC4808C also provides a line undervoltage (LUVLO =
Vref) function. The LUVLO pin is programmed via an exter-
nal resistor divider connected as shown below. The actual
start-up voltage can be calculated by using the equation
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(SC4808C) reference voltage is available that can
be used to source a typical current of 5mA to the external
circuitry. The Vref can be used to provide the oscillator 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
SC4808C. It should be noted that larger capacitor values
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
×
C
R
1
F
TOT
OSC
OSC
where:
Circuit
C
4808
SC
OSC
TOT
C
C
C
+
+
=
pF
22
C
4808
SC
3
REF
10
OSC
deadtime
T
3
5
×
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
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
SC4809A 制造商:SEMTECH 制造商全稱(chēng):Semtech Corporation 功能描述:High Performance Current Mode PWM Controller
SC4809AIMSTR 制造商:Semtech Corporation 功能描述:IC, CURRENT MODE PWM CTRL, 12V, MSOP-10; Output Voltage:500mV; Output Current:1mA; Supply Voltage Min:0V; Supply Voltage Max:12V; Digital IC Case Style:MSOP; No. of Pins:10; Frequency:1MHz; Operating Temperature Min:-40C ;RoHS Compliant: No
SC4809AIMSTRT 制造商:Semtech Corporation 功能描述:Current Mode PWM Controller 10-Pin MSOP T/R 制造商:Semtech Corporation 功能描述:Pulse Width Modulation (PWM) Controller
SC4809B 制造商:SEMTECH 制造商全稱(chēng):Semtech Corporation 功能描述:High Performance Current Mode PWM Controller
SC4809C 制造商:SEMTECH 制造商全稱(chēng):Semtech Corporation 功能描述:High Performance Current Mode PWM Controller
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