參數(shù)資料
型號(hào)： L5991D
廠商： 意法半導(dǎo)體
英文描述： PRIMARY CONTROLLER WITH STANDBY
中文描述： 主控制器具有待機(jī)
文件頁(yè)數(shù)： 10/19頁(yè)
文件大?。?/td> 192K
代理商： L5991D
during ESD tests), it can be connected to VREF
througha 4.7k
resistor.
Figure 23. Duty cycle control.
Pin 4.
VREF (Reference Voltage). The device is
provided with an accurate voltage reference
(5V
±
1.5%) able to deliver some mA to an external
circuit.
A small film capacitor (0.1
μ
F typ.), connected
between this pin and SGND, is recommended to
ensure the stability of the generator and to prevent
noisefromaffectingthereference.
Beforedevice turn-on,this pin has a sink currentca-
pabilityof0.5mA.
Pin 5.
VFB (Error Amplifier Inverting Input). The
feedback signal is applied to this pin and is com-
pared to the E/A internal reference (2.5V). The
E/A output generates the control voltage which
fixesthe duty cycle.
The E/A features high gain-bandwidth product,
which allows to broaden the bandwidth of the
overall controlloop, high slew-rate and current ca-
pability, which improves its large signal behavior.
Usually the compensation network, which stabi-
lizes the overall control loop, is connected be-
tweenthis pin and COMP (pin 6).
Pin 6.
COMP (Error Amplifier Output). Usually,
this pin is used for frequency compensation and
the relevant network is connected between this
pin and VFB (pin 5). Compensation networks to-
wards ground are not possible since the L5991
E/A is a voltage mode amplifier (low output im-
pedance). See application ideas for some exam-
ple ofcompensationtechniques.
It is worth mentioning that the calculation of the
part values of the compensation network must
take the standby frequency operation into ac-
count. In particular,this means that the open-loop
crossover frequency must not exceed f
SB
/4
÷
f
SB
/5.
The voltage on pin 6 is monitored in order to re-
duce the oscillator frequency when the converter
is lightly loaded(standby).
Pin 7.
SS (Soft-Start). At device start-up, a ca-
pacitor (Css) connected between this pin and
SGND (pin 12) is charged by an internal current
generator, ISSC, up to about 7V. During this
ramp, the E/A output is clamped by the voltage
across Css itself and allowed to rise linearly, start-
ing from zero, up to the steady-state value im-
posed by the control loop. The maximum time in-
terval during which the E/A is clamped,referred to
as soft-starttime,is approximately:
T
ss
3
R
sense
I
Qpk
I
SSC
C
ss
(7)
where R
sense
is the current sense resistor (see pin
13) and I
Qpk
is the switch peak current (flowing
through R
sense
), which depends on the output
load. Usually, C
SS
is selected for a T
SS
in the or-
der of milliseconds.
As mentioned before, the soft-start intervenes
also in case of severe overload or short circuit on
the output. Referring to fig. 24, pulse-by-pulse
current limitation is somehow effective as long as
the ON-time of the power switch can be reduced
(from A to B). After the minimum ON-time is
reached (from B onwards) the current is out of
control.
To prevent this risk, a comparator trips an over-
current handling procedure, named ’hiccup’ mode
operation,when a voltage above 1.2V (point C) is
detected on current sense input (ISEN, pin 13).
Basically, the IC is turned off and then soft-started
as long as the fault condition is detected.As a re-
sult, the operating point is moved abruptly to D,
creating a foldback effect. Fig. 25 illustrates the
operation.
The oscillation frequency appearing on the soft-
start capacitorin case of permanentfault,referred
to as ’hiccup” period,is approximatelygiven by:
T
hic
4.5
1
I
SSC
+
1
I
SSD
C
ss
(
8
)
+
-
R2
R1
R
A
C
T
D97IN727A
V
REF
RCT
DC
TO PWM LOGIC
4
3
2
23K
28K
3
μ
A
R
B
ST-BY
16
V
OUT
T
ON
D.C.M.
C.C.M.
D
A
B
C
I
Qpk
T
ON(min)
1-2 ·I
Qpk
I
Qpk(max)
I
OUT
I
SHORT
I
OUT(max)
D97IN495
Figure24. Regulation characteristicand re-
latedquantities.
L5991 - L5991A
10/23
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L5993D 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel
L5993D013TR 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 Prog Current Mode RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel
L5994 功能描述:電流型 PWM 控制器 Adj Triple Out Pwr RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
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