LTC1174
LTC1174-3.3/LTC1174-5
U
OPERATIO
(Refer to Functional Diagram)
The LTC1174 uses a constant off-time architecture to
switch its internal P-channel power MOSFET. The off-time
is set by an internal timing capacitor and the operating
frequency is a function of VIN.
In sleep mode, the LTC1174 is in standby and the load
current is supplied by the output capacitor. All unused
circuitry is shut off, reducing quiescent current from
0.45mAto0.13mA.Whentheoutputcapacitordischarges
by the amount of the hysteresis of the comparator A1, the
P-channel switch turns on again and the process repeats
itself.
The output voltage is set by an internal resistive divider
(LTC1174-3.3 and LTC1174-5) or an external divider re-
turned to VFB Pin 1 (LTC1174). A voltage comparator A1
compares the divided output voltage to a reference voltage
of 1.25V.
Operating Frequency and Inductor
Since the LTC1174 utilizes a constant off-time architecture,
itsoperatingfrequencyisdependentonthevalueofVIN.The
frequency of operation can be expressed as:
Tooptimizeefficiency, theLTC1174automaticallyswitches
between continuous and Burst Mode® operation. The volt-
age comparator is the primary control element when the
device is in Burst Mode operation, while the current com-
parator controls the output voltage in continuous mode.
V − V
V + VD
IN
⎛
⎞
1
tOFF
IN
OUT
f =
Hz
( )
⎜
⎝
⎟
⎠
During the switch“ON” time, switch current flows through
the 0.1Ω sense resistor. When this current reaches the
thresholdofthecurrentcomparatorA2,itsoutputsignalwill
change state, setting the flip-flop and turning the switch off.
The timing capacitor, CT, begins to discharge until its
voltage goes below VTH1. Comparator A4 will then trip,
which resets the flip-flop and causes the switch to turn on
again. Also, the timing capacitor is recharged. The inductor
current will again ramp up until the current comparator A2
trips. The cycle then repeats.
wheretOFF =4µsandVDisthevoltagedropacrossthediode.
Note that the operating frequency is a function of the input
and ouput voltage.
Although the size of the inductor does not affect the fre-
quency, it does affect the ripple current. The peak-to-peak
ripple current is given by:
V
OUT
+ VD
L
⎛
⎜
⎝
⎞
⎟
⎠
IRIPPLE = 4 •10−6
A
P−P
(
)
When the load is relatively light, the LTC1174 automatically
goes into Burst Mode operation. The current mode loop is
interrupted when the output voltage reaches the desired
regulated value. The hysteretic voltage comparator A1 trips
when VOUT is above the desired output voltage, shutting off
the switch and causing the timing capacitor to discharge.
This capacitor discharges past VTH1 until its voltage drops
below VTH2. Comparator A5 then trips and a sleep signal is
generated.
By choosing a smaller inductor, a low ESR output filter
capacitorhastobeused(seeCIN andCOUT).Moreover,core
losswillalsoincrease(seeInductorCoreSelectionsection)
due to higher ripple current.
Burst Mode is a registered trademark of Linear Technology Corporation.
1174fe
7
5秒后页面跳转
一文带你解读74HC244资料手册：特性、应用场景、封装方式、引脚配置说明、电气参数、推荐替代型号
AD623资料手册解读：特性、应用、封装、引脚功能及电气参数
RT9193资料手册解读：RT9193引脚功能、电气参数、替换型号推荐
VIPER22A的资料手册解读、引脚参数说明、代换型号推荐
微信公众号
抖音公众号
浙公网安备 33010502006866号 浙ICP备10014259号-119
营业执照ICP证
数据手册
如果您发现信息不准确，
