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參數(shù)資料
| 型號： | LTC3770 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | Synchronous Controller with Margining, Tracking and PLL |
| 中文描述： | 同步控制器裕，跟蹤和PLL |
| 文件頁數(shù)： | 19/24頁 |
| 文件大?。?/td> | 302K |
| 代理商： | LTC3770 |
19
LTC3770
3770f
operating point the phase comparator output is open and
the filter capacitor C
LP
holds the voltage. The LTC3770
PLLIN pin must be driven from a low impedance source
such as a logic gate located close to the pin.
The loop filter components (C
LP
, R
LP
) smooth out the
current pulses from the phase detector and provide a
stable input to the voltage controlled oscillator. The filter
components C
LP
and R
LP
determine how fast the loop
acquires lock. Typically R
LP
=10k
and C
LP
is 0.01
μ
F to
0.1
μ
F.
Dead Time Control
To further optimize the efficiency, the LTC3770 gives
users some control over the dead time of the Top gate low
and Bottom gate high transition. By applying a DC voltage
on the Z0 pin, the TG low BG high dead time can be
programmed. Because the dead time is a strong function
of the load current and the type of MOSFET used, users
need to be careful to optimize the dead time for their
particular applications. Figure 11 shows the relation be-
tween the TG Low BG High Dead time by varying the Z0
voltages. For an application using LTC3770 with load
current of 5A and IR7811W MOSFETs, the dead time could
be optimized. To make sure that there is no shoot-through
under all conditions, a dead time of 70ns is selected. This
corresponds to a DC voltage about 2.6V on Z0 pin. This
voltage can easily be generated with a resistor divider off
INTV
CC
.
Efficiency Considerations
The percent efficiency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the efficiency and which change would
produce the most improvement. Although all dissipative
elements in the circuit produce losses, four main sources
account for most of the losses in LTC3770 circuits:
1. DC I
2
R losses. These arise from the resistances of the
MOSFETs, inductor and PC board traces and cause the
efficiency to drop at high output currents. In continuous
mode the average output current flows through L, but is
chopped between the top and bottom MOSFETs. If the two
MOSFETs have approximately the same R
DS(ON)
, then the
resistance of one MOSFET can simply be summed with the
resistances of L and the board traces to obtain the DC I
2
R
loss. For example, if R
DS(ON)
= 0.01
and R
L
= 0.005
, the
loss will range from 15mW to 1.5W as the output current
varies from 1A to 10A.
2. Transition loss. This loss arises from the brief amount
of time the top MOSFET spends in the saturated region
during switch node transitions. It depends upon the input
voltage, load current, driver strength and MOSFET
capacitance, among other factors. The loss is significant
at input voltages above 20V and can be estimated from:
Transition Loss
(1.7A
–1
) V
IN2
I
OUT
C
RSS
f
3. INTV
CC
current. This is the sum of the MOSFET driver
and control currents.
4. C
IN
loss. The input capacitor has the difficult job of
filtering the large RMS input current to the regulator. It
must have a very low ESR to minimize the AC I
2
R loss and
sufficient capacitance to prevent the RMS current from
causing additional upstream losses in fuses or batteries.
Other losses, including C
OUT
ESR loss, Schottky diode D1
conduction loss during dead time and inductor core loss
generally account for less than 2% additional loss.
When making adjustments to improve efficiency, the
input current is the best indicator of changes in efficiency.
Z0 VOLTAGE (V)
0
T
60
100
120
140
5
3770 F11
20
80
160
40
–20
0
1
2
4
3
180
I
OUT
= 5A
IRT811W FETs
Figure 11. TG Low BG High Dead Time vs Z0 Voltage
APPLICATIU
W
U
U
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| LTC3770EUH#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 32-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC3770EUH#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 32-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
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