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| 型号： | LTC3788IUH#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | DUAL SWITCHING CONTROLLER, 900 kHz SWITCHING FREQ-MAX, PQCC32 |
| 封装： | 5 X 5 MM, LEAD FREE, PLASTIC, MO-220WHHD, QFN-32 |
| 文件页数： | 15/32页 |
| 文件大小： | 386K |
| 代理商： | LTC3788IUH#PBF |
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LTC3788
22
3788fb
applicaTions inForMaTion
Table 2 summarizes the different states in which the FREQ
pin can be used.
Table 2.
FREQ PIN
PLLIN/MODE PIN
FREQUENCY
0V
DC Voltage
350kHz
INTVCC
DC Voltage
535kHz
Resistor
DC Voltage
50kHz to 900kHz
Any of the Above
External Clock
Phase Locked to
External Clock
Minimum On-Time Considerations
Minimum on-time, tON(MIN), is the smallest time duration
that the LTC3788 is capable of turning on the bottom MOS-
FET. It is determined by internal timing delays and the gate
charge required to turn on the top MOSFET. Low duty cycle
applications may approach this minimum on-time limit.
In forced continuous mode, if the duty cycle falls below
what can be accommodated by the minimum on-time,
the controller will begin to skip cycles but the output will
continuetoberegulated.Morecycleswillbeskippedwhen
VIN increases. Once VIN rises above VOUT, the loop works
to keep the top MOSFET on continuously. The minimum
on-time for the LTC3788 is approximately 110ns.
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 greatest improvement. Percent efficiency can
be expressed as:
%Efficiency = 100% – (L1 + L2 + L3 + ...)
where L1, L2, etc., are the individual losses as a percent-
age of input power.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for most of the
losses in LTC3788 circuits: 1) IC VIN current, 2) INTVCC
regulator current, 3) I2R losses, 4) Bottom MOSFET
transition losses.
1. The VIN current is the DC supply current given in the
ElectricalCharacteristicstable,whichexcludesMOSFET
driver and control currents. VIN current typically results
in a small (<0.1%) loss.
2. INTVCC current is the sum of the MOSFET driver and
control currents. The MOSFET driver current results
from switching the gate capacitance of the power MOS-
FETs. Each time a MOSFET gate is switched from low to
high to low again, a packet of charge, dQ, moves from
INTVCC to ground. The resulting dQ/dt is a current out
of INTVCC that is typically much larger than the control
circuit current. In continuous mode, IGATECHG = f(QT +
QB),whereQTandQBarethegatechargesofthetopside
and bottom side MOSFETs.
3. DC I2R losses. These arise from the resistances of the
MOSFETs,sensingresistor,inductorandPCboardtraces
and cause the efficiency to drop at high output currents.
4. Transition losses apply only to the bottom MOSFET(s),
and become significant only when operating at low
input voltages. Transition losses can be estimated from:
Transition Loss
= (1.7)
VOUT
3
VIN
IO(MAX) CRSS f
Other hidden losses, such as copper trace and internal
battery resistances, can account for an additional 5% to
10% efficiency degradation in portable systems. It is very
important to include these system-level losses during the
design phase.
Figure 6. Relationship Between Oscillator
Frequency and Resistor Value at the FREQ Pin
FREQ PIN RESISTOR (k)
15
FREQUENCY
(kHz) 600
800
1000
35 45 55
25
3788 F06
400
200
500
700
900
300
100
0
65 75 85 95 105 115 125
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| LTC3789EGN#PBF | 功能描述:IC REG CTRLR BST PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC3789EGN#PBF | 制造商:Linear Technology 功能描述:IC DC-DC CONV 600kHz SSOP28 |
| LTC3789EGN#TRPBF | 功能描述:IC REG CTRLR BST PWM CM 28-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
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