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参数资料
| 型号： | LTC3778EF#TR |
| 厂商： | Linear Technology |
| 文件页数： | 16/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 20TSSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 电源电压： | 4 V ~ 36 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 ~ 85°C |
| 封装/外壳： | 20-TSSOP（0.173"，4.40mm 宽） |
| 包装： | 带卷 (TR) |
| 其它名称： | LTC3778EFTR |
LTC3778
APPLICATIO S I FOR ATIO
Overcurrent latchoff operation is not always needed or
desired. Load current is already limited during a short-
circuit by the current foldback circuitry and latchoff
operation can prove annoying during troubleshooting.
The feature can be overridden by adding a pull-up current
greater than 5 μ A to the RUN/SS pin. The additional
current prevents the discharge of C SS during a fault and
also shortens the soft-start period. Using a resistor to V IN
as shown in Figure 6a is simple, but slightly increases
shutdown current. Connecting a resistor to INTV CC as
shown in Figure 6b eliminates the additional shutdown
current, but requires a diode to isolate C SS . Any pull-up
network must be able to maintain RUN/SS above the 4V
maximum latch-off threshold and overcome the 4 μ A
maximum discharge current.
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 for a 1.5V
output.
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 capaci-
tance, 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. This loss can be reduced by supply-
3.3V OR 5V
D1
V IN
RUN/SS
R SS *
C SS
INTV CC
R SS *
D2*
2N7002
RUN/SS
C SS
ing INTV CC current through the EXTV CC pin from a high
efficiency source, such as an output derived boost net-
work or alternate supply if available.
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
*OPTIONAL TO OVERRIDE OVERCURRENT LATCHOFF
(6a) (6b)
3778 F06
sufficient capacitance to prevent the RMS current from
causing additional upstream losses in fuses or batteries.
Figure 6. RUN/SS Pin Interfacing with Latchoff Defeated
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 LTC3778 circuits:
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.
If you make a change and the input current decreases, then
the efficiency has increased. If there is no change in input
current, then there is no change in efficiency.
Checking Transient Response
The regulator loop response can be checked by looking at
1.
DC I 2 R losses. These arise from the resistances of the
the load transient response. Switching regulators take
sense resistor, 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
several cycles to respond to a step in load current. When
a load step occurs, V OUT immediately shifts by an amount
equal to ? I LOAD (ESR), where ESR is the effective series
resistance of C OUT . ? I LOAD also begins to charge or
discharge C OUT generating a feedback error signal used by
the regulator to return V OUT to its steady-state value.
3778f
16
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3780EG | 制造商:Linear Technology 功能描述:DC DC Cntrlr Dual-OUT Synchronous Boost/Buck Controller 4V to 36V Input 24-Pin SSOP |
| LTC3780EG#PBF | 功能描述:IC REG CTRLR BST PWM CM 24-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 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:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
| LTC3780EG#TR | 制造商:Linear Technology 功能描述:DC DC Cntrlr Dual-OUT Synchronous Boost/Buck Controller 4V to 36V Input 24-Pin SSOP T/R |
| LTC3780EG#TRPBF | 功能描述:IC REG CTRLR BST PWM CM 24-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 |
| LTC3780EGPBF | 制造商:Linear Technology 功能描述:4-Switch Buck-Boost Controller SSOP24 |
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