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参数资料
| 型号： | LM2760M5/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHED CAPACITOR REGULATOR, 750 kHz SWITCHING FREQ-MAX, PDSO5 |
| 封装： | SOT-23, 5 PIN |
| 文件页数： | 8/10页 |
| 文件大小： | 242K |
| 代理商： | LM2760M5/NOPB |
Operation Description
OVERVIEW
The LM2760 is a regulated switched capacitor converter that
efficiently provides a regulated 3.3V output capable of sup-
plying a load up to 20mA. The part has two regulation
modes: a doubler mode and a pass mode. The part config-
ures itself for doubler mode (2x) when the input voltage is
low (< 3.4V typ.) and boost of the input voltage is required.
At higher input voltages, voltage boost is not needed, so the
part configures itself for pass mode (1x) to optimize effi-
ciency. Efficiency is optimized even further, especially when
output current is low, through the implementation of pulse-
frequency-modulated (PFM) regulation. The descriptions in
the sections to follow refer to the block diagram on the
previous page.
PULSE FREQUENCY MODULATED (PFM) REGULATION
The LM2760 uses pulse frequency modulation (PFM) to
provide highly efficient output voltage regulation. PFM is a
complicated-sounding term that simply means the part only
pumps when it needs to. If the output voltage is at or above
3.3V, the pump is turned off and supply current is minimized.
While in this rest state, output current is supplied by the
charge on the output capacitor. As charge is pulled off the
output capacitor, the output voltage will steadily fall until it
droops below 3.3V, at which time the pump reactivates and
output voltage is boosted. With PFM, the LM2760 requires
very little supply current "overhead": the input current is
generally only slightly above what is required to deliver
power to the output. This mode of operation allows the
LM2760 to maximize total solution efficiency.
DOUBLER MODE
When in doubler mode, the LM2760 operates as a regulated
switched capacitor voltage doubler. A two-phase non-
overlapping clock generated internally controls the operation
of the doubler. During the charge phase (1), the flying
capacitor (C
FLY) is connected between the input and ground
through internal pass-transistor switches (S1 and S2) and is
charged to the input voltage. In the pump phase that follows
(2), the flying capacitor is connected between the input and
output through similar switches (S3 and S4). Stacked atop
the input, the charge of the flying capacitor boosts the output
voltage and supplies the load current.
PASS MODE
Pass mode of the LM2760 is implemented to improve effi-
ciency at higher input voltages (> 3.4V typ.) where voltage
boost is not required. In this mode of operation, switches S1
and S2 are on continuously, and switch S4 is always off.
Resistance of switch S1 is increased in this mode to optimize
performance. Output voltage regulation is achieved by ap-
plying a PFM clock to switch S3.
N0-LOAD OPERATION
The minimal supply-current overhead of the LM2760 is most
apparent, and beneficial, when the LM2670 is operating
unloaded. With zero output current, supply current of the
LM2760 is only 10A (typ). There are two components to this
10A input current (listed as I
IN in the Electrical Character-
istics): quiescent current (I
Q) and time-averaged pump cur-
rent. Quiescent current is the steady-state DC current con-
sumed by the LM2760 internal circuitry, and is typically 6A
when the part is unloaded. This is best observed by mea-
suring the input current of the part while forcing the voltage
on the output slightly above 3.3V (ensures the pump will not
activate: see below).
Even when output current of the LM2760 is zero, the pump
must occasionally be activated to keep the output voltage
from drooping. There is a resistor divider internal to the
LM2760 that is part of the regulation feedback loop, and is
connected to V
OUT. Current through these resistors slowly
pulls charge from the output capacitor when the LM2760 is in
its rest state. The LM2760 must occasionally activate the
pump to restore charge to the output capacitor, thus keeping
the output voltage at the desired level. With a high-quality
10F ceramic output capacitor (ensures capacitor current
leakage is minimal), the pump is only activated typically once
every 2 seconds. When the input current of these bursts are
averaged over time, they contribute only 4A to the total
unloaded supply current of the LM2760.
The very low input current when the part is virtually unloaded
makes the LM2760 an excellent converter for generating
low-power keep-alive voltage rails.
STARTUP
When voltage is first connected to the input of the LM2760,
the output voltage is typically significantly less than the input
voltage, placing the part in pass mode. Pass mode, with the
increased resistance of switch S1, provides a controlled
start-up that limits input inrush current. Turn-on time of the
part, the time it takes for the output voltage to establish, is
typically 1ms when V
IN = 3.0V.
THERMAL SHUTDOWN
To protect itself from damage caused by overheating, the
LM2760 implements a thermal shutdown mechanism. When
the junction temperature rises to 150oC (typ.), the part
switches itself into shutdown mode. The LM2760 releases
thermal shutdown when the junction temperature of the part
is reduced below 130oC (typ.). Thermal shutdown is most-
often triggered by self-heating, which occurs when there is
excessive power dissipation in the device and/or insufficient
thermal dissipation. When self-heating causes thermal shut-
down, thermal cycling usually occurs. Thermal cycling is the
repeating process where the part self-heats, enters thermal
shutdown (where internal power dissipation is practically
zero), cools, turns-on, and then heats up again to the ther-
mal shutdown threshold. Thermal cycling is recognized by a
pulsing output voltage and can be stopped by reducing the
internal power dissipation (reduce output current or input
voltage) or the ambient temperature.
SHORT CIRCUIT PROTECTION
The LM2760 contains short circuit protection circuitry that
protects the device from damage in the event of output
current and/or output shorts to ground. Current is limited to
170mA (typ.) when the output is shorted directly to ground
(V
IN = 3.0V). When the LM2760 output is shorted, power
dissipation in the device is likely to be quite high, especially
when higher input voltages are present. In this event, ther-
mal cycling should be expected (see "Thermal Shutdown"
section).
Application Information
OUTPUT VOLTAGE RIPPLE
The magnitude of the voltage ripple on the output of the
LM2760 is highly dependent on application conditions: out-
put current and output capacitor properties, specifically. This
LM2760
www.national.com
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| LM2760M5X | 制造商:NSC 制造商全称:National Semiconductor 功能描述:3.3V Regulated Switched Capacitor Voltage Converter |
| LM2760M5X/NOPB | 功能描述:IC REG BST SWITCHED CAP SOT23-5 RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:1 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:3.3V 输入电压:4.5 V ~ 24 V PWM 型:- 频率 - 开关:- 电流 - 输出:125mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-6 包装:Digi-Reel® 供应商设备封装:SOT-6 其它名称:MAX1836EUT33#TG16DKR |
| LM2765 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Switched Capacitor Voltage Converter |
| LM2765M6 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LM2765M6/NOPB | 功能描述:IC REG SWITCHED CAP DBL SOT23-6 RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:1 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:3.3V 输入电压:4.5 V ~ 24 V PWM 型:- 频率 - 开关:- 电流 - 输出:125mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:SOT-23-6 包装:Digi-Reel® 供应商设备封装:SOT-6 其它名称:MAX1836EUT33#TG16DKR |
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