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TPS54260DGQR 参数 Datasheet PDF下载

TPS54260DGQR图片预览
型号: TPS54260DGQR
PDF下载: 下载PDF文件 查看货源
内容描述: 3.5V至60V输入, 2.5A降压转换器具有Eco-Mode ™ [3.5V to 60V INPUT, 2.5A, STEP DOWN CONVERTER WITH ECO-MODE™]
分类和应用: 转换器输入元件
文件页数/大小: 47 页 / 1694 K
品牌: TI [ TEXAS INSTRUMENTS ]
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TPS54260  
SLVSA86 MARCH 2010  
www.ti.com  
DETAILED DESCRIPTION  
Fixed Frequency PWM Control  
The TPS54260 uses an adjustable fixed frequency, peak current mode control. The output voltage is compared  
through external resistors on the VSENSE pin to an internal voltage reference by an error amplifier which drives  
the COMP pin. An internal oscillator initiates the turn on of the high side power switch. The error amplifier output  
is compared to the high side power switch current. When the power switch current reaches the level set by the  
COMP voltage, the power switch is turned off. The COMP pin voltage will increase and decrease as the output  
current increases and decreases. The device implements a current limit by clamping the COMP pin voltage to a  
maximum level. The Eco-Mode™ is implemented with a minimum clamp on the COMP pin.  
Slope Compensation Output Current  
The TPS54260 adds a compensating ramp to the switch current signal. This slope compensation prevents  
sub-harmonic oscillations. The available peak inductor current remains constant over the full duty cycle range.  
Pulse Skip Eco-Mode  
The TPS54260 operates in a pulse skip Eco mode at light load currents to improve efficiency by reducing  
switching and gate drive losses. The TPS54260 is designed so that if the output voltage is within regulation and  
the peak switch current at the end of any switching cycle is below the pulse skipping current threshold, the  
device enters Eco mode. This current threshold is the current level corresponding to a nominal COMP voltage or  
500mV.  
When in Eco-mode, the COMP pin voltage is clamped at 500mV and the high side MOSFET is inhibited. Further  
decreases in load current or in output voltage can not drive the COMP pin below this clamp voltage level.  
Since the device is not switching, the output voltage begins to decay. As the voltage control loop compensates  
for the falling output voltage, the COMP pin voltage begins to rise. At this time, the high side MOSFET is enabled  
and a switching pulse initiates on the next switching cycle. The peak current is set by the COMP pin voltage. The  
output voltage re-charges the regulated value, then the peak switch current starts to decrease, and eventually  
falls below the Eco mode threshold at which time the device again enters Eco mode.  
For Eco mode operation, the TPS54260 senses peak current, not average or load current, so the load current  
where the device enters Eco mode is dependent on the output inductor value. For example, the circuit in  
Figure 49 enters Eco mode at about 5 mA of output current. When the load current is low and the output voltage  
is within regulation, the device enters a sleep mode and draws only 138mA input quiescent current. The internal  
PLL remains operating when in sleep mode. When operating at light load currents in the pulse skip mode, the  
switching transitions occur synchronously with the external clock signal.  
Low Dropout Operation and Bootstrap Voltage (BOOT)  
The TPS54260 has an integrated boot regulator, and requires a small ceramic capacitor between the BOOT and  
PH pins to provide the gate drive voltage for the high side MOSFET. The BOOT capacitor is refreshed when the  
high side MOSFET is off and the low side diode conducts. The value of this ceramic capacitor should be 0.1mF.  
A ceramic capacitor with an X7R or X5R grade dielectric with a voltage rating of 10V or higher is recommended  
because of the stable characteristics overtemperature and voltage.  
To improve drop out, the TPS54260 is designed to operate at 100% duty cycle as long as the BOOT to PH pin  
voltage is greater than 2.1V. When the voltage from BOOT to PH drops below 2.1V, the high side MOSFET is  
turned off using an UVLO circuit which allows the low side diode to conduct and refresh the charge on the BOOT  
capacitor. Since the supply current sourced from the BOOT capacitor is low, the high side MOSFET can remain  
on for more switching cycles than are required to refresh the capacitor, thus the effective duty cycle of the  
switching regulator is high.  
The effective duty cycle during dropout of the regulator is mainly influenced by the voltage drops across the  
power MOSFET, inductor resistance, low side diode and printed circuit board resistance. During operating  
conditions in which the input voltage drops and the regulator is operating in continuous conduction mode, the  
high side MOSFET can remain on for 100% of the duty cycle to maintain output regulation, until the BOOT to PH  
voltage falls below 2.1V.  
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Copyright © 2010, Texas Instruments Incorporated  
Product Folder Link(s): TPS54260  
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