参数资料
型号: TPS40074RHL
厂商: TEXAS INSTRUMENTS INC
元件分类: 稳压器
英文描述: 2 A SWITCHING CONTROLLER, 550 kHz SWITCHING FREQ-MAX, PQCC20
封装: PLASTIC, QFN-20
文件页数: 4/37页
文件大小: 448K
代理商: TPS40074RHL
www.ti.com
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TYPICAL MAXIMUM DUTY CYCLE
vs
INPUT VOLTAGE
VIN Input Voltage V
Duty
Cycle
%
UVLO(on) = 8 V
UVLO(on) = 15 V
UVLO(on) = 4.5 V
UVLO(on) = 12 V
TPS40074
SLUS617–APRIL 2005
APPLICATION INFORMATION (continued)
this scheme, the theoretical maximum output voltage that the converter can produce is approximately two times
the programmed startup voltage. For design, set the programmed startup voltage equal to or greater than the
desired output voltage divided by maximum duty cycle (85% for frequencies 500 kHz and below). For example, a
5-V output converter should not have a programmed startup voltage below 5.9 V. Figure 8 shows the theoretical
maximum duty cycle (typical) for various programmed startup voltages
Figure 8.
Figure 9 shows the effect of changing input voltage on the duty cycle, and how that change takes place. The
pulse width modulator (PWM) ramp input is generated using a current that is proportional to the current into the
KFF pin. The TPS40074 holds this pin at a constant 400 mV, so connecting a resistor from KFF to the input
power supply causes a current to flow into the KFF pin that is proportional to the input voltage. The slope of the
ramp signal to the PWM is therefore proportional to the input voltage. This allows the duty cycle to change with
variations in Vin without requiring much response from the error amplifier, resulting in very good line transient
response. Another benefit is essentially constant PWM gain over the entire input voltage operating range. This
makes the output control loop easier to design for a wide input range converter.
12
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