参数资料
| 型号： | TPS54478RTER |
| 厂商： | Texas Instruments |
| 文件页数： | 15/38页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 4A 16WQFN |
| 标准包装： | 3,000 |
| 系列： | SWIFT™ |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.6 V ~ 4.5 V |
| 输入电压： | 2.95 V ~ 6 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 500kHz |
| 电流 - 输出： | 4A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 150°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 16-WQFN 裸露焊盘（3x3） |
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TPS54478
SLVSAS2 – JUNE 2011
EN1
SS/TR1
PWRGD1
TPS54478
EN2
VOUT1
VOUT 2
E N 1 = 5 / div
R1
R2
SS/TR2
PWRGD2
Time = 1 msec / div
SS2 = 500 mV / div
Vo1 = 500 mV / div
Vo2 = 500 mV / div
Figure 27. Simultaneous Startup Sequence
Figure 28. Simultaneous Start-Up using Coupled
SS/TR Pins
CONSTANT SWITCHING FREQUENCY and TIMING RESISTOR (RT/CLK Pin)
The switching frequency of the TPS54478 is adjustable over a wide range from 200 kHz to 2000 kHz by placing
a maximum of 150 k ? and minimum of 16 k ? , respectively, on the RT/CLK pin. An internal amplifier holds this
pin at a fixed voltage when using an external resistor to ground to set the switching frequency. The RT/CLK is
typically 0.5 V. To determine the timing resistance for a given switching frequency, use the curve in Figure 5 or
RT (k W ) =
vertical spacer
Fs(kHz) =
90066
Fs(kHz) 1.135
23439
RT(k W ) 0.8813
(7)
(8)
To reduce the solution size one would typically set the switching frequency as high as possible, but tradeoffs of
the efficiency, maximum input voltage and minimum controllable on time should be considered.
The minimum controllable on time is typically 100 ns at full current load and 120 ns at no load, and limits the
maximum operating input voltage or output voltage.
OVERCURRENT PROTECTION
The TPS54478 implements current mode control which uses the COMP pin voltage to turn off the high side
MOSFET and turn on the low side MOSFET on a cycle by cycle basis. Each cycle the switch current and the
COMP pin voltage are compared, when the peak switch current intersects the COMP voltage the high side
switch is turned off. During overcurrent conditions that pull the output voltage low, the error amplifier will respond
by driving the COMP pin high, increasing the switch current. The error amplifier output is clamped internally.
This clamp functions as a switch current limit. When the OCP reaches 512 cycles, the converter enters hiccup
mode in which no switching action happens for about 16000 cycles. This helps the reduction of the power
consumption during the over current event.
Copyright ? 2011, Texas Instruments Incorporated
15
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