參數(shù)資料
型號: TPS51220ARTVR
廠商: TEXAS INSTRUMENTS INC
元件分類: 穩(wěn)壓器
英文描述: DUAL SWITCHING CONTROLLER, 333 kHz SWITCHING FREQ-MAX, PQCC32
封裝: 5 X 5 MM, PLASTIC, QFN-32
文件頁數(shù): 18/53頁
文件大?。?/td> 1380K
代理商: TPS51220ARTVR
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www.ti.com
SLUS897D – DECEMBER 2008 – REVISED FEBRUARY 2010
Figure 43. Inductor Current Limit at Pulse Skipping
Table 2. Skip Mode Selection
SKIPSELx
GND
VREF2
VREG3
VREG5
OOA Skip (maximum 7
OOA Skip (maximum 15 skips, for
OPERATING MODE
Continuous Conduction
Auto Skip
skips, for <400 kHz)
equal to or greater than 400kHz)
OUT OF AUDIO SKIP OPERATION
Out-Of-Audio (OOA) light-load mode is a unique control feature that keeps the switching frequency above
acoustic audible frequencies toward virtually no load condition while maintaining state-of-the-art high conversion
efficiency. When OOA is selected, the switching frequency is kept higher than audible frequency range in any
load condition. The TPS51220A automatically reduced switching frequency at light-load conditions. The OOA
control circuit monitors the states of both MOSFETs and forces an ON state if the predetermined number of
pulses are skipped. The high-side MOSFET is turned on before the output voltage declines down to the target
value, so that eventually an overvoltage condition is caused. The OOA control circuit detects this overvoltage
condition and begins modulating the skip-mode on time to keep the output voltage.
The TPS51220A supports a wide-switching frequency range, therefore, the OOA skip mode has two selections.
See Table 2. When the 300-kHz switching frequency is selected, a maximum of seven (7) skips (SKIPSEL=3.3
V) makes the lowest frequency at 37.5 kHz. If a 15-skip maximum is chosen, it becomes 18.8 kHz, hence the
maximum 7 skip is suitable for less than 400 kHz, and the maximum 15 skip is 400 kHz or greater.
99% DUTY CYCLE OPERATION
In a low-dropout condition such as 5-V input to 5-V output, the basic control loop attempts to maintain 100% of
the high-side MOSFET ON. However, with the N-channel MOSFET used for the top switch, it is not possible to
use the 100% on-cycle to charge the boot strap capacitor. When high duty is required, the TPS51220A extends
the ON period (by skipping a maximum of three clock cycles and reducing the switching frequency to 25% of the
steady state value) and asserts the OFF state after extended ON.
Copyright 2008–2010, Texas Instruments Incorporated
25
Product Folder Link(s) :TPS51220A
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