参数资料
型号: TPS54140DGQR
厂商: TEXAS INSTRUMENTS INC
元件分类: 稳压器
英文描述: SWITCHING REGULATOR, 2500 kHz SWITCHING FREQ-MAX, PDSO10
封装: GREEN, PLASTIC, MSOP-10
文件页数: 8/46页
文件大小: 1778K
代理商: TPS54140DGQR
Slow Start/Tracking Pin (SS/TR)
Tss(ms)
Iss( A)
Css(nF) =
Vref (V)
0.8
m
(6)
EN
SS/TR
V
SENSE
VOUT
Overload Recovery Circuit
SLVS889 – OCTOBER 2008 .............................................................................................................................................................................................. www.ti.com
DETAILED DESCRIPTION (continued)
The TPS54140 effectively uses the lower voltage of the internal voltage reference or the SS/TR pin voltage as
the power-supply's reference voltage and regulates the output accordingly. A capacitor on the SS/TR pin to
ground implements a slow start time. The TPS54140 has an internal pull-up current source of 2
A that charges
the external slow start capacitor. The calculations for the slow start time (10% to 90%) are shown in Equation 6.
The voltage reference (VREF) is 0.8 V and the slow start current (ISS) is 2A. The slow start capacitor should
remain lower than 0.47
F and greater than 0.47nF.
At power up, the TPS54140 will not start switching until the slow start pin is discharged to less than 40 mV to
ensure a proper power up, see Figure 30.
Also, during normal operation, the TPS54140 will stop switching and the SS/TR must be discharged to 40 mV,
when the VIN UVLO is exceeded, EN pin pulled below 1.25V, or a thermal shutdown event occurs.
The VSENSE voltage will follow the SS/TR pin voltage with a 45mV offset up to 85% of the internal voltage
reference. When the SS/TR voltage is greater than 85% on the internal reference voltage the offset increases as
the effective system reference transitions from the SS/TR voltage to the internal voltage reference (see
Figure 23). The SS/TR voltage will ramp linearly until clamped at 1.7V.
Figure 30. Operation of SS/TR Pin when Starting
The TPS54140 has an overload recovery (OLR) circuit. The OLR circuit will slow start the output from the
overload voltage to the nominal regulation voltage once the fault condition is removed. The OLR circuit will
discharge the SS/TR pin to a voltage slightly greater than the VSENSE pin voltage using an internal pull down of
100
A when the error amplifier is changed to a high voltage from a fault condition. When the fault condition is
removed, the output will slow start from the fault voltage to nominal output voltage.
16
Copyright 2008, Texas Instruments Incorporated
Product Folder Link(s): TPS54140
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