The TPS54040 device is a 42-V 0

TPS54040-Q1

Manufacturer Part NumberTPS54040-Q1
DescriptionThe TPS54040 device is a 42-V 0
ManufacturerTexas Instruments
TPS54040-Q1 datasheet
 


Specifications of TPS54040-Q1

Iout(max)(a)0.5Vin(min)(v)3.5
Vin(max)(v)42Vout(min)(v)0.8
Vout(max)(v)39Iq(typ)(ma)0.116
Switching Frequency(max)(khz)2500Switch Current Limit(typ)(a)0.6
TopologyBuck,Inverting Buck-BoostOperating Temperature Range(c)-40 to 125
Pin/package10MSOP-PowerPAD, 10SONDuty Cycle(max)(%)95
Regulated Outputs(#)1  
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TPS54040-Q1
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SLVSA26C – JANUARY 2010 – REVISED AUGUST 2011
DETAILED DESCRIPTION (continued)
Slow Start/Tracking Pin (SS/TR)
The TPS54040 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 TPS54040 has an internal pull-up current source of 2μA 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 (V
) is 0.8 V and the slow start current (I
) is 2μA. The slow start capacitor should
REF
SS
remain lower than 0.47μF and greater than 0.47nF.
Tss(ms)
´
Iss( A)
m
Css(nF) =
Vref (V)
0.8
´
(6)
At power up, the TPS54040 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 TPS54040 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.
EN
SS/TR
V
SENSE
VOUT
Figure 30. Operation of SS/TR Pin when Starting
Overload Recovery Circuit
The TPS54040 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
100μA 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.
17
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