Datasheet

UDG−03034
D
A
C
A
47 pF
R
A
499 kW
R
KFF
71.5 kW
1
2
3
4
16
15
14
13
ILIM
VIN
BOOST
HDRV
KFF
RT
BP5
SYNC
5
6
7
8
12
11
10
9
SW
BP10
LDRV
PGND
SGND
SS
VFB
COMP
VIN
+
−
PWP
1N914, 1N4150
Type Signal Diode
TPS40055-EP
www.ti.com SGLS310D –JULY 2005–REVISED FEBRUARY 2012
Figure 10. Hysteresis for Programmable UVLO
Energy in the capacitor is described in Equation 10.
(10)
where:
(11)
where:
V
f
is the final peak capacitor voltage
V
I
is the initial capacitor voltage
Substituting Equation 7 into Equation 6, then substituting Equation 11 into Equation 10, then setting Equation 10
equal to Equation 6, and then solving for C
O
yields the capacitance described in Equation 12.
(12)
PROGRAMMING SOFT START
TPS40055 uses a closed-loop approach to ensure a controlled ramp on the output during start-up. Soft-start is
programmed by charging an external capacitor (C
SS
) via an internally generated current source. The voltage on
C
SS
minus 0.85 V is fed into a separate non-inverting input to the error amplifier (in addition to FB and 0.7-V
VREF). The loop is closed on the lower of the (C
SS
– 0.85 V) voltage or the internal reference voltage (0.7-V
VREF). Once the (C
SS
– 0.85 V) voltage rises above the internal reference voltage, regulation is based on the
internal reference. To ensure a controlled ramp-up of the output voltage the soft-start time should be greater than
the L-C
O
time constant as described in Equation 13.
(13)
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Product Folder Link(s): TPS40055-EP