Datasheet

50 mV/div
100 mA/div
200 mA
0.1 mA
100 s/divm
I
OUT
V
OUT
50 mV/div
100 mA/div
200 mA
1 mA
50 s/divm
I
OUT
V
OUT
100
90
80
70
60
50
40
30
20
10
0
Power-Supply Rejection Ratio (dB)
10 100
1k 10k 100k 1M 10M
Frequency (Hz)
I = 10 mA
OUT
I = 200 mA
OUT
10.00
1.00
0.10
0.01
0
Noise Spectral Density ( V/ )m Hz
Ö
10 100
1k 10k 100k 1M 10M
Frequency (Hz)
I (mA)=C ( F) 0.07(V/ s)+I (mA)m m
LOAD
SOFTSTART OUT
´
TPS72710 , TPS72711 , TPS72715 , TPS727185 , TPS72718 , TPS72719 , TPS72725
TPS72727 , TPS727285 , TPS72728 , TPS72730 , TPS72733 , TPS72748 , TPS72750
www.ti.com SBVS128D –JUNE 2009–REVISED FEBRUARY 2014
Typical Application (continued)
Select adequate input and output capacitors.
The startup current is given by Equation 2:
(2)
This equation shows that soft-start current is directly proportional to C
OUT
.
The output voltage ramp rate is independent of C
OUT
and load current, and has a typical value of 0.07 V/μs.
The TPS727xx automatically adjusts the soft-start current to supply both the load current and the C
OUT
charge
current. For example, if I
LOAD
= 0 mA upon enabling the LDO, I
SOFT START
= 1 μF × 0.07 V/μs + 0 mA = 70 mA,
the current that charges the output capacitor.
If I
LOAD
= 200 mA, I
SOFT START
= 1 μF × 0.07 V/μs + 200 mA = 270 mA, the current required for charging output
capacitor and supplying the load current.
If the output capacitor and load are increased such that the soft-start current exceeds the output current limit, it is
clamped at the typical current limit of 400mA. For example, if C
OUT
= 10 μF and I
OUT
= 200 mA, 10 μF × 0.07
V/μs + 200 mA = 900 mA is not supplied. Instead, it is clamped at 400 mA.
8.2.4 Application Curves
I
OUT
= 10 mA C
IN
= C
OUT
= 1 µF
Figure 27. PSRR vs Frequency Figure 28. Output Spectral Noise Density vs Output
Voltage (TPS72718)
(V
IN
– V
OUT
= 0.5 V, TPS72718)
V
IN
= 2.3 V t
R
= t
F
= 1 µs V
IN
= 2.3 V t
R
= t
F
= 1 µs
Figure 29. Load Transient Response: 0.1 mA to 200 mA Figure 30. Load Transient Response: 1 mA to 200 mA
(TPS72718)
(TPS72718)
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Product Folder Links: TPS72710 TPS72711 TPS72715 TPS727185 TPS72718 TPS72719 TPS72725 TPS72727
TPS727285 TPS72728 TPS72730 TPS72733 TPS72748 TPS72750