DETAILED DESCRIPTION
Start-up
MAS9123 start-up is optimized for bypass capacitor
values of 3 to 20 nF. When values are lower than 3
nF the start-up settling might be unstable for about
20 µs after the start-up. The rise time increases if
bypass capacitor values are bigger than 20 nF.
Start-up settling
Typically 20 µs after the start-up the output voltage
drops about 10 to 20 mV in 250 µs time (figure 3).
The value of this voltage drop depends on the
parasitic components of the bypass-capacitor. After
the voltage drop the output voltage rises slowly to
the final value (figure 4).
Noise reduction
MAS9123 has typically 9.5 µVRMS output noise
voltage with 10 nF bypass capacitor. By increasing
the capacitance value the output noise will slightly
decrease, but the start-up time increases.
MAS9123 start-up
3
10
9
2.5
8
7
2
6
1.5
5
4 VOUT
1
3 CTRL
2
0.5
1
0
0
0
4
8
12
16
20
T/us
Figure 1. Typical start-up. CBYPASS = 10 nF & CL = 1µF.
MAS9123 START-UP
2,82
9
2,81
2,8
7
2,79
5
2,78
VOUT
2,77
CTRL
3
2,76
1
2,75
2,74
0
-1
5
10
15
20
25
30
35
TIME (us)
Figure 2. Typical start-up. CBYPASS = 10 nF & CL = 1µF.
DA9123.002
26 September, 2000
2.82
2.81
2.8
2.79
2.78
2.77
2.76
2.75
0
MAS9123 start-up settling
9
7
5
VOUT
3
CTRL
1
0.2
0.4
0.6
0.8
1
T/ms
-1
1.2
1.4
1.6
Figure 3. Typical start-up settling. CBYPASS = 10 nF & CL = 1µF.
MAS9123 start-up settling
2.82
9
2.81
2.8
7
2.79
5
2.78
3 VOUT
CTRL
2.77
1
2.76
2.75
-1
0
1
2
3
4
5
6
7
T/ms
Figure 4. Typical start-up settling. CBYPASS = 10 nF & CL = 1µF.
5 (10)