Semtech 2006
www.semtech.com
16-30
XE8805/05A
Supply
ADC
PGA1
PGA2
PGA3
TOTAL
Unit
VDD = 5V
250
165
130
175
720
A
VDD = 3V
190
150
120
160
620
A
Table 16-28. Typical quiescent current distributions in acquisition chain (n = 16 bits, fS = 500kHz)
-20
-15
-10
-5
0
5
10
15
0
500
1000
1500
2000
2500
3000
3500
Frequency - fRC [kHz]
R
e
la
ti
ve
Q
u
iescent
C
u
rr
e
nt
C
h
ang
e
IQ
/
I
Q,
2
M
H
z[%
]
500
550
600
650
700
750
800
850
0
500
1000
1500
2000
2500
3000
3500
Frequency - fRC [kHz]
Q
u
ie
s
c
e
n
tC
u
rr
e
n
t
-I
Q
[
A]
(a)
(b)
Figure 16-24. (a) Absolute and (b) relative change in quiescent curent consumption vs. RC oscillator
frequency (all PGAs active, VDD = 5V)
16.8.7
Power Supply Rejection Ratio
Figure 16-25 shows power supply rejection ratio (PSRR) at 3V and 5V supply voltage, and for various PGA gains.
PSRR is defined as the ratio (in dB) of voltage supply change (in V) to the change in the converter output (in V).
PSRR depends on both PGA gain and supply voltage VDD.
60
65
70
75
80
85
90
95
100
105
1
5
10
20
100
PGA Gain [V/V]
PS
RR
[
d
B]
VDD=3V
VDD=5V
Figure 16-25. Power supply rejection ratio (PSRR)
Not
Recommended
for
New
Designs