Datasheet

TPS60300, TPS60301, TPS60302, TPS60303
SINGLE-CELL TO 3.0-V/3.3-V, 20-mA DUAL OUTPUT,
HIGH-EFFICIENCY CHARGE PUMP
SLVS302A – DECEMBER 2000 – REVISED MARCH 2001
16
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
design procedure (continued)
Due to R
(PG,1)
, an output filter can easily be formed with an output capacitor (C
PG
). Cut-off frequency is given
by:
ƒ
c
+
1
2pR
(PG,1)
C
(PG)
(1)
Ť
V
(PG,1)
V
O(OUT2)
Ť
+
1
1 )
ǒ
2pƒR
(PG,1)
C
(PG)
Ǔ
2
Ǹ
and ratio V
OUT
/V
IN
is:
(2)
with R
(PG,1)
= 15 Ω, C
(PG)
= 0.1 µF and f = 600 kHz (at nominal switching frequency)
Ť
V
(PG,1)
V
O(OUT2)
Ť
+ 0.175
Load current sourced by power-good output reduces maximum output current at OUT2. During start-up (power
good going high) current charging C
(PG)
will discharge C
(OUT2)
. Therefore, C
(PG)
must not be larger than 0.1
C
(OUT2)
or the device will not start. By charging C
(PG)
through C
(OUT2)
, the output voltage at OUT2 will decrease.
If the capacitance of C
(PG)
is to large, the circuit will detect power bad. The power-good output will go low and
discharge C
(PG)
. Then the cycle starts again. Figure 22 shows a configuration with an LC-post filter to further
reduce output ripple and noise.
OUT1
5
+
C
(OUT1)
1 µF
OUT2
6
C
(OUT2)
1 µF
R1
10
PG
V
IN
3
C
IN
1 µF
INPUT
0.9 V to 1.8 V
1
EN
OFF/ON
GND
9
TPS60300
PG
7
8
C
2F
1 µF
C2+
C2–
C1+
C1–
C
1F
1 µF
4
2
LP
C
P
V
P(OUT)
++
Figure 22. LC-Post Filter
Table 4. Recommended Values for Lowest Output Voltage Ripple
V
IN
I
O
(
OUT2
)
C
IN
[µF] C
XF
[µF] C
OUT
[µF] L
P
[µH] C
P
[µF]
V
P
(
OUT
)
V
IN
[V]
I
O(OUT2)
[mA]
CERAMIC CERAMIC CERAMIC CERAMIC
V
P(OUT)
V
P–P
[mV]
0.9…1.8 20 1.0 1.0 1.0 0.1 0.1 (X7R) 16
0.9…1.8 20 1.0 1.0 1.0 0.1 1 // 0.1 (X7R) 12
0.9…1.8 20 1.0 1.0 1.0 1.0 0.1 (X7R) 14
0.9…1.8 20 1.0 1.0 10 1.0 1 // 0.1 (X7R) 3