Datasheet

TPS60310, TPS60311, TPS60312, TPS60313
SINGLE-CELL TO 3-V/3.3-V, 20-mA DUAL OUTPUT,
HIGH-EFFICIENCY CHARGE PUMP WITH SNOOZE MODE
SLVS362A – MAY 2001 – REVISED AUGUST 2001
16
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
output filter design (continued)
Due to R
(PG,1),
an output filter can easily be formed with an output capacitor (C
PG
). Cutoff 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
O
/V
I
for the ac ripple 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
(3)
Load current sourced by power-good output reduces maximum output current at OUT2. During start-up
(power-good going high) current charging C
PG
discharges C
(OUT2)
. Therefore, C
PG
must not be larger than C
PG
≤ 0.1 C
(OUT2)
or the device does not start. By charging C
PG
through C
(OUT2)
, the output voltage at OUT2
decreases. If the capacitance of C
PG
is to large, the circuit detects power bad. The power-good output goes low
and discharges C
PG
. Then the cycle starts again. Figure 24 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
SNOOZE
ON/OFF
GND
9
TPS60310
PG
7
8
C
2F
1 µF
C2+
C2–
C1+
C1–
C
1F
1 µF
4
2
LP
C
P
V
P(OUT)
++
Figure 24. 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[H]
C
P
[µF] V
P
(
OUT
)
V
IN
[V]
I
O(OUT2)
[mA]
C
IN
[µF]
CERAMIC
C
XF
[µF]
CERAMIC
C
OUT
[µF]
CERAMIC
L
P
[µH]
C
P
[µF]
CERAMIC
V
P(OUT)
V
P–P
[mV]
0.9…1.8 20 1 1 1 0.1 0.1 (X7R) 16
0.9…1.8 20 1 1 1 0.1 1 // 0.1 (X7R) 12
0.9…1.8 20 1 1 1 1 0.1 (X7R) 14
0.9…1.8 20 1 1 1 1 1 // 0.1 (X7R) 3