Max1664, Table 2. typical dc-dc 2 operation, Diode selection – Rainbow Electronics MAX1664 User Manual
Page 12: Filter capacitor selection
MAX1664
12
______________________________________________________________________________________
Diode Selection
The MAX1664’s high switching frequency requires fast
diodes. Schottky diodes such as the MBR0520L and
MBR0540L (Motorola) are recommended because they
have the necessary power ratings in a low-height SOD-
123 package. Also recommended is the MBRM5817
which is 1.1mm high. Use a Schottky diode with a for-
ward current rating greater than:
For the positive output of DC-DC 2, use a Schottky
diode with a voltage rating that exceeds V
OUT2+
. For
the negative output, use a Schottky diode with a rating
that exceeds V
IN
+
V
OUT2-
. See Table 3 for more
information on Schottky diode manufacturers.
Filter Capacitor Selection
An output filter capacitor’s ESR and size can greatly
influence a switching converter’s output ripple, as
shown in the following equation.
V
I
x R
I
t
C
DC - DC 1 t
1
f
V
V - V
V
V
DC - DC 2 t
1
2 f
RIPPLE(PK PK)
PEAK
ESR
OUT
ON
OUT
ON
DC -DC 1
OUT1
F
IN
OUT1
F
ON
DC -DC 1
−
≅
+
=
+
+
=
.
I
I
V
V
F
OUT
OUT
IN
>
0 9
Table 2. Typical DC-DC 2 Operation
*
Note: Absolute maximum peak current at LX2P and LX2N is 750mA.
Active Matrix Liquid Crystal Display
(AMLCD) Supply
INDUCTOR PEAK
CURRENT*
(mA)
f
DC-DC 2(MAX)
(kHz)
I
OUT2-(MAX)
(mA)
I
OUT2+(MAX)
(mA)
L2
(µH)
f
BPCLK
(kHz)
V
IN
(V)
V
OUT2-
(V)
V
OUT2+
(V)
500
480
15
10
4.7
30.0
5.0
-10
+20
550
400
18
10
4.7
25.0
5.0
-10
+20
640
360
20
11
4.7
22.5
5.0
-10
+20
679
480
17
10
2.7
30.0
4.5
-10
+20
450
480
12
8
4.7
30.0
4.5
-10
+20
500
400
14
8
4.7
25.0
4.5
-10
+20
580
360
16
9
4.7
22.5
4.5
-10
+20
496
480
8
4
4.7
30.0
3.3
-10
+20
340
480
5
4
4.7
30.0
3.3
-10
+20
583
400
10
6
2.7
25.0
3.3
-10
+20
370
400
7
4
4.7
25.0
3.3
-10
+20
643
360
12
6
2.7
22.5
3.3
-10
+20
425
360
8
4
4.7
22.5
3.3
-10
+20
451
480
6
3
2.7
30.0
3.0
-10
+20
300
480
4
3
4.7
30.0
3.0
-10
+20
530
400
8
4
2.7
25.0
3.0
-10
+20
340
400
5
2
4.7
25.0
3.0
-10
+20
585
360
10
5
2.7
22.5
3.0
-10
+20
385
360
6
3
4.7
22.5
3.0
-10
+20
600
360
43
20
4.7
22.5
5.0
-5
+15
550
360
35
15
4.7
22.5
4.5
-5
+15
643
360
27
10
2.7
22.5
3.3
-5
+15
425
360
19
7
4.7
22.5
3.3
-5
+15
585
360
23
8
2.7
22.5
3.0
-5
+15
375
360
15
6
4.7
22.5
3.0
-5
+15