MAX1661 Datasheet, PDF (12/16 Pages) Maxim Integrated Products – Active-Matrix Liquid Crystal Display AMLCD Supply

Active Matrix Liquid Crystal Display
(AMLCD) Supply
Table 2. Typical DC-DC 2 Operation
V_OUT2+ V_OUT2-
V_IN
(V)
(V)
(V)
f_BPCLK
(kHz)
L2
(µH)
I_OUT2+(MAX)
(mA)
+15
-5
3.0
22.5
4.7
6
+15
-5
3.0
22.5
2.7
8
+15
-5
3.3
22.5
4.7
7
+15
-5
3.3
22.5
2.7
10
+15
-5
4.5
22.5
4.7
15
+15
-5
5.0
22.5
4.7
20
+20
-10
3.0
22.5
4.7
3
+20
-10
3.0
22.5
2.7
5
+20
-10
3.0
25.0
4.7
2
+20
-10
3.0
25.0
2.7
4
+20
-10
3.0
30.0
4.7
3
+20
-10
3.0
30.0
2.7
3
+20
-10
3.3
22.5
4.7
4
+20
-10
3.3
22.5
2.7
6
+20
-10
3.3
25.0
4.7
4
+20
-10
3.3
25.0
2.7
6
+20
-10
3.3
30.0
4.7
4
+20
-10
3.3
30.0
4.7
4
+20
-10
4.5
22.5
4.7
9
+20
-10
4.5
25.0
4.7
8
+20
-10
4.5
30.0
4.7
8
+20
-10
4.5
30.0
2.7
10
+20
-10
5.0
22.5
4.7
11
+20
-10
5.0
25.0
4.7
10
+20
-10
5.0
30.0
4.7
10
*Note: Absolute maximum peak current at LX2P and LX2N is 750mA.
I_OUT2-(MAX)
(mA)
15
23
19
27
35
43
6
10
5
8
4
6
8
12
7
10
5
8
16
14
12
17
20
18
15
f_{DC-DC 2(MAX)}
(kHz)
360
360
360
360
360
360
360
360
400
400
480
480
360
360
400
400
480
480
360
400
480
480
360
400
480
INDUCTOR PEAK
CURRENT*
(mA)
375
585
425
643
550
600
385
585
340
530
300
451
425
643
370
583
340
496
580
500
450
679
640
550
500
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:
I_F
>
I_OUT V_OUT
0.9V_IN
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_{RIPPLE(PK−PK)} ≅
I_PEAK x R_ESR
+
I_OUT


t_ON
C_OUT


DC - DC 1 t_ON
=¹
f_{DC -DC 1}


V_OUT1 + V_F
V_OUT1 +
- V_IN
V_F


DC - DC 2 t_ON
=
1
2 f_{DC -DC 1}
12 ______________________________________________________________________________________