MAX1595EGC50-T Maxim Integrated Products, MAX1595EGC50-T Datasheet - Page 5

• Manufacturer Part Number: MAX1595EGC50-T
• Description: Charge Pumps
• Manufacturer: Maxim Integrated Products

Specifications of MAX1595EGC50-T

• Function: Step Up, Step Down
• Output Voltage: 5 V
• Output Current: 125 mA
• Maximum Operating Temperature: + 85 C
• Package / Case: QFN-12
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Using white LEDs to backlight LCDs is an increasingly
popular approach for portable information devices
(Figure 2). Because the forward voltage of white LEDs
exceeds the available battery voltage, the use of a
charge pump such as the MAX1595 provides high effi-
ciency, small size, and constant light output with chang-
ing battery voltages. If the output is used only to light
LEDs, the output capacitor can be greatly reduced. The
frequency modulation of the LED intensity is not dis-
cernible to the human eye, and the smaller capacitor
saves both size and cost.
Adding two Schottky diodes and two capacitors imple-
ments a tripler and allows the MAX1595_ _ _50 to regu-
late a current of 75mA with a supply voltage as low as
2.3V (Figure 3).
The MAX1595 requires only three external capacitors
(Figure 4). Their values are closely linked to the output
current capacity, oscillator frequency, output noise con-
tent, and mode of operation.
Generally, the transfer capacitor (C
and the input capacitor (C
Higher switching frequencies allow the use of the smaller
C
where from 5-times to 50-times larger than C
shows recommended capacitor values.
In addition, the following equation approximates output
ripple:
Table 2 lists the manufacturers of recommended capaci-
tors. Ceramic capacitors will provide the lowest ripple
due to their typically lower ESR.
The power dissipated in the MAX1595 depends on out-
put current and is accurately described by:
P
rating.
All capacitors should be soldered in close proximity to
the IC. Connect ground and power ground through a
short, low-impedance trace. The input supply trace
should be as short as possible. Otherwise, an additional
input supply filter capacitor (tantalum or electrolytic) may
be required.
DISS
X
and C
must be less than that allowed by the package
IN
V
. The output capacitor (C
RIPPLE
P
Applications Information
DISS
_______________________________________________________________________________________
Regulated 3.3V/5.0V Step-Up/Step-Down
≅ I
= I
OUT
OUT
/ (2 x f
IN
Layout Considerations
(2V
) is twice as large as C
Capacitor Selection
IN
OSC
Power Dissipation
- V
X
) will be the smallest,
OUT
x C
OUT
OUT
)
) can be any-
)
X
. Table 1
X
.
Figure 3. Regulated Voltage Tripler
Figure 2. White LED Bias Supply
Figure 4. Standard Operating Circuit
C
IN
INPUT
= 1μF
2.3V
V
IN
1μF
OFF
IN
1μF
C
IN
ON
IN
SHDN
IN
SHDN
MAX1595_ _ _50
PGND
PGND
CXP
MAX1595_ _ _50
C
X
GND
2
3
= 0.1μF
GND
SHDN
IN
AOUT
CXN
PGND
CXN
AOUT
OUT
CXP
5
OUT
Charge Pump
MAX1595
4
GND
0.22μF
1μF
C
0.47μF
OUT
=
0.22μF
AOUT
CXN
CXP
OUT
100Ω
7
6
8
1
1μF
100Ω
C
1μF
C
0.22μF
OUTPUT
REGULATED 5V
75mA
OUT
X
OUT
100Ω
5