EL7584IR Intersil, EL7584IR Datasheet - Page 10

• Manufacturer Part Number: EL7584IR
• Description: IC DC-DC CONVERTER 4CH 24-TSSOP
• Manufacturer: Intersil

Specifications of EL7584IR

• Applications: Converter, TFT, LCD
• Voltage - Input: 2 ~ 14 V
• Number Of Outputs: 2
• Voltage - Output: 5 ~ 17 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

The following table gives typical values:
(Margins are considered 10%, 3%, 20%, 10%, and 15% on
V
Component Considerations
Input Capacitor
It is recommended that C
Theoretically, the input capacitor has ripple current of ∆I
Due to high-frequency noise in the circuit, the input current
ripple may exceed the theoretical value. Larger capacitor will
reduce the ripple further.
Boost Inductor
The inductor has peak and average current decided by:
The inductor should be chosen to be able to handle this
current. Furthermore, due to the fixed internal
compensation, it is recommended that maximum inductance
of 10µH and 15µH to be used in the 5V and 12V or higher
output voltage, respectively.
The output diode has average current of I
the same as the inductor's peak current. Schottky diode is
recommended and it should be able to handle those currents.
Feedback Resistor Network
An external resistor divider is required to divide the output
voltage down to the nominal reference voltage. Current
drawn by the resistor network should be limited to maintain
the overall converter efficiency. The maximum value of the
resistor network is limited by the feedback input bias current
and the potential for noise being coupled into the feedback
pin. A resistor network in the order of 200kΩ is
recommended. The boost converter output voltage is
determined by the following relationship:
where V
I
I
V
LPK
LAVG
IN
BOOST
V
, V
TABLE 1. MAXIMUM CONTINUOUS OUTPUT CURRENT
IN
3.3
3.3
3.3
12
5
5
5
=
O
(V)
=
I
, L, F
LAVG
FBB
-------------
1 - D
=
I
O
R
-------------------- -
is 1.300V.
S
1
+
R
, and I
+
V
∆I
--------
1
R
O
2
12
15
12
15
18
9
9
L
2
(V)
×
LMT
V
FBB
, respectively)
IN
L (µH)
is larger than 10µF.
10
10
10
10
10
10
10
10
F
S
1000
1000
1000
1000
1000
1000
1000
O
(kHz)
, and peak current
I
OMAX
430
320
250
650
470
370
830
(mA)
L
.
EL7584
Schottky Diode
Speed, forward voltage drop, and reverse current are the
three most critical specifications for selecting the Schottky
diode. The entire output current flows through the diode, so
the diode average current is the same as the average load
current and the peak current is the same as the inductor
peak current. When selecting the diode, one must consider
the forward voltage drop at the peak diode current. On the
Elantec demo board, MBRM120 is selected. Its forward
voltage drop is 450mV at 1A forward current.
Output Capacitor
The EL7584 is specially compensated to be stable with
capacitors which have a worst-case minimum value of 10µF
at the particular V
requirements also determine the minimum value and the
type of capacitors. Output ripple voltage consists of two
components - the voltage drop caused by the switching
current though the ESR of the output capacitor and the
charging and discharging of the output capacitor:
For low ESR ceramic capacitors, the output ripple is
dominated by the charging/discharging of the output
capacitor.
In addition to the voltage rating, the output capacitor should
also be able to handle the RMS current is given by:
Positive and Negative Charge Pump (V
V
The EL7584 contains two independent charge pumps (see
charge pump block and connection diagram.) The negative
charge pump inverts the V
a regulated negative output voltage. The positive charge
pump doubles the V
regulated positive output voltage. The regulation of both the
negative and positive charge pumps is generated by the
internal comparator that senses the output voltage and
compares it with and internal reference. The switching
frequency of the charge pump is set to ½ the boost converter
switching frequency.
The pumps use pulse width modulation to adjust the pump
period, depending on the load present. The pumps are short-
circuit protected to 180mA at 12V supply and can provide
15mA to 60mA for 6V to 12V supply.
V
I
CORMS
RIPPLE
OFF
)
=
=
I
LPK
1 ( - D )
×
OUT
ESR
×
DDP




D
being set. Output ripple voltage
+
+
V
------------------------------- -
supply voltage and provides a
------------------- -
I
OUT
LAVG
DDN
∆I
V
OUT
L
2
- V
supply voltage and provides
2
×
IN
----- -
12
1
×




------------------------------
C
×
OUT
I
I
LAVG
OUT
×
FS
ON
February 4, 2005
and
FN7317.2