EUP2624
Input Capacitor
The value of the input capacitor depends the input and
output voltages, the maximum output current, the
inductor value and the noise allowed to put back on the
input line. For most applications, a minimum 10µF is
required. For applications that run close to the maximum
output current limit, input capacitor in the range of 22µF
to 47µF is recommended. The EUP2624 is powered
from the VIN. High frequency 0.1µF by-pass cap is
recommended to be close to the VIN pin to reduce
supply line noise and ensure stable operation.
Loop Compensation
The EUP2624 incorporates an transconductance
amplifier in its feedback path to allow the user some
adjustment on the transient response and better
regulation. The EUP2624 uses current mode control
architecture which has a fast current sense loop and a
slow voltage feedback loop. The fast current feedback
loop does not require any compensation. The slow
voltage loop must be compensated for stable operation.
The compensation network is a series RC network from
COMP pin to ground. The resistor sets the high
frequency integrator gain for fast transient response and
the capacitor sets the integrator zero to ensure loop
stability. For most applications,the compensation resistor
in the range of 2K to 30K and the compensation
capacitor in the range of 1nF to 10nF.
Soft-Start
The soft-start is provided by an internal 5µA current
source charges the external CSS, the peak MOSFET
current is limited by the voltage on the capacitor. This in
turn controls the rising rate of the output voltage. The
regulator goes through the start-up sequence as well after
the SHDN pin is pulled to HI.
Frequency Selection
The EUP2624 switching frequency can be user selected
to operate at either at constant 620kHz or 1.25MHz.
Connecting FSEL pin to ground sets the PWM switching
frequency to 620kHz. When connect FSEL high or VDD,
switching frequency is set to 1.25MHz.
Shut-Down Control
The EUP2624 shuts down to reduce the supply current
to 0.1μA when
SHDN
is low. In this mode, the internal
reference, error amplifier, comparators, and biasing
circuitry turn off while the N-channel MOSFET is
turned off. The boost converter’s output is connected to
IN via the external inductor and catch diode.
Maximum Output Current
The output current capability of the EUP2624 is a
function of current limit, input voltage, operating
frequency, and inductor value. The output current
capability is governed by the following equation:
I L
=
I L - AVG
+
1
/
2
× ∆
I L
(
)
Where:
IL=MOSET current limit
I L - AVG
=
average inductor current
∆
I L
=
inductor ripple current
∆I
L
=
VIN
×
VO
+
VDIODE
−
V
−
VIN
IN
L
×
VO
+
V
DIODE
×
F
S
VDIODE = Schottky diode forward voltage, typically,
0.6V
FS = switching frequency, 620KHz or 1.25MHz
I
I L - AVG
=
OUT
1
−
D
D = MOSFET turn-on ratio:
D
=
1
−
VIN
VOUT
+
V
DIODE
Layout Considerations
Good PC board layout and routing are required in
high-frequency switching power supplies to achieve good
regulation, high efficiency, and stability. It is strongly
recommended that the evaluation kit PC board layouts be
followed as closely as possible. Place power components
as close together as possible, keeping their traces short,
direct, and wide. Avoid interconnecting the ground pins
of the power components using vias through an internal
ground plane. Instead, keep the power components close
together and route them in a “star” ground configuration
using component-side coper, then connect the star ground
to internal ground using multiple vias.
DS2624 Ver1.0
July .2006
8
EUTECH [ EUTECH MICROELECTRONICS INC ]
