ADP2302-EVALZ Analog Devices Inc, ADP2302-EVALZ Datasheet - Page 17

• Manufacturer Part Number: ADP2302-EVALZ
• Description: Nonsynchronous Step-Down Regulator Eval. Board
• Manufacturer: Analog Devices Inc

Specifications of ADP2302-EVALZ

• Silicon Manufacturer: Analog Devices
• Application Sub Type: Step Down DC/DC Converter
• Kit Application Type: Power Management - Voltage Regulator
• Silicon Core Number: ADP2302
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

3.0V ~ 5.0V
OFF
LOW INPUT VOLTAGE CONSIDERATIONS
For low input voltage between 3 V and 5 V, the internal boot
regulator cannot provide enough bootstrap voltage due to the
internal dropout voltage. As a result, the increased MOSFET
R
an external small-signal Schottky diode from a 5.0 V external
bootstrap bias voltage. Because the absolute maximum rating
between the BST and SW pins is 6.0 V, the bias voltage should
be less than 5.5 V. Figure 48 shows the application diagram for
the external bootstrap circuit.
PROGRAMMING THE PRECISION ENABLE
Generally, the EN pin can connect to the VIN pin so that the
device automatically starts up when the input power is applied.
However, the precision enabling feature allows the ADP2302/
ADP2303 to be used as a programmable UVLO by connecting
a resistive voltage divider to VIN, as shown in Figure 49. This
configuration prevents the start-up problems that can occur
when VIN ramps up slowly in soft start with a relatively high
load current.
DS(ON)
Figure 48. External Bootstrap Circuit for Low Input Voltage Application
ON
22
20
18
16
14
12
10
reduces the available load current. To prevent this, add
8
6
4
2
0
VIN
EN
Figure 47. Voltage Conversion Limitations
2
ADP2302/
ADP2303
MINIMUM INPUT VOLTAGE
MAXIMUM INPUT VOLTAGE
GND
4
BST
SW
FB
6
V
OUT
8
(V)
SCHOTTKY
DIODE
10
12
5V BIAS VOLTAGE
14
16
Rev. 0 | Page 17 of 28
The precision enable feature also allows the ADP2302/ADP2303 to
be sequenced precisely by using a resistive voltage divider from
another dc-to-dc power supply, as shown in Figure 50.
With a 1.2 μA pull-down current on the EN pin, the equation for
the start-up voltage in Figure 49 and Figure 50 is
where:
V
R
R
INDUCTOR
The high switching frequency of the ADP2302/ADP2303 allows
the use of small inductors. For best performance, use inductor
values between 1 μH and 15 μH.
The peak-to-peak inductor ripple current is calculated using the
following equation:
where:
f
L is the inductor value.
V
V
V
Inductors of smaller values are usually smaller in size but
increase the ripple current and the output ripple voltage. As a
guideline, the inductor peak-to-peak ripple current is typically
set to 30% of the maximum load current for optimal transient
SW
EN1
EN2
STARTUP
D
IN
OUT
is the switching frequency.
is the diode forward drop.
is the input voltage.
is the resistor from the dc source to EN.
is the resistor from EN to GND.
V
Δ
is the output voltage.
STARTUP
I
Figure 49. Precision Enable Used as a Programmable UVLO
RIPPLE
is the start-up voltage to enable the chip.
Figure 50. Precision Enable Used as a Sequencing Control
SUPPLIER
ANOTHER
DC/DC
=
=
V
IN
(
from Another DC-to-DC Power Supply
⎛
⎜
⎜
⎝
V
R
R
1
R
EN1
EN2
IN
2 .
L
EN2
×
−
V
R
V
f
+
EN1
sw
OUT
R
1
EN2
2 .
)
μA
×
VIN
EN
⎛
⎜
⎜
⎝
ADP2302/
ADP2303
⎞
⎟
⎟
⎠
V
V
×
ADP2302/ADP2303
OUT
IN
R
EN
EN1
+
+
ADP2302/
ADP2303
V
V
+
D
1
D
2 .
⎞
⎟
⎟
⎠
V