ADP3000AN-12 View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADP3000AN-12
Analog Devices
ADP3000AN-12 Datasheet PDF : 16 Pages
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ADP3000
APPLICATIONS INFORMATION
COMPONENT SELECTION
Inductor Selection
For most applications, the inductor used with the ADP3000
falls in the range of 4.7 µH to 33 µH. Table 4 shows
recommended inductors and their vendors.
Table 5. Recommended Capacitors
Vendor Series Type
AVX
TPS
Surface Mount
Sanyo
OS-CON Through Hole
Sprague 595D
Surface Mount
Panasonic HFQ
Through Hole
Phone Number
(843) 448-9411
(619) 661-6835
(603) 224-1961
(800) 344-2112
When selecting an inductor for the ADP3000, it is very important
Diode Selection
to make sure the inductor is able to handle a current higher than
the ADP3000’s current limit, without becoming saturated.
The ADP3000’s high switching speed demands the use of
Schottky diodes. Suitable choices include the 1N5817, the
As a general rule, powdered iron cores saturate softly, whereas
Ferrite cores saturate abruptly. Rod and open drum core
geometry inductors saturate gradually. Inductors that saturate
gradually are easier to use. Even though rod and drum core
inductors are attractive in both price and physical size, they
E must be used with care because they have high magnetic
radiation. When minimizing EMI is critical, toroid and closed
drum core geometry inductors should be used.
T In addition, inductor dc resistance causes power loss. To
minimize power loss, it is best to use an inductor with a dc
resistance lower than 0.2 Ω.
E Table 4. Recommended Inductors
Vendor Series
Core Type
Coiltronics OCTAPAC
Toroid
L Coiltronics UNIPAC
Open
Sumida CR43, CR54 Open
O Sumida
CDRH6D28,
CDRH73,
CDRH64
Semi-Closed
Geometry
Phone Number
(561) 752-5000
(561) 752-5000
(847) 545-6700
(847) 545-6700
Capacitor Selection
S For most applications, the capacitor used with the ADP3000
falls in the range of 33 µF to 220 µF. Table 5 shows
recommended capacitors and their vendors.
B For input and output capacitors, use low ESR type capacitors for
best efficiency and lowest ripple. Recommended capacitors
include the AVX TPS series, the Sprague 595D series, the
O Panasonic HFQ series, and the Sanyo OS-CON series.
1N5818, the 1N5819, the MBRS120LT3, and the MBR0520LT1.
Fast recovery diodes are not recommended because their high
forward drop lowers efficiency. General-purpose and small-
signal diodes should be avoided as well.
PROGRAMMING THE SWITCHING CURRENT LIMIT
The ADP3000’s RLIM pin permits the cycle-by-cycle switch
current limit to be programmed with a single external resistor.
This feature offers major advantages that ultimately decrease
the component’s cost and the PCB’s real estate. First, the RLIM
pin allows the ADP3000 to use low value, low saturation current
and physically small inductors. Additionally, it allows for a
physically small surface-mount tantalum capacitor with a
typical ESR of 0.1 Ω. With this capacitor, it achieves an output
ripple as low as 40 mV to 80 mV, as well as a low input ripple.
The current limit is usually set to approximately 3 to 5 times the
full load current for boost applications, and about 1.5 to 3 times
the full load current in buck applications.
The internal structure of the ILIM circuit is shown in Figure 24.
Q1, the ADP3000’s internal power switch, is paralleled by sense
transistor Q2. The relative sizes of Q1 and Q2 are scaled so that
IQ2 is 0.5% of IQ1. Current flows to Q2 through both the RLIM
resistor and an internal 80 Ω resistor. The voltage on these two
resistors biases the base-emitter junction of the oscillator-disable
transistor, Q3. When the voltage across R1 and RLIM exceeds 0.6 V,
Q3 turns on and terminates the output pulse. If only the 80 Ω
internal resistor is used (when the ILIM pin is connected directly to
VIN), the maximum switch current is 1.5 A. Figure 13, Figure 14,
and Figure 15 give values for lower current limit levels.
RLIM
When selecting a capacitor, it is important to make sure the
(EXTERNAL)
VIN
maximum capacitor ripple current rms rating is higher than the
VIN
ILIM
ADP3000’s rms switching current.
R1 80Ω
(INTERNAL)
It is best to protect the input capacitor from high turn-on
current charging surges by derating the capacitor voltage by 2:1.
For very low input or output voltage ripple requirements, use
capacitors with very low ESR, such as the Sanyo OS-CON
series. Alternatively, two or more tantalum capacitors can be
ADP3000
Q3
IQ1
200
DRIVER
400kHz
Q2
OSCILLATOR
SW1
Q1
POWER
SWITCH
SW2
used in parallel.
Figure 24. ADP3000 Current Limit Operation
Rev. A | Page 10 of 16
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