ADP3000AN AD [Analog Devices], ADP3000AN Datasheet - Page 6

• Manufacturer Part Number: ADP3000AN
• Description: Micropower Step-Up/Step-Down Fixed 3.3 V, 5 V, 12 V and Adjustable High Frequency Switching Regulator
• Manufacturer: AD [Analog Devices]

ADP3000
THEORY OF OPERATION
The ADP3000 is a versatile, high frequency, switch mode
power supply (SMPS) controller. The regulated output
voltage can be greater than the input voltage (boost or step-up
mode) or less than the input (buck or step-down mode). This
device uses a gated oscillator technique to provide high perfor-
mance with low quiescent current.
A functional block diagram of the ADP3000 is shown in
Figure 3a. The internal 1.245 V reference is connected to one
input of the comparator, while the other input is externally
connected (via the FB pin) to a resistor divider connected to
the regulated output. When the voltage at the FB pin falls below
1.245 V, the 400 kHz oscillator turns on. A driver amplifier
provides base drive to the internal power switch and the switching
action raises the output voltage. When the voltage at the FB
pin exceeds 1.245 V, the oscillator is shut off. While the
oscillator is off, the ADP3000 quiescent current is only 500 A.
The comparator’s hysteresis ensures loop stability without
requiring external components for frequency compensation.
The maximum current in the internal power switch can be set
by connecting a resistor between V
the maximum current is exceeded, the switch is turned OFF.
The current limit circuitry has a time delay of about 0.3 s. If
an external resistor is not used, connect I
yields the maximum feasible current limit. Further information
on I
sheet. The ADP3000 internal oscillator provides typically 1.7
An uncommitted gain block on the ADP3000 can be con-
nected as a low battery detector. The inverting input of the
gain block is internally connected to the 1.245 V reference.
The noninverting input is available at the SET pin. A resistor
divider, connected between V
connected to the SET pin, causes the AO output to go LOW
when the low battery set point is exceeded. The AO output is
an open collector NPN transistor that can sink in excess of
300 A.
The ADP3000 provides external connections for both the
collector and emitter of its internal power switch, which permits
both step-up and step-down modes of operation. For the step-
up mode, the emitter (Pin SW2) is connected to GND and the
collector (Pin SW1) drives the inductor. For step-down mode,
the emitter drives the inductor while the collector is connected
to V
The output voltage of the ADP3000 is set with two external
resistors. Three fixed voltage models are also available:
ADP3000–3.3 (+3.3 V), ADP3000–5 (+5 V) and ADP3000–12
(+12 V). The fixed voltage models include laser-trimmed
voltage-setting resistors on the chip. On the fixed voltage models
of the ADP3000, simply connect the feedback pin (Pin 8)
directly to the output voltage.
s ON and 0.8 s OFF times.
LIM
IN
.
is included in the “Applications” section of this data
IN
and GND with the junction
IN
and the I
LIM
to V
LIM
IN
pin. When
. This
–6–
APPLICATIONS INFORMATION
COMPONENT SELECTION
Inductor Selection
For most applications the inductor used with the ADP3000 will
fall in the range between 4.7 H to 33 H. Table I shows
recommended inductors and their vendors.
When selecting an inductor, it is very important to make sure
that the inductor used with the ADP3000 is able to handle a
current that is higher than the ADP3000’s current limit without
saturation.
As a rule of thumb, powdered iron cores saturate softly, whereas
Ferrite cores saturate abruptly. Rod or “open” drum core
geometry inductors saturate gradually. Inductors that saturate
gradually are easier to use. Even though rod or drum core
inductors are attractive in both price and physical size, these
types of inductors must be handled with care because they have
high magnetic radiation. Toroid or “closed” core geometry
should be used when minimizing EMI is critical.
In addition, inductor dc resistance causes power loss. It is best
to use low dc resistance inductors so that power loss in the
inductor is kept to the minimum. Typically, it is best to use an
inductor with a dc resistance lower than 0.2 .
V
Coiltronics
Coiltronics
Sumida
Sumida
Capacitor Selection
For most applications, the capacitor used with the ADP3000
will fall in the range between 33 F to 220 F. Table II shows
recommended capacitors and their vendors.
For input and output capacitors, use low ESR type capacitors
for best efficiency and lowest ripple. Recommended capacitors
include AVX TPS series, Sprague 595D series, Panasonic HFQ
series and Sanyo OS-CON series.
When selecting a capacitor, it is important to make sure the
maximum capacitor ripple current rms rating is higher than the
ADP3000’s rms switching current.
It is best to protect the input capacitor from high turn-on cur-
rent charging surges by derating the capacitor voltage by 2:1.
For very low input or output voltage ripple requirements,
Sanyo OS-CON series capacitors can be used since this type of
capacitor has very low ESR. Alternatively, two or more tanta-
lum capacitors can be used in parallel.
endor
Series
OCTAPAC
UNIPAC
CD43, CD54
CDRH62, CDRH73, Semi-Closed
CDRH64
Table I. Recommended Inductors
Core Type
Toroid
Open
Open
Geometry
Phone Numbers
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