ADP3050-EVAL Analog Devices Inc, ADP3050-EVAL Datasheet - Page 16

• Manufacturer Part Number: ADP3050-EVAL
• Description: BOARD EVAL FOR ADP3050
• Manufacturer: Analog Devices Inc

Specifications of ADP3050-EVAL

• Main Purpose: DC/DC, Step Down
• Voltage - Input: 3.6 ~ 30V
• Regulator Topology: Buck
• Board Type: Fully Populated
• Utilized Ic / Part: ADP3050
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Output: -
• Voltage - Output: -
• Power - Output: -
• Frequency - Switching: -
• Outputs And Type: -
• Lead Free Status / RoHS Status: Not Compliant, Contains lead / RoHS non-compliant

ADP3050
For output voltages greater than 5 V, it may be necessary to add
a small capacitor in parallel with R2, as shown in Figure 25.
This improves stability and transient response. For tantalum
output capacitors, the typical value for C
output capacitors, the typical value for C
CURRENT LIMIT/FREQUENCY FOLDBACK
The ADP3050 uses a cycle-by-cycle current limit to protect the
device under fault and high stress conditions. When the current
limit is exceeded, the power switch turns off until the beginning
of the next oscillator cycle. If the voltage on the feedback pin
drops below 80% of its nominal value, the oscillator frequency
starts to decrease (see Figure 17 in the Typical Performance
Characteristics section). The frequency gradually reduces to a
minimum value of approximately 80 kHz (this minimum
occurs when the feedback voltage falls to 30% of its nominal
value). This reduces the power dissipation in the IC, the
external diode, and the inductor during short-circuit
conditions. This frequency foldback method provides complete
device fault protection without interfering with the normal
device operation.
BIAS PIN CONNECTION
To help improve efficiency, most of the internal operating
current can be drawn from the lower voltage regulated output
voltage instead of the input supply. For example, if the input
voltage is 24 V and the output voltage is 5 V, a quiescent current
of 4 mA wastes 96 mW if drawn from the input supply, but only
20 mW is drawn from the regulated 5 V output. This power
savings is most evident at high input voltages and low load
currents. The output voltage must be 3 V or higher to take
advantage of this feature.
BOOSTED DRIVE STAGE
An external capacitor and diode are used to provide the boosted
voltage needed for the special drive stage. If the output voltage is
above 4 V, connect the anode of the boost diode to the regulated
output; for output voltages less than or equal to voltages of ≤3 V,
connect it to the input supply. For some low voltage systems,
such as 5 V to 3.3 V converters, the anode of the boost diode
can be connected to either the input or output voltage. During
switch off time, the boost capacitor is charged up to the voltage
at the anode of the boost diode. When the switch turns on, this
voltage is added to the switch voltage (the boost diode is reverse-
biased), providing a voltage higher than the input supply. The
peak voltage appearing on the BOOST pin is the sum of the
input voltage and the boost voltage (either V
Ensure that this peak voltage does not exceed the BOOST pin
maximum rating of 45 V.
For most applications, a 1N4148 or 1N914 type diode can be
used with a 220 nF capacitor. A 470 nF capacitor may be needed
for output voltages between 3 V and 4 V. The boost capacitor
should have an ESR of less than 2 Ω to ensure that it is
adequately charged up during switch off time. Almost any type
of film or ceramic capacitor can be used.
F
F
is 100 pF. For ceramic
is 400 pF.
IN
+ V
OUT
or 2 × V
Rev. B | Page 16 of 24
IN
).
START-UP/MINIMUM INPUT VOLTAGE
For most designs, the regulated output voltage provides the
boosted voltage for the drive stage. During startup, the output
voltage is 0, so there is no boosted supply for the drive stage.
To deal with this problem, the ADP3050 contains a backup drive
stage to get everything started. As the output voltage increases,
so does the boost voltage. When the boost voltage reaches approx-
imately 2.5 V, the switch drives transition smoothly from the
backup driver to the boosted driver. If the boost voltage decreases
below approximately 2.5 V, resulting in a short-circuit or
overload condition, the backup stage takes over to provide switch
drive. The minimum input voltage needed for the ADP3050 to
function correctly is about 3.6 V (this ensures proper operation of
the internal circuitry), but a small amount of headroom is
needed for all step-down regulators. The following formula gives
the approximate minimum input voltage needed for a given
system, where V
for the appropriate value of V
typical minimum input voltage needed for 3.3 V and 5 V
systems.
THERMAL CONSIDERATIONS
Several factors contribute to IC power dissipation: ac and dc
switch losses, boost current, and quiescent current. The following
formulas are used to calculate these losses to determine the power
dissipation of the IC. These formulas assume continuous mode
operation, but they provide a reasonable estimate for disconti-
nuous mode systems (do not use these formulas to calculate
efficiency at light loads).
Switch loss
Boost current loss
Quiescent current loss
where:
V
f
t
β
I
I
P
SW
OV
Q
BIAS
SW
SW
SAT
is the quiescent current drawn from V
is the switch frequency (200 kHz).
is the switch current/voltage overlap time (~50 ns).
is the current gain of the NPN power switch (~50).
is the quiescent current drawn from V
=
is ~0.6 V at I
V
P
P
⎛
⎜
⎜
⎝
Q
BOOST
IN
I
=
OUT
(
MIN
(
V
×
=
IN
)
V
=
I
×
β
SAT
OUT
SW
I
SAT
V
Q
OUT
OUT
×
) (
is the switch saturation voltage (see Figure 15
×
+
V
. 0
V
= 800 mA (taken from Figure 15).
V
OUT
V
+
85
IN
V
OUT
OUT
V
IN
SAT
⎞
+ ⎟ ⎟
⎠
2
×
SAT
(
I
t
OV
BIAS
). Figure 13 also shows the
×
)
I
OUT
×
IN
V
IN
OUT
(~1 mA).
×
(~4 mA).
f
SW
)
(12)
(13)
(14)
(15)