ADP3000AN AD [Analog Devices], ADP3000AN Datasheet - Page 8

• 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
The circuit of Figure 18 may produce multiple pulses when
approaching the trip point due to noise coupled into the SET
input. To prevent multiple interrupts to the digital logic,
hysteresis can be added to the circuit (Figure 18). Resistor R
with a value of 1 M to 10 M , provides the hysteresis. The
addition of R
value for R1 will be:
where V
resistor, and R
POWER TRANSISTOR PROTECTION DIODE IN STEP-
DOWN CONFIGURATION
When operating the ADP3000 in the step-down mode, the
output voltage is impressed across the internal power switch’s
emitter-base junction when the switch is off. In order to protect
the switch, a Schottky diode must be placed in a series with
SW2 when the output voltage is set to higher than 6 V. Figure
19 shows the proper way to place the protection diode, D2.
The selection of this diode is identical to the step-down commut-
ing diode (see Diode Selection section for information).
THERMAL CONSIDERATIONS
Power dissipation internal to the ADP3000 can be approximated
with the following equations.
Step-Up
where: I
V
P
IN
externally, or maximum inductor current in the case of
current limit not programmed externally.
R = 1
D = 0.75 (Typical Duty Ratio for a Single Switching
Cycle).
V
I
V
I
L
D
SW
O
Q
O
IN
Figure 19. Step-Down Model V
= 30 (Typical Forced Beta)
is the logic power supply voltage, R
C2
= Output Current.
= 500 A (Typical Shutdown Quiescent Current).
= Output Voltage.
is I
= Input Voltage.
+
I
HYS
SW
LIMIT
HYS
R3
(Typical R
will change the trip point slightly, so the new
2
I
R1
R
LIM
1
ADP3000
creates the hysteresis.
GND
in the case of current limit programmed
5
V
V
2
IN
IN
1.245V
SW1
R2
I
V
3
SW
SW2
CE(SAT)
LOBATT
FB
D1, D2 = 1N5818 SCHOTTKY DIODES
D 1–
8
4
).
D2
D1
V
–1.245V
R
V
V
L
L
IN
O
1.245V
R
L1
HYS
C1
4I
I
SW
+
OUT
O
L
R2
is the pull-up
> 6.0 V
R1
I
Q
V
OUT
V
IN
> 6V
HYS
,
–8–
Step-Down
where: I
The temperature rise can be calculated from:
where:
As example, consider a boost converter with the following
specifications:
V
I
With Step-Up Power Dissipation Equation:
Using the SO-8 Package:
Using the N-8 Package:
At a 70 C ambient, die temperature would be 101.45 C for
SO-8 package and 92.2 C for N-8 package. These junction
temperatures are well below the maximum recommended
junction temperature of 125 C.
Finally, the die temperature can be decreased up to 20% by
using a large metal ground plate as ground pickup for the
ADP3000.
SW
IN
P
= 185 mW
D
= 0.8 A (Externally Programmed).
= 2 V, I
P
externally or maximum inductor current in the case of
current limit is not programmed eternally.
V
1.2 V is typical value.
D = 0.75 (Typical Duty Ratio for a Single Switching
Cycle).
V
I
V
I
P
0.8
SW
O
Q
D
JA
T = Temperature Rise.
D
CE(SAT)
O
IN
= 30 (Typical Forced Beta).
= Output Current.
= 500 A (Typical Shutdown Quiescent Current).
2
= Device Power Dissipation.
= Output Voltage.
= Thermal Resistance (Junction-to-Ambient).
is I
= Input Voltage.
O
I
SW
1
= 180 mA, V
LIMIT
V
= Check this value by applying I
(2)(0.8)
CESAT
30
in the case of current limit is programmed
1
1
0.75 1–
T = 185 mW (120 C/W) = 22.2 C.
T
O
T = 185 mW (170 C/W) = 31.5 C.
= 3.3 V.
V
IN
P
D
– V
V
3.3
O
CE SAT
2
JA
(4) 0.18
0.8
2 I
I
SW
O
SW
to Figure 8b.
I
Q
500 E 6 2
V
IN
REV. 0