ADP3000AN-3.3 View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

ADP3000AN-3.3

Micropower Step-Up/Step-Down Fixed 3.3 V, 5 V, 12 V, Adjustable High Frequency Switching Regulator

Analog Devices 

ADP3000

The delay through the current limiting circuit is approximately

0.3 µs. If the switch-on time is reduced to less than 1.7 µs,

accuracy of the current trip point is reduced as well. An attempt

to program a switch-on time of 0.3 µs or less produces spurious

R1 =

VLOBATT − 1.245 V

⎜⎜⎝⎛

1.245

R2

V

⎟⎟⎠⎞

−

⎜⎜⎝⎛

VL

R

− 1.245 V

L + RHYS

⎟⎟⎠⎞

responses in the switch-on time. However, the ADP3000 still

provides a properly regulated output voltage.

where:

VL is the logic power supply voltage.

PROGRAMMING THE GAIN BLOCK

The ADP3000’s gain block can be used as a low battery detector,

RL is the pull-up resistor.

RHYS creates the hysteresis.

an error amplifier, or a linear post regulator. It consists of an op

POWER TRANSISTOR PROTECTION DIODE IN

amp with PNP inputs and an open-collector NPN output. The

STEP-DOWN CONFIGURATION

inverting input is internally connected to the 1.245 V reference,

and the noninverting input is available at the SET pin. The NPN

output transistor sinks in excess of 300 µA.

Figure 25 shows the gain block configured as a low battery

monitor. Set Resistors R1 and R2 to high values to reduce

E quiescent current, but not so high that bias current in the SET

input causes large errors. A value of 33 kΩ for R2 is a good

compromise. The value for R1 is then calculated as follows:

T R1

=

VLOBATT − 1.245

1.245 V

V

E R2

where VLOBATT is the desired low battery trip point.

Because the gain block output is an open-collector NPN, a

L pull-up resistor should be connected to the positive logic

power supply.

5V

OBSO [ ] VBATT

R1

R2

33kΩ

ADP3000

1.245V

REF

VIN

AO

SET

GND

RL

47kΩ

TO

PROCESSOR

RHYS

1.6MΩ

R1 = VLB – 1.245V

37.7µA

VLB = BATTERY TRIP POINT

When operating the ADP3000 in step-down mode with the

switch off, the output voltage is impressed across the internal

power switch’s emitter-base junction. When the output voltage

is set to higher than 6 V, a Schottky diode must be placed in a

series with SW2 to protect the switch. Figure 26 shows the

proper way to place D2, the protection diode. The selection of

this diode is identical to the step-down commuting diode (refer

to the Diode Selection section).

VIN

+

C2

R3

D1, D2 = 1N5818 SCHOTTKY DIODES

1

2

3

ILIM VIN SW1

VOUT > 6V

FB 8

ADP3000

SW2 4

GND

D2

5

D1

L1

R2

C1 +

R1

Figure 26. Step-Down Mode VOUT > 6.0 V

THERMAL CONSIDERATIONS

Power dissipation internal to the ADP3000 can be

approximated with the following equations.

Step-Up

[ ] PD

=

⎡

⎢I

SW

2

R

+

⎣

VIN I SW

β

⎤⎡

⎥D⎢1

⎦⎣

−

VIN

VO

⎤

⎥

⎦

⎡

⎢

⎣

4IO

I SW

⎤

⎥+

⎦

IQ

VIN

where:

ISW is ILIMIT when the current limit is programmed externally;

Figure 25. Setting the Low Battery Detector Trip Point

otherwise, ISW is the maximum inductor current.

V0 is the output voltage.

The circuit of Figure 25 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, add

hysteresis to the circuit. Resistor RHYS, with a value of 1 MΩ to

10 MΩ, provides the hysteresis. The addition of RHYS alters the

trip point slightly, changing the new value for R1 to

I0 is the output current.

VIN is the input voltage.

R is 1 Ω (typical RCE(SAT)).

D is 0.75 (typical duty ratio for a single switching cycle).

IQ is 500 µA (typical shutdown quiescent current).

β = 30 (typical forced beta).

Rev. A | Page 11 of 16

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