Datasheet ADP1173 Datasheet (Analog Devices)

Micropower

SET

V

IN

GAIN BLOCK/
ERROR AMP

COMPARATOR

SW2

FBGND

SW1

AO

I

LIM

OSCILLATOR

DRIVER

A1

A2

1.245V

REFERENCE

ADP1173

SET

V

IN

GAIN BLOCK/
ERROR AMP

COMPARATOR

SW2

SENSEGND

SW1

AO
I

LIM

OSCILLATOR

DRIVER

A1

A2

1.245V

REFERENCE

ADP1173-3.3
ADP1173-5
ADP1173-12

R2

753kΩ

R1

ADP1173-3.3: R1 = 456kΩ
ADP1173-5: R1 = 250kΩ
ADP1173-12: R1 = 87.4kΩ

a

FEATURES
Operates From 2.0 V to 30 V Input Voltages
Only 110 mA Supply Current (Typical)
Step-Up or Step-Down Mode Operation
Very Few External Components Required
Low Battery Detector On-Chip
User-Adjustable Current Limit
Internal 1 A Power Switch
Fixed or Adjustable Output Voltage Versions
8-Pin DIP or SO-8 Package

APPLICATIONS
Notebook and Palmtop Computers
Cellular Telephones
Flash Memory V
3 V to 5 V, 5 V to 12 V Converters
9 V to 5 V, 12 V to 5 V Converters
Portable Instruments
LCD Bias Generators

GENERAL DESCRIPTION

The ADP1173 is part of a family of step-up/step-down switching
regulators that operates from an input supply voltage of as little as
2 V to 12 V in step-up mode and to 30 V in step-down mode.

The ADP1173 consumes as little as 110 µA in standby mode,
making it ideal for applications that need low quiescent current.
An auxiliary gain amplifier can serve as a low battery detector,
linear regulator (under voltage lockout) or error amplifier.

The ADP1173 can deliver 80 mA at 5 V from a 3 V input in
step-up configuration or 100 mA at 5 V from a 12 V input in
step-down configuration. For input voltages of less than 2 V use
the ADP1073.

Generators

pp

DC-DC Converter

ADP1173

FUNCTIONAL BLOCK DIAGRAMS

REV. 0

Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.

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Tel: [phone] World Wide Web Site: http://www.analog.com
Fax: [phone] © Analog Devices, Inc., 1997

ADP1173–SPECIFICATIONS

(@ TA = 08C to +708C, VIN = 3 V unless otherwise noted)

Model Symbol Conditions Min Typ Max Units

QUIESCENT CURRENT I

QUIESCENT CURRENT, BOOST MODE I

Q

Q

Switch Off 110 150 µA

No Load, T

= +25°C

A

CONFIGURATION ADP1173-3.3 135 µA

ADP1173-5 135 µA
ADP1173-12 250 µA

INPUT VOLTAGE V

IN

Step-Up Mode 2.0 12.6 V
Step-Down Mode 30 V

COMPARATOR TRIP POINT VOLTAGE ADP1173

OUTPUT SENSE VOLTAGE V

OUT

ADP1173-3.3
ADP1173-5
ADP1173-12

1

2

2

2

1.20 1.245 1.30 V

3.14 3.30 3.46 V

4.75 5.00 5.25 V

11.4 12.0 12.6 V

COMPARATOR HYSTERESIS ADP1173 5 12 mV

OUTPUT HYSTERESIS ADP1173-3.3 13 35 mV

ADP1173-5 20 55 mV
ADP1173-12 50 100 mV

OSCILLATOR FREQUENCY f

OSC

16 24 32 kHz

DUTY CYCLE Full Load 43 55 63 %

SWITCH ON TIME t

ON

FEEDBACK PIN BIAS CURRENT ADP1173, V

SET PIN BIAS CURRENT V

GAIN BLOCK OUTPUT LOW V

OL

REFERENCE LINE REGULATION 2.0 V ≤ V

SW

VOLTAGE, STEP-UP MODE V

SAT

SW

VOLTAGE, STEP-DOWN MODE V

SAT

GAIN BLOCK GAIN A

SAT

SAT

V

CURRENT LIMIT 220 Ω from I

I

Tied to V

LIM

= V

SET

I

= 100 µA, V

SINK

5 V ≤ V

V

= 3.0 V, ISW = 650 mA 0.5 0.85 V

IN

V

= 5.0 V, I

IN

T

= +25°C 0.8 1.0 V

A

V

= 5.0 V, ISW = 1 A 1.4 V

IN

V

= 12 V, T

IN

I

= 650 mA 1.1 1.5 V

SW

V

= 12 V, ISW = 650 mA 1.7 V

IN

R

= 100 kΩ

L

T

= +25°C

A

IN

= 0 V 60 290 nA

FB

REF

= 1.00 V 0.15 0.4 V

SET

≤ 5 V 0.2 0.4 %/V

IN

≤ 30 V 0.02 0.075 %/V

IN

= 1 A,

SW

= +25°C,

A

3

to V

LIM

IN

15 23 32 µs

70 150 nA

400 1000 V/V

400 mA

CURRENT LIMIT TEMPERATURE

COEFFICIENT –0.3 %/°C

SWITCH-OFF LEAKAGE CURRENT Measured at SW1 Pin 1 10 µA

T

= +25°C

A

MAXIMUM EXCURSION BELOW GND V

NOTES

1

This specification guarantees that both the high and low trip points of the comparator fall within the 1.20 V to 1.30 V range.

2

The output voltage waveform will exhibit a sawtooth shape due to the comparator hysteresis. The output voltage on the fixed output versions will always be within
the specified range.

3

100 kΩ resistor connected between a 5 V source and the AO pin.

Specifications subject to change without notice.

SW2

I

≤ 10 µA, Switch Off –400 –350 mV

SW1

T

= +25°C

A

–2–

REV. 0

ADP1173

WARNING!

ESD SENSITIVE DEVICE

AO

I

LIM

SW1

GND

V

IN

SW2

*FIXED VERSIONS

1
2
3
4

8
7
6
5

ADP1173

TOP VIEW

(Not to Scale)

FB (SENSE)*

SET

AO

I

LIM

SW1

GND

V

IN

SW2

*FIXED VERSIONS

1
2
3
4

8
7
6
5

ADP1173

TOP VIEW

(Not to Scale)

FB (SENSE)*

SET

ABSOLUTE MAXIMUM RATINGS*

Supply Voltage (VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 V

SW1 Pin Voltage (V
SW2 Pin Voltage (V

) . . . . . . . . . . . . . . . . . . . . . . . . . 50 V

SW1

) . . . . . . . . . . . . . . . . . . –0.5 V to V

SW2

IN

Feedback Pin Voltage (ADP1173) . . . . . . . . . . . . . . . . . . . 5 V

Sense Pin Voltage (ADP1173, –3.3, –5, –12) . . . . . . . . . 36 V

Maximum Power Dissipation . . . . . . . . . . . . . . . . . . 500 mW

Maximum Switch Current . . . . . . . . . . . . . . . . . . . . . . . .1.5 A

Operating Temperature Range . . . . . . . . . . . . . 0°C to +70°C

Storage Temperature Range . . . . . . . . . . . . . –65°C to 150°C

Lead Temperature, (Soldering, 10 sec) . . . . . . . . . . . .+300°C

*Stresses above those listed under Absolute Maximum Ratings may cause perma-

nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those listed in the operational
sections of this specification is not implied. Exposure to absolute maximum
ratings for extended periods of time may affect device reliability.

ORDERING GUIDE

Output Package

Model Voltage Options*

ADP1173AN ADJ N-8
ADP1173AR ADJ SO-8
ADP1173AN-3.3 3.3 V N-8
ADP1173AR-3.3 3.3 V SO-8
ADP1173AN-5 5 V N-8
ADP1173AR-5 5 V SO-8
ADP1173AN-12 12 V N-8
ADP1173AR-12 12 V SO-8

*N = Plastic DIP, SO = Small Outline Package.

L1*

+

4X NICAD

OR

ALKALINE

CELLS

*L1 = COILTRONICS CTX100-4

470µF

7

56Ω

1

I

LIMVIN

ADP1173

SET

5

100µH

2

3

SW1

6

AO

FB

8

SW2GND

4

+

470µF

IRF7203

470kΩ

240Ω

24kΩ

75kΩ

+5V
OUTPUT
AT 100mA

+

470µF

PIN CONFIGURATIONS

N-8 SO-8

8-Lead Plastic DIP 8-Lead Plastic SO

PIN FUNCTION DESCRIPTIONS

Mnemonic Function

I

LIM

For normal conditions this pin is connected to
V

. When lower current is required, a resistor

IN

should be connected between I

LIM

and V

IN.

Limiting the switch current to 400 mA is
achieved by connecting a 220 Ω resistor.

V

IN

Input Voltage.

SW1 Collector Node of Power Transistor.

For step-down configuration, connect to V

;

IN

for step-up configuration, connect to an
inductor/diode.

SW2 Emitter Node of Power Transistor. For step-

down configuration, connect to inductor/
diode; for step-up configuration, connect to
ground. Do not allow this pin to drop more

than a diode drop below ground.
GND Ground.
AO Auxiliary Gain (GB) Output. The open

collector can sink 100 µA.
SET Gain Amplifier Input. The amplifier has

positive input connected to the SET pin and

negative input is connected to 1.245 V

reference.
FB/SENSE On the ADP1173 (adjustable) version this pin

is connected to the comparator input. On the

ADP1173-3.3, ADP1173-5 and ADP1173-12,

the pin goes directly to the internal application

resistor that sets the output voltage.

Figure 1. Step-Up or Step-Down Converter

CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the ADP1173 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.

REV. 0

–3–

ADP1173

TEMPERATURE – °C

120

110

40

–40 0 8525 70

80

70

60

50

100

90

QUIESCENT CURRENT – µA

QUIESCENT CURRENT

–Typical Performance Characteristics

1.2

1.0

0.8

0.6

(SAT) – V

CE

V

0.4

0.2

0

0.2 1.20.4 0.6 0.8 1.0
SWITCH CURRENT – A

VIN = 3V

VIN = 2V

VIN = 5V

Figure 2. Saturation Voltage vs.
Switch Current in Step-Up Mode

1000

VIN =24V WITH L = 500µH @ V

900
800
700
600
500
400
300

SWITCH CURRENT – mA

VIN =12V WITH L = 250µH @ V

200
100

0

100 1000

R

– Ω

LIM

OUT

OUT

= 5V

= 5V

1.6

1.4

1.2

1.0

0.8

0.6

0.4

SWITCH ON VOLTAGE – V

0.2

0.0

0.15 0.25 0.35 0.45 0.55 0.65

0.05

V

CE(SAT)

SWITCH CURRENT – A

0.75

Figure 3. Switch ON Voltage vs.
Switch Current in Step-Down Mode

100

90
80
70
60
50
40
30

SUPPLY CURRENT – mA

20
10

0

0 100 900

VIN = 5V

VIN = 2V

200 300 400 600 700 800500

SWITCH CURRENT – mA

1100
1000

900
800
700
600
500
400

SWITCH CURRENT – mA

300
200
100

10 100 1000

2V < VIN < 5V

R

– Ω

LIM

Figure 4. Maximum Switch Current
vs. R

in Step-Up Mode

LIM

Figure 5. Maximum Switch Current
vs. R

in Step-Down Mode

LIM

25.5

25

24.5

24

23.5

23

22.5

OSCILLATOR FREQUENCY – kHz

22

21.5

OSCILLATOR FREQUENCY

35 30

10 15

INPUT VOLTAGE – Volts

Figure 8. Oscillator Frequency vs.
Input Voltage

20 25

Figure 6. Supply Current vs.
Switch Current

80

70

60

50

40

30

SET PIN BIAS CURRENT – nA

20

10

–40 0 85

TEMPERATURE – °C

V

= 3V

IN

25 70

Figure 9. Set Pin Bias Current vs.
Temperature

–4–

Figure 7. Quiescent Current vs.
Temperature

450

400

350
300
250

200

150
100

50

FEEDBACK PIN BIAS CURRENT – nA

0

–40 0 85

TEMPERATURE – °C

= 3V

V

IN

25 70

Figure 10. Feedback Pin Bias Current
vs. Temperature

REV. 0

ADP1173

APPLICATIONS
Theory of Operation

The ADP1173 is a flexible, low power 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 very high performance
with low quiescent current.

A functional block diagram of the ADP1173 is shown on the
front page. 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 feedback network connected to
the regulated output. When the voltage at the FB pin falls below

1.245 V, the 24 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 ADP1173 quiescent current is only 110 µA. The com-
parator includes a small amount of hysteresis, which 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

and the I

IN

pin. When the

LIM

maximum current is exceeded, the switch is turned OFF. The
current limit circuitry has a time delay of about 2 µs. If an
external resistor is not used, connect I
information on I

is included in the Limiting the Switch

LIM

to VIN. Further

LIM

Current section of this data sheet.
The ADP1173 internal oscillator provides 23 µs ON and 19 µs

OFF times, which is ideal for applications where the ratio
between V

and V

IN

is roughly a factor of two (such as

OUT

converting +3 V to + 5 V). However, wider range conversions
(such as generating +12 V from a +5 V supply) can easily be
accomplished.

An uncommitted gain block on the ADP1173 can be connected
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

and GND with the junction connected to

IN

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 which can sink 100 µA.

The ADP1173 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 step­up 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

.

IN

The output voltage of the ADP1173 is set with two external
resistors. Three fixed-voltage models are also available:
ADP1173-3.3 (+3.3 V), ADP1173-5 (+5 V) and ADP1173-12
(+12 V). The fixed-voltage models are identical to the ADP1173,
except that laser-trimmed voltage-setting resistors are included
on the chip. On the fixed-voltage models of the ADP1173,
simply connect the feedback pin (Pin 8) directly to the output
voltage.

COMPONENT SELECTION
General Notes on Inductor Selection

When the ADP1173 internal power switch turns on, current
begins to flow in the inductor. Energy is stored in the inductor
core while the switch is on, and this stored energy is then
transferred to the load when the switch turns off. Both the
collector and the emitter of the switch transistor are accessible
on the ADP1173, so the output voltage can be higher, lower or
of opposite polarity than the input voltage.

To specify an inductor for the ADP1173, the proper values of
inductance, saturation current and dc resistance must be
determined. This process is not difficult, and specific equations
for each circuit configuration are provided in this data sheet. In
general terms, however, the inductance value must be low
enough to store the required amount of energy (when both
input voltage and switch ON time are at a minimum) but high
enough that the inductor will not saturate when both V

IN

and
switch ON time are at their maximum values. The inductor
must also store enough energy to supply the load without
saturating. Finally, the dc resistance of the inductor should be
low, so that excessive power will not be wasted by heating the
windings. For most ADP1173 applications, an inductor of
47 µH to 470 µH, with a saturation current rating of 300 mA to
1 A and dc resistance <1 Ω is suitable. Ferrite core inductors
which meet these specifications are available in small, surface­mount packages.

To minimize Electro-Magnetic Interference (EMI), a toroid or
pot core type inductor is recommended. Rod core inductors are
a lower cost alternative if EMI is not a problem.

CALCULATING THE INDUCTOR VALUE

Selecting the proper inductor value is a simple three-step
process:

1. Define the operating parameters: minimum input voltage,

maximum input voltage, output voltage and output current.

2. Select the appropriate conversion topology (step-up, step-

down, or inverting).

3. Calculate the inductor value, using the equations in the

following sections.

Inductor Selection—Step-Up Converter

In a step-up, or boost, converter (Figure 14), the inductor must
store enough power to make up the difference between the
input voltage and the output voltage. The power that must be
stored is calculated from the equation:

P

where V

= V

()

L

OUT+VD–VIN(MIN )

is the diode forward voltage (≈ 0.5 V for a 1N5818

D

×I

()

OUT

(1)

Schottky). Energy is only stored in the inductor while the
ADP1173 switch is ON, so the energy stored in the inductor on
each switching cycle must be must be equal to or greater than:

P

L

f

OSC

(2)

in order for the ADP1173 to regulate the output voltage.

REV. 0

–5–

ADP1173

When the internal power switch turns ON, current flow in the
inductor increases at the rate of:

IL(t)=



V

IN



R′



1–e



L





(3)

–R′t

where L is in henrys and R' is the sum of the switch equivalent
resistance (typically 0.8 Ω at +25°C) and the dc resistance of
the inductor. In most applications, where the voltage drop across
the switch is small compared to V

, a simpler equation can be

IN

used:

V

IL(t)=

IN

t

L

(4)

Replacing “t” in the above equation with the ON time of the
ADP1173 (23 µs, typical) will define the peak current for a
given inductor value and input voltage. At this point, the
inductor energy can be calculated as follows:

1

EL=

As previously mentioned, E

2

LI

PEAK

2

must be greater than PL/f

L

OSC

(5)

so the
ADP1173 can deliver the necessary power to the load. For best
efficiency, peak current should be limited to 1 A or less. Higher
switch currents will reduce efficiency, because of increased
saturation voltage in the switch. High peak current also increases
output ripple. As a general rule, keep peak current as low as pos­sible to minimize losses in the switch, inductor and diode.

In practice, the inductor value is easily selected using the equa­tions above. For example, consider a supply that will generate
9 V at 50 mA from a 3 V source. The inductor power required
is, from Equation 1:

PL=(9V +0.5V –3V)×(50 mA)=325mW

On each switching cycle, the inductor must supply:

P

325 mW

L

=

f

24 kHz

OSC

=13.5µJ

The required inductor power is fairly low in this example, so the
peak current can also be low. Assuming a peak current of 500 mA
as a starting point, Equation 4 can be rearranged to recommend
an inductor value:

L =

V

I

L(MAX )

IN

t =

500 mA

3V

23 µs =138 µH

Substituting a standard inductor value of 100 µH, with 0.2 Ω dc
resistance, will produce a peak switch current of:

–1.0Ω×23 µs

I

PEAK

=

3V

1. 0 Ω



1–e




100 µH



=616 mA




Once the peak current is known, the inductor energy can be
calculated from Equation 5:

1

EL=

(100 µH )×(616 mA)2=19 µJ

2

The inductor energy of 19 µJ is greater than the P

L/fOSC

re-

quirement of 13.5 µJ, so the 100 µH inductor will work in this
application. By substituting other inductor values into the same
equations, the optimum inductor value can be selected.

When selecting an inductor, the peak current must not exceed
the maximum switch current of 1.5 A. If the equations shown
above result in peak currents > 1.5 A, the ADP1073 should be
considered. This device has a 72% duty cycle, so more energy is
stored in the inductor on each cycle. This results in greater
output power.

The peak current must be evaluated for both minimum and
maximum values of input voltage. If the switch current is high
when V
ceeded at the maximum value of V

is at its minimum, then the 1.5 A limit may be ex-

IN

. In this case, the ADP1173’s

IN

current limit feature can be used to limit switch current. Simply
select a resistor (using Figure 4) that will limit the maximum
switch current to the I
value of V
stant I

. This will improve efficiency by producing a con-

IN

as VIN increases. See the Limiting the Switch Current

PEAK

value calculated for the minimum

PEAK

section of this data sheet for more information.
Note that the switch current limit feature does not protect the

circuit if the output is shorted to ground. In this case, current is
only limited by the dc resistance of the inductor and the forward
voltage of the diode.

Inductor Selection—Step-Down Converter

The step-down mode of operation is shown in Figure 15. Unlike
the step-up mode, the ADP1173’s power switch does not
saturate when operating in the step-down mode. Therefore,
switch current should be limited to 650 mA in this mode. If the
input voltage will vary over a wide range, the I

pin can be

LIM

used to limit the maximum switch current. If higher output
current is required, the ADP1111 should be considered.

The first step in selecting the step-down inductor is to calculate
the peak switch current as follows:

I

PEAK



OUT



VIN–VSW+V



V

OUT+VD

2I

=

DC






D

(6)

where DC = duty cycle (0.55 for the ADP1173)

V

= voltage drop across the switch

SW

V

= diode drop (0.5 V for a 1N5818)

D

I

= output current

OUT

V

= the output voltage

OUT

V

= the minimum input voltage

IN

As previously mentioned, the switch voltage is higher in step­down mode than step-up mode. V
current and is therefore a function of V
For most applications, a V

value of 1.5 V is recommended.

SW

is a function of switch

SW

, L, time and V

IN

OUT

.

The inductor value can now be calculated:

V

IN(MIN )–VSW–VOUT

where t

L =

ON

I

PEAK

= switch ON time (23 µs)

×t

ON

(7)

If the input voltage will vary (such as an application that must
operate from a 12 V to 24 V source) an R
selected from Figure 5. The R

resistor will keep switch cur-

LIM

resistor should be

LIM

rent constant as the input voltage rises. Note that there are separate
R

values for step-up and step-down modes of operation.

LIM

–6–

REV. 0

ADP1173

For example, assume that +5 V at 300 mA is required from a
12 V to +24 V input. Deriving the peak current from Equation 6
yields:

I

PEAK

2×300 mA

=

0.55



5 +0.5



12 –1.5+0.5





=545mA





The peak current can then be inserted into Equation 7 to calcu­late the inductor value:

12 –1.5– 5

L =

545 mA

×23 µs =232 µH

Since 232 µH is not a standard value, the next lower standard
value of 220 µH would be specified.

To avoid exceeding the maximum switch current when the
input voltage is at +24 V, an R

resistor should be specified.

LIM

Using the step-down curve of Figure 5, a value of 180 Ω will
limit the switch current to 600 mA.

Inductor Selection—Positive-to-Negative Converter

The configuration for a positive-to-negative converter using the
ADP1173 is shown in Figure 17. As with the step-up converter,
all of the output power for the inverting circuit must be supplied
by the inductor. The required inductor power is derived from
the formula:

PL= |V

|+V

()

OUT

×I

()

D

OUT

(8)

The ADP1173 power switch does not saturate in positive-to­negative mode. The voltage drop across the switch can be
modeled as a 0.75 V base-emitter diode in series with a 0.65 Ω
resistor. When the switch turns on, inductor current will rise at
a rate determined by:

_R't






1–e

L






L(DC)

(9)

V

IL(t)=

L

R'

where R' = 0.65 Ω + R

where VL = VIN – 0.75 V

For example, assume that a –5 V output at 50 mA is to be
generated from a +4.5 V to +5.5 V source. The power in the
inductor is calculated from Equation 8:

PL= |−5V|+0.5V

()

×(50 mA)= 275 mW

During each switching cycle, the inductor must supply the
following energy:

P

275 mW

L

=

f

24 kHz

OSC

=11.5µJ

Using a standard inductor value of 220 µH, with 0.2 Ω dc
resistance, will produce a peak switch current of:

–0.85 Ω×23 µs

I

PEAK

4.5V –0.75V

=

0.65 Ω+0.2 Ω



1–e




220 µH



=375mA




Once the peak current is known, the inductor energy can be
calculated from Equation 5:

1

EL=

(220 µH) ×(375 mA)2=15.5µJ

2

The inductor energy of 15.5 µJ is greater than the P

L/fOSC

requirement of 11.5 µJ, so the 220 µH inductor will work in
this application.

The input voltage only varies between 4.5 V and 5.5 V in this
example. Therefore, the peak current will not change enough to
require an R
directly to V

resistor and the I

LIM

. Care should be taken to ensure that the peak

IN

pin can be connected

LIM

current does not exceed 650 mA.

CAPACITOR SELECTION

For optimum performance, the ADP1173’s output capacitor
must be carefully selected. Choosing an inappropriate capacitor
can result in low efficiency and/or high output ripple.

Ordinary aluminum electrolytic capacitors are inexpensive, but
often have poor Equivalent Series Resistance (ESR) and
Equivalent Series Inductance (ESL). Low ESR aluminum ca­pacitors, specifically designed for switch mode converter appli­cations, are also available, and these are a better choice than
general purpose devices. Even better performance can be
achieved with tantalum capacitors, although their cost is higher.
Very low values of ESR can be achieved by using OS-CON*
capacitors (Sanyo Corporation, San Diego, CA). These devices
are fairly small, available with tape-and-reel packaging, and have
very low ESR.

The effects of capacitor selection on output ripple are demon­strated in Figures 11, 12, and 13. These figures show the output
of the same ADP1173 converter, which was evaluated with
three different output capacitors. In each case, the peak switch
current is 500 mA and the capacitor value is 100 µF. Figure 11
shows a Panasonic HF-series* radial aluminum electrolytic.
When the switch turns off, the output voltage jumps by about
90 mV and then decays as the inductor discharges into the
capacitor. The rise in voltage indicates an ESR of about

0.18 Ω. In Figure 12, the aluminum electrolytic has been
replaced by a Sprague 593D-series* tantalum device. In this
case the output jumps about 35 mV, which indicates an ESR of

0.07 Ω. Figure 13 shows an OS-CON SA series capacitor in the
same circuit, and ESR is only 0.02 Ω.

REV. 0

*All trademarks are properties of their respective holders.

–7–

ADP1173

Figure 11. Aluminum Electrolytic

Figure 12. Tantalum Electrolytic

DIODE SELECTION

In specifying a diode, consideration must be given to speed,
forward voltage drop and reverse leakage current. When the
ADP1173 switch turns off, the diode must turn on rapidly if
high efficiency is to be maintained. Schottky rectifiers, as well as
fast signal diodes such as the 1N4148, are appropriate. The
forward voltage of the diode represents power that is not deliv­ered to the load, so V

must also be minimized. Again, Schottky

F

diodes are recommended. Leakage current is especially impor­tant in low current applications, where the leakage can be a
significant percentage of the total quiescent current.

For most circuits, the 1N5818 is a suitable companion to the
ADP1173. This diode has a V

of 0.5 V at 1 A, 4 µA to 10 µA

F

leakage, and fast turn-on and turn-off times. A surface mount
version, the MBRS130T3, is also available. For applications
where the ADP1173 is “off” most of the time, such as when the
load is intermittent, a silicon diode may provide higher overall
efficiency due to lower leakage. For example, the 1N4933 has a
1 A capability, but with a leakage current of less than 1 µA. The
higher forward voltage of the 1N4933 reduces efficiency when
the ADP1173 delivers power, but the lower leakage may outweigh
the reduction in efficiency.

For switch currents of 100 mA or less, a Schottky diode such as
the BAT85 provides a V

of 0.8 V at 100 mA and leakage less

F

than 1 µA. A similar device, the BAT54, is available in a SOT23
package. Even lower leakage, in the 1 nA to 5 nA range, can be
obtained with a 1N4148 signal diode.

General purpose rectifiers, such as the 1N4001, are not suitable
for ADP1173 circuits. These devices, which have turn-on times
of 10 µs or more, are too slow for switching power supply
applications. Using such a diode “just to get started” will result
in wasted time and effort. Even if an ADP1173 circuit appears
to function with a 1N4001, the resulting performance will not
be indicative of the circuit performance when the correct diode
is used.

Figure 13. OS-CON Capacitor

If low output ripple is important, the user should consider the
ADP3000. This device switches at 400 kHz, and the higher
switching frequency simplifies the design of the output filter.
Consult the ADP3000 data sheet for additional details.

All potential current paths must be considered when analyzing
very low power applications, and this includes capacitor leakage
current. OS-CON capacitors have leakage in the 5 µA to 10 µA
range, which will reduce efficiency when the load is also in the
microampere range. Tantalum capacitors, with typical leakage
in the 1 µA to 5 µA range, are recommended for very low power
applications.

–8–

CIRCUIT OPERATION, STEP-UP (BOOST) MODE

In boost mode, the ADP1173 produces an output voltage that
is higher than the input voltage. For example, +12 V can be
generated from a +5 V logic power supply or +5 V can be
derived from two alkaline cells (+3 V).

Figure 16 shows an ADP1173 configured for step-up operation.
The collector of the internal power switch is connected to the
output side of the inductor, while the emitter is connected to
GND. When the switch turns on, pin SW1 is pulled near ground.
This action forces a voltage across L1 equal to V

IN–VCE(SAT),

and current begins to flow through L1. This current reaches a
final value (ignoring second-order effects) of:

V

I

PEAK

IN–VCE(SAT )

≅

L

×23 µs

where 23 µs is the ADP1173 switch’s “on” time.

REV. 0

ADP1173

V

IN

I

* = OPTIONAL

R3*

2

1

LIMVIN

ADP1173

SW2GND

5

4

L1 D1

3

SW1

FB

8

R1

R2

V

OUT

+

C1

Figure 14. Step-Up Mode Operation

When the switch turns off, the magnetic field collapses. The
polarity across the inductor changes, current begins to flow
through D1 into the load and the output voltage is driven above
the input voltage.

The output voltage is fed back to the ADP1173 via resistors R1
and R2. When the voltage at pin FB falls below 1.245 V, SW1
turns “on” again and the cycle repeats. The output voltage is
therefore set by the formula:





V

=1.245 V × 1+

OUT

R1





R2





The circuit of Figure 14 shows a direct current path from VIN to
V

, via the inductor and D1. Therefore, the boost converter

OUT

is not protected if the output is short circuited to ground.

When the switch turns off, the magnetic field collapses. The
polarity across the inductor changes and the switch side of the
inductor is driven below ground. Schottky diode D1 then turns
on and current flows into the load. Notice that the Absolute
Maximum Rating for the ADP1173’s SW2 pin is 0.5 V below
ground. To avoid exceeding this limit, D1 must be a Schottky
diode. Using a silicon diode in this application will generate
forward voltages above 0.5 V, which will cause potentially
damaging power dissipation within the ADP1173.

The output voltage of the buck regulator is fed back to the
ADP1173’s FB pin by resistors R1 and R2. When the voltage at
pin FB falls below 1.245 V, the internal power switch turns
“on” again and the cycle repeats. The output voltage is set by
the formula:





V

OUT

=1.245 V × 1+

R1





R2





When operating the ADP1173 in step-down mode, the output
voltage is impressed across the internal power switch’s emitter­base junction when the switch is off. To protect the switch, the
output voltage should be limited to 6.2 V or less. If a higher
output voltage is required, a Schottky diode should be placed in
series with SW2, as shown in Figure 16.

If high output current is required in a step-down converter, the
ADP1111 or ADP3000 should be considered. These devices
offer higher frequency operation, which reduces inductor size,
and an external pass transistor can be added to reduce R

ON

of

the switch.

CIRCUIT OPERATION, STEP-DOWN (BUCK) MODE

The ADP1173’s step-down mode is used to produce an output
voltage lower than the input voltage. For example, the output of
four NiCd cells (+4.8 V) can be converted to a +3.3 V logic
supply.

A typical configuration for step-down operation of the ADP1173
is shown in Figure 15. In this case, the collector of the internal
power switch is connected to V

and the emitter drives the

IN

inductor. When the switch turns on, SW2 is pulled up toward
V

. This forces a voltage across L1 equal to (VIN–VCE) – V

IN

OUT

,
and causes current to flow in L1. This current reaches a final
value of:

V

I

PEAK

IN–VCE–VOUT

≅

L

×23 µs

where 23 µs is the ADP1173 switch’s “on” time.

V

IN

R3

100Ω

+

C2

1

I

LIMVIN

ADP1173

2

GND

3

SW1

8

FB

SW2

5

L1

4

+

D1
1N5818

C1

V

OUT

R1

R2

Figure 15. Step-Down Mode Operation

V

IN

R

LIM

100Ω

+

C2

1

I

LIMVIN

ADP1173

2

GND

3

SW1

8

FB

1N5818

SW2

4

5

L1

D1
1N5818

Figure 16. Step-Down Mode, V

+

OUT

C1

> 6.2 V

V

OUT

R1

R2

If the input voltage to the ADP1173 varies over a wide range, a
current limiting resistor at Pin 1 may be required. If a particular
circuit requires high peak inductor current with minimum input
supply voltage, the peak current may exceed the switch maxi­mum rating and/or saturate the inductor when the supply
voltage is at the maximum value. See the Limiting the Switch
Current section of this data sheet for specific recommendations.

POSITIVE-TO-NEGATIVE CONVERSION

The ADP1173 can convert a positive input voltage to a negative
output voltage, as shown in Figure 17. This circuit is essentially
identical to the step-down application of Figure 15, except that
the “output” side of the inductor is connected to power ground.
When the ADP1173’s internal power switch turns off, current
flowing in the inductor forces the output (–V

) to a negative

OUT

potential. The ADP1173 will continue to turn the switch on

REV. 0

–9–

ADP1173

until its FB pin is 1.245 V above its GND pin, so the output
voltage is determined by the formula:





+V

IN

C2

–V

OUT

+

=1.245 V × 1+

R3

2

1

I

LIMVIN

ADP1173

GND

5

SW1

R1





R2





3

8

FB

SW2

L1

4

D1
1N5818

+

R1

C1

R2

–V

OUT

Figure 17. A Positive-to-Negative Converter

The design criteria for the step-down application also apply to
the positive-to-negative converter. The output voltage should be
limited to |6.2 V|, unless a diode is inserted in series with the
SW2 Pin (see Figure 16). Also, D1 must again be a Schottky
diode to prevent excessive power dissipation in the ADP1173.

NEGATIVE-TO-POSITIVE CONVERSION

The circuit of Figure 18 converts a negative input voltage to a
positive output voltage. Operation of this circuit configuration is
similar to the step-up topology of Figure 14, except that the current
through feedback resistor R1 is level-shifted below ground by a
PNP transistor. The voltage across R1 is (V

OUT–VBEQ1

). How­ever, diode D2 level-shifts the base of Q1 about 0.6 V below
ground, thereby cancelling the V

of Q1. The addition of D2

BE

also reduces the circuit’s output voltage sensitivity to tempera­ture, which otherwise would be dominated by the –2 mV/°C V

BE

contribution of Q1. The output voltage for this circuit is deter­mined by the formula:





V

OUT

=1.245 V ×

R1









R2

Unlike the positive step-up converter, the negative-to-positive
converter’s output voltage can be either higher or lower than the
input voltage.

LIMITING THE SWITCH CURRENT

The ADP1173’s R

pin permits the switch current to be lim-

LIM

ited with a single resistor. This current limiting action occurs on
a pulse by pulse basis. This feature allows the input voltage to
vary over a wide range, without saturating the inductor or ex­ceeding the maximum switch rating. For example, a particular
design may require peak switch current of 800 mA with a 2.0 V
input. If V

rises to 4 V, however, the switch current will exceed

IN

1.6 A. The ADP1173 limits switch current to 1.5 A and thereby
protects the switch, but increases the output ripple. Selecting
the proper resistor will limit the switch current to 800 mA, even
if V

increases. The relationship between R

IN

and maximum

LIM

switch current is shown in Figures 4 and 5.
The I

feature is also valuable for controlling inductor current

LIM

when the ADP1173 goes into continuous-conduction mode. This
occurs in the step-up mode when the following condition is met:

V

OUT+VDIODE

VIN–V

SW

<

1– DC

1

where DC is the ADP1173’s duty cycle. When this relationship
exists, the inductor current does not go all the way to zero dur­ing the time the switch is OFF. When the switch turns on for
the next cycle, the inductor current begins to ramp up from the
residual level. If the switch ON time remains constant, the in­ductor current will increase to a high level (see Figure 19). This
increases output ripple, and can require a larger inductor and
capacitor. By controlling switch current with the I

resistor,

LIM

output ripple current can be maintained at the design values.
Figure 20 illustrates the action of the I

LIM

circuit.

1N5818

L1

D1

R

NEGATIVE

INPUT

LIM

2

1

+

I

C2

LIMVIN

ADP1173

SET

AO

6

7

NC NC

SW1

FB

SW2GND

4

5

R1

Q1

2N3906

3

8

R2

Figure 18. A Negative-to-Positive Converter

1N4148

D2

10kΩ

POSITIVE
OUTPUT

+

C

L

Figure 19. (I

Figure 20. (I

–10–

Operation, R

LIM

Operation, R

LIM

= 0 Ω)

LIM

= 240 Ω)

LIM

REV. 0

ADP1173

2

V

IN

+5V

GND

ADP1173

R1

AO

SET

5

R2

100kΩ

TO
PROCESSOR

6

1.245V
REF

7

V

BAT

VLB –1.245V

12.5µA

VLB = BATTERY TRIP POINT
R2 = 100kΩ

R1 =

2

V

IN

5V

GND

ADP1173

R1

AO

SET

5

R2

47kΩ

TO
PROCESSOR

6

1.245mV

REF

7

V

BAT

R3

1.6MΩ

The internal structure of the I

circuit is shown in Figure 21.

LIM

Q1 is the ADP1173’s internal power switch, which is paralleled
by sense transistor Q2. The relative sizes of Q1 and Q2 are
scaled so that I
internal 80 Ω resistor and through the R

is 0.5% of IQ1. Current flows to Q2 through an

Q2

resistor. These two

LIM

resistors parallel the base-emitter junction of the oscillator­disable transistor, Q3. When the voltage across R1 and R

LIM

exceeds 0.6 V, Q3 turns on and terminates the output pulse. If
only the 80 Ω internal resistor is used (i.e., the I
nected directly to V

1.5 A. Figures 4 and 5 gives R

), the maximum switch current will be

IN

values for lower current-limit

LIM

pin is con-

LIM

values.

I

DRIVER

LIM

R1

80Ω
(INTERNAL)

Q2

SW1

Q1

SW2

V

IN

Q3

OSCILLATOR

R

LIM

(EXTERNAL)

Figure 21. Current Limit Operation

The delay through the current limiting circuit is approximately
2 µs. If the switch ON time is reduced to less than 4 µs, accu-
racy of the current trip-point is reduced. Attempting to program
a switch ON time of 2 µs or less will produce spurious responses
in the switch ON time. However, the ADP1173 will still provide
a properly regulated output voltage.

Figure 22. Setting the Low Battery Detector Trip Point

Figure 22 shows the gain block configured as a low battery
monitor. Resistors R1 and R2 should be set to high values to
reduce quiescent current, but not so high that bias current in the
SET input causes large errors. A value of 100 kΩ for R2 is a
good compromise. The value for R1 is then calculated from the
formula:

LOBATT

1.245 V

−1.245 V

R2

where V

V

R1=

is the desired low battery trip point. Since the

LOBATT

gain block output is an open-collector NPN, a pull-up resistor
should be connected to the positive logic power supply.

PROGRAMMING THE GAIN BLOCK

The gain block of the ADP1173 can be used as a low-battery
detector, error amplifier or linear post regulator. The gain block
consists of an op amp with PNP inputs and an open-collector
NPN output. The inverting input is internally connected to the

Figure 23. Adding Hysteresis to the Low Battery Detector

ADP1173’s 1.245 V reference, while the noninverting input is
available at the SET pin. The NPN output transistor will sink
about 100 µA.

REV. 0

–11–

ADP1173
Typical Circuit Applications

L1*

68µH

R1

100Ω

2

1

I

2 x 1.5V

CELLS

*L1 = GOWANDA GA10-682K
COILTRONICS CTX68-4
FOR 5V INPUT CHANGE R1 TO 47Ω
CONVERTER WILL DELIVER –22V AT 40mA

LIMVIN

ADP1173

SW2GND

4

5

SW1

FB

1N5818

Figure 24. 3 V–22 V LCD Bias Generator

2

1

I

2 x 1.5V

CELLS

LIMVIN

ADP1173-5

SW2GND

4

5

3

8

L1*

82µH

SW1

SENSE

1N4148

4.7µF

3

8

2.21MΩ

1N5818

+

1%

1N5818

100µF

0.1µF

118kΩ
1%

220kΩ22µF

5V OUTPUT
150mA AT 3V INPUT
60mA AT 2V INPUT

–22V OUTPUT
7mA AT 2.0V INPUT
70% EFFICIENCY

BATTERY

100Ω

2

1

I

9V

LIMVIN

ADP1173-5

SW2GND

5

*L1 = GOWANDA GA10-472K
COILTRONICS CTX50-1
FOR HIGHER OUTPUT CURRENTS SEE ADP1073 DATASHEET

SENSE

4

SW1

1N5818

3

8

L1*

47µH

100µF

+

5V OUTPUT
150mA AT 9V INPUT
50mA AT 6.5V INPUT

Figure 27. 9 V to 5 V Converter

+V

IN

12V-28V

100Ω

2

1

I

LIMVIN

ADP1173-5

SW2GND

4

5

SW1

SENSE

1N5818

3

8

L1*

220µH

100µF

+

5V OUTPUT
300mA

*L1 = GOWANDA GA10-822K

Figure 25. 3 V to 5 V Step-Up Converter

+V

IN

5V INPUT

+

22µF

100Ω

2

1

I

LIMVIN

SW1

3

ADP1173-5

8

SENSE

GND

SW2

4

5

1N5818

*L1 = GOWANDA GA10-103K
COILTRONICS CTX100-1

L1*

100µH

Figure 26. +5 V to –5 V Converter

*L1 = GOWANDA GA10-223K

Figure 28. +20 V to 5 V Step-Down Converter

+

100µF

–5V OUTPUT
75mA

–12–

REV. 0

ADP1173

48V DC

*L1 = CTX110077
I

4 x NICAD

ALKALINE

CELLS

44mH

44mH

= 120µA

Q

OR

~

~

470µF

L1*

100Ω

1

LIMVIN

ADP1173

SW2GND

5

500µH

1N4148

2

SW1

FB

4

+

+

47µF
100V

–

1N965B

10nF

3.6MΩ

10kΩ

15V

VN2222L

+

10µF
16V

12V

I

MUR110

+

220µF
10V

IRF530

3

8

390kΩ

2N5400

110kΩ

+5V
100mA

Figure 29. Telecom Supply

L1*

100µH 1N5818

56Ω

+

7

SET

2

1

I

LIMVIN

ADP1173

SW2GND

4

5

SW1

AO

3

6

FB

8

+

470µF

470kΩ

SI9405DY

240Ω

75k

V

= 5V AT 100mA

OUT

= 2.6V

AT V

IN

+

470µF

24kΩ

*L1 = GOWANDA GA20-103K
COILTRONICS CTX100-4
V

= 2.6V TO 7.2V

IN

Figure 30. 5 V to 5 V Step-Up or Step-Down Converter

470µF

+

2 x NICAD

47kΩ

100kΩ

2N3906

2.2MΩ

100kΩ

*L1 = COILTRONICS CTX-20-5-52

†

1% METAL FILM

100kΩ

6

7

1

I

LIMVIN

AO

ADP1173

SET

5

SW2GND

2

4

20µH, 5A

SW1

FB

L1*

3

8

100kΩ

220Ω

100Ω

†

301kΩ

2N4403

†

47Ω

1N5820

5Ω

MJE200

Figure 31. 2 V to 5 V at 200 mA Step-Up Converter with Undervoltage Lockout

+

+5V OUTPUT
200mA
LOCKOUT AT

1.85V INPUT

470µF

REV. 0

–13–

ADP1173

L1*

51Ω

39kΩ

≤ 150µA

Q

25µH, 2A

1N5820

V

7V-24V

IN

0.22Ω

1

I

LIMVIN

ADP1173

GND

5

SW2

4

2

1N5818

SW1

FB

MTM20P08

18V

2kΩ

1W

3

100Ω
1/2W

8

V

IN

1N4148

2N3904

200kΩ

OP196

*L1 = GOWANDA GT10-100
EFFICIENCY ≥ 80% FOR 10mA ≤ I
STANDBY I

Figure 32. Voltage Controlled Positive-to-Negative Converter

L1*

V

7V-24V

0.22Ω

IN

1N5818

2

1

I

LIMVIN

SW1

ADP1173

SW2GND

4

5

18V

2kΩ

1W

3

100Ω
1/2W

FB

8

1N4148

MTM20P08

2N3904

40.2kΩ

25µH, 2A

1N5820

51Ω

121kΩ

+

470µF

= –5.13*V

–V

+

LOAD

470µF

OUT

VC (0V TO +5V)

≤ 500mA

5V
500mA

C

*L1 = GOWANDA GT10-100

OPERATE STANDBY

EFFICIENCY ≥ 80% FOR 10mA ≤ I
STANDBY I

≤ 150µA

Q

LOAD

≤ 500mA

Figure 33. High Power, Low Quiescent Current Step-Down Converter

–14–

REV. 0

0.210 (5.33)
MAX

0.160 (4.06)

0.115 (2.93)

0.022 (0.558)

0.014 (0.356)

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

8-Lead Plastic DIP

(N-8)

0.430 (10.92)

0.348 (8.84)

8

14

PIN 1

0.100
(2.54)

BSC

5

0.280 (7.11)

0.240 (6.10)

0.060 (1.52)

0.015 (0.38)

0.070 (1.77)

0.045 (1.15)

0.130
(3.30)
MIN

SEATING
PLANE

0.325 (8.25)

0.300 (7.62)

0.015 (0.381)

0.008 (0.204)

8-Lead Small Outline Package

(SO-8)

0.1968 (5.00)

0.1890 (4.80)

ADP1173

0.195 (4.95)

0.115 (2.93)

0.1574 (4.00)

0.1497 (3.80)

PIN 1

0.0098 (0.25)

0.0040 (0.10)

SEATING

PLANE

8

0.0500
(1.27)

BSC

5

0.2440 (6.20)

41

0.2284 (5.80)

0.0688 (1.75)

0.0532 (1.35)

0.0192 (0.49)

0.0138 (0.35)

0.0098 (0.25)

0.0075 (0.19)

0.0196 (0.50)

0.0099 (0.25)

8°
0°

0.0500 (1.27)

0.0160 (0.41)

x 45°

REV. 0

–15–

C2965–12–1/97

–16–

PRINTED IN U.S.A.