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ADP1110AR-ADP1110AR-12-ADP1110AR-5
Micropower, Step-Up/Step-Down Switching Regulator; Adjustable and Fixed 3.3 V, 5 V, 12 V
REV.0
Micropower, Step-Up/Step-Down Switching
Regulator; Adjustable and Fixed 3.3 V, 5 V, 12 V
FUNCTIONAL BLOCK DIAGRAMS
SENSE
ILIM
SW1
SW2
VIN
SET
GNDADP1110 Block Diagram—Fixed Output Version
ILIM
SW1
SW2
VIN
GND
SETADP1110 Block Diagram—Adjustable Output Version
FEATURES
Operates at Supply Voltages From 1.0V to 30V
Step-Up or Step-Down Mode
Minimal External Components Required
Low-Battery Detector
User-Adjustable Current Limiting
Fixed or Adjustable Output Voltage Versions
8-Pin DIP or SO-8 Package
APPLICATIONS
Cellular Telephones
Single-Cell to 5V Converters
Laptop and Palmtop Computers
Pagers
Cameras
Battery Backup Supplies
Portable Instruments
Laser Diode Drivers
Hand-Held Inventory Computers
GENERAL DESCRIPTIONThe ADP1110 is part of a family of step-up/step-down switch-
ing regulators that operate from an input voltage supply as little
as 1.0V. This very low input voltage allows the ADP1110 to be
used in applications that use a single cell as the primary power
source.
The ADP1110 can be configured to operate in either step-up or
step-down mode, but for input voltages greater than 3V, the
ADP1111 would be a more effective solution.
An auxiliary gain amplifier can serve as a low battery detector or
as a linear regulator.
The quiescent current of 300 μA makes the ADP1110 useful in
remote or battery powered applications.
The 70kHz frequency operation also allows for the use of
surface-mount external capacitors and inductors.
Battery protection circuitry limits the effect of reverse current to
safe levels at reverse voltages up to 1.6V.
ADP1110–SPECIFICATIONSNOTESThis specification guarantees that both the high and low trip point of the comparator fall within the 210 mV to 230 mV range.This specification guarantees that the output voltage of the fixed versions will always fall within the specified range. The waveform at the sense pin will exhibit a saw-
tooth shape due to the comparator hysteresis.100 kΩ resistor connected between a 5 V source and the AO pin.The ADP1110 is guaranteed to withstand continuous application of +1.6 V applied to the GND and SW2 pins while VIN, ILIM, and SW1 pins are grounded.All limits at temperature extremes are guaranteed via correlation using standard statistical quality control methods.
Specifications subject to change without notice.
(08C to +708C, VIN = 1.5 V unless otherwise noted)
PIN DESCRIPTION
ABSOLUTE MAXIMUM RATINGSInput Supply Voltage, Step-Up Mode . . . . . . . . . . . . . . . 15 V
Input Supply Voltage, Step-Down Mode . . . . . . . . . . . . . 36 V
SW1 Pin Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 V
SW2 Pin Voltage . . . . . . . . . . . . . . . . . . . . . . . . . –0.5 V to VIN
Feedback Pin Voltage (ADP1110) . . . . . . . . . . . . . . . . . . 5.5 V
Switch Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 A
Maximum Power Dissipation . . . . . . . . . . . . . . . . . . 500 mW
Operating Temperature Range . . . . . . . . . . . . . 0°C to +70°C
Storage Temperature Range . . . . . . . . . . . . . –65°C to 150°C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . 300°C
TYPICAL APPLICATION
47µH
15µF
TANTALUM
OPERATES WITH CELL VOLTAGE ≥1.0V
*ADD 10µF DECOUPLING CAPACITOR IF BATTERY IS
*MORE THAN 2' AWAY FROM ADP1110.Figure 1.1.5 V to 5 V Converter
ORDERING GUIDE
CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the ADP1110 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.
8-Lead SOIC
(SO-8)
ILIM
SW1
GND
VIN
SW2
FB (SENSE)*
SET
*FIXED VERSIONS
TJMAX = 90o, θJA = 150oC/W
8-Lead Plastic DIP
(N-8)
PIN CONFIGURATIONS
ADP1110-Typical Characteristics
ISWITCH CURRENT – A
SATURATION VOLTAGE – VFigure 2.Saturation Voltage vs. ISWITCH Current in Step-Up
Mode
ISWITCH CURRENT – A
ON VOLTAGE – VFigure 3.Switch ON Voltage vs. ISWITCH Current In Step-
Down Mode
INPUT VOLTAGE – V
QUIESCENT CURRENT – µAFigure 4.Quiescent Current vs. Input Voltage
INPUT VOLTAGE – V
OSCILLATOR FREQUENCY – kHzFigure 5.Oscillator Frequency vs. Input Voltage
Figure 6.Maximum Switch Current vs. RLIM
Figure 7.Maximum Switch Current vs. RLIM
TEMPERATURE – 8C07025
OSCILLATOR FREQUENCY – kHzFigure 8.Oscillator Frequency vs. Temperature
TEMPERATURE – 8C
ON TIME – µs
8.7Figure 9.Switch ON Time vs. Temperature
TEMPERATURE – 8C07025
DUTY CYCLE – %Figure 10.Duty Cycle vs. Temperature
TEMPERATURE – 8C
CE(SAT)
– VFigure 11.Switch ON Voltage Step-Down vs. Temperature
TEMPERATURE – 8C
QUIESCENT CURRENT – µAFigure 12.Quiescent Current vs. Temperature
Figure 13.FB Pin Bias Current vs. Temperature
ADP1110
THEORY OF OPERATIONThe ADP1110 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 ADP1110 is shown on the
first page. The internal 220 mV 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
220mV, the 70 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
220 mV, the oscillator is shut off. While the oscillator is off, the
ADP1110 quiescent current is only 300 μA. The comparator
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 VIN and the ILIM pin. When the
maximum current is exceeded, the switch is turned OFF. The
current limit circuitry has a time delay of about 800 ns. If an
external resistor is not used, connect ILIM to VIN. Further informa-
tion on ILIM is included in the “Applications” section of this data
sheet.
The ADP1110 internal oscillator provides 10 μs ON and 5 μs
OFF times, which is ideal for applications where the ratio between
VIN and VOUT is roughly a factor of three (such as generating +5 V
from a single 1.5 V cell). Wider range conversions, as well as
step-down converters, can also be accomplished with a slight
loss in the maximum output power that can be obtained.
An uncommitted gain block on the ADP1110 can be connected
as a low–battery detector. The inverting input of the gain block
is internally connected to the 220mV reference. The noninverting
input is available at the SET pin. A resistor divider, connected
between VIN and GND with the junction 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
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 VIN.
The output voltage of the ADP1110 is set with two external
resistors. Three fixed-voltage models are also available:
ADP1110–3.3 (+3.3 V), ADP1110–5 (+5 V) and ADP1110-12
(+12 V). The fixed-voltage models are identical to the
ADP1110 except that laser-trimmed voltage-setting resistors are
included on the chip. Only three external components are
required to form a +3.3 V, +5 V or +12 V converter. On the
fixed-voltage models of the ADP1110, simply connect the
SENSE pin (Pin8) directly to the output voltage.
COMPONENT SELECTION
General Notes on Inductor SelectionWhen the ADP1110 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. Because both
the collector and the emitter of the switch transistor are
accessible on the ADP1110, the output voltage can be higher,
lower, or of opposite polarity than the input voltage.
To specify an inductor for the ADP1110, 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 VIN 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 ADP1110 applications, an inductor ofμH to 100μH with a saturation current rating of 300mA to
1A and dc resistance <0.4 Ω is suitable. Ferrite-core inductors
that meet these specifications are available in small, surface-
mount packages.
TEMPERATURE – 8C
BIAS CURRENT – nA100Figure 14.Set Pin Bias Current vs. Temperature
Figure 15.Reference Voltage vs. Temperature
CALCULATING THE INDUCTOR VALUESelecting the proper inductor value is a simple three-step
process:Define the operating parameters: minimum input voltage,
maximum input voltage, output voltage and output current.Select the appropriate conversion topology (step-up, step-
down, or inverting).Calculate the inductor value, using the equations in the
following sections.
INDUCTOR SELECTION–STEP-UP CONVERTERIn a step-up or boost converter (Figure 19), 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:PL=VOUT+VD−VINMIN()()•IOUT()(Equation 1)
where VD is the diode forward voltage (≈ 0.5 V for a 1N5818
Schottky). Because energy is only stored in the inductor while
the ADP1110 switch is ON, the energy stored in the inductor
on each switching cycle must be must be equal to or greater
than:
OSC(Equation 2)
in order for the ADP1110 to regulate the output voltage.
When the internal power switch turns ON, current flow in the
inductor increases at the rate of: (t)=VIN1−e
±R©t(Equation 3)
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. If the voltage drop across the switch is small
compared to VIN, a simpler equation can be used: (t)=VINt(Equation 4)
Replacing ‘t’ in the above equation with the ON time of the
ADP1110 (10 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: =1L•I2PEAK(Equation 5)
As previously mentioned, EL must be greater than PL/fOSC so
that the ADP1110 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 12 V at
120 mA from a 4.5 V to 8 V source. The inductor power required
is from Equation 1: PL=12V+0.5V−4.5V()•120mA=960mW
Assuming a peak current of 1 A as a starting point, (Equation 4)
can be rearranged to recommend an inductor value: =VIN
IL(MAX)t=4.5V10μs=45μH
Substituting a standard inductor value of 47 μH with 0.2 Ω dc
resistance will produce a peak switch current of:
IPEAK=4.5V
1.0Ω1−e
±1.0Ω•10μs
47μH=862mA
Once the peak current is known, the inductor energy can be
calculated from Equation 5: EL=147μH()•862mA()=17.5μJ
Since the inductor energy of 17.5 μJ is greater than the PL/fOSC
requirement of 13.7 μJ, the 47 μH inductor will work in this
application. By substituting other inductor values into the same
equations, the optimum inductor value can be determined.
When selecting an inductor, the peak current must not exceed
the maximum switch current of 1.5 A.
The peak current must be evaluated for both minimum and
maximum values of input voltage. If the switch current is high
when VIN is at its minimum, the 1.5 A limit may be exceeded at the
maximum value of VIN. In this case, the ADP1110’s current limit
feature can be used to limit switch current. Simply select a resistor
(using Figure 7) that will limit the maximum switch current to the
IPEAK value calculated for the minimum value of VIN. This will
improve efficiency by producing a constant IPEAK as VIN increases.
See the “Limiting the Switch Current” 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 CONVERTERThe step-down mode of operation is shown in Figure 20.
Unlike the step-up mode, the ADP1110’s power switch does not
saturate when operating in the step-down mode; therefore,
switch current should be limited to 800 mA in this mode. If the
input voltage will vary over a wide range, the ILIM pin can be
used to limit the maximum switch current. Higher switch
current is possible by adding an external switching transistor as
shown in Figure 22.
The first step in selecting the step-down inductor is to calculate
the peak switch current as follows:
IPEAK=2IOUT
VOUT+VD
VIN±VSW+VD(Equation 6)
where:DC = duty cycle (0.69 for the ADP1110)
VSW = voltage drop across the switch
VD = diode drop (0.5 V for a 1N5818)
IOUT = output current
VOUT = the output voltage
ADP1110As previously mentioned, the switch voltage is higher in step-
down mode than in step-up mode. VSW is a function of switch
current and is therefore a function of VIN, L, time and VOUT.
For most applications, a VSW value of 1.5 V is recommended.
The inductor value can now be calculated: =VIN(MIN)±VSW±VOUT
IPEAK•tON(Equation 7)
where:tON = Switch ON time (10 μs)
If the input voltage will vary (such as an application that must
operate from a 9V, 12V or 15V source), an RLIM resistor
should be selected from Figure 6. The RLIM resistor will keep
switch current constant as the input voltage rises. Note that
there are separate RLIM values for step-up and step-down modes
of operation.
For example, assume that +5 V at 250 mA is required from aV to +18 V source. Deriving the peak current from Equation
6 yields:
IPEAK=2•250mA
5+0.5−1.5+0.5=498mA
Then, the peak current can be inserted into Equation 7 to
calculate the inductor value: =9±1.5±5
498mA•10μs=50μs
Since 50 μH is not a standard value, the next lower standard
value of 47 μH would be specified.
To avoid exceeding the maximum switch current when the
input voltage is at +18 V, an RLIM resistor should be specified.
Using the step-down curve of Figure 6, a value of 560 Ω will
limit the switch current to 500 mA.
INDUCTOR SELECTION—POSITIVE-TO-NEGATIVE
CONVERTERThe configuration for a positive-to-negative converter using the
ADP1110 is shown in Figure 23. 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: P = ILOUTOUTD+()•()(Equation 8)
The ADP1110 power switch does not saturate in positive-to-
negative 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: (t)=VL1−e
±R©t(Equation 9)
where:R' = 0.65 Ω + RL(DC)
VL = VIN – 0.75 V
For example, assume that a –5 V output at 75 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()•75mA()=413mW
During each switching cycle, the inductor must supply the
following energy:
fOSC=413mWkHz=5.9μJ
Using a standard inductor value of 56 μH with 0.2 Ω dc
resistance will produce a peak switch current of:
IPEAK=4.5V±0.75V
0.65Ω+0.2Ω1−e
±0.85Ω•10μs
56μH=621mA
Once the peak current is known, the inductor energy can be
calculated from Equation 9: EL=156μH()•621mA()=10.8μJ
Since the inductor energy of 10.8 μJ is greater than the PL/fOSC
requirement of 5.9 μJ, the 56 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 RLIM resistor and the ILIM pin can be connected
directly to VIN. Care should be taken, of course, to ensure that
the peak current does not exceed 800 mA.
CAPACITOR SELECTIONFor optimum performance, the ADP1110’s output capacitor
must be selected carefully. 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 demon-
strated in Figures 16, 17 and 18. These figures show the output
of the same ADP1110 converter, that 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 16
shows a Panasonic HF-series 16-volt radial cap. 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 17,
the aluminum electrolytic has been replaced by a Sprague 293D
series, a 6 V tantalum device. In this case the output jumps
