參數(shù)資料
型號(hào): ADP1108AN
廠商: ANALOG DEVICES INC
元件分類: 穩(wěn)壓器
英文描述: Circular Connector; No. of Contacts:19; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:25-19
中文描述: 1.5 A SWITCHING REGULATOR, 25 kHz SWITCHING FREQ-MAX, PDIP8
封裝: PLASTIC, DIP-8
文件頁數(shù): 5/12頁
文件大?。?/td> 234K
代理商: ADP1108AN
ADP1108
–5–
REV. 0
T HE ORY OF OPE RAT ION
T he ADP1108 is a flexible, low power Switch Mode Power
Supply (SMPS) controller. T he 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). T his device uses a
gated-oscillator technique to provide very high performance
with low quiescent current.
A functional block diagram of the ADP1108 is shown on
the front page. T he 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 19 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 ADP1108 quiescent current is only 110
μ
A. T he
comparator includes a small amount of hysteresis, which
ensures loop stability without requiring external components
for frequency compensation.
T he maximum current in the internal power switch can be set
by connecting a resistor between V
IN
and the I
LIM
pin. When
the maximum current is exceeded, the switch is turned OFF.
T he current limit circuitry has a time delay of about 2
μ
s. If
an external resistor is not used, connect I
L IM
to V
IN
. Further
information on I
L IM
is included in the L imiting the Switch
Current section of this data sheet.
T he ADP1108 internal oscillator provides 36
μ
s ON and 17
μ
s
OFF times, which is ideal for applications where the ratio
between V
IN
and V
OUT
is roughly a factor of three (such as
generating +5 V from a +2 V input). T he 36
μ
s/17
μ
s ratio
permits continuous mode operation in such cases, which
increases the available output power.
An uncommitted gain block on the ADP1108 can be connected
as a low-battery detector. T he inverting input of the gain block
is internally connected to the 1.245 V reference. T he noninverting
input is available at the SET pin. A resistor divider, connected
between V
IN
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. T he AO output is an open collector NPN
transistor that can sink 100
μ
A.
T he ADP1108 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 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 V
IN
.
T he output voltage of the ADP1108 is set with two external
resistors. T hree fixed-voltage models are also available: ADP1108-
3.3 (+3.3 V), ADP1108-5 (+5 V) and ADP1108-12 (+12 V). T he
fixed-voltage models are identical to the ADP1108, except that
laser-trimmed voltage-setting resistors are included on the chip.
On the fixed-voltage models of the ADP1108, simply connect
the feedback pin (Pin 8) directly to the output voltage.
COMPONE NT SE LE CT ION
General Notes on Inductor Selection
When the ADP1108 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 ADP1108, so the output voltage can be higher, lower, or
of opposite polarity than the input voltage.
T o specify an inductor for the ADP1108, the proper values of
inductance, saturation current, and dc resistance must be
determined. T his 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. T he 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 ADP1108 applications, an inductor of
47
μ
H to 330
μ
H
, with a saturation current rating of 300 mA to
1 A and dc resistance < 0.4
V
is suitable. Ferrite core inductors
that meet these specifications are available in small, surface-
mount packages.
T o 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.
TEMPERATURE –
°
C
V
C
0.58
0.53
0.28
–40
0
85
25
70
0.48
0.43
0.38
0.33
V
CE (SAT)
@ I
SW
= 0.65A
Figure 10. Switch Saturation Voltage In
Step-Up Mode vs. Temperature
TEMPERATURE –
°
C
V
C
1.2
1.15
0.9
–40
0
85
25
70
1.1
1.05
1
0.95
V
CE (SAT)
@ I
SW
= 0.65A
Figure 11. Switch Saturation Voltage In
Step-Down Mode vs. Temperature
相關(guān)PDF資料
PDF描述
ADP1108AN-12 Circular Connector; No. of Contacts:128; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Pin; Circular Shell Style:Straight Plug; Insert Arrangement:25-1
ADP1108AN-33 Circular Connector; No. of Contacts:128; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:25-1
ADP1108AN-5 Circular Connector; No. of Contacts:30; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:25-20
ADP1108AR Circular Connector; No. of Contacts:24; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Socket; Circular Shell Style:Straight Plug; Insert Arrangement:25-24
ADP1108AR-12 Circular Connector; No. of Contacts:128; Series:LJT06R; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:25; Circular Contact Gender:Pin; Circular Shell Style:Straight Plug; Insert Arrangement:25-35
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
ADP1108AN-12 制造商:Rochester Electronics LLC 功能描述:- Bulk
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ADP1108AN-5 制造商:AD 制造商全稱:Analog Devices 功能描述:Micropower DC-DC Converter Adjustable and Fixed 3.3 V, 5 V, 12 V
ADP1108AR 制造商:Rochester Electronics LLC 功能描述:- Bulk