LT1109A
Micropower
DC/DC Converter
Flash Memory VPP Generator
Adjustable and Fixed 5V, 12V
FEATURES
s
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DESCRIPTIO
Uses Off-the-Shelf Inductors
Low Cost
8-Pin DIP or SO Package
Fixed 5V or 12V Output or Adjustable Version
Only Four External Components Required
360µA Standby Current
Logic-Controlled Shutdown
The LT1109A is a simple step-up DC/DC converter. The 8-
pin DIP or SOIC devices require only four external compo-
nents to construct a complete DC/DC converter. Current
drain is just 360µA at no load, making the device ideal for
cost-sensitive applications where standby current must
be kept to a minimum.
The LT1109A-12 can deliver 12V at over 150mA from a 5V
supply, enough power to program four flash memory
chips simultaneously. The LT1109A-5 can deliver 5V at up
to 110mA from a 2V input. The devices feature a shutdown
pin that turns off the oscillator when taken low. The gated-
oscillator design requires no frequency compensation
components. High frequency 120kHz operation permits
the use of small surface mount inductors and capacitors.
APPLICATI
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Flash Memory VPP Generators
5V to 12V Converters
3.3V to 12V Converters
Disk Drives
PC Plug-In Cards
Peripherals
Battery-Powered Equipment
TYPICAL APPLICATI
All Surface Mount
Flash Memory VPP Generator
L1*
33µH
MBRS130T3
3
SW
V
IN
SENSE
Output Current
13.0
12V
12.5
OUTPUT VOLTAGE (V)
+V
IN
5V
C1
22µF
10V
1
8
V
OUT
12V
C2
47µF
20V
12.0
11.5
11.0
10.5
V
IN
= 5V
+
7
LT1109ACS8-12
SHUTDOWN
PGND
GND
4
5
+
V
IN
= 4.5V
SHUTDOWN
5V/DIV
500µs/DIV
1109A TA03
**
* COILTRONICS CTX33-2
SUMIDA CD54-330LC
** 1 = PROGRAM
0 = SHUTDOWN
10.0
1109A TA01
0
50
250
100
150
200
OUTPUT CURRENT (mA)
300
1109A TA02
U
Output Voltage
V
OUT
2V/DIV
UO
UO
1
LT1109A
ABSOLUTE
AXI U
RATI GS
Switch Current .......................................................... 2A
Maximum Power Dissipation ............................ 300mW
Operating Temperature Range .................... 0°C to 70°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
(Voltages Referred to GND Pin)
Supply Voltage (V
IN
) ................................ – 0.4V to 20V
SW Pin Voltage ........................................ – 0.4V to 50V
Feedback Pin Voltage (LT1109A) ........................... 5.5V
Shutdown Pin Voltage ........................................... 5.5V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
IN
1
NC 2
SW 3
PGND 4
8
7
6
5
FB (SENSE)*
SHUTDOWN
NC
GND
ORDER PART
NUMBER
LT1109ACN8
LT1109ACN8-5
LT1109ACN8-12
N8 PACKAGE
8-LEAD PLASTIC DIP
*FIXED VERSIONS
T
JMAX
= 90°C,
θ
JA
= 130°C/W
ELECTRICAL CHARACTERISTICS
SYMBOL
I
Q
V
IN
V
OUT
PARAMETER
Quiescent Current
Input Voltage
Comparator Trip Point Voltage
Output Sense Voltage
Comparator Hysteresis
Output Voltage Ripple
f
OSC
t
ON
DC
V
CESAT
Oscillator Frequency
T
A
= 25°C, V
IN
= 3V, unless otherwise noted.
MIN
q
q
CONDITIONS
Switch Off
LT1109A
LT1109A-5; 2V
≤
V
IN
≤
5V
LT1109A-12; 2V
≤
V
IN
≤
12V
LT1109A
LT1109A-5
LT1109A-12
Switch On Time
q
Duty Cycle
Switch Saturation Voltage
Switch Leakage Current
Full Load
V
IN
= 3V, I
SW
= 650mA
V
IN
= 5V, I
SW
= 1A
V
SW
= 12V
V
IH
V
IL
I
IH
I
L
SHUTDOWN Pin High
SHUTDOWN Pin Low
SHUTDOWN Pin Input Current
SHUTDOWN Pin Input Current
V
SHUTDOWN
≥
2.0V
0V
≤
V
SHUTDOWN
≤
0.8V
The
q
denotes specifications which apply over the full operating
temperature range.
2
U
U
W
W W
U
W
TOP VIEW
V
IN
1
NC 2
SW 3
PGND 4
8 FB (SENSE)*
7 SHUTDOWN
6 NC
5 GND
ORDER PART
NUMBER
LT1109ACS8
LT1109ACS8-5
LT1109ACS8-12
S8 PART
MARKING
1109A
1109A5
1109A1
S8 PACKAGE
8-LEAD PLASTIC SO
*FIXED VERSIONS
T
JMAX
= 90°C,
θ
JA
= 150°C/W
TYP
360
MAX
500
9
1.30
5.25
12.55
12.5
50
120
135
155
6.9
7.4
77
0.65
1.00
10
0.8
10
20
UNITS
µA
V
V
V
V
mV
mV
mV
kHz
kHz
µs
µs
%
V
V
µA
V
V
µA
µA
2
1.20
4.75
11.52
1.25
5.00
12.00
8
25
60
105
95
4.1
3.8
60
120
5.5
68
0.5
0.7
1
2.0
q
q
q
q
q
q
q
q
q
q
q
q
q
LT1109A
OPERATIO
The LT1109A is a micropower step-up DC/DC converter.
It uses Burst Mode
TM
operation to achieve micropower
operation yet still deliver more than 2W of output power
from a 5V supply. Circuit operation can be best under-
stood by referring to the LT1109A block diagram. With
SHUTDOWN high, comparator A1 compares the feedback
(FB) pin voltage with the 1.25V reference signal. When FB
APPLICATI
S I FOR ATIO
Inductor Selection
A DC/DC converter operates by storing energy as mag-
netic flux in an inductor core, and then switching this
energy into the load. To operate as an efficient energy
transfer element, the inductor must fulfill three require-
ments: inductance value, saturation current and DC resis-
tance. A fourth requirement is physical size. The inductors
recommended with the LT1109A circuits are small, sur-
face-mountable and are designed for switch-mode appli-
cations. Avoid using RF chokes or air core units since they
have very low peak current ratings. The LT1109A works
best in situations where the input voltage does not vary
much since the device has no internal switch current limit
function. For situations where the input voltage varies,
such as battery inputs, the LT1107 or LT1111 is suggested
instead.
Capacitor Selection
The output capacitor should be chosen on the basis of its
equivalent series resistance (ESR) and capacitance value.
Low ESR tantalum surface-mountable capacitors such as
those made by AVX are well-suited for DC/DC converter
applications. Inexpensive aluminum electrolytics may have
excessive ESR, resulting in high output ripple. These
should be avoided.
Diode Selection
Speed, forward drop, and leakage current are the three
main considerations in selecting a diode for LT1109A
converters. General purpose rectifiers such as the 1N4001
U
W
U
UO
U
drops below 1.25V, A1 switches on the 120kHz oscillator.
The driver amplifier boosts the signal level to drive the
output NPN power switch. When the FB voltage is sufficient
to trip A1, the oscillator is turned off. A low signal on the
shutdown pin gates off the oscillator, overriding A1. With
SHUTDOWN low, quiescent current remains at 360µA.
Burst Mode
TM
is a trademark of Linear Technology Corporation
are
unsuitable
for use in
any
switching regulator applica-
tion. Although they are rated at 1A, the switching time of
a 1N4001 is in the 10µs to 50µs range. At best, efficiency
will be severely compromised if this diode is used; at
worst, the circuit may not work at all. The 1N5818 is an
ideal choice for LT1109A circuits. Surface-mountable
versions, such as the MBRS130T3, are available as well.
Table 1. Inductor Manufacturers
MANUFACTURER
Coiltronics International
984 S.W. 13th Court
Pompano Beach, FL 33069
305-781-8900
Sumida Electric Co., Ltd.
637 E. Golf Road, Suite 209
Arlington Heights, IL 60005
708-956-0666
OCTA-PAC
TM
is a trademark of Coiltronics International
PART NUMBERS
Surface Mount
OCTA-PAC
TM
Series
CD54
CD105
Surface Mount
Table 2. Capacitor Manufacturers
MANUFACTURER
AVX
Myrtle Beach, SC 29578
803-946-0690
Philips Components
2001 W. Blue Heron Blvd.
P.O. Box 10330
Riviera Beach, FL 33404
407-881-3200
Sanyo Video Components
1201 Sanyo Avenue
San Diego, CA 92073
619-661-6322
PART NUMBERS
TPS Series
49MC Series
OS-CON Series
5
Analog electronics
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