LTC1514-3.3/LTC1514-5 - Step-Up/Step-Down Switched Capacitor DC/DC Converters with Low-Battery Comparator

LTC1514-3.3/LTC1514-5
Step-Up/Step-Down Switched
Capacitor DC/DC Converters
with Low-Battery Comparator
U
DESCRIPTION
FEATURES
■
■
■
■
■
■
■
■
■
■
■
■
The LTC®1514-3.3/LTC1514-5 are micropower switched
capacitor DC/DC converters that produce a regulated
output voltage by either stepping up or stepping down
the input voltage. Output voltage is fixed at either 3.3V
(LTC1514-3.3) or 5V (LTC1514-5) by an internal resistor
divider.
3.3V or 5V Output Voltages
2V to 10V Input Voltage Range
Up to 50mA Output Current
Only Three External Capacitors Required
Soft Start Limits Inrush Current at Turn-On
Low Operating Current: 60µA
Low Shutdown Current: 10µA
Shutdown Disconnects Load from VIN
Short-Circuit and Overtemperature Protected
650kHz Switching Frequency
Low-Battery Comparator Active in Shutdown
Available in SO-8 Package
A unique architecture allows the parts to accommodate
a wide input voltage range (2V to 10V) while maintaining
±4% regulation. Additional circuitry prevents excessive
inrush current and output voltage ripple when large VIN
to VOUT differentials are present.
An internal uncommitted comparator is kept active in
shutdown. The comparator has an open-drain output for
flexible interfacing.
U
APPLICATIONS
■
■
■
■
■
Battery-Operated Equipment
Smart Card Readers
Local Power Supplies
Handheld Instruments
Battery Backup Supplies
The parts are short-circuit and overtemperature protected. Battery life is maximized by very low operating
currents (ICC = 60µA typ, 10µA in shutdown). Both parts
are available in an SO-8 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
U
TYPICAL APPLICATION
LTC1514-5 Output Voltage
vs Input Voltage
5V Step-Up/Step-Down Power Supply with Low-Battery Detect
5.2
IOUT = 10mA
100k
1.33M
1%
ON OFF
2
LOW BAT
3
499k
1%
4
SHDN
VOUT
8
7
LBO
VIN
LBI
C1+
6
–
5
GND
C1
VOUT = 5V
IOUT = 50mA
+
10µF
0.22µF
+
10µF
1514 TA01
VIN
4-CELL
NiCd
OUTPUT VOLTAGE (V)
LTC1514-5
1
5.1
5.0
4.9
4.8
2
3
4
5
8
6
7
INPUT VOLTAGE (V)
9
10
LT1514 • TA02
1
LTC1514-3.3/LTC1514-5
W
U
U
W W
U
W
ABSOLUTE MAXIMUM RATINGS
PACKAGE/ORDER INFORMATION
(Note 1)
VIN to GND ................................................ – 0.3V to 12V
VOUT to GND ............................................. – 0.3V to 12V
SHDN, LBI, LBO to GND ........................... – 0.3V to 12V
VOUT Short-Circuit Duration ............................. Indefinite
Operating Temperature Range
Commercial ............................................. 0°C to 70°C
Industrial ........................................... – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
TOP VIEW
SHDN 1
LTC1514CS8-3.3
LTC1514CS8-5
LTC1514IS8-3.3
LTC1514IS8-5
8 VOUT
LBO 2
7 VIN
LBI 3
6 C1+
GND 4
5 C1–
S8 PACKAGE
8-LEAD PLASTIC SO
S8 PART MARKING
TJMAX = 125°C, θJA = 110°C/ W
15143
15145
1514I3
1514I5
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
VIN = 2V to 10V, SHDN = 3V, C1 = 0.22µF, CIN = COUT = 10µF, unless otherwise noted (Note 2).
PARAMETER
CONDITIONS
VIN Operating Voltage
LTC1514-3.3
LTC1514-5
●
●
2.0
2.7
VOUT (LTC1514-3.3)
2V ≤ VIN ≤ 8V, IOUT ≤ 15mA
3V ≤ VIN ≤ 8V, IOUT ≤ 50mA
●
●
3.17
3.17
VOUT (LTC1514-5)
2.7V ≤ VIN ≤ 10V, IOUT ≤ 15mA
3.3V ≤ VIN ≤ 10V, IOUT ≤ 50mA
●
●
4.8
4.8
VIN Operating Current
VIN ≤ 5V, IOUT = 0, SHDN = 3V
VIN > 5V, IOUT = 0, SHDN = 3V
VIN Shutdown Current
SHDN = 0V, VIN ≤ 5V
SHDN = 0V, VIN > 5V
Output Ripple
Full Load (Note 2)
Switching Frequency
MIN
TYP
MAX
UNITS
8
10
V
V
3.3
3.3
3.43
3.43
V
V
5
5
5.2
5.2
V
V
●
●
60
75
100
120
µA
µA
●
10
20
35
µA
µA
100
mVP-P
●
500
650
800
LBI Ramping Negative
●
1.110
1.145
1.180
V
LBI Input Current
LBI = 1.145V
●
– 50
50
nA
LBO VOL
ISINK = 100µA, VIN = 3V
●
0.4
V
LBO Leakage Current
VLBO = 5V, LBI = VIN
●
–1
1
µA
SHDN Input Threshold
VIL
VIH
●
●
0.4
1.6
V
V
SHDN Input Current
SHDN = VIN
SHDN = 0V
●
●
–1
–1
1
1
µA
µA
IOUT Short-Circuit Current
VOUT = 0V
●
40
mA
tON
Soft Start Turn-On Time
LBI Trip Point
LBI Trip Point Hysteresis
1
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: Absolute Maximum Ratings are those values beyond which the life of
the device may be impaired.
2
0.025
1
1
12
4
Note 2: For VIN ≥ 8V, COUT = 22µF.
kHz
%
ms
LTC1514-3.3/LTC1514-5
U W
TYPICAL PERFORMANCE CHARACTERISTICS
LTC1514-3.3
Efficiency vs Output Current
LTC1514-5
Efficiency vs Output Current
100
100
VIN = 2.7V
VIN = 2V
80
250
80
EFFICIENCY (%)
VIN = 4.4V
VIN = 2.7V
60
VIN = 6V
OUTPUT VOLTAGE RIPPLE (mVP-P)
VOUT = 3.3V
TA = 25°C
EFFICIENCY (%)
LTC1514-3.3 Output Voltage
Ripple vs Input Voltage
VIN = 6V
40
20
VIN = 3.3V
60
VIN = 8V
40
20
VOUT = 5V
TA = 25°C
0
0.01
0.1
1
10
OUTPUT CURRENT (mA)
0
0.01
100
COUT = 22µF
100
COUT = 47µF
3.30
0
2
6
4
INPUT VOLTAGE (V)
8
LTC1514-3.3
Efficiency vs Input Voltage
20
8
10
1514 G07
40
0
2
6
4
INPUT VOLTAGE (V)
8
SHDN = 0V
60
20
10
1514 G06
SHUTDOWN SUPPLY CURRENT (µA)
EFFICIENCY (%)
–40°C
25
VOUT = 5V
IOUT = 10mA
TA = 25°C
80
EFFICIENCY (%)
6
4
INPUT VOLTAGE (V)
85°C
LTC1514-X Shutdown Supply
Current vs Input Voltage
40
2
25°C
60
20
10
100
VOUT = 3.3V
IOUT = 10mA
TA = 25°C
0
80
LTC1514-5
Efficiency vs Input Voltage
100
10
100
1514 G05
1514 G04
40
8
VOUT = 5V
IOUT = 0mA
3.35
10
60
6
4
INPUT VOLTAGE (V)
1514 G03
3.20
80
2
120
3.25
0
8
COUT = 47µF
0
OPERATING CURRENT (µA)
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE RIPPLE (mVP-P)
COUT = 10µF
6
4
INPUT VOLTAGE (V)
50
LTC1514-5 Operating Current
vs Input Voltage
VOUT = 3.3V
COUT = 10µF
TA = 25°C
3.40
150
COUT = 22µF
100
100
3.45
VOUT = 5V
IOUT = 10mA
TA = 25°C
2
COUT = 10µF
LTC1514-3.3 Output Voltage
vs Input Voltage
250
0
150
1514 G02
LTC1514-5 Output Voltage Ripple
vs Input Voltage
50
200
0
0.1
1
10
OUTPUT CURRENT (mA)
1514 G01
200
VOUT = 3.3V
IOUT = 10mA
TA = 25°C
20
15
25°C
85°C
10
–40°C
5
0
2
4
8
6
INPUT VOLTAGE (V)
10
12
1514 G08
0
2
6
4
INPUT VOLTAGE (V)
8
10
1514 G09
3
LTC1514-3.3/LTC1514-5
U W
TYPICAL PERFORMANCE CHARACTERISTICS
LTC1514-5 Step-Down Mode
Load Transient Response
LTC1514-5 Step-Up Mode
Load Transient Response
VOUT
AC COUPLED
100mV/DIV
VOUT
AC COUPLED
100mV/DIV
50mA
IOUT
50mA/DIV
IOUT
50mA/DIV
0mA
VIN = 8V, VOUT = 5V, COUT = 10µF, TA = 25°C
VIN = 3.3V, VOUT = 5V, COUT = 10µF, TA = 25°C
1514 G10
1514 G11
W
BLOCK DIAGRAM
C1 –
VIN
C1 +
STEP-UP/STEP-DOWN
CHARGE PUMP
VOUT
SHDN
–
650kHz
OSCILLATOR
+
LBO
–
LBI
+
1.145V
VREF
GND
1514 BD
U
U
U
PIN FUNCTIONS
SHDN (Pin 1): Shutdown Input. A logic low on the SHDN
pin puts the part into shutdown mode. A logic high
(VSHDN ≥ 1.6V) enables the charge pump regulator. At
high VIN voltages, the SHDN pin may still be controlled
with 3V logic without causing a large rise in VIN quiescent
current. The SHDN pin may not float; connect to VIN if
unused.
4
LBO (Pin 2): Open-Drain, Low-Battery Comparator Output. This pin will pull low whenever the voltage on the LBI
pin is less than the internal reference voltage (1.145V typ).
LBI (Pin 3): Low-Battery Comparator Input. The voltage
on this pin is compared to the internal reference voltage
(1.145V). The LBO output will sink current when the
voltage on the LBI pin is less than 1.145V typ. The low-
LTC1514-3.3/LTC1514-5
U
U
U
PIN FUNCTIONS
battery comparator and 1.145V reference are kept alive in
shutdown.
GND (Pin 4): Ground. Should be tied to a ground plane for
best performance.
C1 – (Pin 5): Charge Pump Flying Capacitor, Negative
Terminal.
C1 + (Pin 6): Charge Pump Flying Capacitor, Positive
Terminal.
VIN (Pin 7): Charge Pump Input Voltage. May be between
2V and 8V (LTC1514-3.3) or between 2.7V and 10V
(LTC1514-5). VIN should be bypassed with a ≥ 10µF low
ESR capacitor as close as possible to the pin for best
performance.
VOUT (Pin 8): Regulated Output Voltage. The output voltage is internally set to either 3.3V (LTC1514-3.3) or to 5V
(LTC1514-5) using an internal resistor divider. VOUT should
be bypassed with a ≥ 10µF low ESR capacitor as close as
possible to the pin for best performance.
U
W
U
U
APPLICATIONS INFORMATION
Regulator Operation
The regulator section of the LTC1514-3.3/LTC1514-5
consists of a charge pump, reference, comparator and
some logic. The divided down output voltage is compared to the internal reference voltage. When the divided
output drops below the reference voltage, the charge
pump is enabled, which boosts the output back into
regulation. Hysteresis in the comparator forces the regulator to burst on and off and causes approximately
100mV of peak-to-peak ripple to appear at the output. By
enabling the charge pump only when needed, the
LTC1514-3.3 and LTC1514-5 are able to achieve high
efficiencies with low output load currents.
Each part’s charge pump has a unique architecture that
allows the input voltage to be either stepped up or
stepped down to produce a regulated output. Internal
circuitry senses the VIN to VOUT differential voltage and
controls the charge pump operating mode. In addition,
the effective output impedance of the charge pump is
internally adjusted to prevent large inrush currents and
allow for a wide input voltage range. When the input
voltage is lower than the output voltage, the charge pump
operates as a step-up voltage doubler. When the input
voltage is greater than the output, the charge pump
operates as a step-down gated switch.
Capacitor Selection
For best performance, low ESR capacitors are recommended for both CIN and COUT to reduce noise and ripple.
The CIN and COUT capacitors should be either ceramic or
tantalum and should be 10µF or greater. If the input
source impedance is very low (< 0.5Ω), CIN may not be
needed. Increasing the size of COUT to 22µF or greater will
reduce output voltage ripple—particularly with high VIN
voltages (8V or greater). A ceramic capacitor is recommended for the flying capacitor C1 with a value of 0.1µF
or 0.22µF. Smaller value flying capacitors may be used in
low output current applications.
Output Ripple
Normal LTC1514-3.3/LTC1514-5 operation produces
voltage ripple on the VOUT pin. Output voltage ripple is
required for the parts to regulate. Low frequency ripple
exists due to the hysteresis in the sense comparator and
propagation delays in the charge pump enable/disable
circuits. High frequency ripple is also present mainly
from the ESR (equivalent series resistance) in the output
capacitor. Typical output ripple (VIN < 8V) under maximum load is 100mV peak-to-peak with a low ESR (< 0.5Ω)
10µF output capacitor. For applications requiring VIN to
exceed 8V, a 22µF or larger COUT capacitor is recommended to maintain max ripple in the 100mV range.
The magnitude of the ripple voltage depends on several
factors. High input voltages increase the output ripple
since more charge is delivered to COUT per charging
cycle. A large C1 flying capacitor (> 0.22µF) also
increases ripple in step-up mode for the same reason.
Large output current load and/or a small output capacitor
(< 10µF) results in higher ripple due to higher output
voltage dV/dt. High ESR capacitors (ESR > 0.5Ω) on the
5
LTC1514-3.3/LTC1514-5
U
U
W
U
APPLICATIONS INFORMATION
output pin cause high frequency voltage spikes on VOUT
with every clock cycle.
There are several ways to reduce the output voltage
ripple. A larger COUT capacitor (22µF or greater) will
reduce both the low and high frequency ripple due to the
lower COUT charging and discharging dV/dt and the lower
ESR typically found with higher value (larger case size)
capacitors. A low ESR ceramic output capacitor will
minimize the high frequency ripple, but will not reduce
the low frequency ripple unless a high capacitance value
is chosen. A reasonable compromise is to use a 10µF to
22µF tantalum capacitor in parallel with a 1µF to 3.3µF
ceramic capacitor on VOUT to reduce both the low and
high frequency ripple. An RC or LC filter may also be used
to reduce high frequency voltage spikes (see Figure 1).
VOUT
8
+
LTC1514-X
VOUT
LTC1514-X
VOUT
1µF
CERAMIC
15µF
TANTALUM
2Ω
8
+
10µF
TANTALUM
+
VOUT
10µF
TANTALUM
1514 F01
Figure 1. Output Ripple Reduction Techniques
Inrush Currents
A common problem with switched capacitor regulators
is inrush current — particularly during power-up and
coming out of shutdown mode. Whenever large VIN (or
boosted VIN) to VOUT voltage differentials are present,
most charge pumps will pull large current spikes from
the input supply. Only the effective charge pump output
impedance limits the current while the charge pump is
enabled. This may disrupt input supply regulation, especially if the input supply is a low power DC/DC converter
or linear regulator. The LTC1514-3.3/LTC1514-5 minimize inrush currents both at start-up and under normal
high VIN to VOUT operation.
Internal soft start circuitry controls the rate at which VOUT
may be charged from 0V to its final regulated value. The
typical start-up time from VOUT = 0V to 5V is 4ms. This
corresponds to an effective VOUT charging current of only
12.5mA for a 10µF output capacitor (27.5mA for 22µF,
etc). Note that any output current load present during
start-up will add directly to the charging currents mentioned above. The soft start circuitry limits start-up
current both at initial power-up and when coming out of
shutdown.
As the VIN (or boosted VIN) to VOUT voltage differential
grows, the effective output impedance of the charge
pump is automatically increased by internal voltage
sensing circuitry. This feature minimizes the current
spikes pulled from VIN whenever the charge pump is
enabled and helps to reduce both input and output ripple.
Protection Features
The LTC1514-X contain thermal shutdown and shortcircuit protection features. The parts will shut down when
the junction temperature reaches approximately 150°C
and will resume operation once the junction temperature
has dropped back to approximately 140°C. The parts will
limit output current to 12mA (typ) when a short-circuit
condition (VOUT < 100mV) exists. The parts can survive
an indefinite short to GND. The LTC1514-X devices use
a low thermal resistance SO-8 package (110°C/W vs
150°C/W for standard SO-8). This permits full output
current, even at high input supply voltages.
Low-Battery Comparator
The internal low-battery comparator trips at 1.145 ±3%
(LBI ramping negative). Programming the comparator to
trip at a higher voltage can easily be done with an external
LTC1514-X
VBAT
R1
1
2
3
R2
4
SHDN
VOUT
8
7
LBO
VIN
LBI
C1+
6
GND
C1–
5
VTRIP = 1.145V(1 + R1/R2)
(LBI RAMPING NEGATIVE)
1514 F02
Figure 2. Programming the Low-Battery Comparator Trip Voltage
6
LTC1514-3.3/LTC1514-5
U
U
W
U
APPLICATIONS INFORMATION
resistor divider (see Figure 2). Since the low-battery
comparator is kept alive in shutdown, it may be used to
protect batteries against deep discharge by shutting
down the power supply when the battery voltage gets too
low. The open-drain comparator output allows for flexible interfacing between the LBO output and external
logic. LBO pull-up resistors in the 50k to 1M range are
recommended.
U
TYPICAL APPLICATIONS N
3.3V Step-Up/Step-Down Supply with Power Good Output
806k
1%
100k LTC1514-3.3
1
SHDN VOUT
2
LBO
VIN
3V VTRIP
3
C1+
LBI
499k
4
C1–
GND
1%
ON OFF
POWER GOOD
8
7
6
5
VIN
2V TO 8V
+
VOUT = 3.3V ± 4%
IOUT = 15mA, VIN > 2V
IOUT = 50mA, VIN > 3V
10µF
+
0.22µF
10µF
1514 TA05
Low Power Battery Backup Supply with Autoswitchover and No Reverse Current
BACKED-UP
CIRCUITRY
MAIN
5V SUPPLY
BAT54
499k
LTC1514-5
TP0610T
1
1.5M
1%
499k
1%
2
4.6V VTRIP 3
4
499k
SHDN
VOUT
8
5V BACKUP SUPPLY
IOUT = 15mA
7
LBO
VIN
LBI
C1+
6
GND
C1–
5
TRICKLE CHARGE
AND LTC1514 IDD
+
10µF
3-CELL
NiCd BATTERY
+
0.1µF
10µF
1514 TA03
Battery/External Power Autoswitch Regulator
MBR0520L
6V
WALL
ADAPTER
INPUT
499k
1M
1%
LTC1514-5
ON OFF
1
2
3
499k
1%
EXTERNAL
POWER GOOD
4
SHDN
VOUT
22µF
7
LBO
VIN
LBI
C1+
6
GND
C1–
5
5V
+
8
0.22µF
+
CHARGE PATH
10µF
3-CELL
NiCd
BATTERY
1514 TA06
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
7
LTC1514-3.3/LTC1514-5
U
TYPICAL APPLICATIONS N
Low Power Dual Output Supply (Maximum Combined IOUT = 50mA)
ON
OFF
10Ω
Q2
220k
1
Q1
VOUT
3.3V
±4%
47k
+
750k
1%
2
VIN
LBO
2.2nF
LTC1514-5
3
LBI
10µF
402k
1%
VOUT
SHDN
4
C1+
C1
GND
–
8
VOUT
5V ±4%
VIN
2.7V TO 10V
7
6
+
0.22µF
5
+
22µF
10µF
Q1: TP0610T
Q2: MMBT3906LT1
1514 TA04
Step-Up/Step-Down Power Supply with Input Autoswitching
CENTRAL SEMI
CMPD6263C
Si6943DQ
Si6943DQ
Si6943DQ
+6VDC
WALL
ADAPTER
4 × AAA
ALKALINE
CELLS
MMBZ
5235BLT1
(6.8V)
MMBD
914LT1
470k
EXT_PWR_GOOD
10k
10k
+
7
10µF
25V
1
2.4k
1k
1M
VIN
LBI LTC1514-5 C1+
6
2
–
5
2N7002
C1
LBO
VOUT
5V
50mA
8
3
+
22µF
10V
0.22µF
GND
MMBT
3904LT1
100k
VOUT
SHDN
4
1514 TA07
MMBT
3904LT1
ON OFF
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
0.189 – 0.197*
(4.801 – 5.004)
(LTC DWG # 05-08-1610)
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
8
7
5
6
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
TYP
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
2
3
4
SO8 0996
RELATED PARTS
PART NUMBER
LTC1515 Series
LTC1516
LTC1517-5
LTC1522
LTC1555/LTC1556
LTC660
8
DESCRIPTION
Step-Up/Step-Down Switched Capacitor DC/DC Converters with Reset
Micropower, Regulated 5V Charge Pump DC/DC Converter
Micropower, Regulated 5V Charge Pump DC/DC Converter
Micropower, Regulated 5V Charge Pump DC/DC Converter
SIM Power Supply and Level Translators
100mA CMOS Voltage Converter
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900
FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com
COMMENTS
VIN 2V to 10V, 3.3V, 5V and ADJ Versions, IOUT to 50mA
IOUT = 20mA (VIN ≥ 2V), IOUT = 50mA (VIN ≥ 3V)
LTC1522 Without Shutdown and Packaged in SOT-23
Available in 8-Pin MSOP, 6µA Quiescent Current, IOUT = 20mA
Step-Up/Step-Down SIM Power Supply and Level Translators
5V to – 5V Conversion with Low Voltage Loss
151435f LT/TP 0298 4K • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 1997