LT1612
Synchronous, Step-Down
800kHz PWM
DC/DC Converter
FEATURES
s
s
s
s
s
s
s
s
DESCRIPTIO
Operates from Input Voltage As Low As 2V
Internal 0.7A Synchronous Switches
Uses Ceramic Input and Output Capacitors
620mV Reference Voltage
800kHz Fixed Frequency Switching
Programmable Burst Mode Operation
Low Quiescent Current: 160µA
8-Lead MSOP or SO Package
APPLICATIO S
s
s
s
s
The LT
®
1612 is an 800kHz, synchronous step-down DC/
DC converter that operates from an input voltage as low
as 2V. Internal 0.45Ω switches deliver output currents up
to 500mA, and the 800kHz switching frequency allows the
use of small, low value ceramic input and output capaci-
tors. Input voltage ranges from 5.5V down to 2V and
output voltage can be set as low as the 620mV reference.
The device features Burst Mode
TM
operation, keeping
efficiency high at light loads. Burst Mode operation can be
defeated by pulling the MODE pin high, enabling constant
switching throughout the load range for low noise.
No-load quiescent current is 160µA and shutdown current
is less than 1µA. The device is available in 8-lead SO and
MSOP packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
Portable Devices
Lithium-Ion Step-Down Converters
5V to 3.3V Conversion
2-Cell Alkaline Step-Down Converters
TYPICAL APPLICATION
0.1µF
V
IN
2V
V
IN
SHDN
LT1612
C1
10µF
MODE
V
C
33.2k
330pF
FB
GND
R2
232k
1%
R1
215k
1%
C2
68µF
3.15V
BOOST
SW
100pF
L1
10µH
V
OUT
1.2V
500mA
Efficiency for LT1612 vs Linear Regulator
V
OUT
= 1.2V
90
80
V
IN
= 2V
V
IN
= 3V
V
IN
= 2V (LINEAR)
EFFICIENCY (%)
70
60
50
40
V
IN
= 3V (LINEAR)
10
100
LOAD CURRENT (mA)
500
1612 • F01b
C1: TAIYO-YUDEN JMK325BJ106MN
C2: PANASONIC EEFCDOF680R
L1: SUMIDA CD43-100
1612 F01a
30
Figure 1. 2V to 1.2V Converter
U
sn1612 1612fs
U
U
1
LT1612
ABSOLUTE
MAXIMUM
RATINGS
Supply Voltage (V
IN
) ............................................... 5.5V
SW Pin Voltage ....................................................... 5.5V
FB Pin Voltage ............................................... V
IN
+ 0.3V
V
C
Pin Voltage ........................................................... 2V
SHDN Pin Voltage ................................................... 5.5V
MODE Pin Voltage .................................................. 5.5V
PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
TOP VIEW
V
C
FB
V
IN
GND
1
2
3
4
8
7
6
5
SHDN
MODE
BOOST
SW
LT1612EMS8
MS8 PART MARKING
LTMS
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 200°C/ W
Consult factory for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
I
Q
Quiescent Current
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are TA = 25°C, VIN = VSHDN = 3V
CONDITIONS
MODE = 5V
MODE = 0V, Not Switching
SHDN = 0V
q
q
q
q
V
FB
FB Voltage
FB Line Regulation
FB Pin Bias Current (Note 3)
q
q
g
m
Error Amplifier Transconductance
Min Input Voltage
Max Input Voltage
2
f
OSC
Oscillator Frequency
q
f
OSC
Line Regulation
Maximum Duty Cycle
q
Shutdown Threshold
Minimum Voltage for Active
Maximum Voltage for Shutdown
2
U
U
W
W W
U
W
(Note 1)
BOOST Pin Voltage ....................................... V
IN
+ 5.5V
Junction Temperature ........................................... 125°C
Operating Temperature Range (Note 2) ... –40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
V
C
1
FB 2
V
IN
3
GND 4
8
7
6
5
SHDN
MODE
BOOST
SW
ORDER PART
NUMBER
LT1612ES8
S8 PART MARKING
1612
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 120°C/ W
MIN
TYP
1
160
MAX
2
220
1
0.635
0.635
0.15
50
UNITS
mA
µA
µA
V
V
%/V
nA
µmhos
V
V
kHz
kHz
%/ V
%
%
0.605
0.60
0.62
0.62
0.02
7
250
5.5
700
550
85
80
2
0.2
800
1
90
900
1100
q
q
V
V
sn1612 1612fs
LT1612
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
SHDN Pin Current
BOOST Pin Current
Switch Current Limit (Note 4)
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are TA = 25°C, VIN = VSHDN = 3V
CONDITIONS
SHDN = 2V
SHDN = 5V
BOOST = V
IN
+ 2V
Duty Cycle = 0%
MODE = OV
MODE = 5V
Burst Mode Operation Current Limit
Switch Voltage Drop
Rectifier Voltage Drop
SW Pin Leakage
MODE = 0V
I
SW
= 500mA
I
RECT
= 500mA
V
SW
= 5V, V
SHDN
= 0V
q
q
q
MIN
TYP
10
30
4
MAX
15
45
900
900
UNITS
µA
µA
mA
mA
mA
mA
600
550
710
650
180
200
300
280
400
1
mV
mV
µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT1612E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
Bias current flows out of the FB pin.
Note 4:
Duty cycle affects current limit due to slope compensation.
TYPICAL PERFOR A CE CHARACTERISTICS
FB Voltage vs Temperature
0.64
QUIESCENT CURRENT (µA)
0.63
FB PIN CURRENT (nA)
FB VOLTAGE (V)
0.62
0.61
0.60
0.59
– 50
–25
0
25
50
TEMPERATURE (°C)
U W
75
1612 • G01
Quiescent Current vs Temperature
190
MODE = 0V
180
170
160
150
140
130
120
110
100
0
–2
–4
–6
–8
–10
–12
–14
–16
–18
FB Pin Bias Current
100
– 50
–25
0
25
50
TEMPERATURE (°C)
75
100
–20
– 50
– 25
25
50
0
TEMPERATURE (°C)
75
100
1612 • G02
1612 • G03
sn1612 1612fs
3
LT1612
TYPICAL PERFOR A CE CHARACTERISTICS
SHDN Pin Bias Current
80
70
SHDN PIN CURRENT (µA)
SWITCH CURRENT (mA)
60
50
40
30
20
10
0
0
1
4
3
SHDN PIN VOLTAGE (V)
2
5
1612 • G04
MODE = 5V
600
500
400
300
200
–50
OSCILLATOR FREQUENCY (kHz)
75
100
Maximum Duty Cycle vs
Temperature
94
90
600
500
400
300
200
100
0
RECTIFIER VOLTAGE DROP (mV)
86
82
78
74
70
–50
SWITCH VOLTAGE DROP (mV)
MAXIMUM DUTY CYCLE (%)
–25
0
25
50
TEMPERATURE (°C)
4
U W
75
1612 • G07
Switch Current Limit vs
Temperature
800
MODE = 0V
700
900
800
700
600
500
1000
Oscillator Frequency vs
Temperature
–25
0
25
50
TEMPERATURE (°C)
400
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1612 • G05
1612 • G06
Switch Voltage Drop
600
500
400
300
200
100
0
Rectifier Voltage Drop
100
0
100
500
200
300
400
SWITCH CURRENT (mA)
600
0
100
500
200
300
400
RECTIFIER CURRENT (mA)
600
1612 • G08
1612 • G09
sn1612 1612fs
LT1612
PIN FUNCTIONS
V
C
(Pin 1):
Compensation Pin. This is the current sink/
source output of the error amplifier. By connecting an RC
network from this pin to ground, frequency response can
be tuned for a wide range of circuit configurations. The
voltage at this pin also sets the current limit, and if
grounded, the switch will remain in the OFF state.
FB (Pin 2):
Feedback Pin. This pin is the negative input to
the error amplifier. Connect the resistor divider tap to this
point which sets V
OUT
according to:
V
OUT
= 0.62V (1 + R1/R2)
V
IN
(Pin 3):
Supply Pin. Bypass capacitor C1 must be right
next to this pin.
GND (Pin 4):
Ground Pin. Connect directly to local ground
plane.
SW (Pin 5):
Switch Pin. Connect inductor and boost
capacitor here. Minimize trace area at this pin to keep EMI
down.
BOOST (Pin 6):
This is the supply pin for the switch driver
and must be above V
IN
by 1.5V for proper switch opera-
tion. Connect the boost capacitor to this pin.
MODE (Pin 7):
Burst Mode Operation Disable Pin. For
continuous switching operation (low noise), pull this pin
above 2V. For Burst Mode operation which gives better
light load efficiency, tie to ground. Output ripple voltage in
Burst Mode operation is typically 30mV
P-P
. See applica-
tions section for more information about this function.
SHDN (Pin 8):
Shutdown Pin. Pull this pin low for shut-
down mode. Tie to a voltage between 2V and 5.5V for
normal operation.
BLOCK DIAGRA
V
IN
3
V
C
1
FB 2
A1
0.62V
SWITCH
SWITCH
DRIVER
5 SW
MODE
7
0.7V
SHDN
8
SHUTDOWN
W
U
+
–
U
U
R
SENSE
0.08Ω
BOOST DIODE
6 BOOST
+
V/I
A2
–
SLOPE
COMPENSATION
–
A3
+
FLIP-FLOP
R
ENABLE
S
Q
RECTIFIER
DRIVE
RECTIFIER
OSCILLATOR
4 GND
1612 BD
sn1612 1612fs
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