LT1616
600mA, 1.4MHz Step-Down
Switching Regulator
in SOT-23
FEATURES
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DESCRIPTIO
Wide Input Range: 3.6V to 25V
5V at 400mA from 7V to 25V Input
3.3V at 400mA from 4.7V to 25V Input
Fixed Frequency 1.4MHz Operation
Uses Tiny Capacitors and Inductors
Internally Compensated
Low Shutdown Current: <1µA
Low V
CESAT
Switch: 220mV at 300mA
Tiny 6-Lead SOT-23 Package
APPLICATIO S
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The LT
®
1616 is a current mode PWM step-down DC/DC
converter with internal 0.6A power switch, packaged in a
tiny 6-lead SOT-23. The wide input range of 3.6V to 25V
makes the LT1616 suitable for regulating a wide variety of
power sources, from 4-cell batteries and 5V logic rails to
unregulated wall transformers and lead-acid batteries. Its
high operating frequency allows the use of tiny, low cost
inductors and ceramic capacitors. With its internal com-
pensation eliminating additional components, a complete
400mA step-down regulator fits onto 0.15 square inches
of PC board area.
The constant frequency current mode PWM architecture
and stable operation with ceramic capacitors results in
low, predictable output ripple. Current limiting provides
protection against shorted outputs. The low current (<1µA)
shutdown provides complete output disconnect, enabling
easy power management in battery-powered systems.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Wall Transformer Regulation
Local Logic Supply Conversion:
12V to 5V
12V or 5V to 3.3V, 2.5V or 1.8V
Distributed Supply Regulation
Digital Cameras
Battery-Powered Equipment
TYPICAL APPLICATIO
3.3V Step-Down Converter
V
IN
4.5V TO 25V
5
V
IN
BOOST
LT1616
OFF ON
4
SHDN
GND
2
C1
1µF
SW
FB
3
R2
10k
6
R1
16.5k
1
D2
C3
0.01µF
L1
10µH
100
90
EFFICIENCY (%)
D1
V
OUT
3.3V
300mA: V
IN
= 4.5V TO 25V
400mA: V
IN
= 4.7V TO 25V
C2
10µF
C1: TAIYO-YUDEN TMK316BJ105
C2: TAIYO-YUDEN JMK316BJ106ML
D1: ON SEMICONDUCTOR MBR0530
D2: 1N4148
L1: SUMIDA CR43-100
1616 TA01
U
Efficiency
V
IN
= 5V
V
IN
= 12V
80
70
60
50
40
30
0
100
300
400
LOAD CURRENT (mA)
200
500
1616 G02
U
U
V
IN
= 20V
1
LT1616
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
BOOST 1
GND 2
FB 3
6 SW
5 V
IN
4 SHDN
Input Voltage (V
IN
) ................................................. 25V
BOOST Pin Voltage ................................................. 35V
BOOST Pin Above SW Pin ...................................... 25V
SHDN Pin ............................................................... 25V
FB Voltage ................................................................ 6V
Current Into FB Pin ...............................................
±1mA
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Maximum Junction Temperature .......................... 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
LT1616ES6
S6 PACKAGE
6-LEAD PLASTIC SOT-23
S6 PART MARKING
LTNB
T
JMAX
= 125°C,
θ
JA
= 250°C/ W
Consult factory for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
IN
= 10V, V
BOOST
= 15V, unless otherwise noted. (Note 2)
PARAMETER
Undervoltage Lockout
Feedback Voltage
FB Pin Bias Current
Quiescent Current
Quiescent Current in Shutdown
Reference Line Regulation
Switching Frequency
Frequency Shift Threshold on FB Pin
Maximum Duty Cycle
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
Minimum Boost Voltage Above Switch
BOOST Pin Current
SHDN Input Voltage High
SHDN Input Voltage Low
SHDN Bias Current
V
SHDN
= 3V
V
SHDN
= 0V
8
0.01
I
SW
= 300mA
I
SW
= 300mA
1.8
0.4
15
0.1
1.6
7
(Note 3)
I
SW
= 300mA
V
FB
= Measured V
REF
+ 10mV
Not Switching
V
SHDN
= 0V
V
IN
= 5V to 25V
V
FB
= 1.1V
f
SW
= 700kHz
q
q
q
q
CONDITIONS
MIN
1.225
TYP
3.35
1.25
150
1.9
0.01
0.005
MAX
3.6
1.275
600
2.5
2
1.8
UNITS
V
V
nA
mA
µA
%/V
MHz
V
%
mA
1
80
630
1.4
0.44
87
850
220
350
10
2.5
12
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
The LT1616E 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:
Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycle.
2
U
mV
µA
V
mA
V
V
µA
µA
W
U
U
W W
W
LT1616
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency, V
OUT
= 5V
100
90
80
EFFICIENCY (%)
V
IN
= 8V
V
IN
= 12V
EFFICIENCY (%)
80
70
60
50
40
30
V
IN
= 20V
SWITCH VOLTAGE (mV)
70
60
50
40
30
0
100
V
IN
= 24V
300
400
LOAD CURRENT (mA)
200
Maximum Load Current
at V
OUT
= 5V
500
L = 15µH
400
400
500
BOOST PIN CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
L = 10µH
L = 6.8µH
300
OUTPUT LIMITED
BY DISSIPATION
200
100
0
5
15
10
INPUT VOLTAGE (V)
Switch Current Limit
1000
1.27
SWITCH CURRENT LIMIT (mA)
TYPICAL
600
MINIMUM
400
FEEDBACK PIN VOLTAGE (V)
800
1.26
UNDERVOLTAGE LOCKOUT (V)
200
0
0
20
60
40
DUTY CYCLE (%)
U W
1616 G01
Efficiency, V
OUT
= 3.3V
100
90
V
IN
= 5V
V
IN
= 12V
500
Switch Voltage Drop
400
300
200
100
0
0
100
300
400
LOAD CURRENT (mA)
200
500
1616 G02
500
0
200
400
SWITCH CURRENT (mA)
600
1616 G03
Maximum Load Current
at V
OUT
= 3.3V
16
L = 10µH
14
12
10
8
6
4
2
100
20
25
1616 G04
BOOST Pin Current
L = 4.7µH
OUTPUT LIMITED
BY DISSIPATION
300
200
0
5
15
10
INPUT VOLTAGE (V)
20
25
1616 G05
0
0
200
400
600
1616 G06
SWITCH CURRENT (mA)
Feedback Pin Voltage
3.7
3.6
3.5
3.4
3.3
3.2
Undervoltage Lockout
1.25
1.24
1.23
80
100
1616 G07
1.22
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1616 G08
3.1
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1616 G11
3
LT1616
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
2.00
1.75
SWITCHING FREQUENCY (MHz)
120
100
1.50
1.25
1.00
0.75
0.50
0.25
0
–50
–25
50
25
TEMPERATURE (°C)
0
75
100
1616 G09
SHDN PIN CURRENT (µA)
PI FU CTIO S
BOOST (Pin 1):
The BOOST pin is used to provide a drive
voltage, higher than the input voltage, to the internal
bipolar NPN power switch.
GND (Pin 2):
Tie the GND pin to a local ground plane below
the LT1616 and the circuit components. Return the feed-
back divider to this pin.
FB (Pin 3):
The LT1616 regulates its feedback pin to 1.25V.
Connect the feedback resistor divider tap to this pin. Set
the output voltage according to V
OUT
= 1.25V (1 + R1/R2).
A good value for R2 is 10k.
SHDN (Pin 4):
The SHDN pin is used to put the LT1616 in
shutdown mode. Tie to ground to shut down the LT1616.
Tie to 2V or more for normal operation. If the shutdown
feature is not used, tie this pin to the V
IN
pin.
V
IN
(Pin 5):
The V
IN
pin supplies current to the LT1616’s
internal regulator and to the internal power switch. This pin
must be locally bypassed.
SW (Pin 6):
The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.
4
U W
SHDN Pin Current
80
60
40
20
0
0
5
10
15
20
SHDN PIN VOLTAGE
25
1616 G10
U
U
U
LT1616
BLOCK DIAGRA
V
IN
5
SHDN
4
INT REG
AND
UVLO
OSC
OPERATIO
(Refer to Block Diagram)
The LT1616 is a constant frequency, current mode Buck
regulator. The 1.4MHz oscillator enables an RS flip-flop,
turning on the internal 600mA power switch Q1. An ampli-
fier and comparator monitor the current flowing between
the V
IN
and SW pins, turning the switch off when this current
reaches a level determined by the voltage at V
C
. An error
amplifier measures the output voltage through an external
resistor divider tied to the FB pin. This amplifier servos the
switch current to regulate the FB pin voltage to 1.25V. An
active clamp on the V
C
node provides current limit.
An internal regulator provides power to the control cir-
cuitry. This regulator includes an undervoltage lockout to
prevent switching when V
IN
is less than ~ 3.5V. The
W
1 BOOST
SLOPE
COMP
Σ
R
S
Q
Q
DRIVER
Q1
6 SW
FREQUENCY
FOLDBACK
V
C
g
m
1.25V
2
GND
3
FB
1616BD
U
SHDN pin is used to place the LT1616 in shutdown,
disconnecting the output and reducing the input current
to less than 1µA.
The switch driver operates from either the input or from
the BOOST pin. An external capacitor and diode are used
to generate a voltage at the BOOST pin that is higher than
the input supply. This allows the driver to fully saturate the
internal bipolar NPN power switch for efficient operation.
The oscillator reduces the LT1616’s operating frequency
when the voltage at the FB pin is low. This frequency
foldback helps to control the output current during start-
up and overload.
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