LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5
Monolithic 1.5A, 1.25MHz
Step-Down Switching Regulators
FEATURES
s
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DESCRIPTIO
1.5A Switch in a Small MSOP Package
Constant 1.25MHz Switching Frequency
High Power Exposed Pad (MS8E) Package
Wide Operating Voltage Range: 3V to 25V
High Efficiency 0.22Ω Switch
1.2V Feedback Reference Voltage
Fixed Output Voltages of 1.8V, 2.5V, 3.3V, 5V
2% Overall Output Tolerance
Uses Low Profile Surface Mount Components
Low Shutdown Current: 6µA
Synchronizable to 2MHz
Current Mode Loop Control
Constant Maximum Switch Current Rating at All Duty
Cycles*
The LT
®
1767 is a 1.25MHz monolithic buck switching
regulator. A high efficiency 1.5A, 0.22Ω switch is included
on the die together with all the control circuitry required to
complete a high frequency, current mode switching regu-
lator. Current mode control provides fast transient re-
sponse and excellent loop stability.
New design techniques achieve high efficiency at high
switching frequencies over a wide operating range. A low
dropout internal regulator maintains consistent perfor-
mance over a wide range of inputs from 24V systems to Li-
Ion batteries. An operating supply current of 1mA im-
proves efficiency, especially at lower output currents.
Shutdown reduces quiescent current to 6µA. Maximum
switch current remains constant at all duty cycles. Syn-
chronization allows an external logic level signal to in-
crease the internal oscillator from 1.4MHz to 2MHz.
The LT1767 is available in an 8-pin MSOP fused leadframe
package and a low thermal resistance exposed pad pack-
age. Full cycle-by-cycle short-circuit protection and ther-
mal shutdown are provided. High frequency operation
allows the reduction of input and output filtering compo-
nents and permits the use of chip inductors.
, LTC and LT are registered trademarks of Linear Technology Corporation.
*Patent Pending
APPLICATIO S
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DSL Modems
Portable Computers
Wall Adapters
Battery-Powered Systems
Distributed Power
TYPICAL APPLICATIO
12V to 3.3V Step-Down Converter
D2
CMDSH-3
C2
0.1µF
V
IN
12V
BOOST
V
IN
OPEN
OR
HIGH
= ON
LT1767-3.3
SHDN
SYNC
FB
GND
V
C
C
C
1.5nF
R
C
4.7k
*MAXIMUM OUTPUT CURRENT IS SUBJECT TO THERMAL DERATING.
1767 TA01
L1
5µH
EFFICIENCY (%)
C3
2.2µF
CERAMIC
V
SW
OUTPUT
3.3V
1.2A*
D1
UPS120
C1
10µF
CERAMIC
U
Efficiency vs Load Current
95
V
IN
= 10V
V
OUT
= 5V
90
85
V
IN
= 5V
V
OUT
= 3.3V
80
75
70
0
0.2
0.4 0.6 0.8
1
LOAD CURRENT (A)
1.2
1.4
1767 TA01a
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sn1767 1767fas
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LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5
ABSOLUTE
MAXIMUM
RATINGS
Input Voltage .......................................................... 25V
BOOST Pin Above SW ............................................ 20V
Max BOOST Pin Voltage .......................................... 35V
SHDN Pin ............................................................... 25V
FB Pin Voltage .......................................................... 6V
FB Pin Current ....................................................... 1mA
PACKAGE/ORDER INFORMATION
ORDER PART NUMBER
TOP VIEW
BOOST
V
IN
SW
GND
1
2
3
4
8
7
6
5
SYNC
V
C
FB
SHDN
MS8 PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 110°C/W
GROUND PIN CONNECTED
TO LARGE COPPER AREA
LT1767EMS8
LT1767EMS8-1.8
LT1767EMS8-2.5
LT1767EMS8-3.3
LT1767EMS8-5
MS8 PART MARKING
LTLS
LTWG
LTWD
LTWE
LTWF
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
IN
= 15V, V
C
= 0.8V, Boost = V
IN
+ 5V, SHDN, SYNC and switch open unless otherwise noted.
PARAMETER
Maximum Switch Current Limit
Oscillator Frequency
Switch On Voltage Drop
V
IN
Undervoltage Lockout
V
IN
Supply Current
Shutdown Supply Current
Feedback Voltage
CONDITION
T
A
= 0°C to 125°C
T
A
= < 0°C
3.3V < V
IN
< 25V
q
I
SW
= –1.5A, 0°C
≤
T
A
≤
125°C and –1.3A, T
A
< 0°C
q
(Note 3)
V
FB
= V
NOM
+ 17%
V
SHDN
= 0V, V
IN
= 25V, V
SW
= 0V
3V < V
IN
< 25V, 0.4V < V
C
< 0.9V
(Note 3)
FB Input Current
LT1767 (Adj)
2
U
U
W
W W
U
W
(Note 1)
SYNC Pin Current .................................................. 1mA
Operating Junction Temperature Range (Note 2)
LT1767E .......................................... – 40°C to 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART NUMBER
TOP VIEW
BOOST
V
IN
SW
GND
1
2
3
4
8
7
6
5
SYNC
V
C
FB
SHDN
MS8E PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 40°C/W
EXPOSED GND PAD
CONNECTED TO LARGE
COPPER AREA ON PCB
LT1767EMS8E
LT1767EMS8E-1.8
LT1767EMS8E-2.5
LT1767EMS8E-3.3
LT1767EMS8E-5
MS8E PART MARKING
LTZG
LTZH
LTZJ
LTZK
LTZL
MIN
1.5
1.3
1.1
1.1
TYP
2
1.25
330
MAX
3
3
1.4
1.5
400
500
2.73
1.3
20
45
1.218
1.224
1.836
2.55
3.366
5.1
– 0.5
UNITS
A
A
MHz
MHz
mV
mV
V
mA
µA
µA
V
V
V
V
V
V
µA
q
q
q
2.47
2.6
1
6
LT1767 (Adj)
q
1.182
1.176
1.764
2.45
3.234
4.9
1.2
1.8
2.5
3.3
5
– 0.25
LT1767-1.8
LT1767-2.5
LT1767-3.3
LT1767-5
q
q
q
q
q
sn1767 1767fas
LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
IN
= 15V, V
C
= 0.8V, Boost = V
IN
+ 5V, SHDN, SYNC and switch open unless otherwise noted.
PARAMETER
FB Input Resistance
CONDITION
LT1767-1.8
LT1767-2.5
LT1767-3.3
LT1767-5
0.4V < V
C
< 0.9V
∆I
VC
=
±10µA
V
FB
= V
NOM
– 17%
V
FB
= V
NOM
+ 17%
Duty Cycle = 0%
V
C
= 1.2V, I
SW
= 400mA
q
q
q
q
q
q
q
q
MIN
10.5
14.7
19
29
150
500
80
70
TYP
15
21
27.5
42
350
850
120
110
2.5
0.35
0.9
MAX
21
30
39
60
1300
160
180
UNITS
kΩ
kΩ
kΩ
kΩ
µMho
µA
µA
A/V
V
V
%
%
Error Amp Voltage Gain
Error Amp Transconductance
V
C
Pin Source Current
V
C
Pin Sink Current
V
C
Pin to Switch Current Transconductance
V
C
Pin Minimum Switching Threshold
V
C
Pin 1.5A I
SW
Threshold
Maximum Switch Duty Cycle
Minimum Boost Voltage Above Switch
Boost Current
SHDN Threshold Voltage
SHDN Input Current (Shutting Down)
SHDN Threshold Current Hysteresis
SYNC Threshold Voltage
SYNC Input Frequency
SYNC Pin Resistance
85
80
90
1.8
10
30
2.7
15
45
1.40
–13
10
2.2
2
20
I
SW
= –1.5A, 0°C
≤
T
A
≤
125°C and –1.3A, T
A
< 0°C
I
SW
= – 0.5A (Note 4)
I
SW
= –1.5A, 0°C
≤
T
A
≤
125°C and –1.3A, T
A
< 0°C (Note 4)
SHDN = 60mV Above Threshold
SHDN = 100mV Below Threshold
q
q
q
q
q
q
V
mA
mA
V
µA
µA
V
MHz
kΩ
1.27
–7
4
1.5
1.33
–10
7
1.5
I
SYNC
= 1mA
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT1767E is guaranteed to meet performance specifications
from 0°C to 125°C. Specifications over the – 40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3:
Minimum input voltage is defined as the voltage where the internal
regulator enters lockout. Actual minimum input voltage to maintain a
regulated output will depend on output voltage and load current. See
Applications Information.
Note 4:
Current flows into the BOOST pin only during the on period of the
switch cycle.
TYPICAL PERFORMANCE CHARACTERISTICS
FB vs Temperature (Adj)
1.22
400
125°C
350
SWITCH VOLTAGE (mV)
1.21
FREQUENCY (MHz)
FB VOLTAGE (V)
1.20
1.19
1.18
–50
–25
0
25
50
75
TEMPERATURE (°C)
U W
100
Switch On Voltage Drop
1.50
1.45
25°C
Oscillator Frequency
300
250
1.40
1.35
1.30
1.25
1.20
1.15
1.10
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
–40°C
200
150
100
50
125
1767 G01
0
0
0.5
1
SWITCH CURRENT (A)
1.5
1767 G02
1767 G03
sn1767 1767fas
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LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5
TYPICAL PERFOR A CE CHARACTERISTICS
SHDN Threshold vs Temperature
1.40
1.38
SHDN THRESHOLD (V)
V
IN
CURRENT (µA)
SHDN INPUT (µA)
1.36
1.34
1.32
1.30
–50
–25
0
25
50
75
TEMPERATURE (°C)
Minimum Input Voltage for 2.5V Out
3.5
300
3.3
INPUT VOLTAGE (V)
V
IN
CURRENT (µA)
V
IN
CURRENT (µA)
3.1
2.9
2.7
2.5
0.001
0.1
0.01
LOAD CURRENT (A)
Current Limit Foldback
2.0
40
1.5
SWITCH PEAK CURRENT (A)
OUTPUT CURRENT (A)
SWITCH CURRENT
1.0
20
1.1
OUTPUT CURRENT (A)
1.5
0.5
FB CURRENT
0
0
0.2
0.4
0.6
0.8
FEEDBACK VOLTAGE (V)
4
U W
100
1767 G04
SHDN Supply Current vs V
IN
7
SHDN = 0V
6
5
4
3
2
1
0
0
5
10
15
V
IN
(V)
20
25
30
1767 G05
SHDN I
P
Current vs Temperature
–12
–10
SHUTTING DOWN
–8
–6
–4
–2
0
–50
STARTING UP
125
–25
0
25
50
75
TEMPERATURE (°C)
100
125
1767 G06
SHDN Supply Current
1200
V
IN
= 15V
250
200
150
100
50
0
1000
800
600
400
200
0
Input Supply Current
MINIMUM
INPUT
VOLTAGE
1
1767 G07
0
0.2
0.4 0.6 0.8
1
1.2
SHUTDOWN VOLTAGE (V)
1.4
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1767 G09
1767 G08
Maximum Load Current,
V
OUT
= 5V
1.5
Maximum Load Current,
V
OUT
= 2.5V
1.3
30
L = 4.7µH
1.3
L = 4.7µH
FB INPUT CURRENT (µA)
L = 2.2µH
1.1
L = 1.5µH
0.9
0.9
L = 2.2µH
10
0.7
L = 1.5µH
1
0
1.2
1767 G10
0.5
0
5
10
15
INPUT VOLTAGE (V)
20
25
1767 G11
0.7
0
5
10
15
INPUT VOLTAGE (V)
20
25
1767 G12
sn1767 1767fas
LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5
PIN FUNCTIONS
FB:
The feedback pin is used to set output voltage using an
external voltage divider that generates 1.2V at the pin with
the desired output voltage. The fixed voltage 1.8V, 2.5V,
3.3V and 5V versions have the divider network included
internally and the FB pin is connected directly to the
output. If required, the current limit can be reduced during
start up or short-circuit when the FB pin is below 0.5V (see
the Current Limit Foldback graph in the Typical Perfor-
mance Characteristics section). An impedance of less
than 5kΩ (adjustable part only) at the FB pin is needed for
this feature to operate.
BOOST:
The BOOST pin is used to provide a drive voltage,
higher than the input voltage, to the internal bipolar NPN
power switch. Without this added voltage, the typical
switch voltage loss would be about 1.5V. The additional
boost voltage allows the switch to saturate and voltage
loss approximates that of a 0.22Ω FET structure.
V
IN
:
This is the collector of the on-chip power NPN switch.
This pin powers the internal circuitry and internal regula-
tor. At NPN switch on and off, high dI/dt edges occur on
this pin. Keep the external bypass capacitor and catch
diode close to this pin. All trace inductance in this path will
create a voltage spike at switch off, adding to the V
CE
voltage across the internal NPN.
GND:
The GND pin acts as the reference for the regulated
output, so load regulation will suffer if the “ground” end of
the load is not at the same voltage as the GND pin of the
IC. This condition will occur when load current or other
currents flow through metal paths between the GND pin
and the load ground point. Keep the ground path short
between the GND pin and the load and use a ground plane
when possible. Keep the path between the input bypass
and the GND pin short. The GND pin of the MS8 package
is directly attached to the internal tab. This pin should be
attached to a large copper area to improve thermal
resistance. The exposed pad of the MS8E package is also
connected to GND. This should be soldered to a large
copper area to improve its thermal resistance.
V
SW
:
The switch pin is the emitter of the on-chip power
NPN switch. This pin is driven up to the input pin voltage
during switch on time. Inductor current drives the switch
pin negative during switch off time. Negative voltage must
be clamped with an external catch diode with a V
BR
<0.8V.
SYNC:
The sync pin is used to synchronize the internal
oscillator to an external signal. It is directly logic compat-
ible and can be driven with any signal between 20% and
80% duty cycle. The synchronizing range is equal to
initial
operating frequency, up to 2MHz. See Synchronization
section in Applications Information for details. When not
in use, this pin should be grounded.
SHDN:
The shutdown pin is used to turn off the regulator
and to reduce input drain current to a few microamperes.
The 1.33V threshold can function as an accurate under-
voltage lockout (UVLO), preventing the regulator from
operating until the input voltage has reached a predeter-
mined level. Float or pull high to put the regulator in the
operating mode.
V
C
:
The V
C
pin is the output of the error amplifier and the
input of the peak switch current comparator. It is normally
used for frequency compensation, but can do double duty
as a current clamp or control loop override. This pin sits
at about 0.35V for very light loads and 0.9V at maximum
load. It can be driven to ground to shut off the output.
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sn1767 1767fas
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