FB Pin Current ....................................................... 1mA
SYNC Pin Current .................................................. 1mA
Operating Junction Temperature Range (Note 2)
LT1961E, LT1961I ........................... – 40°C to 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
MS8E PACKAGE
8-LEAD PLASTIC MSOP
GROUND PAD CONNECTED
TO LARGE COPPER AREA
T
JMAX
= 125°C,
θ
JA
= 50°C/W
ORDER I FOR ATIO
LEAD FREE FINISH
LT1961EMS8E#PBF
LT1961IMS8E#PBF
LEAD BASED FINISH
LT1961EMS8E
LT1961IMS8E
TAPE AND REEL
PART MARKING*
LTQY
LTQY
PART MARKING*
LTQY
LTQY
PACKAGE DESCRIPTION
8-Lead Plastic MSOP
8-Lead Plastic MSOP
PACKAGE DESCRIPTION
8-Lead Plastic MSOP
8-Lead Plastic MSOP
LT1961EMS8E#TRPBF
LT1961IMS8E#TRPBF
TAPE AND REEL
LT1961EMS8E#TR
LT1961IMS8E#TR
Consult LTC Marketing for parts specified with wider operating temperature ranges. *Temperature grades are identified by a label on the shipping container.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
PARAMETER
Recommended Operating Voltage
Maximum Switch Current Limit
Oscillator Frequency
Switch On Voltage Drop
V
IN
Undervoltage Lockout
V
IN
Supply Current
V
IN
Supply Current/I
SW
Shutdown Supply Current
Feedback Voltage
3.3V < V
IN
< 25V
I
SW
= 1.5A
(Note 3)
I
SW
= 0A
I
SW
= 1.5A
CONDITION
The
●
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, SHDN, SYNC and switch open unless otherwise noted.
MIN
●
●
●
●
●
●
3
1.5
1
310
2.47
2.6
0.9
27
6
2
V
SHDN
= 0V, V
IN
= 25V, V
SW
= 25V
●
3V < V
IN
< 25V, 0.4V < V
C
< 0.9V
●
1.182
1.176
2
U
8
7
6
5
SYNC
V
C
FB
SHDN
U
U
U
U
W W
W
W
U
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
TYP
MAX
25
3
1.5
500
2.73
1.3
20
45
1.218
1.224
UNITS
V
A
MHz
mV
V
mA
mA/A
μA
μA
V
V
1.2
1961fa
LT1961
ELECTRICAL CHARACTERISTICS
PARAMETER
FB Input Current
FB to V
C
Voltage Gain
FB to V
C
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
Duty Cycle = 0%
0.4V < V
C
< 0.9V
ΔI
VC
=
±10μA
V
FB
= 1V
V
FB
= 1.4V
CONDITION
The
●
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, SHDN, SYNC and switch open unless otherwise noted.
MIN
●
●
●
●
TYP
– 0.2
350
850
– 120
110
2.4
0.3
0.9
MAX
– 0.4
1300
– 165
165
UNITS
μA
μMho
μA
μA
A/V
V
V
%
%
%
0
150
500
– 85
70
V
C
= 1.2V, I
SW
= 100mA
V
C
= 1.2V, I
SW
= 1A, 25°C
≤
T
A
≤
125°C
V
C
= 1.2V, I
SW
= 1A, T
A
≤
25°C
SHDN = 60mV Above Threshold
SHDN = 100mV Below Threshold
●
80
75
70
1.28
–7
4
1.5
90
80
75
1.35
–10
7
1.5
1.42
–13
10
2.2
2
20
SHDN Threshold Voltage
SHDN Input Current (Shutting Down)
SHDN Threshold Current Hysteresis
SYNC Threshold Voltage
SYNC Input Frequency
SYNC Pin Resistance
I
SYNC
= 1mA
●
●
V
μA
μA
V
MHz
kΩ
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LT1961E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the – 40°C to
125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT1961I is guaranteed over the – 40ºC to 125ºC operating junction
temperature range.
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.
1961fa
3
LT1961
TYPICAL PERFORMANCE CHARACTERISTICS
FB vs Temperature
1.22
400
125°C
350
SWITCH VOLTAGE (mV)
1.21
300
250
200
150
100
50
1.18
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
0
0
0.5
1
SWITCH CURRENT (A)
1.5
1961 G02
1.20
–40°C
FREQUENCY (MHz)
FB VOLTAGE (V)
1.19
SHDN Threshold vs Temperature
1.40
7
6
1.38
SHDN THRESHOLD (V)
V
IN
CURRENT (μA)
SHDN INPUT (μA)
5
4
3
2
1
1.36
1.34
1.32
1.30
–50
–25
0
25
50
75
TEMPERATURE (°C)
SHDN Supply Current
300
250
V
IN
CURRENT (μA)
200
150
100
50
0
T
A
= 25°C
V
IN
= 15V
1200
1000
V
IN
CURRENT (μA)
800
600
400
200
0
SWITCH PEAK CURRENT (A)
0
0.2
0.4 0.6 0.8
1
1.2
SHUTDOWN VOLTAGE (V)
4
U W
100
Switch On Voltage Drop
1.5
Oscillator Frequency
T
A
= 25°C
25°C
1.4
1.3
1.2
1.1
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
1961 G01
1961 G03
SHDN Supply Current vs V
IN
T
A
= 25°C
SHDN = 0V
–12
–10
SHDN I
P
Current vs Temperature
SHUTTING DOWN
–8
–6
–4
–2
0
–50
STARTING UP
0
125
0
5
10
15
V
IN
(V)
20
25
30
1961 G05
–25
0
25
50
75
TEMPERATURE (°C)
100
125
1961 G04
1961G06
Input Supply Current
T
A
= 25°C
2.0
Current Limit Foldback
T
A
= 25°C
40
FB INPUT CURRENT (μA)
1.5
SWITCH CURRENT
1.0
30
MINIMUM
INPUT
VOLTAGE
20
0.5
FB CURRENT
0
10
1.4
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1961 G08
0
0.2
0.4
0.6
0.8
FEEDBACK VOLTAGE (V)
1
0
1.2
1961 G09
1961 G07
1961fa
LT1961
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. If required, the current limit
can be reduced during start up when the FB pin is below
0.5V (see the Current Limit Foldback graph in the Typical
Performance Characteristics section). An impedance of
less than 5kΩ at the FB pin is needed for this feature to
operate.
V
IN
:
This pin powers the internal circuitry and internal
regulator. Keep the external bypass capacitor close to this
pin.
GND:
Short GND pins 3 and 4 and the exposed pad on the
PCB. The GND is 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 of the IC. This
condition occurs when the load current flows through the
metal path between the GND pins and the load ground
point. Keep the ground path short between the GND pins
and the load and use a ground plane when possible. Keep
the path between the input bypass and the GND pins short.
The exposed pad should be attached to a large copper area
to improve thermal resistance.
V
SW
:
The switch pin is the collector of the on-chip power
NPN switch and has large currents flowing through it.
Keep the traces to the switching components as short as
possible to minimize radiation and voltage spikes.
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 1.35V 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 0.3V for very light loads and 0.9V at maximum
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