LM2695
High Voltage (30V, 1.25A) Step Down Switching
Regulator
General Description
The LM2695 Step Down Switching Regulator features all of
the functions needed to implement a low cost, efficient, buck
bias regulator capable of supplying 1.25A to the load. This
buck regulator contains a 33V N-Channel Buck Switch, and
is available in the thermally enhanced LLP-10 and TSSOP-
14EP packages. The hysteretic regulation scheme requires
no loop compensation, results in fast load transient re-
sponse, and simplifies circuit implementation. The operating
frequency remains constant with line and load variations due
to the inverse relationship between the input voltage and the
on-time. The current limit detection is set at 1.25A. Additional
features include: VCC under-voltage lockout, thermal shut-
down, gate drive under-voltage lockout, and maximum duty
cycle limiter.
Features
n
Integrated 33V, N-Channel buck switch
n
Integrated start-up regulator
n
Input Voltage Range: 8V to 30V
n
No loop compensation required
n
Ultra-Fast transient response
n
Operating frequency remains constant with load current
and input voltage
n
Maximum Duty Cycle Limited During Start-Up
n
Adjustable output voltage
n
Valley Current Limit At 1.25A
n
Precision internal reference
n
Low bias current
n
Highly efficient operation
n
Thermal shutdown
Typical Applications
n
High Efficiency Point-Of-Load (POL) Regulator
n
Non-Isolated Telecommunication Buck Regulator
n
Secondary High Voltage Post Regulator
Package
n
LLP-10 (4 mm x 4 mm)
n
TSSOP-14EP
n
Exposed Thermal Pad For Improved Heat Dissipation
Basic Step Down Regulator
20170431
January 2006
LM2695
High
V
oltage
(30V
,
1.25A)
Step
Down
Switching
Regulator
2006 National Semiconductor Corporation
DS201704
www.national.com
Connection Diagrams
20170432
14-Lead TSSOP(EP)
20170402
10-Lead LLP
Ordering Information
Order Number
Package Type
NSC Package
Drawing
Junction Temperature
Range
Supplied As
LM2695SD
LLP-10 (4x4)
SDC10A
-40C to + 125C
1000 Units on Tape and Reel
LM2695SDX
LLP-10 (4x4)
SDC10A
-40C to + 125C
4500 Units on Tape and Reel
LM2695MH
TSSOP-14EP
MXA14A
-40C to + 125C
94 Units in Rail
LM2695MHX
TSSOP-14EP
MXA14A
-40C to + 125C
2500 Units on Tape and Reel
LM2695
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2
Pin Descriptions
Pin Number
Name
Description
Application Information
LLP-10
TSSOP-14
1
2
SW
Switching Node
Internally connected to the buck switch source.
Connect to the inductor, free-wheeling diode, and
bootstrap capacitor.
2
3
BST
Boost pin for bootstrap capacitor
Connect a 0.022 F capacitor from SW to this pin.
The capacitor is charged from V
CC
via an internal
diode during each off-time.
3
4
I
SEN
Current sense
The re-circulating current flows through the internal
sense resistor, and out of this pin to the
free-wheeling diode. Current limit is nominally set at
1.25A.
4
5
S
GND
Sense Ground
Re-circulating current flows into this pin to the
current sense resistor.
5
6
RTN
Circuit Ground
Ground for all internal circuitry other than the current
limit detection.
6
9
FB
Feedback input from the
regulated output
Internally connected to the regulation and
over-voltage comparators. The regulation level is
2.5V.
7
10
SS
Softstart
An internal 12.3 A current source charges an
external capacitor to 2.5V, providing the softstart
function.
8
11
R
ON
/SD
On-time control and shutdown
An external resistor from V
IN
to this pin sets the
buck switch on-time. Grounding this pin shuts down
the regulator.
9
12
V
CC
Output from the startup regulator
Nominally regulates at 7.0V. An external voltage
(8V-14V) can be applied to this pin to reduce
internal dissipation. An internal diode connects V
CC
to V
IN
.
10
13
V
IN
Input supply voltage
Nominal input range is 8.0V to 30V.
1,7,8,14
NC
No connection.
No internal connection.
EP
Exposed Pad
Exposed metal pad on the underside of the device.
It is recommended to connect this pad to the PC
board ground plane to aid in heat dissipation.
LM2695
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3
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN to RTN
33V
BST to RTN
47V
SW to RTN (Steady State)
-1.5V
ESD Rating (Note 2)
Human Body Model
2kV
BST to VCC
33V
VIN to SW
33V
BST to SW
14V
VCC to RTN
14V
SGND to RTN
-0.3V to +0.3V
Current out of ISEN
See Text
SS to RTN
-0.3V to 4V
All Other Inputs to RTN
-0.3 to 7V
Storage Temperature Range
-65C to +150C
JunctionTemperature
150C
Operating Ratings
(Note 1)
VIN
8.0V to 30V
Junction Temperature
-40C to + 125C
Electrical Characteristics
Specifications with standard type are for T
J
= 25C only; limits in boldface type
apply over the full Operating Junction Temperature (T
J
) range. Minimum and Maximum limits are guaranteed through test,
design, or statistical correlation. Typical values represent the most likely parametric norm at T
J
= 25C, and are provided for
reference purposes only. Unless otherwise stated the following conditions apply: V
IN
= 24V, R
ON
= 200k
. See (Note 5).
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Start-Up Regulator, V
CC
V
CC
Reg
V
CC
regulated output
6.6
7
7.4
V
V
IN
-V
CC
dropout voltage
I
CC
= 0 mA,
V
CC
= UVLO
VCC
+ 250 mV
1.3
V
V
CC
output impedance
0 mA
I
CC
5 mA
140
V
CC
current limit (Note 3)
V
CC
= 0V
9.7
mA
UVLO
VCC
V
CC
under-voltage lockout
threshold
V
CC
increasing
5.7
V
UVLO
VCC
hysteresis
V
CC
decreasing
150
mV
UVLO
VCC
filter delay
100 mV overdrive
3
s
I
IN
operating current
Non-switching, FB = 3V
0.5
0.8
mA
I
IN
shutdown current
RON/SD = 0V
95
200
A
Switch Characteristics
Rds(on)
Buck Switch Rds(on)
I
TEST
= 200 mA
0.33
0.7
UVLO
GD
Gate Drive UVLO
V
BST
- V
SW
Increasing
3.0
4.4
5.5
V
UVLO
GD
hysteresis
480
mV
Softstart Pin
Pull-up voltage
2.5
V
Internal current source
12.3
A
Current Limit
I
LIM
Threshold
Current out of ISEN
1
1.25
1.5
A
Resistance from ISEN to
SGND
130
m
Response time
150
ns
On Timer
t
ON
- 1
On-time
V
IN
= 10V, R
ON
= 200 k
2.1
2.8
3.6
s
t
ON
- 2
On-time
V
IN
= 30V, R
ON
= 200 k
950
ns
Shutdown threshold
Voltage at RON/SD rising
0.45
0.8
1.2
V
Threshold hysteresis
Voltage at RON/SD falling
37
mV
Off Timer
t
OFF
Minimum Off-time
250
ns
Regulation and Over-Voltage Comparators (FB Pin)
V
REF
FB regulation threshold
SS pin = steady state
2.440
2.5
2.550
V
FB over-voltage threshold
2.9
V
LM2695
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Electrical Characteristics
Specifications with standard type are for T
J
= 25C only; limits in boldface type
apply over the full Operating Junction Temperature (T
J
) range. Minimum and Maximum limits are guaranteed through test,
design, or statistical correlation. Typical values represent the most likely parametric norm at T
J
= 25C, and are provided for
reference purposes only. Unless otherwise stated the following conditions apply: V
IN
= 24V, R
ON
= 200k
. See (Note
5). (Continued)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
FB bias current
1
nA
Thermal Shutdown
T
SD
Thermal shutdown
temperature
175
C
Thermal shutdown hysteresis
20
C
Thermal Resistance
JA
Junction to Ambient
0 LFPM Air Flow
Both Packages
37
C/W
JC
Junction to Case
Both Packages
6.6
C/W
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device
is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: The human body model is a 100pF capacitor discharged through a 1.5k
resistor into each pin.
Note 3: V
CC
provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading
Note 4: For detailed information on soldering plastic LLP packages, refer to the Packaging Data Book available from National Semiconductor Corporation.
Note 5: Typical specifications represent the most likely parametric norm at 25C operation.
LM2695
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