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Linear Technology Electronic Components Datasheet

LT1432-3.3 Datasheet

3.3V High Efficiency Step-Down Switching Regulator Controller

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FEATURES
s Accurate Preset 3.3V Output
s Up to 87% Efficiency
s Optional Burst ModeTM Operation for Light Loads
s Can Be Used with Many LTC Switching ICs
s Accurate Ultra-Low-Loss Current Limit
s Operates with Inputs from 4.5V to 30V
s Shutdown Mode Draws Only 15µA
s Uses Small 30µH Inductor
APPLICATI S
s Laptop and Palmtop Computers
s Portable Data-Gathering Instruments
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
LT1432-3.3
3.3V High Efficiency Step-Down
Switching Regulator Controller
DESCRIPTIO
The LT®1432-3.3 is a control chip designed to operate
with the LT1171/LT1271 family of switching regulators to
make a very high efficiency 3.3V step-down (buck) switch-
ing regulator. A minimum of external components is
needed.
Included is an accurate current limit which uses only
60mV sense voltage and uses “free” PC board trace
material for the sense resistor. Logic controlled electronic
shutdown mode draws only 15µA battery current. The
switching regulator operates down to 4.5V input.
The LT1432-3.3 has a logic controlled Burst Mode operation
to achieve high efficiency at very light load currents (0mA to
100mA) such as memory keep-alive. In normal switching
mode, the standby power loss is about 30mW, limiting
efficiency at light loads. In Burst Mode operation, standby
loss is reduced to approximately 11mW. Output current in
this mode is typically in the 5mA to 100mA range.
The LT1432-3.3 is available in 8-pin SO and PDIP pack-
ages. The LT1171/LT1271 is also available in surface
mount DD packages.
TYPICAL APPLICATI
D2
1N5818
VIN
+
C1
330µF
35V
VSW
C6
0.02µF
FB
VC
D1
MBR330p
LT1271
VIN
GND
C5
0.03µF
C3 +
10µF
TANT
VC DIODE
D2**
10µH
3A
+
100µF
16V
OPTIONAL
OUTPUT
FILTER
L1
30µH
V+
R2*
0.013
+
× VOUT***
3.3V
C2 3A
390µF
16V
MODE LOGIC
220pF
<0.3V = NORMAL MODE
>2.5V = SHUTDOWN
OPEN = Burst Mode
OPERATION
VIN
MODE
LT1432-3.3
VLIM
VOUT
GND
*R2 IS MADE FROM PC BOARD
COPPER TRACES.
FOR CIRCUITS WHICH DO NOT USE
**OPTIONAL CONNECTION FOR D2.
EFFICIENCY IS HIGHER, BUT MINIMUM
Burst Mode OPERATION, C5 MAY
BE PARALLEL WITH A 680, 0.1µF
V IN INCREASES. SEE APPLICATION
INFORMATION SECTION.
IN SERIES TO GIVE WIDE PHASE MARGIN ***MAXIMUM CURRENT IS DETERMINED
WITH DIFFERENT SWITCHING ICs AND
BY THE CHOICE OF LT1071 FAMILY MAIN SWITCHER IC.
OUTPUT CAPACITORS
SEE APPLICATION INFORMATION SECTION.
LT1432-3.3 TA01
Figure 1. High Efficiency 5V Buck Converter
Efficiency
100
LT1271, L = 30µH
VIN = 7V
D2 CONNECTED
90 TO OUTPUT
D2 CONNECTED
80 TO INPUT
70
Burst Mode OPERATION
(USE mA SCALE)
60
0
0
1A
20mA
2A
40mA
3A
60mA
LT1432-3.3 TA02
1


Linear Technology Electronic Components Datasheet

LT1432-3.3 Datasheet

3.3V High Efficiency Step-Down Switching Regulator Controller

No Preview Available !

LT1432-3.3
ABSOLUTE AXI U RATI GS
VVI+NPPinin.........................................................................................................................................
30V
40V
VC ........................................................................... 35V
VLIM and VOUT Pins ................................................... 7V
Diode Pin Voltage ................................................... 30V
Mode Pin Current (Note 2) ..................................... 1mA
Operating Temperature Range .................... 0°C to 70°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
PACKAGE/ORDER I FOR ATIO
VLIM 1
VOUT 2
VIN 3
V+ 4
TOP VIEW
8 MODE
7 GND
6 VC
5 DIODE
ORDER PART
NUMBER
LT1432CN8-3.3
LT1432CS8-3.3
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 100°C, θJA = 150°C/W (N8)
TJMAX = 100°C, θJA = 170°C/W (S8)
Consult factory for Military and Industrial grade parts.
ELECTRICAL CHARACTERISTICS
VC = 4V, VIN = 4V, V+ = 8V, VDIODE = Open, VLIM = VOUT, VMODE = 0V, TJ = 25°C
Device is in standard test loop unless otherwise noted.
PARAMETER
Regulated Output Voltage
Output Voltage Line Regulation
Input Supply Current (Note 1)
Quiescent Output Load Current
Mode Pin Current
Mode Pin Threshold Voltage
(Normal to Burst)
VC Pin Saturation Voltage
VC Pin Maximum Sink Current
VC Pin Source Current
Current Limit Sense Voltage (Note 3)
VLIM Pin Current
Supply Current in Shutdown
Burst Mode Operation Output Ripple
Burst Mode Operation Average Output Voltage
Clamp Diode Forward Voltage
Start-up Drive Current
Restart Time Delay
Transconductance, Output to VC Pin
CONDITIONS
VC Current = 220µA
VIN = 4V to 30V
VIN = 4V to 30V, V+ = VIN + 5V, VC = VIN + 1V
VMODE = 0V (Current Is Out of Pin)
VMODE = 3.3V (Shutdown)
IMODE = 10µA (Out of Pin)
VOUT = 3.6V (Forced)
VOUT = 3.6V (Forced)
VOUT = 3.0V (Forced)
Device in Current Limit Loop
Device in Current Limit Loop
(Current Is Out of Pin)
VMODE > 3V, VIN < 30V, VC and V+ = 0V
Device in Burst Test Circuit
Device in Burst Test Circuit
IF = 1mA, All Other Pins Open
VVO+U=T
= 1.5V (Forced), VIN
VIN – 1V, VC = VIN
= 4V
1.5V
to
26V,
(Note 4)
IC = 150µA to 250µA
MIN
q 3.24
q
q
q
q
q 0.6
q
q 0.45
q 35
56
q 30
q 3.15
q
q 30
0.7
q 2700
TYP MAX UNITS
3.30 3.36
5 20
0.3 0.5
V
mV
mA
0.9 1.2
mA
30 50
15 30
0.9 1.5
µA
µA
V
0.25 0.45
0.8 1.5
60 100
60 64
45 70
V
mA
µA
mV
µA
15 60
µA
100 mVp-p
3.30 3.45
V
0.5 0.65
V
45 mA
1.2 10
ms
3600 5000 µmho
2


Part Number LT1432-3.3
Description 3.3V High Efficiency Step-Down Switching Regulator Controller
Maker Linear Technology
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