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1
LT1432
5V High Efficiency Step-Down
Switching Regulator Controller
S
FEATURE
The LT1432 is a control chip designed to operate with the
LT1170/LT1270 family of switching regulators to make a
very high efficiency 5V step-down (buck) switching regula-
tor. 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 15
A battery current. The switching
regulator operates down to 6V input.
The LT1432 has a logic controlled "burst" mode to achieve
high efficiency at very light load currents (0 to 100mA) such
as memory keep-alive. In normal switching mode, the
standby power loss is about 60mW, limiting efficiency at
light loads. In burst mode, standby loss is reduced to
approximately 15mW. Output current in this mode is
typically in the 5mA to 100mA range.
The LT1432 is available in 8-pin surface mount and DIP
packages. The LT1170/LT1270 family will also be available
in a surface mount version of the 5-pin TO-220 package.
For 3.3V versions contact Linear Technology Corporation.
D
U
ESCRIPTIO
s
Accurate Preset +5V Output
s
Up to 90% Efficiency
s
Optional Burst Mode for Light Loads
s
Can be Used with Many LTC Switching ICs
s
Accurate Ultra-Low-Loss Current Limit
s
Operates with Inputs from 6V to 30V
s
Shutdown Mode Draws Only 15
A
s
Uses Small 50
H Inductor
U
S
A
O
PPLICATI
s
Laptop and Palmtop Computers
s
Portable Data-Gathering Instruments
s
DC Bus Distribution Systems
s
Battery-Powered Digital Widgets
0
60
EFFICIENCY (%)
70
80
90
100
1A
2A
3A
20mA
LT1432 TA02
40mA
60mA
0
NORMAL MODE
(USE AMPS SCALE)
BURST MODE
(USE mA SCALE)
LT1271, L = 50
H
Efficiency
Figure 1. High Efficiency 5V Buck Converter
U
A
O
PPLICATI
TYPICAL
+
V
SW
FB
GND
V
IN
V
C
LT1170
LT1271
V
C
GND
V
IN
MODE
DIODE
V
OUT
V
LIM
V
+
+
C1
330
F
35V
C6
0.02
F
C4
0.1
F
R1
680
C5
0.03
F
D1
MBR330p
C3
4.7
F
TANT
D2
1N4148
L1
50
H
R2*
0.013
C2
390
F
16V
V
OUT
5V
3A**
+
MODE LOGIC
220pF
<0.3V = NORMAL MODE
>2.5V = SHUTDOWN
OPEN = BURST MODE
* R2 IS MADE FROM PC BOARD
COPPER TRACES.
** MAXIMUM CURRENT IS DETERMINED
BY THE CHOICE OF LT1070 FAMILY.
SEE APPLICATION SECTION.
LT1432
V
IN
LT1432 TA01
OPTIONAL
OUTPUT
FILTER
100
F
16V
10
H
3A
+
2
LT1432
V
IN
Pin .................................................................... 30V
V
+
Pin ..................................................................... 40V
V
C
........................................................................... 35V
V
LIM
and V
OUT
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
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
W
U
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
LT1432CN8
LT1432CS8
ELECTRICAL C
C
HARA TERISTICS
V
C
= 6V, V
IN
= 12V, V
+
= 10V, V
DIODE
= Open, V
LIM
= V
OUT
, V
MODE
= 0V, T
J
= 25
C
Device is in standard test loop unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Regulated Output Voltage
V
C
Current = 220
A
q
4.9
5.0
5.1
V
Output Voltage Line Regulation
V
IN
= 6V to 30V
q
5
20
mV
Input Supply Current (Note 1)
V
IN
= 6V to 30V, V
+
= V
IN
+ 5V, V
C
= V
IN
+ 1V
q
0.3
0.5
mA
Quiescent Output Load Current
0.9
1.2
mA
Mode Pin Current
V
MODE
= 0V (current is out of pin)
q
30
50
A
V
MODE
= 5V (shutdown)
q
15
30
A
Mode Pin Threshold Voltage
I
MODE
= 10
A (out of pin)
q
0.6
0.9
1.5
V
(Normal to Burst)
V
C
Pin Saturation Voltage
V
OUT
= 5.5V (forced)
q
0.25
0.45
V
V
C
Pin Maximum Sink Current
V
OUT
= 5.5V (forced)
q
0.45
0.8
1.5
mA
V
C
Pin Source Current
V
OUT
= 4.5V (forced)
q
40
60
100
A
Current Limit Sense Voltage (Note 3)
Device in Current Limit Loop
56
60
64
mV
V
LIM
Pin Current
Device in Current Limit Loop
q
30
45
70
A
(current is out of pin)
Supply Current in Shutdown
V
MODE
> 3V, V
IN
< 30V, V
C
and V
+
= 0V
q
15
60
A
Burst Mode Output Ripple
Device in Burst Test Circuit
100
mV
p-p
Burst Mode Average Output Voltage
Device in Burst Test Circuit
q
4.8
5
5.2
V
Clamp Diode Forward Voltage
I
F
= 1mA, All Other Pins Open
q
0.5
0.65
V
Startup Drive Current
V
OUT
= 2.5V (forced), V
+
= 5V to 25V,
q
30
45
mA
V
IN
= 6V to 26V, V
+
= V
IN
1V, V
C
= V
IN
1.5V
Restart Time Delay
(Note 4)
1
1.8
10
ms
Transconductance, Output to V
C
Pin
I
C
= 150
A to 250
A
q
1500
2000
2800
mho
The
q
denotes specifications which apply over the operating temperature
range.
Note 1: Does not include current drawn by the LT1070 IC. See operating
parameters in standard circuit.
Note 2: Breakdown voltage on the mode pin is 7V. External current must
be limited to value shown.
Note 3: Current limit sense voltage temperature coefficient is +0.33%/
C
to match TC of copper trace material.
Note 4: V
OUT
pin switched from 5.5Vto 4.5V.
1
2
3
4
TOP VIEW
V
LIM
V
OUT
V
IN
V
+
MODE
GND
V
C
DIODE
N8 PACKAGE
8-LEAD PLASTIC DIP
S8 PACKAGE
8-LEAD PLASTIC SO
8
7
6
5
3
LT1432
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Burst Mode Quiescent Input Supply Current
1.3
1.8
mA
Burst Mode Output Ripple Voltage
I
OUT
= 0
100
mV
p-p
I
OUT
= 50mA
130
mV
p-p
Normal Mode Equivalent Input Supply Current
Extrapolated from I
OUT
= 20mA
6
mA
Normal Mode Minimum Operating Input Voltage
100mA < I
OUT
< 1.5A
6
V
Burst Mode Minimum Operating Input Voltage
5mA < I
OUT
< 50mA
6.2
V
Efficiency
Normal Mode I
OUT
= 0.5A
91
%
Burst Mode
I
OUT
= 25mA
77
%
Load Regulation
Normal Mode 50mA < I
OUT
< 2A
10
25
mV
Burst Mode
0 < I
OUT
< 50mA
50
mV
ELECTRICAL C
C
HARA TERISTICS
Operating parameters in standard circuit configuration.
V
IN
= +12V, I
OUT
= 0, unless otherwise noted. These parameters guaranteed where indicated, but not tested.
S
W
A
CHE
TIC
EQUIVALE
U
T
Figure 2
V
IN
+
+
3
4
6
5
2
7
8
MODE
CONTROL
V
LIM
+5V
GND
MODE
S3*
S1**
S2**
* S3 IS CLOSED ONLY DURING STARTUP.
** S1 AND S2 ARE SHOWN IN NORMAL
MODE. REVERSE FOR BURST MODE.
1
V
+
V
C
V
IN
DIODE
LT1432 F02
60mV
V
OUT
V
SW
V
C
GND
FB
V
IN
LT1271
4
LT1432
Shutdown Current vs Input
Voltage
Battery Current in Shutdown*
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
Minimum Input Voltage Normal
Mode (1270/1271)
Efficiency vs Input Voltage
Efficiency vs Load Current
Minimum Input Voltage Normal
Mode (1170 Family)
Burst Mode Minimum Input
Voltage
Minimum Input Voltage Normal
Mode (1070 Family)
OUTPUT CURRENT (A)
0
INPUT VOLTAGE (V)
6.5
7.0
7.5
4
LT1432 G04
6.0
5.5
5.0
1
2
3
5
LT1070 FAMILY(40kHz)
T
J
= 25C
LT1070
LT1071
LT1072
OUTPUT CURRENT (A)
0
INPUT VOLTAGE (V)
6.5
7.0
7.5
4
LT1432 G05
6.0
5.5
5.0
1
2
3
5
LT1170 FAMILY(100kHz)
T
J
= 25C
LT1170
LT1171
LT1172
LOAD CURRENT (mA)
0
INPUT VOLTAGE (V)
6.0
6.5
40
LT1432 G06
5.5
5.0
10
20
30
50
7.0
LT1170
LT1070
T
J
= 25C
INPUT VOLTAGE (V)
0
0
CURRENT (
A)
10
20
30
40
50
5
10
15
20
LT1432 G07
25
30
T
J
= 25C
TEMPERATURE (C)
0
CURRENT (
A)
20
30
100
LT1432 G08
10
0
25
50
75
40
V
IN
= 6V
V
IN
= 30V
*DOES NOT INCLUDE LT1271 SWITCH LEAKAGE.
Current Limit Sense Voltage*
JUNCTION TEMPERATURE (C)
0
SENSE VOLTAGE (mV)
60
70
100
LT1432 G11
50
40
25
50
75
80
* TEMPERATURE COEFFICIENT OF SENSE VOLTAGE IS
DESIGNED TO TRACK COPPER RESISTANCE.
INPUT VOLTAGE (V)
0
60
EFFICIENCY (%)
70
80
90
100
5
10
15
20
LT1432 G01
25
30
I
LOAD
= 0.5A
I
LOAD
= 2A
I
LOAD
= 1A
T
J
= 25C
LT1271, L = 50
H
OUTPUT CURRENT (A)
0
INPUT VOLTAGE (V)
6.5
7.0
7.5
4
LT1432 G03
6.0
5.5
5.0
1
2
3
5
LT1270
LT1271
LT1270/1271
T
J
= 25C
0
60
EFFICIENCY (%)
70
80
90
100
0.5
1.0
1.5
2.0
LT1432 G02
2.5
3.0
LT1270
L = 50
H
LT1170
L = 25
H
T
J
= 25C
LOAD CURRENT (A)
LT1271
L = 50
H
5
LT1432
Restart Load Current
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
No Load Battery Current in Burst
Mode
BATTERY VOLTAGE (V)
0
BATTERY CURRENT (mA)
3
4
5
20
LT1432 G09
2
1
0
5
10
15
25
T
J
= 25C
JUNCTION TEMPERATURE (C)
0
TRANSCONDUCTANCE (
mho)
2000
3000
100
LT1432 G12
1000
40
25
50
75
4000
Gm =
I(V
C
PIN)
V
OUT
Transconductance V
OUT
to V
C
Current
Line Regulation
Burst Mode Load Regulation
0
0
20
20
LT1432 G13
20
40
5
10
15
40
BURST MODE
NORMAL MODE
OUTPUT CHANGE (mV)
INPUT VOLTAGE (V)
T
J
= 25C
LOAD CURRENT (mA)
0
OUTPUT CHANGE (mV)
25
0
80
50
75
20
40
60
100
25
LT1432 G14
T
J
= 25C
Mode Pin Current
JUNCTION TEMPERATURE (C)
0
CURRENT (mA)
20
30
100
LT1432 G16
10
0
25
50
75
40
V
OUT
= 4.5V
Restart Time Delay
JUNCTION TEMPERATURE (C)
0
TIME DELAY (ms)
2
3
100
LT1432 G16
1
0
25
50
75
4
Startup Switch Characteristics
BATTERY VOLTAGE (V)
0
INCREMENTAL FACTOR (mA/mA)
1.0
1.5
20
LT1432 G10
0.5
0
5
10
15
25
2.0
* TO CALCULATE TOTAL BATTERY CURRENT IN BURST
MODE, MULTIPLY LOAD CURRENT BY INCREMENTAL
FACTOR AND ADD NO-LOAD CURRENT.
T
J
= 25C
Incremental Battery Current * in
Burst Mode
MODE PIN VOLTAGE (V)
0
CURRENT (
A)
20
40
60
8
LT1432 G15
0
20
40
2
4
6
10
MODE DRIVE MUST
SINK
30
A AT 0V
T
J
= 25C
V
+
TO V
IN
VOLTAGE
2
V+ PIN CURRENT (mA)
20
0
5
20
LT1432 G18
40
60
80
1
0
10
30
T
J
= 25C
NOTE VERTICAL &
HORIZONTAL SCALE
CHANGES AT 0,0
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