LT1432
5V High Efficiency Step-Down
Switching Regulator Controller
FEATURES
s
s
s
s
s
s
s
s
DESCRIPTIO
Accurate Preset +5V Output
Up to 90% Efficiency
Optional Burst Mode for Light Loads
Can be Used with Many LTC Switching ICs
Accurate Ultra-Low-Loss Current Limit
Operates with Inputs from 6V to 30V
Shutdown Mode Draws Only 15µA
Uses Small 50µH Inductor
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 15µA 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.
APPLICATI
s
s
s
s
S
Laptop and Palmtop Computers
Portable Data-Gathering Instruments
DC Bus Distribution Systems
Battery-Powered Digital Widgets
TYPICAL APPLICATI
V
IN
+
V
SW
C1
330µF
35V
C6
0.02µF
R1
680Ω
C4
0.1µF
D1
MBR330p
C5
0.03µF
FB
V
C
LT1170
LT1271
V
IN
10µH
3A
100µF
16V
+
GND
D2
1N4148
OPTIONAL
OUTPUT
FILTER
L1
50µH
R2*
0.013Ω
+
V
C
V
IN
LT1432
DIODE
V
+
×
C2
390µF
16V
V
OUT
5V
3A**
EFFICIENCY (%)
C3
4.7µF
TANT
+
V
LIM
V
OUT
MODE LOGIC
220pF
<0.3V = NORMAL MODE
>2.5V = SHUTDOWN
OPEN = BURST MODE
MODE
GND
* R2 IS MADE FROM PC BOARD
COPPER TRACES.
** MAXIMUM CURRENT IS DETERMINED
BY THE CHOICE OF LT1070 FAMILY.
SEE APPLICATION SECTION.
LT1432 TA01
Figure 1. High Efficiency 5V Buck Converter
U
Efficiency
100
NORMAL MODE
(USE AMPS SCALE)
90
80
BURST MODE
(USE mA SCALE)
70
LT1271, L = 50µH
60
0
0
1A
20mA
2A
40mA
3A
60mA
LT1432 TA02
UO
UO
1
LT1432
ABSOLUTE
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
LIM
1
V
OUT
2
V
IN
3
V
+
4
8
7
6
5
MODE
GND
V
C
DIODE
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
ORDER PART
NUMBER
LT1432CN8
LT1432CS8
N8 PACKAGE
8-LEAD PLASTIC DIP
S8 PACKAGE
8-LEAD PLASTIC SO
ELECTRICAL CHARACTERISTICS
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
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)
V
C
Pin Saturation Voltage
V
C
Pin Maximum Sink Current
V
C
Pin Source Current
Current Limit Sense Voltage (Note 3)
V
LIM
Pin Current
Supply Current in Shutdown
Burst Mode Output Ripple
Burst Mode Average Output Voltage
Clamp Diode Forward Voltage
Startup Drive Current
Restart Time Delay
Transconductance, Output to V
C
Pin
V
MODE
= 0V (current is out of pin)
V
MODE
= 5V (shutdown)
I
MODE
= 10µA (out of pin)
V
OUT
= 5.5V (forced)
V
OUT
= 5.5V (forced)
V
OUT
= 4.5V (forced)
Device in Current Limit Loop
Device in Current Limit Loop
(current is out of pin)
V
MODE
> 3V, V
IN
< 30V, V
C
and V
+
= 0V
Device in Burst Test Circuit
Device in Burst Test Circuit
I
F
= 1mA, All Other Pins Open
V
OUT
= 2.5V (forced), V = 5V to 25V,
V
IN
= 6V to 26V, V
+
= V
IN
– 1V, V
C
= V
IN
– 1.5V
(Note 4)
I
C
= 150µA to 250µA
q
+
CONDITIONS
V
C
Current = 220µA
V
IN
= 6V to 30V
V
IN
= 6V to 30V, V
+
= V
IN
+ 5V, V
C
= V
IN
+ 1V
q
q
q
MIN
4.9
TYP
5.0
5
0.3
0.9
30
15
MAX
5.1
20
0.5
1.2
50
30
1.5
0.45
1.5
100
64
70
60
5.2
0.65
UNITS
V
mV
mA
mA
µA
µA
V
V
mA
µA
mV
µA
µA
mV
p-p
V
V
mA
q
q
q
q
q
q
0.6
0.9
0.25
0.45
40
56
30
0.8
60
60
45
15
100
q
q
q
q
q
4.8
30
1
1500
5
0.5
45
1.8
2000
10
2800
µmho
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.
2
U
ms
W
U
U
W W
W
LT1432
ELECTRICAL CHARACTERISTICS
Operating parameters in standard circuit configuration.
V
IN
= +12V, I
OUT
= 0, unless otherwise noted. These parameters guaranteed where indicated, but not tested.
PARAMETER
Burst Mode Quiescent Input Supply Current
Burst Mode Output Ripple Voltage
Normal Mode Equivalent Input Supply Current
Normal Mode Minimum Operating Input Voltage
Burst Mode Minimum Operating Input Voltage
Efficiency
Load Regulation
I
OUT
= 0
I
OUT
= 50mA
Extrapolated from I
OUT
= 20mA
100mA < I
OUT
< 1.5A
5mA < I
OUT
< 50mA
Normal Mode I
OUT
= 0.5A
Burst Mode I
OUT
= 25mA
Normal Mode 50mA < I
OUT
< 2A
Burst Mode 0 < I
OUT
< 50mA
CONDITIONS
MIN
TYP
1.3
100
130
6
6
6.2
91
77
10
50
25
MAX
1.8
UNITS
mA
mV
p-p
mV
p-p
mA
V
V
%
%
mV
mV
EQUIVALE T SCHE ATIC
V
IN
V
SW
LT1271
FB
V
C
GND
+5V
V
LIM
60mV
1
2
V
OUT
V
IN
3
V
IN
S3*
* S3 IS CLOSED ONLY DURING STARTUP.
** S1 AND S2 ARE SHOWN IN NORMAL
MODE. REVERSE FOR BURST MODE.
S2**
MODE
CONTROL
7
8
MODE
GND
LT1432 F02
Figure 2
–
+
W
U
+
4
V
+
6
V
C
5
DIODE
–
S1**
3
LT1432
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Input Voltage
100
I
LOAD
= 0.5A
90
EFFICIENCY (%)
EFFICIENCY (%)
I
LOAD
= 1A
I
LOAD
= 2A
80
INPUT VOLTAGE (V)
70
T
J
= 25°C
LT1271, L = 50µH
60
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
Minimum Input Voltage – Normal
Mode (1070 Family)
7.5
LT1070 FAMILY(40kHz)
T
J
= 25°C
7.0
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
LT1172
6.5
6.5
LT1072
INPUT VOLTAGE (V)
LT1071
LT1070
6.0
5.5
5.0
0
1
3
4
2
OUTPUT CURRENT (A)
Shutdown Current vs Input
Voltage
50
T
J
= 25°C
40
30
CURRENT (µA)
CURRENT (µA)
V
IN
= 30V
30
20
V
IN
= 6V
10
SENSE VOLTAGE (mV)
20
10
0
0
5
10
15
20
INPUT VOLTAGE (V)
4
U W
LT1432 G01
Efficiency vs Load Current
100
LT1271
L = 50µH
7.5
Minimum Input Voltage – Normal
Mode (1270/1271)
LT1270/1271
T
J
= 25°C
7.0
LT1270
L = 50µH
90
LT1170
L = 25µH
6.5
LT1271
LT1270
6.0
80
70
5.5
T
J
= 25°C
60
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
2.5
3.0
5.0
0
1
3
4
2
OUTPUT CURRENT (A)
5
LT1432 G03
LT1432 G02
Minimum Input Voltage – Normal
Mode (1170 Family)
7.5
LT1170 FAMILY(100kHz)
T
J
= 25°C
7.0
LT1171
LT1170
6.5
7.0
Burst Mode Minimum Input
Voltage
T
J
= 25°C
LT1170
6.0
LT1070
5.5
6.0
5.5
5
LT1432 G04
5.0
0
1
3
4
2
OUTPUT CURRENT (A)
5
LT1432 G05
5.0
0
10
30
40
20
LOAD CURRENT (mA)
50
LT1432 G06
Battery Current in Shutdown*
40
Current Limit Sense Voltage*
80
70
60
50
25
30
0
0
25
50
TEMPERATURE (°C)
75
100
LT1432 G08
40
0
50
75
25
JUNCTION TEMPERATURE (°C)
100
LT1432 G11
LT1432 G07
*DOES NOT INCLUDE LT1271 SWITCH LEAKAGE.
* TEMPERATURE COEFFICIENT OF SENSE VOLTAGE IS
DESIGNED TO TRACK COPPER RESISTANCE.
LT1432
TYPICAL PERFOR A CE CHARACTERISTICS
Incremental Battery Current * in
Burst Mode
2.0
T
J
= 25°C
5
T
J
= 25°C
INCREMENTAL FACTOR (mA/mA)
1.5
BATTERY CURRENT (mA)
4
TRANSCONDUCTANCE (µmho)
1.0
0.5
0
0
5
15
20
10
BATTERY VOLTAGE (V)
* TO CALCULATE TOTAL BATTERY CURRENT IN BURST
MODE, MULTIPLY LOAD CURRENT BY INCREMENTAL
FACTOR AND ADD NO-LOAD CURRENT.
Line Regulation
40
T
J
= 25°C
20
BURST MODE
OUTPUT CHANGE (mV)
OUTPUT CHANGE (mV)
CURRENT (µA)
0
NORMAL MODE
–20
–40
0
5
10
INPUT VOLTAGE (V)
15
Restart Load Current
40
V
OUT
= 4.5V
30
V+ PIN CURRENT (mA)
TIME DELAY (ms)
CURRENT (mA)
20
10
0
0
50
75
25
JUNCTION TEMPERATURE (°C)
U W
LT1432 G10
LT1432 G13
No Load Battery Current in Burst
Mode
4000
Transconductance – V
OUT
to V
C
Current
Gm =
3000
∆I(V
C
PIN)
∆V
OUT
3
2000
2
1000
1
25
0
40
0
5
15
20
10
BATTERY VOLTAGE (V)
25
LT1432 G09
0
50
75
25
JUNCTION TEMPERATURE (°C)
100
LT1432 G12
Burst Mode Load Regulation
25
T
J
= 25°C
0
40
60
Mode Pin Current
T
J
= 25°C
20
–25
0
–50
–20
MODE DRIVE MUST
SINK
≈
30µA AT 0V
20
–75
0
20
60
80
40
LOAD CURRENT (mA)
100
LT1432 G14
–40
0
2
6
8
4
MODE PIN VOLTAGE (V)
10
LT1432 G15
Restart Time Delay
4
5
Startup Switch Characteristics
T
J
= 25°C
3
0
NOTE VERTICAL &
HORIZONTAL SCALE
CHANGES AT 0,0
–20
2
–40
1
–60
100
LT1432 G16
0
0
50
75
25
JUNCTION TEMPERATURE (°C)
100
LT1432 G16
–80
–2
–1
10
0
V TO V
IN
VOLTAGE
+
20
30
LT1432 G18
5
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