FEATURES
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LTC1438/LTC1439
Dual High Efficiency,
Low Noise, Synchronous
Step-Down Switching Regulators
DESCRIPTIO
The LTC
®
1438/LTC1439 are dual, synchronous step-
down switching regulator controllers which drive external
N-channel power MOSFETs in a phase-lockable fixed
frequency architecture. The Adaptive Power
TM
output stage
selectively drives two N-channel MOSFETs at frequencies
up to 400kHz while reducing switching losses to maintain
high efficiencies at low output currents.
An auxiliary 0.5A linear regulator using an external PNP
pass device provides a low noise, low dropout voltage
source. A secondary winding feedback control pin (SFB1)
guarantees regulation regardless of load on the main
output by forcing continuous operation.
An additional comparator is available for use as a low
battery detector. A power-on reset timer (POR) is included
which generates a signal delayed by 65536/f
CLK
(typ
300ms) after the output is within 5% of the regulated
output voltage. Internal resistive dividers provide pin
selectable output voltages with remote sense capability on
one of the two outputs.
The operating current levels are user-programmable via
external current sense resistors. Wide input supply range
allows operation from 3.5V to 30V (36V maximum).
, LTC and LT are registered trademarks of Linear Technology Corporation. Adaptive
Power is a trademark of Linear Technology Corporation. All other trademarks are the prop-
erty of their respective owners. Protected by U.S. Patents including 5481178, 6304066,
5929620, 6580258, 5705919, 5731731.
Maintains Constant Frequency at Low Output
Currents
Dual N-Channel MOSFET Synchronous Drive
Programmable Fixed Frequency (PLL Lockable)
Wide V
IN
Range: 3.5V to 36V Operation
Ultrahigh Efficiency
Very Low Dropout Operation: 99% Duty Cycle
Low Dropout, 0.5A Linear Regulator for VPP
Generation or Low Noise Audio Supply
Built-In Power-On Reset Timer
Programmable Soft Start
Low-Battery Detector
Remote Output Voltage Sense
Foldback Current Limiting (Optional)
Pin Selectable Output Voltage
Logic-Controlled Micropower Shutdown: I
Q
< 30µA
Output Voltages from 1.19V to 9V
Available in 28- and 36-Lead SSOP Packages
APPLICATIO S
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Notebook and Palmtop Computers, PDAs
Portable Instruments
Battery-Operated Devices
DC Power Distribution Systems
TYPICAL APPLICATIO
M1
L1
10µH
D1
MBR140T3
M3*
C
B1
0.1µF
M2
D
B1
, CMDSH-3
BOOST 1
TGL1
TGS1
SW1
BG1
SENSE
+
1
R
SENSE1
0.03Ω
V
OUT1
5V
3.5A
1000pF
C
C1
1000pF
C
C1A
220pF
SENSE
–
1
I
TH1
RUN/SS1
R
C1
10k
C
SS1
0.1µF
C
OSC
V
PROG2
C
OSC
56pF
SGND
LTC1439
V
PROG1
V
IN
INTV
CC
D
B2
, CMDSH-3
BOOST 2
TGL2
TGS2
SW2
BG2
SENSE
+
2
SENSE
–
2
V
OSENSE2
I
TH2
PGND RUN/SS2
C
SS2
0.1µF
+
4.7µF
16V
C
B2
, 0.1µF
M5
1000pF
+
C
OUT1
220µF
10V
M1, M2, M4, M5: Si4412ADY
C
C2
1000pF
R
C2
10k
C
C2A
470pF
M3, M6: IRLML2803
*NOT REQUIRED FOR LTC1438
BOLD LINES INDICATE HIGH CURRENT PATHS
Figure 1. High Efficiency Dual 5V/3V Step-Down Converter
14389fb
U
U
U
+
C
IN
22µF
35V
×
4
V
IN
5.2V TO 28V
M4
M6*
L2
10µH
D2
MBR140T3
R
SENSE2
0.03Ω
V
OUT2
3.3V
3.5A
+
1438 F01
C
OUT
220µF
10V
1
LTC1438/LTC1439
ABSOLUTE
AXI U RATI GS
Input Supply Voltage (V
IN
)......................... 36V to –0.3V
Topside Driver Voltage (BOOST 1, 2) ........ 42V to –0.3V
Switch Voltage (SW1, 2) ....................... V
IN
+ 5V to –5V
EXTV
CC
Voltage ......................................... 10V to –0.3V
POR2, LBO Voltages ................................. 12V to –0.3V
AUXFB Voltage ......................................... 20V to –0.3V
AUXDR Voltage ......................................... 28V to –0.3V
SENSE
+
1, SENSE
+
2, SENSE
–
1, SENSE
–
2,
V
OSENSE2
Voltages ................. INTV
CC
+ 0.3V to –0.3V
V
PROG1
, V
PROG2
Voltages ..................... INTV
CC
to –0.3V
PLL LPF, I
TH1
, I
TH2
Voltages .................... 2.7V to –0.3V
PACKAGE/ORDER INFORMATION
TOP VIEW
SENSE
+
1
SENSE
–
1
V
PROG1
*
I
TH1
POR2**
C
OSC
SGND
LBI
LBO
1
2
3
4
5
6
7
8
9
28 RUN/SS1
27 BOOST 1
26 TGL1
25 SW1
24 V
IN
23 BG1
22 INTV
CC
21 PGND
20 BG2
19 EXTV
CC
18 SW2
17 TGL2
16 BOOST 2
15 RUN/SS2
ORDER
PART NUMBER
LTC1438CG
LTC1438CG-ADJ
LTC1438IG
LTC1438IG-ADJ
LTC1438XCG
SFB1 10
I
TH2
11
V
OSENSE2
12
SENSE
–
2 13
SENSE
+
2 14
G PACKAGE
28-LEAD PLASTIC SSOP
*
V
OSENSE1
ON LTC1438-ADJ
**
NC ON THE LTC1438XCG
T
JMAX
= 125°C,
θ
JA
= 95°C/W
Consult factory for Military grade parts.
2
U
U
W
W W
U
W
(Note 1)
AUXON, PLLIN, SFB1,
RUN/SS1, RUN/SS2, LBI Voltages ....... 10V to –0.3V
Peak Output Current < 10µs (TGL1, 2, BG1, 2) .......... 2A
Peak Output Current < 10µs (TGS1, 2) ............... 250mA
INTV
CC
Output Current ........................................ 50mA
Operating Ambient Temperature Range
Commercial ............................................ 0°C to 70°C
Extended (Note 7)............................... –40°C to 85°C
Industrial ............................................ –40°C to 85°C
Junction Temperature (Note 2) ............................. 125°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
RUN/SS1
SENSE
+
1
SENSE
–
1
1
2
3
4
5
6
7
8
9
36 PLL LPF
35 PLLIN
34 BOOST 1
33 TGL1
32 SW1
31 TGS1
30 V
IN
29 BG1
28 INTV
CC
27 PGND
26 BG2
25 EXTV
CC
24 TGS2
23 SW2
22 TGL2
21 BOOST 2
20 AUXON
19 AUXFB
ORDER
PART NUMBER
LTC1439CG
LTC1439EG
LTC1439IG
LTC1439CGW
LTC1439IGW
V
PROG1
I
TH1
POR2
C
OSC
SGND
LBI
LBO 10
SFB1 11
I
TH2
12
V
PROG2
13
V
OSENSE2
14
SENSE
–
2
15
SENSE
+
2 16
RUN/SS2 17
AUXDR 18
G PACKAGE
GW PACKAGE
36-LEAD PLASTIC SSOP
36-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 95°C/W (G)
T
JMAX
= 125°C,
θ
JA
= 85°C/W (GW)
14389fb
LTC1438/LTC1439
The
●
denotes the specifications which apply over the full operating
temperature range. T
A
= 25°C, V
IN
= 15V, V
RUN/SS1,2
= 5V unless otherwise noted.
SYMBOL
PARAMETER
Main Control Loops
I
IN
V
OSENSE1,2
Feedback Current
Regulated Output Voltage
V
OUT1,2
1.19V (Adjustable) Selected
3.3V Selected
5V Selected
V
LINEREG1,2
Reference Voltage Line Regulation
V
LOADREG1,2
Output Voltage Load Regulation
V
SFB1
I
SFB1
V
OVL
I
PROG1,2
I
Q
Secondary Feedback Threshold
Secondary Feedback Current
Output Overvoltage Lockout
V
PROG1,2
Input Current
CONDITIONS
V
PROG1,
V
PROG2
Pins Open (Note 3)
(Note 3)
V
PROG1,
V
PROG2
Pins Open
V
PROG1,
V
PROG2
= 0V
V
PROG1,
V
PROG2
= INT V
CC
V
IN
= 3.6V to 20V (Note 3), V
PROG1,2
Pins Open
I
TH1,2
Sinking 5µA (Note 3)
I
TH1,2
Sourcing 5µA
V
SFB1
Ramping Negative
V
SFB1
= 1.5V
V
PROG1,2
, SENSE
–
1 and V
OSENSE1,2
Pins Open
0.5V > V
PROG1,2
INTV
CC
– 0.5V < V
PROG1,2
< INTV
CC
EXTV
CC
= 5V (Note 4)
3.6V < V
IN
< 30V, V
AUXON
= 0V
V
RUN/SS1,2
= 0V, 3.6V < V
IN
< 15V
V
RUN/SS1,2
= 0V
V
OSENSE1,2
= 0V, 5V V
PROG1,2
= Pins Open
C
LOAD
= 3000pF
C
LOAD
= 3000pF
C
LOAD
= 500pF
C
LOAD
= 500pF
C
LOAD
= 3000pF
C
LOAD
= 3000pF
6V < V
IN
< 30V, V
EXTVCC
= 4V
I
INTVCC
= 20mA, V
EXTVCC
= 4V
I
INTVCC
= 20mA, V
EXTVCC
= 5V
I
INTVCC
= 20mA, EXTV
CC
Ramping Positive
C
OSC
= 100pF, LTC1439: PLL LPF = 0V (Note 5)
LTC1439, V
PLLLPF
= 2.4V
LTC1439
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
I
POR2
= 1.6mA, V
OSENSE2
= 1V,
V
PROG2
Pin Open
V
POR2
= 12V, V
OSENSE2
= 1.2V, V
PROG2
Pin Open
V
PROG2
Pin Open % of V
REF
V
OSENSE2
Ramping Negative
V
PROG2
Pin Open
●
ELECTRICAL CHARACTERISTICS
MIN
TYP
10
MAX
50
1.202
3.380
5.100
0.01
0.8
– 0.8
1.22
–2
1.32
–6
6
UNITS
nA
V
V
V
%/V
%
%
V
µA
V
µA
µA
µA
µA
V
µA
mV
ns
ns
ns
ns
ns
ns
V
%
mV
V
kHz
kHz
kΩ
µA
µA
V
µA
%
Cycles
14389fb
●
●
●
●
●
●
1.178
3.220
4.900
1.16
1.24
1.19
3.30
5.00
0.002
0.5
– 0.5
1.19
–1
1.28
–3
3
320
16
1.3
3
150
50
50
100
50
50
50
Input DC Supply Current
Normal Mode
Shutdown
V
RUN/SS1,2
Run Pin Threshold
I
RUN/SS1,2
Soft Start Current Source
∆V
SENSE(MAX)
Maximum Current Sense Threshold
TGL1, 2 t
r
, t
f
TGL1, TGL2 Transition Time
Rise Time
Fall Time
TGS1, 2 t
r
, t
f
TGS1, TGS2 Transition Time
Rise Time
Fall Time
BG1, 2 t
r
, t
f
BG1, BG2 Transition Time
Rise Time
Fall Time
Internal V
CC
Regulator
V
INTVCC
Internal V
CC
Voltage
V
LDO
INT
INTV
CC
Load Regulation
V
LDO
EXT
EXTV
CC
Voltage Drop
V
EXTVCC
EXTV
CC
Switchover Voltage
Oscillator and Phase-Locked Loop
f
OSC
Oscillator Frequency
VCO High
R
PLLIN
PLLIN Input Resistance
I
PLLLPF
Phase Detector Output Current
Sinking Capability
Sourcing Capability
Power-On Reset
V
SATPOR2
POR2 Saturation Voltage
I
LPOR2
V
THPOR2
t
DPOR2
POR2 Leakage
POR2 Trip Voltage
POR2 Delay
●
0.8
1.5
130
30
2
4.5
180
150
150
200
150
150
150
5.2
–1
300
4.8
●
4.5
112
200
5.0
– 0.2
170
4.7
125
240
50
15
15
0.6
0.2
138
10
10
20
20
1
1
–4
– 11
– 7.5
65536
3
LTC1438/LTC1439
The
●
denotes the specifications which apply over the full operating
temperature range. T
A
= 25°C, V
IN
= 15V, V
RUN/SS1,2
= 5V unless otherwise noted.
SYMBOL
PARAMETER
Low-Battery Comparator
V
SATLBO
LBO Saturation Voltage
I
LLBO
LBO Leakage
V
THLB1
LBI Trip Voltage
I
INLB1
LBI Input Current
V
HYSLBO
LBO Hysteresis
Auxiliary Regulator/Comparator
I
AUXDR
AUXDR Current
Max Current Sinking Capability
Control Current
Leakage when OFF
I
INAUXFB
AUXFB Input Current
I
INAUXON
AUXON Input Current
V
THAUXON
AUXON Trip Voltage
V
SATAUXDR
AUXDR Saturation Voltage
V
AUXFB
AUXFB Voltage
V
THAUXDR
AUXFB Divider Disconnect Voltage
CONDITIONS
I
LBO
= 1.6mA, V
LBI
= 1.1V
V
LBO
= 12V, V
LBI
= 1.4V
High to Low Transition on LBO
V
LBI
= 1.19V
MIN
TYP
0.6
0.01
1.19
1
20
MAX
1
1
1.22
50
UNITS
V
µA
V
nA
mV
ELECTRICAL CHARACTERISTICS
●
●
●
1.16
V
EXTVCC
= 0V
V
AUXDR
= 4V, V
AUXFB
= 1.0V, V
AUXON
= 5V
V
AUXDR
= 5V, V
AUXFB
= 1.5V, V
AUXON
= 5V
V
AUXDR
= 24V, V
AUXFB
= 1.5V, V
AUXON
= 0V
V
AUXFB
= 1.19V, V
AUXON
= 5V
V
AUXON
= 5V
V
AUXDR
= 4V, V
AUXFB
= 1V
I
AUXDR
= 1.6mA, V
AUXFB
= 1V, V
AUXON
= 5V
V
AUXON
= 5V, 11V < V
AUXDR
< 24V (Note 6)
V
AUXON
= 5V, 3V < V
AUXDR
< 7V
V
AUXON
= 5V (Note 6); Ramping Negative
10
1.0
●
●
11.5
1.14
7.5
15
1
0.01
0.01
0.01
1.19
0.4
12.0
1.19
8.5
5
1
1
1
1.4
0.8
12.5
1.24
9.5
mA
µA
µA
µA
µA
V
V
V
V
V
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1438CG, LTC1439CG: T
J
= T
A
+ (P
D
)(95°C/W)
LTC1439CGW: T
J
= T
A
+ (P
D
)(85°C/W)
Note 3:
The LTC1438 and LTC1439 are tested in a feedback loop which
servos V
OSENSE1,2
to the balance point for the error amplifier
(V
ITH1,2
= 1.19V).
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 5:
Oscillator frequency is tested by measuring the C
OSC
charge and
discharge current (I
OSC
) and applying the formula:
f
OSC
(kHz) = 8.4(10
8
)[C
OSC
(pF) + 11]
–1
(1/I
CHG
+ 1/I
DISC
)
–1
Note 6:
The auxiliary regulator is tested in a feedback loop which servos
V
AUXFB
to the balance point for the error amplifier. For applications with
V
AUXDR
> 9.5V, V
AUXFB
uses an internal resistive divider. See Applications
Information section.
Note 7:
The LTC1439EG is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
14389fb
4
LTC1438/LTC1439
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Input Voltage
V
OUT
= 3.3V
100
V
OUT
= 3.3V
95
I
LOAD
= 1A
EFFICIENCY (%)
EFFICIENCY (%)
90
85
I
LOAD
= 100mA
80
75
70
90
I
LOAD
= 100mA
85
80
75
70
95
I
LOAD
= 1A
100
V
OUT
= 5V
EFFICIENCY (%)
0
5
10
15
20
INPUT VOLTAGE (V)
V
IN
– V
OUT
Dropout Voltage
vs Load Current
0.5
0
R
SENSE
= 0.033Ω
V
OUT
DROP OF 5%
M1, M2: Si4412
0.4
V
IN
– V
OUT
(V)
∆V
OUT
(%)
– 0.75
–1.00
V
ITH
(V)
0.3
0.2
0.1
0
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
2.5
3.0
1438 G04
Input Supply Current
vs Input Voltage
2.5
35
30
2.0
SUPPLY CURRENT (mA)
SHUTDOWN CURRENT (µA)
INTV
CC
% CHANGE, NORMALIZED (V)
25
20
15
70°C
EXTV
CC
– INTV
CC
(mV)
SHUTDOWN
CURRENT
1.5
1.0
5V AND
3.3V ON
0.5
5V ON
3.3V OFF
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1438 G07
5V OFF
3.3V ON
0
Burst Mode is a registered trademark of Linear Technology Corporation.
14389fb
U W
25
30
1438 G01
Efficiency vs Input Voltage
V
OUT
= 5V
100
95
90
85
80
75
70
65
60
55
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1438 G02
Efficiency vs Load Current
V
IN
= 10V
V
OUT
= 5V
R
SENSE
= 0.033Ω
CONTINUOUS
MODE
Burst Mode
®
OPERATION
Adaptive Power
MODE
50
0.001
1
0.01
0.1
LOAD CURRENT (A)
10
1435 G03
Load Regulation
3.0
R
SENSE
= 0.033Ω
– 0.25
– 0.50
V
ITH
Pin Voltage vs Output Current
2.5
2.0
1.5
Burst Mode
OPERATION
1.0
0.5
0
CONTINUOUS/Adaptive
Power MODE
–1.25
–1.50
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
2.5
3.0
1438 G05
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (%)
1438 G06
INTV
CC
Regulation
vs INTV
CC
Load Current
2
EXTV
CC
= 0V
300
EXTV
CC
Switch Drop
vs INTV
CC
Load Current
1
70°C
200
25°C
– 45°C
100
0
25°C
–1
10
5
0
–2
0
20
30
40
10
INTV
CC
LOAD CURRENT (mA)
50
1438 G08
0
0
5
15
20
25
10
INTV
CC
LOAD CURRENT (mA)
30
1438 G09
5
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