FEATURES
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LTC1538-AUX/LTC1539
Dual High Efficiency,
Low Noise, Synchronous
Step-Down Switching Regulators
DESCRIPTION
The LTC
®
1538-AUX/LTC1539 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.
A 5V/20mA regulator, internal 1.19V reference and an
uncommitted comparator remain active when both con-
trollers are shut down. A power-on reset timer (POR) is
included which generates a signal delayed by 65536/f
CLK
(typ 300ms) after the controller’s output is within 5% of
the regulated first voltage. Internal resistive dividers pro-
vide 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.
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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
5V Standby Regulator Active in Shutdown: I
Q
< 200µA
Output Voltages from 1.19V to 9V
Available in 28- and 36-Lead SSOP Packages
APPLICATIONS
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Notebook and Palmtop Computers, PDAs
Portable Instruments
Battery-Operated Devices
DC Power Distribution Systems
TYPICAL APPLICATION
D
B1
, CMDSH-3
BOOST 1
M1
L1
10µH
D1
MBR140T3
M3*
C
B1
0.1µF
M2
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
DSC
V
PROG2
C
OSC
56pF
SGND
V
OSENSE2
I
TH2
PGND RUN/SS2
C
SS2
0.1µF
+
5V STANDBY
D
B2
, CMDSH-3
V
PROG1
V
IN
INTV
CC
BOOST 2
TGL2
TGS2
SW2
BG2
LTC1539
SENSE
+
2
SENSE
–
2
1000pF
R
SENSE2
0.03Ω
V
OUT2
3.3V
3.5A
C
C2A
470pF
C
B2
, 0.1µF
M5
M6*
M4
L2
10µH
D2
MBR140T3
+
+
C
OUT1
220µF
10V
M1, M2, M4, M5: Si4412DY
C
C2
1000pF
R
C2
10k
M3, M6: IRLML2803
*NOT REQUIRED FOR LTC1538-AUX
BOLD LINES INDICATE HIGH CURRENT PATHS
Figure 1. High Efficiency Dual 5V/3V Step-Down Converter
U
U
U
4.7µF
16V
+
V
IN
C
IN
5.2V TO 28V
22µF
35V
×
4
+
1538 F01
C
OUT
220µF
10V
1
LTC1538-AUX/LTC1539
ABSOLUTE
MAXIMUM
RATINGS
Input Supply Voltage (V
IN
)....................... 36V to – 0.3V
Topside Driver Voltage (BOOST 1, 2) ...... 42V to – 0.3V
Peak Switch Voltage > 10µs (SW 1, 2) ... V
IN
+ 5V to – 5V
EXTV
CC
Voltage........................................ 10V to – 0.3V
POR1, 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
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 Temperature Range
LTC1538-AUXCG/LTC1539CGW............ O°C to 70°C
LTC1538-AUXIG/LTC1539IGW .......... – 40°C to 85°C
Junction Temperature (Note 1) ............................ 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
PACKAGE/ORDER INFORMATION
TOP VIEW
BOOST 1
RUN/SS1
SENSE
+
1
SENSE
–
1
V
PROG1
I
TH1
C
OSC
SGND
SFB1
1
2
3
4
5
6
7
8
9
28 TGL1
27 SW1
26 V
IN
25 BG1
24 INTV
CC
/5V
23 PGND
22 BG2
21 EXTV
CC
20 SW2
19 TGL2
18 BOOST 2
17 AUXON
16 AUXFB
15 AUXDR
ORDER
PART NUMBER
LTC1538CG-AUX
LTC1538IG-AUX
I
TH2
10
V
OSENSE2
11
SENSE
–
2 12
SENSE
+
2 13
RUN/SS2 14
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 95°C/ W
Consult factory for Military grade parts.
2
U
U
W
W W
U
W
TOP VIEW
RUN/SS1
SENSE
+
1
SENSE
–
1
V
PROG1
I
TH1
POR1
C
OSC
SGND
LBI
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
/5V
27 PGND
26 BG2
25 EXTV
CC
24 TGS2
23 SW2
22 TGL2
21 BOOST 2
20 AUXON
19 AUXFB
ORDER
PART NUMBER
LTC1539CGW
LTC1539IGW
LBO 10
SFB1 11
I
TH2
12
V
PROG2
13
V
OSENSE2
14
SENSE
–
2 15
SENSE
+
2 16
RUN/SS2 17
AUXDR 18
GW PACKAGE
36-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 85°C/ W
LTC1538-AUX/LTC1539
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
Main Control Loops
I
IN
V
OSENSE2
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
T
A
= 25°C, V
IN
= 15V, V
RUN/SS1,2
= 5V unless otherwise noted.
MIN
TYP
10
q
q
q
q
q
q
CONDITIONS
V
PROG1,
V
PROG2
Pins Open (Note 2)
(Note 2)
V
PROG1,
V
PROG2
Pins Open
V
PROG1,
V
PROG2
= 0V
V
PROG1,
V
PROG2
= INTV
CC
V
IN
= 3.6V to 20V (Note 2), V
PROG1,2
Pins Open
I
TH1,2
Sinking 5µA (Note 2)
I
TH1,2
Sourcing 5µA
V
SFB1
Ramping Negative
V
SFB1
= 1.5V
V
PROG1,2
Pin Open, SENSE
–
1 and V
OSENSE2
Pins
0.5V > V
PROG1,2
INTV
CC
– 0.5V < V
PROG1,2
< INTV
CC
EXTV
CC
= 5V (Note 3)
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
INTV
CC
= 20mA, V
EXTVCC
= 4V
INTV
CC
= 20mA, V
EXTVCC
= 5V
INTV
CC
= 20mA, EXTV
CC
Ramping Positive
C
OSC
= 100pF, LTC1539: PLL LPF = 0V (Note 4)
LTC1539, V
PLLLPF
= 2.4V
LTC1539
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
I
POR1
= 1.6mA, V
OSENSE1
= 1V,
V
PROG1
Pins Open
V
POR1
= 12V, V
OSENSE1
= 1.19V, V
PROG1
Pin Open
V
PROG1
Pin Open % of V
REF
V
OSENSE1
Ramping Negative
V
PROG1
Pin Open
q
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
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
70
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, BG2 Transition Time
BG1, 2 t
r
, t
f
Rise Time
Fall Time
Internal V
CC
Regulator – 5V Standby
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
Oscillator Frequency
f
OSC
VCO High
R
PLLIN
PLLIN Input Resistance
Phase Detector Output Current
I
PLLLPF
Sinking Capability
Sourcing Capability
Power-On Reset
POR1 Saturation Voltage
V
SATPOR1
I
LPOR1
V
THPOR1
t
DPOR1
POR1 Leakage
POR1 Trip Voltage
POR1 Delay
q
0.8
1.5
130
200
2
4.5
180
150
150
150
150
150
150
5.2
–1
300
4.8
q
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
LTC1538-AUX/LTC1539
ELECTRICAL CHARACTERISTICS
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
AUXDR Current
I
AUXDR
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
T
A
= 25°C, V
IN
= 15V, V
RUN/SS1,2
= 5V unless otherwise noted.
MIN
TYP
0.6
0.01
1.19
1
20
MAX
1
1
1.22
50
UNITS
V
µA
V
nA
mV
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
q
q
q
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 5)
V
AUXON
= 5V, 3V < V
AUXDR
< 7V
V
AUXON
= 5V (Note 5); Ramping Negative
10
1.0
q
q
11.5
1.14
7.5
15
1
0.01
0.01
0.01
1.19
0.4
12.00
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
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1538CG-AUX: T
J
= T
A
+ (P
D
)(95°C/W)
LTC1539CGW: T
J
= T
A
+ (P
D
)(85°C/W)
Note 2:
The LTC1538-AUX and LTC1539 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 3:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 4:
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 5:
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.
4
LTC1538-AUX/LTC1539
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
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
90
I
LOAD
= 100mA
85
80
75
70
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
95
I
LOAD
= 1A
EFFICIENCY (%)
V
IN
– V
OUT
Dropout Voltage vs
Load Current
0.5
0
R
SENSE
= 0.033Ω
V
OUT
DROP OF 5%
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
Input Supply Current
vs Input Voltage
INTV
CC
PERCENT CHANGE, NORMALIZED (V)
2.5
2.0
SUPPLY CURRENT (mA)
5V, 3.3V OFF
5V STANDBY
1.5
60
70°C
EXTV
CC
– INTV
CC
(mV)
1.0
5V, 3.3V ON
5V OFF, 3.3V ON
0.5
5V ON, 3.3V OFF
0
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
LTC1538/39 • TPC07
Adaptive Power and Burst Mode are trademarks of Linear Technology Corporation.
U W
1538/39 • G01
1538/39 • G04
Efficiency vs Input Voltage:
V
OUT
= 5V
100
V
OUT
= 5V
100
95
90
85
80
75
70
65
60
55
Efficiency vs Load Current
V
IN
= 10V
V
OUT
= 5V
R
SENSE
= 0.33Ω
CONTINUOUS
MODE
Burst Mode
TM
OPERATION
Adaptive Power
TM
MODE
50
0.001
1
0.01
0.1
LOAD CURRENT (A)
10
1538/39 • G03
1538/39 • G02
Load Regulation
R
SENSE
= 0.033Ω
– 0.25
– 0.50
V
ITH
Pin Voltage vs Output Current
3.0
2.5
2.0
1.5
Burst Mode
OPERATION
1.0
0.5
0
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (%)
1538/39 • G06
CONTINUOUS/
Adaptive Power
MODE
–1.25
–1.50
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
2.5
3.0
1538/39 • G05
INTV
CC
Regulation
vs INTV
CC
Load Current
100
2
EXTV
CC
= 0V
1
EXTV
CC
Switch Drop
vs INTV
CC
Load Current
300
80
5V STANDBY CURRENT (µA)
70°C
200
25°C
– 45°C
100
0
25°C
–1
40
20
0
–2
0
0
20
30
40
10
INTV
CC
LOAD CURRENT (mA)
50
0
5
15
20
25
10
INTV
CC
LOAD CURRENT (mA)
30
1538/39 • G08
1538/39 • G09
5
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