LTC1436A
LTC1436A-PLL/LTC1437A
High Efficiency Low Noise
Synchronous Step-Down
Switching Regulators
DESCRIPTIO
The LTC
®
1436A/LTC1437A are synchronous step-down
switching regulator controllers that 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 (SFB)
guarantees regulation regardless of the 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
(300ms
typically) after the output is within 5% of the regulated
output voltage. Internal resistive dividers provide pin
selectable output voltages with remote sense capability.
The operating current level is user-programmable via an
external current sense resistor. 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 property of their respective owners.
Protected by U.S. Patents, including 5481178, 6304066, 5929620, 6580258,
5705919, 5731731
FEATURES
■
■
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■
■
■
■
■
■
■
■
■
■
■
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Maintains Constant Frequency at Low Output Currents
Programmable Fixed Frequency (PLL Lockable)
Wide V
IN
Range: 3.5V to 36V Operation
Low Minimum On-Time (
≤
300ns) for High
Frequency, Low Duty Cycle Applications
Dual N-Channel MOSFET Synchronous Drive
Very Low Dropout Operation: 99% Duty Cycle
Low Dropout, 0.5A Linear Regulator for CPU I/O
or Low Noise Audio Supplies
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
< 25µA
Output Voltages from 1.19V to 9V
Available in 24-Lead Narrow SSOP and 28-Lead
SSOP Packages
APPLICATIO S
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Notebook and Palmtop Computers, PDAs
Cellular Telephones and Wireless Modems
Portable Instruments
Battery-Operated Devices
DC Power Distribution Systems
TYPICAL APPLICATIO
C
OSC
43pF
C
SS
0.1µF
R
C
10k
C
OSC
RUN/SS
V
IN
4.5V TO 22V
V
IN
TGL
TGS
I
TH
C
C
510pF
SGND
100pF
V
PROG
V
OSENSE
SENSE
–
1000pF
1436 F01
M3
IRLML2803
D
B
CMDSH-3
M1
Si4412DY
SW
LTC1436A
INTV
CC
BOOST
BG
PGND
SENSE
+
C
B
0.1µF
L1
4.7µH
+
4.7µF
M2
Si4412DY
D1
MBRS140T3
Figure 1. High Efficiency Step-Down Converter
14367afb
U
+
U
U
C
IN
22µF
35V
×
2
R
SENSE
0.02Ω
V
OUT
1.6V
5A
R1
35.7k
R2
102k
+
C
OUT
100µF
6.3V
×
2
1
LTC1436A
LTC1436-PLL-A/LTC1437A
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
Input Supply Voltage (V
IN
).........................36V to – 0.3V
Topside Driver Supply Voltage (Boost) ......42V to – 0.3V
Switch Voltage (SW) ....................................36V to – 5V
EXTV
CC
Voltage .........................................10V to – 0.3V
POR, LBO Voltages ....................................12V to – 0.3V
AUXFB Voltage ..........................................20V to – 0.3V
AUXDR Voltage ..........................................28V to – 0.3V
SENSE
+
, SENSE
–
,
V
OSENSE
Voltages ................. INTV
CC
+ 0.3V to – 0.3V
V
PROG
Voltage .................................... INTV
CC
to – 0.3V
PLL LPF, I
TH
Voltages ...............................2.7V to – 0.3V
PACKAGE/ORDER INFORMATION
TOP VIEW
C
OSC
1
RUN/SS 2
LBO 3
LBI 4
I
TH
5
SFB 6
SGND 7
V
PROG
8
V
OSENSE
9
SENSE
–
10
SENSE
+
11
AUXON 12
24 POR
23 BOOST
22 TGL
21 SW
20 TGS
19 V
IN
18 INTV
CC
17 BG
16 PGND
15 EXTV
CC
14 AUXDR
13 AUXFB
PLL LPF 1
C
OSC
2
RUN/SS 3
I
TH
4
SFB 5
SGND 6
V
PROG
7
V
OSENSE
8
SENSE
–
9
SENSE
+
10
AUXON 11
AUXFB 12
GN PACKAGE
24-LEAD PLASTIC SSOP
(150 MIL SSOP)
GN PACKAGE
24-LEAD PLASTIC SSOP
(150 MIL SSOP)
T
JMAX
= 125°C,
θ
JA
= 110°C/W
T
JMAX
= 125°C,
θ
JA
= 110°C/W
ORDER PART NUMBER
LTC1436ACGN
LTC1436AIGN
LTC1436AEGN
ORDER PART NUMBER
LTC1436ACGN-PLL
LTC1436AIGN-PLL
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
SYMBOL
I
IN
V
OSENSE
V
OUT
PARAMETER
Feedback Current
Regulated Output Voltage
1.19V (Adjustable) Selected
3.3V Selected
5V Selected
CONDITIONS
V
PROG
Pin Open (Note 3)
(Note 3)
V
PROG
Pin Open
V
PROG
= 0V
V
PROG
= INTV
CC
●
●
●
ELECTRICAL CHARACTERISTICS
Main Control Loop
2
U
U
W
W W
U
W
AUXON, PLLIN, SFB,
RUN/SS, LBI Voltages ..........................10V to – 0.3V
Peak Driver Output Current < 10µs (TGL, BG) .......... 2A
Peak Driver Output Current < 10µs (TGS) ......... 250mA
INTV
CC
Output Current ......................................... 50mA
Operating Temperature Range
LTC143XAC ............................................. 0°C to 70°C
LTC143XAI/LTC143XAE (Note 8) ...... – 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
24 PLLIN
23 POR
22 BOOST
21 TGL
20 SW
19 TGS
18 V
IN
17 INTV
CC
16 BG
15 PGND
14 EXTV
CC
13 AUXDR
PLL LPF 1
C
OSC
2
RUN/SS 3
LBO 4
LBI 5
I
TH
6
SFB 7
SGND 8
V
PROG
9
V
OSENSE
10
NC 11
SENSE
–
12
SENSE
+
TOP VIEW
28 PLLIN
27 POR
26 BOOST
25 TGL
24 SW
23 TGS
22 V
IN
21 INTV
CC
20 DRV
CC
19 BG
18 PGND
17 EXTV
CC
16 AUXDR
15 AUXFB
G PACKAGE
28-LEAD PLASTIC SSOP
13
AUXON 14
T
JMAX
= 125°C,
θ
JA
= 95°C/W
ORDER PART NUMBER
LTC1437ACG
LTC1437AIG
MIN
TYP
10
MAX
50
1.202
3.380
5.100
UNITS
nA
V
V
V
14367afb
1.178
3.220
4.900
1.19
3.30
5.00
LTC1436A
LTC1436A-PLL/LTC1437A
ELECTRICAL CHARACTERISTICS
SYMBOL
V
LINEREG
V
LOADREG
V
SFB
I
SFB
V
OVL
I
PROG
PARAMETER
Reference Voltage Line Regulation
Output Voltage Load Regulation
Secondary Feedback Threshold
Secondary Feedback Current
Output Overvoltage Lockout
V
PROG
Input Current
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
V
IN
= 3.6V to 20V (Note 3), V
PROG
Pin Open
I
TH
Sinking 5µA (Note 3)
I
TH
Sourcing 5µA (Note 3)
V
SFB
Ramping Negative
V
SFB
= 1.5V
V
PROG
Pin Open
0.5V > V
PROG
INTV
CC
– 0.5V < V
PROG
< INTV
CC
I
Q
Input DC Supply Current
Normal Mode
Shutdown
RUN Pin Threshold
Soft Start Current Source
Minimum On-Time
TGL Transition Time
Rise Time
Fall Time
TGS Transition Time
Rise Time
Fall Time
BG Transition Time
Rise Time
Fall Time
Internal V
CC
Voltage
INTV
CC
Load Regulation
EXTV
CC
Voltage Drop
EXTV
CC
Switchover Voltage
Oscillator Frequency
VCO High
R
PLLIN
I
PLLLPF
PLL IN Input Resistance
Phase Detector Output Current
Sinking Capability
Sourcing Capability
POR Saturation Voltage
POR Leakage
POR Trip Voltage
POR Delay
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
I
POR
= 1.6mA, V
OSENSE
= 1V, V
PROG
Pin Open
V
POR
= 12V, V
OSENSE
= 1.2V, V
PROG
Pin Open
V
PROG
Pin Open, V
OSENSE
Ramping Negative
V
PROG
Pin Open
– 11
10
10
V
RUN/SS
= 0V
V
CM
= 0V, 5V, V
PROG
Pin Open
Tested with Square Wave, SENSE
–
= 1.6V,
∆V
SENSE
= 20mV (Note 7)
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
= 15mA, V
EXTVCC
= 4V
I
INTVCC
= 15mA, V
EXTVCC
= 5V
I
INTVCC
= 15mA, V
EXTVCC
Ramping Positive
C
OSC
= 100pF, LTC1436 (Note 5),
LTC1436A-PLL/LTC1437A, V
PLLLPF
= 0V
LTC1436A-PLL/LTC1437A, V
PLLLPF
= 2.4V
●
●
●
●
●
MIN
TYP
0.002
0.5
– 0.5
MAX
0.01
0.8
– 0.8
1.22
–2
1.32
–6
6
UNITS
%/V
%
%
V
µA
V
µA
µA
µA
µA
V
µA
mV
ns
1.16
1.24
1.19
–1
1.28
–3
3
280
16
EXTV
CC
= 5V (Note 4)
3.6V < V
IN
< 30V, V
AUXON
= 0V
V
RUN/SS
= 0V, 3.6V < V
IN
< 15V
●
25
2
4.5
180
300
V
RUN/SS
I
RUN/SS
t
ON(MIN)
0.8
1.5
130
1.3
3
150
250
∆V
SENSE(MAX)
Maximum Current Sense Threshold
TGL t
r
TGL t
f
TGS t
r
TGS t
f
BG t
r
BG t
f
V
INTVCC
V
LDO
INT
V
LDO
EXT
V
EXTVCC
f
OSC
50
50
90
50
50
40
4.8
5.0
– 0.2
130
4.5
112
200
4.7
125
240
50
15
15
0.6
0.2
– 7.5
65536
150
150
200
150
150
150
5.2
–1
230
ns
ns
ns
ns
ns
ns
V
%
mV
V
Internal V
CC
Regulator
Oscillator and Phase-Locked Loop
138
kHz
kHz
kΩ
20
20
1
1
–4
µA
µA
V
µA
%
Cycles
Power-On Reset
V
SATPOR
I
LPOR
V
THPOR
t
DPOR
14367afb
3
LTC1436A
LTC1436-PLL-A/LTC1437A
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
SYMBOL
V
SATLBO
I
LLBO
V
THLBI
I
INLBI
V
HYSLBO
I
AUXDR
PARAMETER
LBO Saturation Voltage
LBO Leakage
LBI Trip Voltage
LBI Input Current
LBO Hysteresis
AUXDR Current
Max Current Sinking Capability
Control Current
Leakage When Off
AUXFB Input Current
AUXON Input Current
AUXON Trip Voltage
AUXDR Saturation Voltage
AUXFB Voltage
AUXFB Divider Disconnect Voltage
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
= 1.0V
I
AUXDR
= 1.6mA, V
AUXFB
= 1.0V, V
AUXON
= 5V
V
AUXON
= 5V, 11V < V
AUXDR
< 24V (Note 5)
V
AUXON
= 5V, 3V < V
AUXDR
< 7V (Note 5)
V
AUXON
= 5V (Note 6), Ramping Negative
●
●
ELECTRICAL CHARACTERISTICS
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
MAX
1
1
1.22
50
UNITS
V
µA
V
nA
mV
Low-Battery Comparator
1.16
1.19
1
20
Auxiliary Regulator/Comparator
10
15
1
0.01
0.01
0.01
1.0
11.5
1.14
7.5
1.19
0.4
12
1.19
8.5
mA
µA
µA
µA
µA
V
V
V
V
V
5
1
1
1
1.4
0.8
12.5
1.24
9.5
I
IN AUXFB
I
IN AUXON
V
TH AUXON
V
SAT AUXDR
V
AUXFB
V
TH AUXDR
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a 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:
LTC1436ACGN/LTC1436ACGN-PLL/LTC1436AEGN/LTC1436AIGN/
LTC1436AIGN-PLL: T
J
= T
A
+ (P
D
)(110
°C/W)
LTC1437ACG/LTC1437AIG: T
J
= T
A
+ (P
D
)(95
°C/W)
Note 3:
The LTC1436A/LTC1437A are tested in a feedback loop which
servos V
OSENSE
to the balance point for the error amplifier
(V
ITH
= 1.19V).
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information
section.
Note 5:
Oscillator frequency is tested by measuring the C
OSC
charge and
discharge currents and applying the formula:
8.4(10
8
)
1 + 1
–1
f
OSC
(kHz) = C
OSC
(pF) + 11 I
CHG
I
DIS
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.
Note 7:
The minimum on-time test condition corresponds to an inductor
peak-to-peak ripple current
≥
40% of I
MAX
(see Minimum On-Time
Considerations in the Applications Information section).
Note 8:
The LTC1436AE 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.
(
)(
)
14367afb
4
LTC1436A
LTC1436A-PLL/LTC1437A
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
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%
0.4
V
IN
– V
OUT
(V)
– 0.75
–1.00
V
ITH
(V)
0.3
∆V
OUT
(%)
0.2
0.1
0
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
2.5
3.0
1436 G04
Input Supply Current
vs Input Voltage
2.5
100
0.5
2.0
SUPPLY CURRENT (mA)
EXTV
CC
– INTV
CC
(mV)
∆INTV
CC
(%)
1.5
V
OUT
= 5V
EXTV
CC
= V
OUT
V
OUT
= 3.3V
EXTV
CC
= OPEN
1.0
0.5
SHUTDOWN
0
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1436 G07
Burst Mode is a registered trademark of Linear Technology Corporation.
14367afb
U W
25
30
1436 G01
Efficiency vs Input Voltage
V
OUT
= 5V
100
V
OUT
= 5V
Efficiency vs Load Current
100
95
90
85
80
75
70
65
60
55
Adaptive Power
MODE
Burst Mode
®
OPERATION
V
IN
= 10V
V
OUT
= 5V
R
SENSE
= 0.033Ω
CONTINUOUS
MODE
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1436 G02
50
0.001
1
0.01
0.1
LOAD CURRENT (A)
10
1435 G03
Load Regulation
3.0
V
ITH
Pin Voltage vs Output Current
R
SENSE
= 0.033Ω
2.5
2.0
1.5
Burst Mode
OPERATION
1.0
0.5
0
CONTINUOUS/Adaptive
Power MODE
– 0.25
– 0.50
–1.25
–1.50
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
2.5
3.0
1436 G05
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (%)
1436 G06
INTV
CC
Regulation
vs INTV
CC
Load Current
200
V
EXTVCC
= 0V
EXTV
CC
Switch Drop
vs INTV
CC
Load Current
180
160
70°C
80
SHUTDOWN CURRENT (µA)
0.3
70°C
0
25°C
– 0.3
140
120
100
80
60
40
20
25°C
– 55°C
60
40
20
0
– 0.5
0
0
10
15
5
INTV
CC
LOAD CURRENT (mA)
20
1436 G08
0
2
4 6 8 10 12 14 16 18 20
INTV
CC
LOAD CURRENT (mA)
1436 G09
5
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