LTC1775
High Power
No R
SENSE
TM
Current Mode
Synchronous Step-Down
Switching Regulator
FEATURES
s
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DESCRIPTIO
Highest Efficiency Current Mode Controller
No Sense Resistor Required
300mV Maximum Current Sense Voltage
Stable High Current Operation
Dual N-Channel MOSFET Synchronous Drive
Wide V
IN
Range: 4V to 36V
Wide V
OUT
Range: 1.19V to V
IN
±1%
1.19V Reference
Programmable Fixed Frequency with Injection Lock
Very Low Drop Out Operation: 99% Duty Cycle
Forced Continuous Mode Control Pin
Optional Programmable Soft Start
Pin Selectable Output Voltage
Foldback Current Limit
Output Overvoltage Protection
Logic Controlled Micropower Shutdown: I
Q
< 30µA
Available in 16-Lead Narrow SSOP and SO Packages
The LTC
®
1775 is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using few external components. Current mode
control with MOSFET V
DS
sensing eliminates the need for
a sense resistor and improves efficiency. Largely similar
to the LTC1625, the LTC1775 has twice the maximum
sense voltage for high current applications. The frequency
of a nominal 150kHz internal oscillator can be synchro-
nized to an external clock over a 1.5:1 frequency range.
Burst Mode
TM
operation at low load currents reduces
switching losses and low dropout operation extends oper-
ating time in battery-powered systems. A forced continu-
ous mode control pin can assist secondary winding
regulation by disabling Burst Mode operation when the
main output is lightly loaded.
Fault protection is provided by foldback current limiting
and an output overvoltage comparator. An external ca-
pacitor attached to the RUN/SS pin provides soft start
capability for supply sequencing. A wide supply range
allows operation from 4V (4.3V for LTC1775I) to 36V at the
input and 1.19V to V
IN
at the output.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No R
SENSE
and Burst Mode are trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
s
s
Notebook Computers
Automotive Electronics
Battery Chargers
Distributed Power Systems
TYPICAL APPLICATION
LTC1775
SYNC
C
SS
0.1µF
RUN/SS
V
PROG
R
C
10k
C
C
2.2nF
I
TH
SGND
V
IN
TK
TG
SW
BOOST
INTV
CC
BG
C
B
0.33µF
D
B
CMDSH-3
D1
MBRS340
M2
SUD50N03-10
M1
SUD50N03-10
L1
6µH
+
EFFICIENCY (%)
C
IN
22µF
30V
×
4
V
IN
5V TO
28V
+
V
OUT
3.3V
C
OUT
10A
680µF
6.3V
+
V
OSENSE
PGND
C
VCC
4.7µF
1775 F01
Figure 1. High Efficiency Step-Down Converter
U
Efficiency vs Load Current
100
95
90
85
80
75
70
0.01
V
IN
= 10V
f = 150kHz
FCB = INTV
CC
V
OUT
= 5V
V
OUT
= 3.3V
0.1
1
LOAD CURRENT (A)
10
1775 F01b
U
U
1
LTC1775
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
EXTV
CC
1
SYNC 2
RUN/SS 3
FCB 4
I
TH
5
SGND 6
V
OSENSE
7
V
PROG
8
GN PACKAGE
16-LEAD NARROW
PLASTIC SSOP
16 V
IN
15 TK
14 SW
13 TG
12 BOOST
11 INTV
CC
10 BG
9
PGND
Input Supply Voltage (V
IN
, TK) ................. 36V to – 0.3V
Boosted Supply Voltage (BOOST) ............. 42V to – 0.3V
Boosted Driver Voltage (BOOST – SW) ...... 7V to – 0.3V
Switch Voltage (SW) ....................................36V to – 5V
EXTV
CC
Voltage ...........................................7V to – 0.3V
I
TH
Voltage ................................................2.7V to – 0.3V
FCB, RUN/SS, SYNC Voltages .....................7V to – 0.3V
V
OSENSE
, V
PROG
Voltages ........(INTV
CC
+ 0.3V) to – 0.3V
Peak Driver Output Current < 10µs (TG, BG) ............ 2A
INTV
CC
Output Current ........................................ 50mA
Operating Ambient Temperature Range
LTC1775C .............................................. 0°C to 70°C
LTC1775I (Note 5) .............................. – 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
ORDER PART
NUMBER
LTC1775CGN
LTC1775CS
LTC1775IGN
LTC1775IS
GN PART MARKING
1775
1775I
S PACKAGE
16-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 130°C/W (GN)
T
JMAX
= 125°C,
θ
JA
= 110°C/W (S)
Consult factory for Military grade parts.
The
q
denotes specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V 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
Reference Voltage Line Regulation
Output Voltage Load Regulation
Forced Continuous Threshold
Forced Continuous Bias Current
Output Overvoltage Lockout
V
PROG
Input Current
3.3V V
OUT
5V V
OUT
Input DC Supply Current
Normal Mode
Shutdown
RUN/SS Pin Threshold
Soft Start Current Source
V
RUN/SS
= 0V
V
OSENSE
= 1V, V
PROG
Pin Open
CONDITIONS
V
PROG
Pin Open, I
TH
= 1.19V (Note 3)
I
TH
= 1.19V (Note 3)
V
PROG
Pin Open
V
PROG
= 0V
V
PROG
= INTV
CC
V
IN
= 4V to 20V, I
TH
= 1.19V (Note 3),
V
PROG
Pin Open
I
TH
= 2V (Note 3)
I
TH
= 0.5V (Note 3)
V
FCB
Ramping Negative
V
FCB
= 1.19V
V
PROG
Pin Open
V
PROG
= 0V
V
PROG
= 5V
EXTV
CC
= 5V (Note 4)
V
RUN/SS
= 0V, 4V < V
IN
< 15V
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
Main Control Loop
MIN
TYP
10
MAX
50
1.202
3.380
5.100
0.01
– 0.2
0.2
1.22
–2
1.32
–7
7
UNITS
nA
V
V
V
%/V
%
%
V
µA
V
µA
µA
µA
µA
V
µA
mV
1.178
3.220
4.900
1.190
3.300
5.000
0.001
– 0.020
0.035
V
LINEREG
V
LOADREG
V
FCB
I
FCB
V
OVL
I
PROG
1.16
1.24
1.19
–1
1.28
– 3.5
3.5
500
15
I
Q
30
2
–4
340
V
RUN/SS
I
RUN/SS
0.8
–1.2
260
1.4
–2.5
300
∆V
SENSE(MAX)
Maximum Current Sense Threshold
2
U
W
U
U
W W
W
LTC1775
The
q
denotes specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V unless otherwise noted.
SYMBOL
TG t
R
TG t
F
BG t
R
BG t
F
V
INTVCC
V
LDOINT
V
LDOEXT
V
EXTVCC
Oscillator
f
OSC
f
H
/f
OSC
V
SYNC
R
SYNC
Oscillator Freqency
Maximum Synchronized Frequency Ratio
SYNC Pin Threshold (Figure 4)
SYNC Pin Input Resistance
Ramping Positive
SYNC = 0V
135
150
1.5
0.9
50
Note 4:
Typical in application circuit with EXTV
CC
tied to V
OUT
= 5V,
I
OUT
= 0A and FCB = INTV
CC
. Dynamic supply current is higher due
to the gate charge being delivered at the switching frequency. See
Applications Information.
Note 5:
Minimum input supply voltage is 4.3V at – 40°C for industrial
grade parts.
Note 6:
Rise and fall times are measured at 10% to 90% levels.
1.2
V
kΩ
165
kHz
PARAMETER
TG 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
CONDITIONS
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
6V < V
IN
< 30V, V
EXTVCC
= 4V
I
CC
= 20mA, V
EXTVCC
= 4V
I
CC
= 20mA, V
EXTVCC
= 5V
I
CC
= 20mA, V
EXTVCC
Ramping Positive
q
q
ELECTRICAL CHARACTERISTICS
MIN
TYP
50
50
50
50
MAX
150
150
150
150
5.4
–1
300
UNITS
ns
ns
ns
ns
V
%
mV
V
Internal V
CC
Regulator
5.0
5.2
– 0.2
180
4.5
4.7
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 formula:
LTC1775CGN/LTC1775IGN: T
J
= T
A
+ (P
D
• 130°C/W)
LTC1775CS/LTC1775IS: T
J
= T
A
+ (P
D
• 110°C/W)
Note 3:
The LTC1775 is tested in a feedback loop that adjusts V
OSENSE
to
achieve a specified error amplifier output voltage (I
TH
).
3
LTC1775
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Load Current
100
100
95
I
LOAD
= 5A
90
EFFICIENCY (%)
EFFICIENCY (%)
80
BURST
MODE
CONTINUOUS
MODE
I
LOAD
= 500mA
85
80
75
V
OUT
= 5V
FIGURE 1 CIRCUIT
70
EFFICIENCY (%)
70
60
V
IN
= 10V
V
OUT
= 5V
EXTV
CC
= V
OUT
0.1
0.01
1.0
LOAD CURRENT (A)
10
1775 • G01
50
0.001
Load Regulation
0
FIGURE 1 CIRCUIT
– 0.1
∆V
OUT
(%)
V
ITH
(V)
– 0.2
1.5
CONTINUOUS
MODE
1.0
V
IN
– V
OUT
(mV)
– 0.3
– 0.4
– 0.5
0
2
6
4
LOAD CURRENT (A)
8
10
1775 • G04
Input and Shutdown Current
vs Input Voltage
1200
1000
EXTV
CC
OPEN
60
50
1.0
∆INTV
CC
(%)
800
SHUTDOWN
600
400
EXTV
CC
= 5V
200
0
40
30
20
10
0
35
EXTV
CC
– INTV
CC
(mV)
INPUT CURRENT (µA)
0
5
20
15
25
10
INPUT VOLTAGE (V)
4
U W
30
1775 • G07
Efficiency vs Input Voltage
100
95
Efficiency vs Input Voltage
I
LOAD
= 5A
90
90
I
LOAD
= 500mA
85
80
75
V
OUT
= 3.3V
FIGURE 1 CIRCUIT
70
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1775 • G02
1775 • G03
I
TH
Pin Voltage vs Load Current
3.0
2.5
2.0
FIGURE 1 CIRCUIT
V
IN
= 20V
V
OUT
= 5V
300
400
V
IN
– V
OUT
Dropout Voltage
vs Load Current
FIGURE 1 CIRCUIT
V
OUT
= 5V, 5% DROP
200
100
0.5
0
BURST
MODE
0
2
8
6
10
4
LOAD CURRENT (A)
12
14
0
0
2
6
CURRENT LOAD (A)
4
8
10
1775 • G06
1775 • G05
INTV
CC
Load Regulation
V
IN
= 15V
500
EXTV
CC
Switch Drop
vs INTV
CC
Load Current
V
IN
= 15V
EXTV
CC
= 5V
400
SHUTDOWN CURRENT (µA)
0.5
300
0
200
– 0.5
100
–1.0
0
20
10
30
40
INTV
CC
LOAD CURRENT (mA)
50
1775 • G08
0
0
10
30
40
20
INTV
CC
LOAD CURRENT (mA)
50
1775 • G09
LTC1775
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Current Sense Voltage
vs Duty Cycle
MAXIMUM CURRENT SENSE VOLTAGE (mV)
MAXIMUM CURRENT SENSE VOLTAGE (mV)
350
300
250
200
150
100
50
0
0
0.2
0.6
DUTY CYCLE
0.4
0.8
1.0
1775 • G10
FREQUENCY (kHz)
FCB Pin Current vs Temperature
0
RUN/SS CURRENT (µA)
– 0.5
FCB CURRENT (µA)
– 1.0
– 1.5
– 2.0
–40 –15
60
35
85
10
TEMPERATURE (°C)
Transient Response
V
OUT
100mV
/DIV
I
L
5A/DIV
100µs/DIV
V
IN
= 20V
V
OUT
= 5V
I
LOAD
= 2A TO 8A
FIGURE 1 CIRCUIT
U W
110
1530 G18
Maximum Current Sense Voltage
vs Temperature
320
Oscillator Frequency
vs Temperature
300
250
310
SYNC = 1.5V
200
150
100
50
SYNC = 0V
300
290
280
–40 –15
60
35
85
10
TEMPERATURE (°C)
110
135
0
–40 –15
60
35
85
10
TEMPERATURE (°C)
110
135
1775 • G11
1775 • G12
RUN/SS Pin Current vs
Temperature
0
RUN/SS
5V/DIV
V
OUT
5V/DIV
Soft Start
–1
–2
–3
I
L
5A/DIV
–4
135
–5
–40 –15
60
35
85
10
TEMPERATURE (°C)
110
135
1775 • G13
1775 • G14
V
IN
= 20V
20ms/DIV
V
OUT
= 5V
R
LOAD
= 0.5Ω
FIGURE 1 CIRCUIT
1530 G16
Transient Response
(Burst Mode Operation)
Burst Mode Operation
V
OUT
100mV
/DIV
V
OUT
50mV
/DIV
I
TH
100mV
/DIV
I
L
5A/DIV
I
L
2A/DIV
V
IN
= 20V
200µs/DIV
V
OUT
= 5V
I
LOAD
= 100mA TO 2A
FIGURE 1 CIRCUIT
1530 G17
V
IN
= 20V
20µs/DIV
V
OUT
= 5V
I
LOAD
= 100mA
FIGURE 1 CIRCUIT
1530 G15
5
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