LTC1736
5-Bit Adjustable
High Efficiency Synchronous
Step-Down Switching Regulator
FEATURES
s
s
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
s
s
Dual N-Channel MOSFET Synchronous Drive
Synchronizable/Programmable Fixed Frequency
Wide V
IN
Range: 3.5V to 36V Operation
5-Bit Digital-to-Analog V
OUT
Selection:
0.925V to 2.00V Range with 50mV/25mV Steps
OPTI-LOOP
TM
Compensation Minimizes C
OUT
±
1% Output Voltage Accuracy
Power Good Output Voltage Monitor
Active Voltage Positioning Compatible
Output Overvoltage Crowbar Protection
Internal Current Foldback
Latched Short-Circuit Shutdown Timer
with Defeat Option
Forced Continuous Control Pin
Optional Programmable Soft-Start
Remote Output Voltage Sense
Available in 24-Lead SSOP Package
The LTC
®
1736 is a synchronous step-down switching
regulator controller optimized for CPU power. The output
voltage is programmed by a 5-bit digital-to-analog con-
verter (DAC) that adjusts the output voltage from 0.925V
to 2.00V according to Intel mobile VID specifications. The
0.8V reference is compatible with future microprocessor
generations.
The operating frequency (synchronizable up to 500kHz) is
set by an external capacitor allowing maximum flexibility
in optimizing efficiency. The output voltage is monitored by
a power good window comparator that indicates when the
output is within 7.5% of its programmed value.
Protection features include: internal foldback current lim-
iting, output overvoltage crowbar and optional short-cir-
cuit shutdown. Soft-start is provided by an external capaci-
tor that can be used to properly sequence supplies. The
operating current level is user-programmable via an exter-
nal current sense resistor. Wide input supply range allows
operation from 3.5V to 30V (36V maximum).
Pin defeatable Burst Mode
TM
operation provides high effi-
ciency at low load currents. OPTI-LOOP compensation
allows the transient response to be optimized over a wide
range of output capacitance and ESR values.
APPLICATIO S
s
s
s
Notebook and Palmtop Computers, PDAs
Power Supply for Mobile Pentium
®
II and
Pentium III Processors
Low Voltage Power Supplies
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP and Burst Mode are trademarks of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
TYPICAL APPLICATIO
C
OSC
47pF
C
SS
0.1µF
C
C1
330pF
V
IN
5V TO 24V
C
OSC
V
IN
TG
RUN/SS
SW
I
TH
PGOOD
VID4
VID3
VID2
VID1
VID0
SGND
LTC1736
VIDV
CC
INTV
CC
BOOST
BG
PGND
D
B
CMDSH-3
C
B
0.22µF
M1
FDS6680A
C
IN
22µF/50V
×
2
CERAMIC
L1
1.2µH
R
C
33k
C
C2
47pF
+
4.7µF
M2
FDS6680A
×
2
D1
MBRS340T3
V
OSENSE
SENSE
–
SENSE
+
1000pF
47pF
Figure 1. High Efficiency Step-Down Converter
U
R
SENSE
0.004Ω
V
OUT
1.35V TO 1.60V
12A
U
U
+
C
OUT
180µF/4V
×
4
C
OUT
: PANASONIC EEFUEOG181R
C
IN
: MARCON THCR70EIH226ZT
L1: PANASONIC ETQP6RZIR20HFA
R
SENSE
: IRC LRF2010-01-R004J
1736 F01
1
LTC1736
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
C
OSC
RUN/SS
I
TH
FCB
SGND
PGOOD
SENSE
–
SENSE
+
V
FB
1
2
3
4
5
6
7
8
9
24 TG
23 BOOST
22 SW
21 V
IN
20 INTV
CC
19 BG
18 PGND
17 EXTV
CC
16 VIDV
CC
15 VID4
14 VID3
13 VID2
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
, VIDV
CC
, (BOOST – SW) Voltages ..7V to – 0.3V
SENSE
+
, SENSE
–
.......................... 1.1(INTV
CC
) to – 0.3V
FCB Voltage ............................(INTV
CC
+ 0.3V) to – 0.3V
I
TH
, V
OSENSE
, V
FB
Voltage .........................2.7V to – 0.3V
RUN/SS, VID0 to VID4, PGOOD Voltages ....7V to – 0.3V
Peak Driver Output Current <10µs (TG, BG) .............. 3A
INTV
CC
Output Current ......................................... 50mA
Operating Ambient Temperature Range
LTC1736C ............................................... 0°C to 85°C
LTC1736I ............................................ – 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
LTC1736CG
LTC1736IG
V
OSENSE
10
VID0 11
VID1 12
G PACKAGE
24-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 110°C/W
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, V
RUN/SS
= 5V unless otherwise noted.
SYMBOL
V
OSENSE
∆V
LINEREG
∆V
LOADREG
PARAMETER
Output Voltage Set Accuracy
Reference Voltage Line Regulation
Output Voltage Load Regulation
CONDITIONS
(Note 3) See Table 1
V
IN
= 3.6V to 30V (Note 3)
(Note 3)
Measured in Servo Loop; V
ITH
= 0.7V
Measured in Servo Loop; V
ITH
= 2V
q
q
q
ELECTRICAL CHARACTERISTICS
Main Control Loop
MIN
TYP
MAX
1
UNITS
%
%/V
%
%
mmho
V
µA
V
µA
µA
V
V
µA
µA
V
mV
µA
ns
ns
ns
0.001
0.1
– 0.1
1.3
q
0.02
0.3
– 0.3
0.84
– 0.3
0.88
g
m
V
FCB
I
FCB
V
OVL
I
Q
Transconductance Amplifier g
m
Forced Continuous Threshold
Forced Continuous Current
Feedback Overvoltage Lockout
Input DC Supply Current
Normal Mode
Shutdown
Run Pin Start Threshold
Run Pin Begin Latchoff Threshold
Soft-Start Charge Current
RUN/SS Discharge Current
Undervoltage Lockout
Maximum Current Sense Threshold
SENSE Pins Total Source Current
Minimum On-Time
TG Transition Time:
Rise Time
Fall Time
(Note 4)
V
RUN/SS
= 0V
V
RUN/SS
, Ramping Positive
V
RUN/SS
, Ramping Positive
V
RUN/SS
= 0V
Soft Short Condition, V
FB
= 0.5V,
V
RUN/SS
= 4.5V
Measured at V
IN
Pin (V
IN
Ramping Down)
V
FB
= 0.7V
V
SENSE–
= V
SENSE+
= 0.8V
Tested with a Square Wave (Note 8)
(Note 9)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
q
q
0.76
0.84
0.8
– 0.17
0.86
450
15
V
FCB
= 0.85V
q
25
1.9
4.5
4
3.9
85
80
200
90
90
V
RUN/SS
V
RUN/SS
I
RUN/SS
I
SCL
UVLO
∆V
SENSE(MAX)
I
SENSE
t
ON(MIN)
TG t
r
TG t
f
1.0
– 0.7
0.5
1.5
4.1
– 1.2
2
3.5
60
75
60
160
50
50
2
U
W
U
U
W W
W
LTC1736
The
q
denotes 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
BG t
r
BG t
f
TG/BG T1D
TG/BG T2D
PARAMETER
BG Transition Time:
Rise Time
Fall Time
Top Gate Off to Synchronous
Gate-On Delay Time
Synchronous Gate Off to Top
Gate-On Delay Time
Internal V
CC
Voltage
Internal V
CC
Load Regulation
EXTV
CC
Drop Voltage
EXTV
CC
Switchover Voltage
EXTV
CC
Hysteresis
Oscillator Frequency
Maximum Sync Frequency Ratio
FCB Pin Threshold For Sync
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level
Ramping Negative
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
OSENSE
with Respect to Set Output Voltage
V
OSENSE
Ramping Negative
V
OSENSE
Ramping Positive
– 6.0
6.0
2.7
(Note 6) VIDV
CC
= 3.3V
Programmed from 0.925V to 2.00V
(Note 7) V
DIODE
= 0.6V
0.4
(Note 7) VIDV
CC
< VID < 7V
VIDV
CC
= 3.3V
VIDV
CC
= 5V
0.01
10
±0.05
40
1.0
0.01
2.8
4.5
1.6
±1
– 7.5
7.5
0.9
(Note 5), C
OSC
= 43pF
265
CONDITIONS
(Note 9)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
MIN
TYP
50
40
100
70
MAX
90
80
UNITS
ns
ns
ns
ns
ELECTRICAL CHARACTERISTICS
Internal V
CC
Regulator
V
INTVCC
V
LDO(INT)
V
LDO(EXT)
V
EXTVCC
V
EXTVCC(HYS)
Oscillator
f
OSC
f
H
/f
OSC
f
FCB(SYNC)
PGOOD Output
V
PGL
I
PGOOD
V
PG
110
200
±1
– 9.5
9.5
5.5
5
mV
µA
%
%
V
µA
kΩ
%
kΩ
V
µA
V
V
300
1.3
1.2
V
335
kHz
6V < V
IN
< 30V, V
EXTVCC
= 4V
I
CC
= 0mA to 20mA, V
EXTVCC
= 4V
I
CC
= 20mA, V
EXTVCC
= 5V
I
CC
= 20mA, EXTV
CC
Ramping Positive
q
5.0
5.2
0.2
130
5.4
1
200
V
%
mV
V
V
4.5
4.7
0.2
VID Control
VIDV
CC
I
VIDVCC
R
VFB/VOSENSE
R
RATIO
R
PULL-UP
V
IDT
I
VIDLEAK
V
PULL-UP
VID Operating Supply Voltage
VID Supply Current
Resistance Between V
OSENSE
and V
FB
Resistor Ratio Accuracy
VID0 to VID4 Pull-Up Resistance
VID Input Voltage Threshold
VID Input Leakage Current
VID Pull-Up Voltage
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:
LTC1736CG, LTC1736IG: T
J
= T
A
+ (P
D
• 110°C/W)
Note 3:
The LTC1736 is tested in a feedback loop that servos V
FB
to the
balance point for the error amplifier (V
ITH
= 1.2V).
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
current (I
OSC
) and applying the formula:
–1
8.477(10
11
)
1
1
+
f
OSC
=
C
OSC
(pF)
+
11
I
CHG
I
DIS
Note 6:
With all five VID inputs floating (or tied to VIDV
CC
) the VIDV
CC
current is typically < 1µA. However, the VIDV
CC
current will rise and be
approximately equal to the number of grounded VID input pins times
(VIDV
CC
– 0.6V)/40k. (See the Applications Information section for more
detail.)
Note 7:
Each built-in pull-up resistor attached to the VID inputs also has a
series diode to allow input voltages higher than the VIDV
CC
supply without
damage or clamping. (See the Applications Information section for more
detail.)
Note 8:
The minimum on-time condition corresponds to the on inductor
peak-to-peak ripple current
≥
40% of I
MAX
(see minimum on-time
considerations in the Applications Information section).
Note 9:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
3
LTC1736
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Load Current
(3 Operating Modes)
100
90
80
BURST
EXTV
CC
OPEN
EFFICIENCY (%)
70
CONT
60
50
40
30
20
0.001
V
IN
= 5V
V
OUT
= 1.6V
R
S
= 0.01Ω
f
O
= 300kHz
0.1
0.01
1
LOAD CURRENT (A)
10
1736 G01
EFFICIENCY (%)
EFFICIENCY (%)
SYNC
Efficiency vs Input Voltage
100
EXTV
CC
OPEN
V
OUT
= 1.6V
95 FIGURE 1
90
I
OUT
= 5A
85
I
OUT
= 0.5A
80
75
NORMALIZED V
OUT
(%)
I
TH
VOLTAGE (V)
EFFICIENCY (%)
70
0
5
10
15
20
INPUT VOLTAGE (V)
Input and Shutdown Currents
vs Input Voltage
500
ALL VID BITS OPEN
EXTV
CC
OPEN
100
6
5
4
3
2
1
0
400
300
60
EXTV
CC
– INTV
CC
(mV)
INPUT CURRENT (µA)
INTV
CC
VOLTAGE (V)
200
SHUTDOWN
100
EXTV
CC
= 5V
0
0
5
20
15
10
25
INPUT VOLTAGE (V)
30
35
4
U W
25
1736 G04
Efficiency vs Load Current
100
90
80
70
V
IN
= 24V
60
50
40
10mA
V
IN
= 5V
EXTV
CC
= 5V
100
95
90
85
Efficiency vs Input Voltage
EXTV
CC
= 5V
V
OUT
= 1.6V
FIGURE 1
I
OUT
= 5A
V
IN
= 15V
I
OUT
= 0.5A
80
75
70
100mA
1A
LOAD CURRENT (A)
10A
1736 G02
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1736 G03
Load Regulation
0
I
TH
Voltage vs Load Current
2.5
FCB = 0V
V
IN
= 15V
FIGURE 1
–0.1
2.0
V
IN
= 5V
V
OUT
= 1.6V
R
SENSE
= 0.01Ω
f
O
= 300kHz
CONTINUOUS
MODE
SYNCHRONIZED f = f
O
1.5
–0.2
1.0
Burst Mode
OPERATION
–0.3
0.5
30
–0.4
0
0
2
6
8
4
LOAD CURRENT (A)
10
12
1736 G05
0
1
2
3
4
LOAD CURRENT (A)
5
6
1736 G06
INTV
CC
Line Regulation
1mA LOAD
500
EXTV
CC
Switch Drop
vs INTV
CC
Load Current
80
400
SHUTDOWN CURRENT (µA)
300
40
200
20
100
0
0
5
20
15
25
10
INPUT VOLTAGE (V)
30
35
0
0
10
30
40
20
INTV
CC
LOAD CURRENT (mA)
50
1736 G09
1736 G07
1736 G08
LTC1736
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Current Sense Threshold
vs Normalized Output Voltage
(Foldback)
80
CURRENT SENSE THRESHOLD (mV)
CURRENT SENSE THRESHOLD (mV)
CURRENT SENSE THRESHOLD (mV)
70
60
50
40
30
20
10
0
0
50
25
75
NORMALIZED OUTPUT VOLTAGE (%)
100
Maximum Current Sense Threshold
vs I
TH
Voltage
90
CURRENT SENSE THRESHOLD (mV)
80
70
60
50
40
30
20
10
0
–10
–20
–30
0
0.5
1
1.5
V
ITH
(V)
2
2.5
1736 G13
CURRENT SENSE THRESHOLD (mV)
70
V
ITH
(V)
RUN/SS Pin Current
vs Temperature
0
V
RUN/SS
= 0V
0
AVERAGE OUTPUT CURRENT I
OUT
/I
MAX
(%)
–1
RUN/SS CURRENT (µA)
–2
FCB CURRENT (µA)
–3
–4
–5
–40
–15
60
35
10
85
TEMPERATURE (°C)
U W
1736 G10
Maximum Current Sense Threshold
vs V
RUN/SS
80
V
SENSE(CM)
= 1.6V
Maximum Current Sense Threshold
vs Sense Common Mode Voltage
80
60
76
72
40
68
20
64
0
0
1
2
3
V
RUN/SS
(V)
1736 G11
4
5
6
60
0
0.5
1
1.5
COMMON MODE VOLTAGE (V)
2
1736 G12
Maximum Current Sense Threshold
vs Temperature
80
2.5
V
SENSE(CM)
= 1.6V
2.0
V
ITH
vs V
RUN/SS
V
OSENSE
= 0.7V
75
1.5
1.0
65
0.5
60
–40 –15
0
85
10
35
60
TEMPERATURE (°C)
110
135
0
1
2
3
V
RUN/SS
(V)
4
5
6
1736 G15
1736 G18
FCB Pin Current vs Temperature
V
FCB
= 0.85V
Output Current vs Duty Cycle
100
I
OUT
/I
MAX
(SYNCHRONIZED)
80
I
OUT
/I
MAX
(FREE RUN)
–0.2
–0.4
60
–0.6
40
–0.8
20
f
SYNC
= f
O
0
0
20
40
60
DUTY CYCLE (%)
80
100
1736 G14
110
135
–1.0
–40
–15
60
35
10
85
TEMPERATURE (°C)
110
135
1736 G16
1736 G17
5
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