LTC3734
Single-Phase,
High Efficiency DC/DC
Controller for Intel Mobile CPUs
FEATURES
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DESCRIPTION
The LTC
®
3734 is a single-phase synchronous step-down
switching regulator controller that drives all N-channel
power MOSFETs in a constant frequency architecture. The
output voltage is programmable by six VID bits during
normal operation and by external resistors during initial
boot-up and deeper sleep state. The LTC3734 drives its
output stage at frequencies up to 550kHz. Powerful on-
chip gate drivers eliminate the need for external gate driver
ICs, thus simplifying the design.
An Intel compatible PSIB input is provided to select between
two modes of operation. Fully enhanced synchronous
mode achieves a very small output ripple and very fast
transient response while power saving mode realizes
very high efficiency. OPTI-LOOP
®
compensation allows
the transient response to be optimized for a wide range
of output capacitance and ESR values.
The LTC3734 is available in a small 5mm
×
5mm QFN
package. For 2-phase applications refer to the LTC3735.
L,
LT, LTC, LTM, OPTI-LOOP Burst Mode, Linear Technology and the Linear logo are registered
,
trademarks and Stage Shedding is a trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
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Wide Input Voltage Range: 4V to 30V
±1% Output Voltage Accuracy
6-Bit IMVP-IV VID Code: V
OUT
= 0.7V to 1.708V
Intel Compatible Power Saving Mode (PSIB)
Power Good Output with Adaptive Masking
Lossless Voltage Positioning
Resistor Programmable V
OUT
at Boot-Up and
Deeper Sleep State
Resistor Programmable Deep Sleep Offset
Programmable Fixed Frequency: 210kHz to 550kHz
Adjustable Soft-Start Current Ramping
Foldback Output Current Limit
Short-Circuit Shutdown Timer with Defeat Option
Overvoltage Protection
Available in 32-Lead 5mm
×
5mm
×
0.8mm (Profile)
QFN Package
APPLICATIONS
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Mobile and Desktop Computers
Internet Servers
TYPICAL APPLICATION
MCH_PG
DPRSLPVR
STP_CPUB
PSIB
FREQSET
6-BIT VID
VID5-VID0
PGOOD
R
C
3k
C
C
680pF
I
TH
RUN/SS
0.1µF
SGND
PV
CC
4.7µF BAT54A
BOOST
0.47µF
SW
SV
CC
4.5V TO 7V
0.1µF
3734 F01
TG
SW
BG
PGND
SENSE
+
SENSE
–
RBOOT
M1
M2
0.8µH
D1
0.002
C
IN
10µF
35V
×4
V
IN
5V TO 24V
+
12.7k
56.2k
1.27M
13.3k
1.27M
13.3k
LTC3734
C
OUT
270µF
2V
×3
V
OUT
0.7V TO 1.708V
20A
RDPRSLP
RDPSLP
V
OA+
OAOUT
V
OA–
100pF
4.5V TO 7V
Figure 1. High Current Step-Down Converter
3734fa
1
LTC3734
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
DPRSLPVR
FREQSET
MCH_PG
PGOOD
VID2
BOOST
24 TG
23 SW
22 PV
CC
33
21 BG
20 PGND
19 VID5
18 VID4
17 VID3
9 10 11 12 13 14 15 16
VID0
VID1
RDPSLP
RUN/SS
RBOOT
I
TH
NC
SV
CC
PSIB
V
FB
Input Supply Voltage (PV
CC
, SV
CC
) ............. 7V to – 0.3V
Topside Driver Voltages (BOOST) .............. 38V to –0.3V
Switch Voltage (SW) ..................................... 32V to –5V
Boosted Driver Voltages (BOOST-SW) ......... 7V to –0.3V
DPRSLPVR, STP_CPUB, MCH_PG, PGOOD,
RDPRSLP, RDPSLP, RBOOT Voltages ......... 5V to –0.3V
RUN/SS, FREQSET, PSIB Voltages ..............7V to – 0.3V
VID0-VID5 Voltages ....................................5V to – 0.3V
V
FB
Voltage ................................................. 2V to –0.3V
V
OA+
, V
OA–
Voltage .................................... 3.6V to –0.3V
Peak Gate Drive Current <1µs (TG, BG) ......................5A
Operating Ambient Temperature Range
(Note 2) ...................................................– 40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range................... –65°C to 125°C
Reflow Peak Body Temperature ............................ 245°C
32 31 30 29 28 27 26 25
V
OA+
1
V
OA
–
2
OAOUT 3
STP_CPUB 4
SGND 5
SENSE
+
6
7
SENSE
–
RDPRSLP 8
UH PACKAGE
32-LEAD (5mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 33) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3734EUH#PBF
TAPE AND REEL
LTC3734EUH#TRPBF
PART MARKING
3734
PACKAGE DESCRIPTION
32-Lead Plastic (5mm
×
5mm) QFN
TEMPERATURE RANGE
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
SYMBOL
Reference
V
SENSEMAX
V
LOADREG
V
REFLNREG
V
PSIB
I
PSIB
V
OVL
g
m
g
mOL
V
ACTIVE
PARAMETER
Regulated Feedback Voltage
Maximum Current Sense Threshold
Output Voltage Load Regulation
Main Control Loop
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
PVCC
= V
SVCC
= 5V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
I
TH
Voltage = 0.5V; Measured at V
FB
(Note 4)
I
TH
Voltage = Max; V
CM
= 1.7V
l
MIN
TYP
0.600
MAX
UNITS
V
59
72
0.1
–0.1
0.02
85
0.5
–0.5
0.1
0.63
–1
0.68
7.5
1.370
1.376
mV
%
%
%/V
V
µA
V
mmho
V/mV
V
V
3734fa
(Note 4)
Measured in Servo Loop, ∆I
TH
Voltage: 1.2V to 0.7V
l
l
Measured in Servo Loop, ∆I
TH
Voltage: 1.2V to 2V
V
PVCC
= V
SVCC
= 4.5V to 7V
0.57
V
PSIB
= 0V
Measured with Respect to V
FB
= 0.6V
I
TH
= 1.2V, Sink/Source 25µA (Note 4)
I
TH
= 1.2V, (g
m
• Z
L
; No Ext Load) (Note 4)
VID = 010110, I
TH
= 0.5V (0°C – 85°C)
VID = 010110, I
TH
= 0.5V (Note 2)
l
l
Reference Voltage Line Regulation
Forced Continuous Threshold
Forced Continuous Current
Output Overvoltage Threshold
Transconductance Amplifier g
m
Transconductance Amplifier Gain
Output Voltage in Active Mode
0.6
–0.5
0.66
6
3
1.356
1.356
0.64
4.5
1.342
1.336
2
LTC3734
ELECTRICAL CHARACTERISTICS
SYMBOL
I
Q
UVR
I
RUN/SS
V
RUN/SS
V
RUN/SSARM
V
RUN/SSLO
I
SCL
I
SDLHO
I
SENSE
DF
MAX
TG t
r
TG t
f
BG t
r
BG t
f
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
R
ATTEN
ATTEN
ERR
VID
THLOW
VID
THHIGH
VID
LEAK
Oscillator
I
FREQSET
f
NOM
f
LOW
f
HIGH
V
PGL
I
PGOOD
V
PG
t
MASK
t
DELAY
FREQSET Input Current
Nominal Frequency
Lowest Frequency
Highest Frequency
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level
V
FREQSET
= 0V
V
FREQSET
= 1.2V
V
FREQSET
= 0V
V
FREQSET
≥ 2.4V
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
FB
with Respect to Set Output Voltage
V
FB
Ramping Negative
V
FB
Ramping Positive
–7
7
100
–10
10
110
15
320
190
490
–2
355
210
550
0.1
–1
390
240
610
0.3
±1
–13
13
120
µA
kHz
kHz
kHz
V
µA
%
%
µs
cycles
PARAMETER
Input DC Supply Current
Normal Mode
Shutdown
Undervoltage RUN/SS Reset
Soft-Start Charge Current
RUN/SS Pin ON Threshold
RUN/SS Pin Latchoff Arming
RUN/SS Pin Latchoff Threshold
RUN/SS Discharge Current
Shutdown Latch Disable Current
Total Sense Pins Source Current
Maximum Duty Factor
Top Gate Transition Time:
Rise Time
Fall Time
Bottom Gate Transition Time:
Rise Time
Fall Time
(Note 5)
V
RUN/SS
= 0V
V
CC
Lowered Until the RUN/SS Pin is Pulled Low
V
RUN/SS
= 1.9V
V
RUN/SS
Rising
V
RUN/SS
Rising from 3V
V
RUN/SS
Ramping Negative
Soft Short Condition V
FB
= 0.375V, V
RUN/SS
= 4.5V
V
FB
= 0.375V, V
RUN/SS
= 4.5V
V
SENSE–
= V
SENSE+
= 0V
In Dropout
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
–85
95
–5
3.2
–2.3
1.0
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
PVCC
= V
SVCC
= 5V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
MIN
TYP
2
20
3.7
–1.5
1.5
3.9
3.2
–1.5
1.5
–60
98.5
30
40
60
50
50
60
100
5.33
(Note 8)
l
MAX
3
100
4.2
–0.8
1.9
UNITS
mA
µA
V
µA
V
V
V
µA
5
µA
µA
%
90
90
90
90
ns
ns
ns
ns
ns
ns
ns
kΩ
Top Gate Off to Bottom Gate On Delay C
LOAD
= 3300pF (Note 6)
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay C
LOAD
= 3300pF (Note 6)
Top Switch-On Delay Time
Minimum On-Time
VID Top Resistance
Resistive Divider Error
VID0 to VID5 Logic Threshold Low
VID0 to VID5 Logic Threshold High
VID0 to VID5 Leakage
0.7
–0.25
Tested with a Square Wave (Note 7)
VID Parameters
0.25
0.3
±1
%
V
V
µA
PGOOD Output
PGOOD Mask Timer
MCH_PG Delay Time
3734fa
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LTC3734
ELECTRICAL CHARACTERISTICS
SYMBOL
I
B
V
OS
CM
CMRR
I
CL
A
VOL
GBP
SR
V
O(MAX)
PARAMETER
Input Bias Current
Input Offset Voltage Magnitude
Common Mode Input Voltage Range
Common Mode Rejection Ratio
Output Source Current
Open-Loop DC Gain
Gain-Bandwidth Product
Slew Rate
Maximum High Output Voltage
I
OUT
= 1mA
I
OUT
= 1mA
R
L
= 2k
I
OUT
= 1mA
I
OUT
= 1mA
V
OA+
= V
OA–
1.2V, I
OUT
= 1mA
0
46
10
70
35
30
2
5
PV
CC
– 1.2 PV
CC
– 0.9
Operational Amp
15
0.8
200
5
PV
CC
– 1.4
nA
mV
V
dB
mA
V/mV
MHz
V/µs
V
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
PVCC
= V
SVCC
= 5V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3734E 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.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
LTC3734EUH: T
J
= T
A
+ (P
D
• 34°C/W)
Note 4:
The LTC3734 is tested in a feedback loop that servos V
ITH
to a
specified voltage and measures the resultant V
FB
.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 6:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 7:
The minimum on-time condition corresponds to the on inductor
peak-to-peak ripple current
≥40%
I
MAX
(see Minimum On-Time
Considerations in the Applications Information section).
Note 8:
The ATTEN
ERR
specification is in addition to the output voltage
accuracy specified at VID code = 010110.
TYPICAL PERFORMANCE CHARACTERISTICS
Active Mode Efficiency
(VID = 1.186V, PSI = 0) (Figure 9)
100
90
Deeper Sleep Mode Efficiency
(Figure 9)
100
Efficiency vs Input Voltage
(Figure 9)
I
OUT
= 20A
V
OUT
= 1.6V
90
EFFICIENCY (%)
V
IN
= 20V
80
V
IN
= 7.5V
EFFICIENCY (%)
80
V
IN
= 7.5V
EFFICIENCY (%)
90
V
IN
= 20V
80
70
70
70
60
60
0
2
4
I
OUT
(A)
6
8
10
3735 GO1
60
0.01
0.1
I
OUT
(A)
1
10
3734 G02
50
5
15
10
INPUT VOLTAGE (V)
20
3734 G03
3734fa
4
LTC3734
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs SV
CC
Voltage
and Mode
2500
ON
50
75
Maximum Current Sense
Threshold vs Duty Factor
80
70
60
V
SENSE
(mV)
V
SENSE
(mV)
0
20
40
60
DUTY FACTOR (%)
80
100
3734 G05
Maximum Current Sense
Threshold vs Percent of Nominal
Output Voltage (Foldback)
2000
SUPPLY CURRENT (µA)
1500
50
40
30
20
1000
25
500
SHUTDOWN
4
6
5
SV
CC
VOLTAGE (V)
7
3734 G04
10
0
0
50
100
0
25
75
PERCENT OF NOMINAL OUTPUT VOLTAGE (%)
3734 G06
0
Maximum Current Sense
Threshold vs V
RUN/SS
(Soft-Start)
80
70
60
V
SENSE
(mV)
V
SENSE
(mV)
50
40
30
20
10
0
0
1
2
3
V
RUN/SS
(V)
4
5
3734 G07
Maximum Current Sense Threshold
vs Sense Common Mode Voltage
76
90
80
70
72
V
SENSE
(mV)
1
3
4
2
COMMON MODE VOLTAGE (V)
60
50
40
30
20
10
64
0
–10
–20
60
0
5
3734 G08
Current Sense Threshold
vs I
TH
Voltage
V
SENSE(CM)
= 1.25V
68
–30
0
0.5
1
1.5
V
ITH
(V)
2
2.5
3734 G09
Load Regulation (without AVP)
0.0
V
PSIB
= 5V
V
IN
= 15V
FIGURE 1
100
SENSE Pins Total Source Current
NORMALIZED V
OUT
(%)
–0.1
I
SENSE
(µA)
50
–0.2
0
–0.3
–50
–0.4
0
5
15
10
LOAD CURRENT (A)
20
25
3734 G10
–100
0
2
4
6
3734 G12
V
SENSE
COMMON MODE VOLTAGE (V)
3734fa
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