LTC3735

Manufacturer Part NumberLTC3735
Description2-Phase, High Efficiency DC/DC Controller for Intel Mobile CPUs
ManufacturerLINER [Linear Technology]
LTC3735 datasheet
 
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FEATURES
Output Stages Operate Antiphase
n
±1% Output Voltage Accuracy
n
6-Bit IMVP-IV VID Code: V
= 0.7V to 1.708V
n
OUT
Intel Compatible Power Saving Mode (PSIB)
n
Stage Shedding Improves Low Current Efficiency
n
Power Good Output with Adaptive Masking
n
Lossless Voltage Positioning
n
Dual Input Supply Capability for Load Sharing
n
Resistor Programmable V
at Boot-Up and Deeper
n
OUT
Sleep State
Resistor Programmable Deep Sleep Offset
n
Programmable Fixed Frequency: 210kHz to 550kHz
n
Adjustable Soft-Start Current Ramping
n
Foldback Output Current Limit
n
Short-Circuit Shutdown Timer with Defeat Option
n
Overvoltage Protection
n
Available in 36-Lead SSOP (0.209 Wide) and 38-Lead
n
(5mm × 7mm) Packages
APPLICATIONS
Mobile and Desktop Computers
n
Internet Servers
n
TYPICAL APPLICATION
R
C
100pF
4.74k
232k
C
C
470pF
V
+
OA
4.5V TO 7V
4.7µF
BAT54A
0.47µF
SW2
SW1
2-Phase, High Efficiency
DESCRIPTION
The LTC
®
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 LTC3735 drives its two
output stages out-of-phase at frequencies up to 550kHz
to minimize the RMS ripple currents in both input and
output capacitors. This antiphase technique also doubles
the apparent switching frequency, improving the transient
response while operating each phase at an optimum fre-
quency for efficiency. Thermal design is further simplified
by cycle-by-cycle current sharing between the two phases.
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
the transient response to be optimized for a wide range
of output capacitance and ESR values.
L, LT, LTC, LTM, OPTI-LOOP , PolyPhase, Linear Technology and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
M1
MCH_PG
TG1
1µH
0.002
DPRSLPVR
SW1
STP_CPUB
PSIB
BG1
M2
D1
FREQSET
PGND
VID5-VID0
+
PGOOD
SENSE1
SENSE1
I
TH
RUN/SS
TG2
M3
1µH
0.002
SW2
0.1µF
SGND
BG2
M4
D2
LTC3735
+
SENSE2
PV
CC
SENSE2
13.3k
12.7k
RBOOT
56.2k
BOOST1
RDPRSLP
1.27M
BOOST2
RDPSLP
0.47µF
+
V
V
+
OA
OA
13.3k
549k
OAOUT
V
OA
3735 F01
Figure 1. High Current 2-Phase Step-Down Converter
LTC3735
DC/DC Controller for
Intel Mobile CPUs
3735 is a 2-phase synchronous step-down
compensation allows
®
V
IN
5V TO 24V
V
OUT
0.7V TO 1.708V
+
C
C
40A
OUT
IN
330µF
10µF
2V
35V
×5
×4
3735fa
1

LTC3735 Summary of contents

  • Page 1

    ... 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 LTC3735 drives its two output stages out-of-phase at frequencies up to 550kHz to minimize the RMS ripple currents in both input and output capacitors ...

  • Page 2

    ... VID3 21 VID2 20 VID1 19 VID0 EXPOSED PAD (PIN 39) IS SIGNAL GROUND, MUST BE CONNECTED TO PCB AND SGND PART MARKING* PACKAGE DESCRIPTION LTC3735 36-Lead Plastic SSOP LTC3735 38-Lead (7mm × 5mm) Plastic QFN http://www.linear.com/leadfree/ http://www.linear.com/tapeandreel/ TOP VIEW ...

  • Page 3

    ... SENSEMAX (Note 3300pF LOAD C = 3300pF LOAD (Note 3300pF LOAD C = 3300pF LOAD C = 3300pF Each Driver (Note 6) LOAD C = 3300pF Each Driver (Note 6) LOAD Tested with a Square Wave (Note 7) (Note 8) LTC3735 MIN TYP MAX UNITS 0.600 0.1 0 –0.1 –0 0.02 0.1 %/V 0.57 ...

  • Page 4

    ... 1mA OUT Note 4: The LTC3735 is tested in a feedback loop that servos V specified voltage and measures the resultant V 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 ...

  • Page 5

    ... DUTY FACTOR (%) Maximum Current Sense Threshold vs Sense Common Mode Voltage COMMON MODE VOLTAGE (V) LTC3735 Efficiency vs Input Voltage (Figure 14) 100 I = 20A OUT V = 1.6V OUT INPUT VOLTAGE (V) 3735 G02 Maximum Current Sense ...

  • Page 6

    ... LTC3735 TYPICAL PERFORMANCE CHARACTERISTICS Load Regulation (Without AVP) 0.0 –0.1 –0.2 –0.3 –0 LOAD CURRENT (A) Maximum Current Sense Threshold vs Temperature –50 – 100 TEMPERATURE (°C) 3735 G13 Oscillator Frequency vs Temperature 700 600 V = 2.4V FREQSET 500 400 V = 1.2V FREQSET ...

  • Page 7

    ... RDPSLP resistor sets the output voltage of the regulator in deeper sleep state. RDPSLP (Pin 15/Pin 14): Deep Sleep Resistor Pin. Con- nect a resistor from this pin to V percentage offset of output voltage in deep sleep state. LTC3735 VID Transition (Figure 14) 1 VIDs 0 1 ...

  • Page 8

    ... LTC3735 PIN FUNCTIONS (G/UHF) RUN/SS (Pin 16/Pin 15): Combination of Soft-Start, Run Control Input and Short-Circuit Detection Timer. A capacitor to ground at this pin sets the ramp time to full current output. Forcing this pin below 1V causes the IC to shut down all internal circuitry. All functions are disabled in shutdown ...

  • Page 9

    ... SHDN I 1 – – – + 5.33 SLOPE 54k COMP PSI 1.5µA SHDN RST 6V 5.33 RUN 6-BIT VID DECODER VID0 VID1 VID2 VID3 VID4 VID5 LTC3735 R5 DPRSLPVR RBOOT MD DELAY BOOST TOP D1 PSI SW SWITCH PV CC LOGIC BG BOT PGND R L SENSE PV ...

  • Page 10

    ... I voltage is gradually released allowing normal, TH full-current operation. Frequency Programming and Antiphase Operation The switching frequency of the LTC3735 is determined by the DC voltage at the FREQSET pin voltage ranging from 0V to 2.4V moves the internal oscillator frequency from 210kHz to 550kHz. 10 This frequency is the actual switching frequency of either channel. Because the two channels operate 180° ...

  • Page 11

    ... This current shortens the soft-start period but also prevents net discharge of the RUN/SS capacitor during a severe overcurrent and/or short-circuit condition. Foldback current limiting is activated when the output voltage falls below 70% of its nominal level whether or not the short- circuit latchoff circuit is enabled. LTC3735 voltage when MCH_PG BOOT 3735fa 11 ...

  • Page 12

    ... SENSE MAX Operating Frequency The LTC3735 uses a constant frequency architecture with the frequency determined by an internal capacitor. This capacitor is charged by a fixed current plus an additional current which is proportional to the DC voltage applied to the FREQSET pin. The FREQSET voltage is internally set to 1.2V recommended that this pin is actively ...

  • Page 13

    ... 3735 F03 continuous drain current I When the LTC3735 is operating at continuous mode O(P-P) step-down configuration, the duty cycles for the top and bottom MOSFETs of each power stage are approximately: Top MOSFET Duty Cycle = Bottom MOSFET Duty Cycle = LTC3735 , gate charge Q ...

  • Page 14

    ... Please notice that the above gate driving losses are usually not dissipated by the MOSFETs. Instead they are mainly dis- sipated on the internal drivers of the LTC3735, if there are no resistors connected between the drive pins (TG, BG) and the gates of the MOSFETs. ...

  • Page 15

    ... OUT RIPPLE where f = operating frequency of each stage, C output capacitance and ∆I ripple currents. ∆I can be calculated from the duty factor and the RIPPLE ∆I of each stage. A closed form equation can be found in L LTC3735 0.3 0.4 0.5 0.6 0.7 0.8 0.9 DUTY FACTOR ( OUT IN 3735 F04 is driven by the required effective requirements ...

  • Page 16

    ... Do NOT apply greater than 7V to the PV CC The PV CC circuitry of the LTC3735. This supply current is much lower than that of the current for the external MOSFET gate drive. Ceramic capacitors are very good for high frequency filtering and a 0.1µF ~ 1µF ceramic capacitor 0.7 ...

  • Page 17

    ... CC The time for the output current to ramp up is then: CC(MAX). t IRAMP By pulling the RUN/SS pin below 1V the LTC3735 is put into low current shutdown (I can be driven directly from logic as shown in Figure 6. Diode D1 in Figure 6 reduces the start delay but allows C to ramp up slowly providing the soft-start function. ...

  • Page 18

    ... LTC3735 1.196V 1.180V 1.164V 1.148V 1.132V 1.116V 1.100V 1.084V 1.068V 1.052V 1.036V 1.020V 1.004V 0.988V 0.972V 0.956V 0.940V 0.924V 0.908V 0.892V 0.876V 0.860V 0.844V 0.828V 0.812V 0.796V 0.780V ...

  • Page 19

    ... MD. BOOT As soon asserted, the output voltage changes from voltage level totally controlled by BOOT VID the six VID bits. In the LTC3735, the time switching cycles BOOT set at 210kHz 71µ ...

  • Page 20

    ... LTC3735 APPLICATIONS INFORMATION The masking circuitry also adaptively tracks VID and state changes new change in VID or state happens before the 110µs masking timer expires, the timer resets and starts a fresh count of 110µs. This prevents the system from rebooting under frequent output voltage transitions. ...

  • Page 21

    ... Minimum On-Time Considerations Minimum on-time the smallest time duration ON(MIN) that the LTC3735 is capable of turning on the top MOSFET determined by internal timing delays and the gate charge required to turn on the top MOSFET. Low duty cycle applications may approach this minimum on-time ...

  • Page 22

    ... RMS input current to the regulator. It must have a very low ESR to minimize the AC I sufficient capacitance to prevent the RMS current from causing additional upstream losses in fuses or batteries. The LTC3735 2-phase architecture typically halves the input and output capacitor requirements over 1-phase solutions. , then the ...

  • Page 23

    ... Although the LT3735 has a maximum input voltage of 32V, most applications will be limited to 30V by the MOSFET LTC3735 is increased by the Figure 10. Automotive Application Protection LTC3735 . DSS + CC CC 3735 F10 V BAT 12V ...

  • Page 24

    ... V 1.5V OUT ON(MIN) V • f 21V • 350kHz IN which is larger than 150ns, the typical minimum on time of the LTC3735. R and R can be calculated by using a con- SENSE1 SENSE2 servative maximum sense voltage threshold of 40mV and taking into account of the peak current: 40mV 0.002Ω SENSE ...

  • Page 25

    ... C length possible. 3) Are the SENSE with minimum PC trace spacing? The filter capacitors between SENSE close as possible to the LTC3735. Ensure accurate cur- rent sensing with Kelvin connections at the current sense resistor. See Figure 11. 4) Does the (+) plate of C P-P topside MOSFETs as closely as possible? This capacitor provides the AC current to the MOSFETs ...

  • Page 26

    ... LTC3735 APPLICATIONS INFORMATION BOLD LINES INDICATE HIGH, SWITCHING CURRENT LINES. KEEP LINES TO A MINIMUM LENGTH. Figure 12. Instantaneous Current Path Flow in a Multiple Phase Switching Regulator The ground terminations of the sychronous MOSFETs and Schottky diodes should return to the negative plate(s) of the input capacitor(s) with a short isolated PC trace since very high switched currents are present ...

  • Page 27

    ... D is duty factor. The input and output ripple frequency is increased by the number of stages used, reducing the output capacity requirements. When V as illustrated in Figures 3 and 4, very low input and output ripple currents result. LTC3735 = V /2, in the single phase design OUT IN /L discharge current OUT – ...

  • Page 28

    ... LTC3735 TYPICAL APPLICATION Figure 14 shows a typical application using the LTC3735 to power the mobile CPU core. The input can vary from 5V to 24V; the output voltage can be programmed from 0.7V to 1.708V with a maximum current of 32A. By only modifying the external MOSFET and inductor selection, higher load current capability (up to 40A) can be achieved ...

  • Page 29

    ... BSC 0° – 8° 0.65 (.0256) BSC 0.22 – 0.38 (.009 – .015) TYP LTC3735 7.40 – 8.20 (.291 – .323 2.0 (.079) MAX 0.05 (.002) MIN G36 SSOP 0204 ...

  • Page 30

    ... LTC3735 PACKAGE DESCRIPTION 5.50 ± 0.05 4.10 ± 0.05 3.00 REF 5.00 ± 0.10 PIN 1 TOP MARK (SEE NOTE 6) 7.00 ± 0.10 NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE M0-220 VARIATION WHKD 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 30 UHF Package 38-Lead Plastic QFN (5mm × 7mm) (Reference LTC DWG # 05-08-1701 Rev C) 5.15 ± ...

  • Page 31

    ... Updated Related Parts Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. LTC3735 PAGE NUMBER 28 32 ...

  • Page 32

    ... LTC3735 RELATED PARTS PART NUMBER DESCRIPTION LTC3816 Single Phase DC/DC Controller for Intel IMVP-6/6+/6.5 CPUs LTC3732 3-Phase, 5-Bit VID, 600kHz, Synchronous Controller LTC3734 Single Phase DC/DC Controller for IMVP-4 LTC3869/LTC3869-2 Dual, 2-Phase Synchronous Step-Down DC/DC Controllers with Excellent Current Share when Paralleled LTC3856 2-Phase, Single Output Synchronous Step-Down DC/DC Controller ...