MAX1970EEE+T ,Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-Down Regulator with POR and RSI/PFOFeaturesThe MAX1970/MAX1971/MAX1972 dual-output current-♦ Current-Mode, 1.4MHz Fixed-Frequency PWMm ..
MAX19710ETN+T ,10-Bit, 7.5Msps, Full-Duplex, Analog Front-Endapplications operating in full-duplex (FD)♦ Ultra-Low Powermode. Optimized for high dynamic perform ..
MAX19712 ,10-Bit, 22Msps, Full-Duplex, Analog Front-Endapplications operating in full-duplex ♦ Ultra-Low Power50.4mW at f = 22MHz, FD Mode(FD) mode. Optim ..
MAX19713ETN+ ,10-Bit, 45Msps, Full-Duplex, Analog Front-EndApplicationsV 51 20 AD7DDQDN 52 19 AD6● WiMAX CPEs ● Portable Communication QDP 53 18 AD5● 801.11a/ ..
MAX1971EEE ,Dual / 180 Out-of-Phase / 1.4MHz / 750mA Step- Down Regulator with POR and RSI/PFOELECTRICAL CHARACTERISTICS(V = V = V = 5V, R = 100kΩ to IN, R = 100kΩ to IN, V = 0, C = 0.1µF, FBSE ..
MAX1971EEE+ ,Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-Down Regulator with POR and RSI/PFOMAX1970/MAX1971/MAX197219-2297; Rev 1; 2/09Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-Down Regulat ..
MAX4945LELA+T ,Overvoltage-Protection Controllers with Internal FETFeaturesThe MAX4943–MAX4946/MAX4949 family of overvolt- ♦ Input Voltage Protection Up to +28Vage-pr ..
MAX4946ELA+ ,Overvoltage-Protection Controllers with Internal FETELECTRICAL CHARACTERISTICS(V = +5V (MAX4943/MAX4944_/MAX4945_/MAX4949), V = +3V (MAX4946), T = -40° ..
MAX4947ETG+ ,Hex SPDT Data SwitchApplications♦ Wide Supply Capability1.8V to 5.5V Supply Voltage RangeUSB Signal Switching Cell Phon ..
MAX494CSD ,Single/Dual/Quad, Micropower, Single-Supply Rail-to-Rail Op AmpsGeneral Description ________
MAX494CSD+ ,Single/Dual/Quad, Micropower, Single-Supply, Rail-to-Rail Op AmpsGeneral Description ________
MAX494CSD+T ,Single/Dual/Quad, Micropower, Single-Supply, Rail-to-Rail Op AmpsApplications *Dice are specified at TA = +25°C, DC parameters only.__________Typical Operating Circ ..
MAX1970EEE+-MAX1970EEE+T-MAX1971EEE+-MAX1972EEE+
Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-Down Regulator with POR and RSI/PFO
General DescriptionThe MAX1970/MAX1971/MAX1972 dual-output current-
mode PWM buck regulators operate from 2.6V to 5.5V
input and deliver a minimum of 750mA on each output.
The MAX1970 and MAX1972 operate at a fixed 1.4MHz
(MAX1971 operates at 700kHz) to reduce output induc-
tor and capacitor size and cost. Switching the regula-
tors 180°out-of-phase also reduces the input capacitor
size and cost. Ceramic capacitors can be used for
input and output.
The output voltages are programmable from 1.2V to VIN
using external feedback resistors, or can be preset to
1.8V or 3.3V for output 1 and 1.5V or 2.5V for output 2.
When one output is higher than 1.2V, the second can
be configured down to sub-1V levels. Output accuracy
is better than ±1% over variations in load, line, and tem-
perature. Internal soft-start reduces inrush current dur-
ing startup.
All devices feature power-on reset (POR). The
MAX1971 includes a reset input (RSI), which forces
PORlow for 175ms after RSI goes low. The MAX1970
and MAX1972 include an open-drain power-fail output
(PFO) that monitors input voltage and goes high when
the input falls below 3.94V. For USB-powered xDSL
modems, this output can be used to detect USB power
failure. A minimum switching frequency of 1.2MHz
ensures operation outside the xDSL band.
Applications
FeaturesCurrent-Mode, 1.4MHz Fixed-Frequency PWM
Operation180°Out-of-Phase Operation Reduces Input
Capacitor±1% Output Accuracy Over Load, Line, and
Temperature Ranges750mA Guaranteed Output Current2.6V to 5.5V InputPower-On Reset Delay of 16.6ms (MAX1970) or
175ms (MAX1971 and MAX1972)Power-Fail Output (MAX1970 and MAX1972 Only)Power-On Reset Input (MAX1971 Only)Operation Outside xDSL BandUltra-Compact Design with Smallest External
ComponentsOutputs Adjustable from 0.8V to VINor 1.8V/3.3V
and 1.5V/2.5V PresetAll-Ceramic Capacitor ApplicationSoft-Start Reduces Inrush Current
MAX1970/MAX1971/MAX1972
Dual, 180°Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFOLX1PGND
LX2
FBSEL1
FBSEL2
PF0 (MAX1970/MAX1972)
RSI (MAX1971)
POR
TOP VIEW
MAX1970
MAX1971
MAX1972
QSOPVCC
COMP1
COMP2
FB1
FB2
REF
GND
Pin ConfigurationVCC
VCC
RSI
COMP1
COMP2
FBSEL1
FBSEL2
REF
POR
POR
OUT1
1.8V
750mA
OUT2
2.5V
750mA
RSI
LX1
FB2
FB1
LX2
PGND
MAX1971
VIN 2.6V TO 5.5V
ypical Operating Circuit19-2297; Rev 1; 2/09
xDSL Modems
xDSL Routers
Copper Gigabit SFP
and GBIC Modules
USB-Powered Devices
Dual LDO Replacement
Ordering Information
PARTTEMP RANGEPIN-PACKAGE
MAX1970EEE-40°C to +85°C16 QSOP
MAX1971EEE-40°C to +85°C16 QSOP
MAX1972EEE-40°C to +85°C16 QSOP
MAX1970/MAX1971/MAX1972
Dual, 180°Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
ABSOLUTE MAXIMUM RATINGSStresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
IN, EN, FBSEL1, FBSEL2, PFO, POR,
RSI, VCCto GND...................................................-0.3V to +6V
COMP1, COMP2, FB1, FB2,
REF to GND.............................................-0.3V to (VCC+ 0.3V)
LX1, LX2 to PGND.......................................-0.3V to (VIN+ 0.3V)
PGND to GND.......................................................-0.3V to +0.3V
Continuous Power Dissipation (TA = +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW
Operating Temperature Range...........................-40°C to +85°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
ELECTRICAL CHARACTERISTICS(VIN= VCC= VEN= 5V, RPOR= 100kΩto IN, RPFO= 100kΩto IN, VRSI= 0, CREF= 0.1µF, FBSEL1 = unconnected, FBSEL2 =
unconnected, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERCONDITIONSMINTYPMAXUNITS
IN AND VCCIN Voltage Range2.65.5V
MAX1971510IN Supply CurrentSwitching with no load
VIN = 3.3VMAX1970/MAX19721020mA
MAX1970/MAX19721100IN Shutdown CurrentVIN = 5.5V, VEN = 0MAX1971160µA
VCC rising2.402.55VCC Undervoltage
Lockout ThresholdVCC falling2.202.35V
REFREF VoltageIREF = 0, VIN = 2.6V to 5.5V1.1881.2001.212V
REF Shutdown ResistanceREF to GND, VEN = 01025Ω
REF Soft-Start CurrentVREF = 1V202530µA
FB1 AND FB2FB_ Regulation VoltageFBSEL_ = unconnected, OUT1 = FB1, OUT2 = FB2,
VCOMP_ = 1.20V to 1.80V, VIN = 2.6V to 5.5V1.1881.2001.212V
OUT_ Voltage RangeFBSEL_ = unconnected1.2VINV
VIN = 2.6V to 5.5VVCOMP1 = 1.2V, FBSEL1= GND1.7821.8001.818OUT1 Regulation VoltageVIN = 4.5V to 5.5VVCOMP1 = 1.2V, FBSEL1 = VCC3.26703.33.330V
VCOMP2 = 1.2V, FBSEL2 = GND1.4851.51.150OUT2 Regulation VoltageVIN = 2.6V to 5.5VVCOMP2 = 1.2V, FBSEL2 = VCC2.4752.52.525V
Maximum Output CurrentGuaranteed by design (Note 1)750mA
FBSEL1 = GND3060120FB1 Input ResistanceMeasured from FB1 to
GNDFBSEL1 = VCC3060120kΩ
FBSEL2 = GND22.54590FB2 Input ResistanceMeasured from FB2 to
GNDFBSEL2 = VCC22.54590kΩ
FB_ Input Bias CurrentFB1 or FB2, FBSEL_ = unconnected, VFB1 = VFB2 = 1.15V0.010.1µA
MAX1970/MAX1971/MAX1972
Dual, 180°Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
ELECTRICAL CHARACTERISTICS (continued)(VIN= VCC= VEN= 5V, RPOR= 100kΩto IN, RPFO= 100kΩto IN, VRSI= 0, CREF= 0.1µF, FBSEL1 = unconnected, FBSEL2 =
unconnected, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERCONDITIONSMINTYPMAXUNITS
COMP1 AND COMP2COMP1
Transconductance
FB1 = COMP1,
VCOMP1 = 1.2VFBSEL1 = unconnected355585µS
COMP2
Transconductance
FB2 = COMP2,
VCOMP2 = 1.2VFBSEL2 = unconnected355585µS
LX1 AND LX2VIN = 5.0V0.200.32
VIN = 3.3V0.240.37Internal High-Side
MOSFET On-ResistanceILX = -180mA
VIN =2.6V0.28
VIN = 5.0V0.120.23
VIN = 3.3V0.140.25Internal Low-Side
MOSFET On-ResistanceILX = 180mA
VIN = 2.6V0.16
LX_ Current-Sense
Transresistance0.40.50.6V/A
High side0.801.21.60LX_ Current-Limit
Threshold
Duty Cycle = 100%,
VIN = 2.6V to 5.5VLow side-1.6-0.85-0.40A
VLX1 = VLX2 = 5.5V20LX_ Leakage CurrentVIN = 5.5VVLX1 = VLX2 = 0-20µA
MAX1970/MAX19721.21.41.6LX_ Switching FrequencyVIN = 2.6V to 5.5VMAX19710.600.700.80MHz
LX_ Maximum Duty Cycle100%
MAX1970/MAX19721520LX_ Minimum Duty CycleVIN = 2.6V to 5.5VMAX19711015%
POR
VOUT rising9294POR ThresholdsPercentage of VOUT,
VIN = 2.6V to 5.5VVOUT falling8790%
MAX197013.316.620POR Delay Time (TD)MAX1971/MAX1972140175210ms
POR Output Current, HighV POR = VIN = 5.5V, VFB1 = VFB2 = 1.15V-11µA
POR Output Voltage, LowVFB1 = 1.05V or VFB2 = 1.05V or RSI = IN (MAX1971 only),
I POR = 1mA0.010.05V
POR Startup VoltageFB1 = FB2 = GND, I POR = 100µA, VIN = 1.2V0.010.05V
MAX1970/MAX1971/MAX1972
Dual, 180°Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
ELECTRICAL CHARACTERISTICS (continued)(VIN= VCC= VEN= 5V, RPOR= 100kΩto IN, RPFO= 100kΩto IN, VRSI= 0, CREF= 0.1µF, FBSEL1 = unconnected, FBSEL2 =
unconnected, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERCONDITIONSMINTYPMAXUNITS
PFO (MAX1970 and MAX1972 Only)VCC rising4.044.12PFO Trip ThresholdIN = VCCVCC falling3.863.94V
PFO Output Current, HighPFO = IN-11µA
PFO Output Voltage, LowIPFO = 1mA, VIN = 4.3V0.010.05V
EN AND RSI (MAX1971 Only)VIL0.40.95Logic Input ThresholdsIN = 2.6V to 5.5VVIH1.01.6V
RSI Input ResistanceInternal pullup resistor to IN51020kΩ
VIL-11EN Logic Input CurrentLogic input at 0 or
5.5V, VIN = 5.5VVIH-11µA
ELECTRICAL CHARACTERISTICS(VIN= VCC= VEN= 5V, VFB1= VFB2= 1.15V, RPOR= 100kΩto IN, RPFO= 100kΩto IN, RSI = 0, CVCC= 0.1µF, CREF= 0.1µF,
FBSEL1 = unconnected, FBSEL2 = unconnected, TA
= -40°C to +85°C.) (Note 2)
PARAMETERCONDITIONSMINTYPMAXUNITS
IN AND VCCIN Voltage Range2.65.5V
MAX197110IN Supply CurrentSwitching with no load
VIN = 3.3VMAX1970/MAX197220mA
MAX1970/MAX197220IN Shutdown CurrentVIN = 5.5V, VEN = 0MAX1971100µA
VCC rising2.55VCC Undervoltage
Lockout ThresholdVCC falling2.20V
REFREF VoltageIREF = 0, VIN = 2.6V to 5.5V1.1851.212V
REF Shutdown ResistanceREF to GND, VEN=025Ω
REF Soft-Start CurrentVREF = 1V2030µA
FB1 AND FB2FB_ Regulation VoltageFBSEL_ = unconnected, OUT1 = FB1, OUT2 = FB2,
VCOMP_ = 1.20V to 1.80V, VIN = 2.6V to 5.5V1.1851.212V
OUT_ Voltage RangeFBSEL_ = unconnected1.2VINV
VIN = 2.6V to 5.5VVCOMP1 = 1.2V, FBSEL1= GND1.7781.818OUT1 Regulation VoltageVIN = 4.5V to 5.5VVCOMP1 = 1.2V, FBSEL1 = VCC3.2593.333V
VCOMP2 = 1.2V, FBSEL2 = GND1.4811.515OUT2 Regulation VoltageVIN = 2.6V to 5.5VVCOMP2 = 1.2V, FBSEL2 = VCC2.4692.525V
Maximum Output CurrentGuaranteed by design (Note 1)750mA
MAX1970/MAX1971/MAX1972
Dual, 180°Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
ELECTRICAL CHARACTERISTICS (continued)(VIN= VCC= VEN= 5V, VFB1= VFB2= 1.15V, RPOR= 100kΩto IN, RPFO= 100kΩto IN, RSI = 0, CVCC= 0.1µF, CREF= 0.1µF,
FBSEL1 = unconnected, FBSEL2 = unconnected, TA
= -40°C to +85°C.) (Note 2)
PARAMETERCONDITIONSMINTYPMAXUNITSFBSEL1 = GND30120FB1 Input ResistanceMeasured from FB1 to
GNDFBSEL1 = VCC30120kΩ
FBSEL2 = GND22.590FB2 Input ResistanceMeasured from FB2 to
GNDFBSEL2 = VCC22.590kΩ
FB_ Input Bias CurrentFB1 or FB2, FBSEL_ = unconnected, VFB1 = VFB2 = 1.15V0.1µA
COMP1 AND COMP2COMP1
Transconductance
FB1 = COMP1,
VCOMP1 = 1.2VFBSEL1 = unconnected3585µS
COMP2
Transconductance
FB2 = COMP2,
VCOMP2 = 1.2VFBSEL2 = unconnected3585µS
LX1 AND LX2VIN = 5.0V0.32Internal High-Side
MOSFET On-ResistanceILX = -180mAVIN = 3.3V0.37Ω
VIN = 5.0V0.23Internal Low-Side
MOSFET On-ResistanceILX = 180mAVIN = 3.3V0.25Ω
LX_ Current-Sense
Transresistance0.40.6V/A
High side0.761.60LX_ Current-Limit
Threshold
Duty cycle = 100%,
VIN = 2.6V to 5.5VLow side-1.6-0.40A
VLX1 = VLX2 = 5.5V20LX_ Leakage CurrentVIN = 5.5VVLX1 = VLX2 = 0-20µA
MAX1970/MAX19721.21.6LX_ Switching FrequencyVIN = 2.6V to 5.5VMAX19710.600.80MHz
MAX1970/MAX197220LX_ Minimum Duty CycleVIN = 2.6V to 5.5VMAX197115%
POR
VOUT rising94POR ThresholdsPercentage of VOUT,
VIN = 2.6V to 5.5VVOUT falling87%
MAX197013.320POR Delay Time (TD)MAX1971/MAX1972140210ms
POR Output Current, HighV POR = VIN = 5.5V, VFB1 = VFB2 = 1.15V-11µA
POR Output Voltage, LowVFB1 = 1.05V or VFB2 = 1.05V or RSI = IN (MAX1971 only),
I POR = 1mA0.05V
POR Start-Up VoltageFB1 = FB2 = GND, I POR = 100µA, VIN = 1.2V0.05V
MAX1970/MAX1971/MAX1972
Dual, 180°Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
ELECTRICAL CHARACTERISTICS (continued)(VIN= VCC= VEN= 5V, VFB1= VFB2= 1.15V, RPOR= 100kΩto IN, RPFO= 100kΩto IN, RSI = 0, CVCC= 0.1µF, CREF= 0.1µF,
FBSEL1 = unconnected, FBSEL2 = unconnected, TA
= -40°C to +85°C.) (Note 2)
PARAMETERCONDITIONSMINTYPMAXUNITS
PFO (MAX1970 and MAX1972 Only)VCC rising4.12PFO Trip ThresholdIN = VCCVCC falling3.86V
PFO Output Current, HighPFO = IN-11µA
PFO Output Voltage, LowIPFO = 1mA, VIN = 4.3V0.05V
EN AND RSI (MAX1971 Only)VIL0.4Logic Input ThresholdsIN = 2.6V to 5.5VVIH1.6V
RSI Input ResistanceInternal pullup resistor to IN520kΩ
VIL-11EN Logic Input CurrentLogic Input at 0 or
5.5V, VIN = 5.5VVIH-11µA
Note 1:See the Output Voltage Selectionsection.
Note 2:Specifications to TA= -40°C are guaranteed by design and not production tested.
MAX1970/MAX1971/MAX1972
Dual, 180°Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFOEFFICIENCY vs. LOAD CURRENT
MAX1970TOC01
LOAD CURRENT (A)
EFFICIENCY (%)40VOUT2 = 2.5V
VOUT1 = 3.3V
MAX1970/
MAX1972
VIN = 5.0V
VOUT1 = 1.8V
VOUT2 = 1.5V
EFFICIENCY vs. LOAD CURRENT
MAX1970TOC02
LOAD CURRENT (A)
EFFICIENCY (%)40
VOUT2 = 2.5V
VOUT1 = 3.3V
MAX1971
VIN = 5.0V
VOUT1 = 1.8V
VOUT2 = 1.5V
EFFICIENCY vs. LOAD CURRENT
MAX1970TOC03
LOAD CURRENT (A)
EFFICIENCY (%)40
VOUT2 = 2.5V
MAX1970/
MAX1972
VIN = 3.3V
VOUT1 = 1.8VVOUT2 = 1.5V
EFFICIENCY vs. LOAD CURRENT
MAX1970TOC04
LOAD CURRENT (A)
EFFICIENCY (%)40VOUT2 = 2.5V
MAX1971
VIN = 3.3V
VOUT1 = 1.8VVOUT2 = 1.5V
INPUT CURRENT vs. OUTPUT CURRENT
MAX1970TOC05
OUTPUT CURRENT (mA)
INPUT CURRENT (mA)
450VOUT1 = 3.3V
VIN = 5.0V
VOUT2 = 2.5V
VOUT1 = 1.8V
VOUT2 = 1.5V
MAX1970/MAX1972
REFERENCE VOLTAGE vs.
REFERENCE LOAD CURRENT
MAX1970TOC06
REFERENCE LOAD CURRENT (μA)
REFERENCE VOLTAGE (V)
OSCILLATOR FREQUENCY
vs. INPUT VOLTAGE
MAX1970TOC07
INPUT VOLTAGE (V)
OSCILLATOR FREQUENCY (MHz)
TA = +85°CMAX1970/MAX1972
TA = +25°CTA = -40°C
TA = +85°C
MAX1971
TA = +25°C
TA = -40°C400800600200
CHANGE IN OUTPUT VOLTAGE
vs. LOAD CURRENTMAX1970TOC08
LOAD CURRENT (mA)
CHANGE IN OUTPUT VOLTAGE (mV)
VOUT1 = 3.3VVOUT1 = 1.8V
VOUT2 = 1.5V
VOUT2 = 2.5V
VIN = 5.0V
MAX1970/MAX1972
Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
MAX1970/MAX1971/MAX1972
Dual, 180°Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFOIOUT1
VOUT1
40μs/div
MAX1970TOC09
VIN = 5V
VOUT1 = 3.3V, 100mV/div
IOUT1 = 300mA TO 600mA
RC1 = 82kΩ, CC1 = 680pF
LOAD-TRANSIENT RESPONSEMAX1970/MAX1972
Typical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)
IOUT2
VOUT2
40μs/div
MAX1970TOC10
VIN = 5V
VOUT2 = 1.5V, 100mV/div
IOUT2 = 300mA TO 600mA
RC2 = 39kΩ, CC2 = 680pF
LOAD-TRANSIENT RESPONSEMAX1970/MAX1972
VLX1
IL2
VLX2
IL1
200ns/div
MAX1970TOC11
VIN = 5V
VOUT1 = 1.8V, VOUT2 = 2.5V
IOUT1 = 500mA, IOUT2 = 500mA
SWITCHING WAVEFORMSMAX1970/MAX1972
5V/div
200mA/div
5V/div
200mA/div
MAXIMUM OUTPUT TRANSIENT DURATION
vs. POR COMPARATOR OVERDRIVE
MAX1970TOC12
MAXIMUM OUTPUT TRANSIENT DURATION (μs)
POR COMPARATOR OVERDRIVE (%)
40ms/div
2V/div
MAX1970TOC13
VIN = 5V
VOUT1 = 1.8V, VOUT2 = 2.5V
IOUT1 = 500mA, IOUT2 = 500mA
RSI AND POR TIMING VRSI
VPOR
Typical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)
4ms/div
2V/div
MAX1970TOC14
VOUT1 = 1.8V, VOUT2 = 2.5V
VIN
PF0
PFO AND RISING INPUT VOLTAGE4ms/div
2V/div
MAX1970TOC15
VOUT1 = 1.8V, VOUT2 = 2.5V
VIN
PF0
PFO AND FALLING INPUT VOLTAGE5ms/div
5V/div
MAX1970TOC16
MAX1970
VIN = 5V
VOUT1 = 3.3V, VOUT2 = 2.5V
IOUT1 = 375mA, IOUT2 = 375mA
VOUT1
POR
ENABLE RESPONSEVOUT2
MAX1970/MAX1971/MAX1972
Dual, 180°Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
MAX1970/MAX1971/MAX1972
Dual, 180°Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO5ms/div
5V/div
MAX1970TOC17
SHUTDOWN RESPONSEPOR
VOUT1
VOUT2
MAX1970
VIN = 5V
VOUT1 = 3.3V, VOUT2 = 2.5V
IOUT1 = 375mA, IOUT2 = 375mA
Typical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)
NAMEPINMAX1970/MAX1972MAX1971FUNCTIONLX1LX1Inductor Connection 1. Connect an inductor between LX1 and OUT1.
2VCCVCCAnalog Supply Voltage. Bypass with 0.1µF to ground.COMP1COMP1
OUT1 Regulator Compensation. Connect series RC network from COMP1 to GND.
COMP1 is pulled to GND when the outputs are shut down. See the Compensation
Design section for component values.FB1FB1
OUT1 Feedback. Connected to OUT1 for internal mode (FBSEL1 = GND or VCC).
Use an external resistor-divider from OUT1 to GND to set the output voltage from
1.2V to VIN for external mode (FBSEL1 = unconnected). See the Output Voltage
Selection section for <1.2V output.FB2FB2
OUT2 Feedback. Connected to OUT2 for internal mode (FBSEL2 = GND or VCC).
Use an external resistor-divider from OUT2 to GND to set the output voltage from
1.2V to VIN for external mode (FBSEL2 = unconnected). See the Output Voltage
Selection section for <1.2V output.COMP2COMP2
OUT2 Regulator Compensation. Connect series RC network from COMP2 to GND.
COMP2 is pulled to GND when the outputs are shut down. See the Compensation
Design section for component values.REFREFReference. Bypass with 0.01µF to 1.0µF capacitor. REF controls the soft-start
ramp and is pulled to GND when the outputs are shut down.GNDGNDGround
Pin Description
Detailed DescriptionThe MAX1970/MAX1971/MAX1972 are dual-output,
fixed-frequency, current-mode, PWM, step-down
DC-DC converters. The MAX1970 and MAX1972 switch
at 1.4 MHz while the MAX1971 switches at 700kHz. The
two converters on each IC switch 180°out of phase
with each other to reduce input ripple current. The
high-switching frequency allows use of smaller capaci-
tors for filtering and decoupling. Internal synchronous
rectifiers improve efficiency and eliminate the typical
Schottky freewheeling diode. The on-resistances of the
internal MOSFETs are used to sense the switch cur-
rents for controlling and protecting the MOSFETs, elimi-
nating current-sensing resistors to further improve
efficiency and cost.
The input voltage range is 2.6V to 5.5V. Each converter
has a three-mode feedback input. Internally, OUT1 is
set to either 3.3V or 1.8V, and OUT2 to 2.5V or 1.5V by
connecting FBSEL1 and FBSEL2 to VCCor GND,
respectively. When FBSEL1 or FBSEL2 are floating,
each output can be set to any voltage between 1.2V
and VINthrough an external resistive divider. Having an
output below 1.2V is also possible (see the Output
Voltage Selection section).
DC-DC ControllerThe MAX1970/MAX1971/MAX1972 family of step-down
converters uses a pulse-width-modulating (PWM) current-
mode control scheme. The heart of the current-mode
PWM controller is an open-loop comparator that com-
pares the integrated voltage-feedback signal against
the sum of the amplified current-sense signal and the
slope compensation ramp. At each rising edge of the
internal clock, the internal high-side MOSFET turns on
until the PWM comparator trips. During this on time,
current ramps up through the inductor, sourcing cur-
rent to the output and storing energy in a magnetic
field. The current-mode feedback system regulates the
peak inductor current as a function of the output volt-
age error signal. Since the average inductor current is
nearly the same as the peak inductor current (assum-
ing that the inductor value is relatively high to minimize
ripple current), the circuit acts as a switch-mode
transconductance amplifier. It pushes the output LC filter
pole, normally found in a voltage-mode PWM, to a higher
frequency.To preserve inner loop stability and eliminate
inductor stair casing, a slope-compensation ramp is
summed into the main PWM comparator. During the
second half of the cycle, the internal high-side MOSFET
MAX1970/MAX1971/MAX1972
Dual, 180°Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
NAMEPINMAX1970/MAX1972MAX1971FUNCTIONPORPOR
Active-Low Power-On Reset Output. Open-drain output goes high 16.6ms
(MAX1970) or 175ms (MAX1971 or MAX1972) after both outputs reach 92% of
nominal value, and RSI (MAX1971 only) is low.ENENEnable Input. Drive high to turn on both OUT1 and OUT2. Drive low to place the
device in shutdown.
PFO—Power-Fail Output. Open-drain output goes high when VCC drops below 3.94V.
Useful for detecting a valid USB input voltage.RSINoninverting Reset Input. Causes POR to go low when RSI is high. Allows POR to
go high 175ms after RSI falls, if outputs are in regulation.FBSEL2FBSEL2Regulator 2 Feedback Select. Connect to VCC to set VOUT2 to 2.5V. Connect to
GND to set VOUT2 to 1.5V. Leave unconnected to use external feedback resistors.FBSEL1FBSEL1Regulator 1 Feedback Select. Connect to VCC to set VOUT1 to 3.3V. Connect to
GND to set VOUT1 to 1.8V. Leave unconnected to use external feedback resistors.ININPower-Supply Voltage. Input range from 2.6V to 5.5V. Bypass with 10µF capacitor
to PGND.LX2LX2Inductor Connection 2. Connect an inductor between LX2 and OUT2.PGNDPGNDPower Ground
Pin Description (continued)
