MAX1951ESA+ ,1MHz, All-Ceramic, 2.6V to 5.5V Input, 2A PWM Step-Down DC-to-DC Regulatorsapplications. The MAX1951total output error is less than 1% over load, line, and ♦ 1% Output Accura ..
MAX1951ESA+T ,1MHz, All-Ceramic, 2.6V to 5.5V Input, 2A PWM Step-Down DC-to-DC RegulatorsApplicationsSelector GuideASIC/DSP/µP/FPGA Core and I/O VoltagesSet-Top Boxes PIN-PART TEMP RANGE O ..
MAX1952ESA+ ,1MHz, All-Ceramic, 2.6V to 5.5V Input, 2A PWM Step-Down DC-to-DC RegulatorsELECTRICAL CHARACTERISTICS(V = V = 3.3V, PGND = GND, FB in regulation, C = 0.1µF, T = 0°C to +85°C, ..
MAX1952ESA+T ,1MHz, All-Ceramic, 2.6V to 5.5V Input, 2A PWM Step-Down DC-to-DC RegulatorsELECTRICAL CHARACTERISTICS (continued)(V = V = 3.3V, PGND = GND, FB in regulation, C = 0.1µF, T = 0 ..
MAX19538ETL+T ,12-Bit, 95Msps, 3.3V ADCfeatures a 63µW power-down mode to con-♦ Common-Mode Referenceserve power during idle periods.♦ CMO ..
MAX1953EUB ,Low-Cost / High-Frequency / Current-Mode PWM Buck ControllerApplicationsPrinters and ScannersILIM 1 10 BSTGraphic Cards and Video CardsCOMP 2 9 LXPCs and Serve ..
MAX490EEPA ,15kV ESD-Protected / Slew-Rate-Limited / Low-Power / RS-485/RS-422 TransceiversMAX481E/MAX483E/MAX485E/MAX487E–MAX491E/MAX1487E19-0410; Rev 3; 7/96±15kV ESD-Protected, Slew-Rate- ..
MAX490EEPA+ ,±15kV ESD-Protected, Slew-Rate-Limited, Low-Power, RS-485/RS-422 TransceiversELECTRICAL CHARACTERISTICS(V = 5V ±5%, T = T to T , unless otherwise noted.) (Notes 1, 2)CC A MIN M ..
MAX490EESA ,15kV ESD-Protected / Slew-Rate-Limited / Low-Power / RS-485/RS-422 TransceiversELECTRICAL CHARACTERISTICS(V = 5V ±5%, T = T to T , unless otherwise noted.) (Notes 1, 2)CC A MIN M ..
MAX490EESA ,15kV ESD-Protected / Slew-Rate-Limited / Low-Power / RS-485/RS-422 TransceiversApplicationsMAX481EESA -40°C to +85°C 8 SOLow-Power RS-485 TransceiversOrdering Information continu ..
MAX490EESA+ ,±15kV ESD-Protected, Slew-Rate-Limited, Low-Power, RS-485/RS-422 TransceiversApplications:MAX491E, and MAX1487E are low-power transceivers forMAX3430: ±80V Fault-Protected, Fai ..
MAX490EESA+T ,±15kV ESD-Protected, Slew-Rate-Limited, Low-Power, RS-485/RS-422 TransceiversApplications:state. The receiver input has a fail-safe feature that guar-MAX3440E–MAX3444E: ±15kV E ..
MAX1951ESA+-MAX1951ESA+T-MAX1952ESA+-MAX1952ESA+T
1MHz, All-Ceramic, 2.6V to 5.5V Input, 2A PWM Step-Down DC-to-DC Regulators
General DescriptionThe MAX1951/MAX1952 high-efficiency, DC-to-DC
step-down switching regulators deliver up to 2A of out-
put current. The devices operate from an input voltage
range of 2.6V to 5.5V and provide an output voltage
from 0.8V to VIN, making the MAX1951/MAX1952 ideal
for on-board postregulation applications. The MAX1951
total output error is less than 1% over load, line, and
temperature.
The MAX1951/MAX1952 operate at a fixed frequency of
1MHz with an efficiency of up to 94%. The high operating
frequency minimizes the size of external components.
Internal soft-start control circuitry reduces inrush current.
Short-circuit and thermal-overload protection improve
design reliability.
The MAX1951 provides an adjustable output from 0.8V
to VIN, whereas the MAX1952 has a preset output of
1.8V. Both devices are available in a space-saving 8-pin
SO package.
ApplicationsASIC/DSP/µP/FPGA Core and I/O Voltages
Set-Top Boxes
Cellular Base Stations
Networking and Telecommunications
FeaturesCompact 0.385in2Circuit Footprint10µF Ceramic Input and Output Capacitors, 2µH
Inductor for 1.5A OutputEfficiency Up to 94%1% Output Accuracy Over Load, Line, and
Temperature (MAX1951, Up to 1.5A)Guaranteed 2A Output CurrentOperate from 2.6V to 5.5V SupplyAdjustable Output from 0.8V to VIN (MAX1951)Preset Output of 1.8V (1.5% Accuracy) (MAX1952)Internal Digital Soft-SoftShort-Circuit and Thermal-Overload Protection
MAX1951/MAX1952
1MHz, All-Ceramic, 2.6V to 5.5V Input,
2A PWM Step-Down DC-to-DC Regulators
Ordering Information/
Selector Guide19-2622; Rev 2; 6/09
PARTTEMP RANGEPIN-
PACKAGEOUTPUT
MAX1951ESA+-40°C to +85°C8 SOAdj 0.8V to VIN
MAX1952ESA+-40°C to +85°C8 SOFixed 1.8V
MAX1951
OFF
COMP
OUTPUT
0.8V TO VIN, UP TO 2AINPUT
2.6V TO 5.5V
REF
PGNDGND
VCC
OPTIONAL
Typical Operating CircuitPin ConfigurationPGND
COMPFBREF
GND
VCC
TOP VIEW
MAX1951
MAX1952
+Denotes a lead(Pb)-free/RoHS-compliant package.
MAX1951/MAX1952
1MHz, All-Ceramic, 2.6V to 5.5V Input,
2A PWM Step-Down DC-to-DC Regulators
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VIN= VCC= 3.3V, PGND = GND, FB in regulation, CREF= 0.1µF, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at= +25°C.)
Stresses 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.
PARAMETERCONDITIONSMINTYPMAXUNITS
IN AND VCCIN Voltage Range2.65.5V
Supply CurrentS w i tchi ng w i th no l oad , LX unconnected VIN = 5.5V610mA
Shutdown CurrentCOMP = GND0.51.0mA
VCC rising2.352.5VCC Undervoltage Lockout
ThresholdWhen LX starts/stops switchingVCC falling22.25V
REFREF VoltageIREF = 0µA, VIN = 2.6V to 5.5V1.9622.03V
REF Load RegulationIREF = 0 to 40µA, VIN = 2.6V to 5.5V0.010.2%
REF Line RegulationIREF = 20µA, VIN = 2.6V to 5.5V0.010.4%
REF Shutdown ResistanceFrom REF to GND, COMP = GND1222Ω
COMPMAX1951406080COMP TransconductanceFrom FB to COMP, VCOMP = 1.25VMAX195226.74053.3µS
COMP Clamp Voltage, LowVIN = 2.6V to 5.5V, VFB = 1.3V0.611.2V
COMP Clamp Voltage, HighVIN = 2.6V to 5.5V, VFB = 1.1V1.972.152.28V
COMP Shutdown ResistanceFrom COMP to GND, VIN = 2V1530Ω
COMP rising0.61COMP Shutdown ThresholdWhen LX starts/stops switchingCOMP falling0.170.4V
COMP Startup CurrentCOMP = GND152540µA
Output Voltage Range
(MAX1951)When using external feedback resistors to drive FB0.8 VINV
VIN = 2.6V to 5.5VMAX19510.7870.7950.803FB Regulation Voltage
(Error Amp Only)C OM P = 1V to 2V ,
IOU T = 0 to 1.5AVIN = 2.8V to 5.5VMAX19521.7731.81.827V
FB Input ResistanceMAX1952131828kΩ
IN, VCCto GND........................................................-0.3V to +6V
COMP, FB, REF to GND.............................-0.3V to (VCC+ 0.3V)
LX to Current (Note 1).........................................................±4.5A
PGND to GND.............................................Internally Connected
Continuous Power Dissipation (TA = +85°C)
8-Pin SO (derate 12.2mW/°C above +70°C)................976mW
Package Junction-to-Ambient
Thermal Resistance (θJA) (Note 2)...............................82°C/W
Package Junction-to-Case
Thermal Resistance (θJC) (Note 2)..............................32°C/W
Operating Temperature Range
MAX195_ ESA..................................................-40°C to +85°C
Junction Temperature Range............................-40°C to +150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
Note 1:LX has internal clamp diodes to PGND and IN. Applications that forward bias these diodes should take care not to exceed
the IC’s package power dissipation limits.
Note 2:Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on package thermal considerations, refer to /thermal-tutorial.
MAX1951/MAX1952
1MHz, All-Ceramic, 2.6V to 5.5V Input,
2A PWM Step-Down DC-to-DC Regulators
ELECTRICAL CHARACTERISTICS (continued)(VIN= VCC= 3.3V, PGND = GND, FB in regulation, CREF= 0.1µF, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at= +25°C.)
PARAMETERCONDITIONSMINTYPMAXUNITSVIN = 5V116
VIN = 3.3V140266LX On-Resistance, PMOS
VIN = 2.6V163
VIN = 5V93
VIN = 3.3V106206LX On-Resistance, NMOS
VIN = 2.6V116
LX Current-Sense
TransimpedanceFrom LX to COMP, VIN = 2.6V to 5.5V0.160.240.35Ω
High side2.43.14.5LX Current-Limit ThresholdDuty cycle = 100%, VIN = 2.6V to 5.5VLow side-0.6A
VLX = 5.5V10LX Leakage CurrentVIN = 5.5VLX = GND-10µA
LX Switching FrequencyVIN = 2.6V to 5.5V0.8511.1MHz
LX Maximum Duty CycleVCOMP = 1.5V, LX = Hi-Z, VIN = 2.6V to 5.5V100%
LX Minimum Duty CycleVCOMP = 1V, VIN = 2.6V to 5.5V15%
THERMAL CHARACTERISTICSTJ rising160Thermal-Shutdown ThresholdWhen LX starts/stops switchingTJ falling145°C
ELECTRICAL CHARACTERISTICS(VIN= VCC= 3.3V, PGND = GND, FB in regulation, CREF= 0.1µF, TA
= -40°C to +85°C, unless otherwise noted.) (Note 3)
PARAMETERCONDITIONSMINTYPMAXUNITS
IN AND VCCIN Voltage Range2.65.5V
Supply CurrentSwitching with no load, VIN = 5.5V10mA
Shutdown CurrentCOMP = GND1mA
VCC rising2.5VCC Undervoltage Lockout
ThresholdWhen LX starts/stops switchingVCC falling1.95V
REFREF VoltageIREF = 0µA, VIN = 2.6V to 5.5V1.952.03V
REF Load RegulationIREF = 0 to 40µA, VIN = 2.6V to 5.5V0.2%
REF Line RegulationIREF = 20µA, VIN = 2.6V to 5.5V0.4%
REF Shutdown ResistanceFrom REF to GND, COMP = GND22Ω
MAX1951/MAX1952
1MHz, All-Ceramic, 2.6V to 5.5V Input,
2A PWM Step-Down DC-to-DC Regulators
Note 3:Specifications to -40°C are guaranteed by design and not production tested.
Note 4:The LX output is designed to provide 2.4A RMS current.
ELECTRICAL CHARACTERISTICS (continued)(VIN= VCC= 3.3V, PGND = GND, FB in regulation, CREF= 0.1µF, TA
= -40°C to +85°C, unless otherwise noted.) (Note 3)
PARAMETERCONDITIONSMINTYPMAXUNITS
COMPMAX19514080COMP TransconductanceFrom FB to COMP, VCOMP = 1.25VMAX195226.753.3µS
COMP Clamp Voltage, LowVIN = 2.6V to 5.5V, VFB = 1.3V0.61.2V
COMP Clamp Voltage, HighVIN = 2.6V to 5.5V, VFB = 1.1V1.972.28V
COMP Shutdown ResistanceFrom COMP to GND, VIN = 2V30Ω
COMP rising1.2COMP Shutdown ThresholdWhen LX starts/stops switchingCOMP falling0.17V
COMP Startup CurrentCOMP = GND1440µA
Output Voltage Range
(MAX1951)When using external feedback resistors to drive FB0.8VINV
MAX19510.7830.807FB Regulation Voltage
(Error Amp Only)VCOMP = 1V to 2V, VIN = 2.6V to 5.5VMAX19521.7641.836V
FB Input ResistanceFrom FB to GNDMAX19521030kΩ
FB Input Bias CurrentMAX1951-0.1+0.1µA
LX (Note 4)LX On-Resistance, PMOS266mΩ
LX On-Resistance, NMOS206mΩ
LX Current SenseFrom LX to COMP, VIN = 2.6V to 5.5V0.160.35Ω
LX Current-Limit ThresholdDuty cycle = 100%, VIN = 2.6V to 5.5V, high side2.44.5A
VLX = 5.5V10LX Leakage CurrentVIN = 5.5VLX = GND-10µA
LX Switching FrequencyVIN = 2.6V to 5.5V0.81.1MHz
LX Maximum Duty CycleVCOMP = 1.5V, LX = Hi-Z, VIN = 2.6V to 5.5V100%
MAX1951/MAX1952
1MHz, All-Ceramic, 2.6V to 5.5V Input,
2A PWM Step-Down DC-to-DC Regulators
EFFICIENCY vs. LOAD CURRENT
(VCC = VIN = 5V)MAX 1951 toc01
LOAD CURRENT (mA)
EFFICIENCY (%)
10010,000
VOUT = 3.3V
VOUT = 2.5V
VOUT = 1.5V
VOUT = 0.8V
EFFICIENCY vs. LOAD CURRENT
(VCC = VIN = 3.3V)MAX 1951 toc02
LOAD CURRENT (mA)
EFFICIENCY (%)
10010,000
VOUT = 2.5V
VOUT = 1.8V
VOUT = 1.5V
VOUT = 0.8V
REF VOLTAGE
vs. REF OUTPUT CURRENTMAX1951 toc03
REF OUTPUT CURRENT (μA)
REF VOLTAGE (V)30252015105
TA = +85°C
TA = +25°C
TA = -40°C
SWITCHING FREQUENCY
vs. INPUT VOLTAGEMAX1951 toc04
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (MHz)
TA = +85°C
TA = +25°C
TA = -40°C
OUTPUT VOLTAGE DEVIATION
vs. LOAD CURRENTMAX1951 toc05
LOAD CURRENT (A)
OUTPUT VOLTAGE DEVIATION (mV)
VOUT = 2.5VVOUT = 3.3V
VOUT = 0.8VVOUT = 1.8V
Typical Operating Characteristics(Typical values are at VIN= VCC= 5V, VOUT= 1.5V, IOUT= 1.5A, and TA= +25°C, unless otherwise noted. See Figure 2.)
LOAD-TRANSIENT RESPONSEMAX1951 toc06
40μs/div
OUTPUT VOLTAGE:
100mV/div,
AC-COUPLED
OUTPUT CURRENT:
0.5A/div
VIN = 5V
VOUT = 2.5V
IOUT = 0.5 TO 1A
LOAD-TRANSIENT RESPONSEMAX1951 toc07
40μs/div
OUTPUT VOLTAGE:
100mV/div,
AC-COUPLED
OUTPUT CURRENT:
0.5A/div
VIN = 3.3V
VOUT = 1.5V
IOUT = 0.5 TO 1A
MAX1951/MAX1952
1MHz, All Ceramic, 2.6V to 5.5V Input,
2A PWM Step-Down DC-to-DC Regulatorsypical Operating Characteristics (continued)(Typical values are at VIN= VCC= 5V, VOUT= 1.5V, IOUT= 1.5A, and TA= +25°C, unless otherwise noted. See Figure 2.)
SHUTDOWN CURRENT
vs. INPUT VOLTAGEMAX1951 toc12
INPUT VOLTAGE (V)
SHUTDOWN CURRENT (mA)
SWITCHING WAVEFORMS
MAX1951 toc08
200ns/div
INDUCTOR CURRENT
1A/div
VLX
5V/div
OUTPUT VOLTAGE
10mV/div,
AC-COUPLEDVIN = 3.3V
VOUT = 1.8V
ILOAD = 1.5A
SOFT-START WAVEFORMSMAX1951 toc09
1ms/div
VCOMP
2V/div
OUTPUT VOLTAGE
1V/div
VIN = VCC = 3.3V
VOUT = 2.5V
ILOAD = 1.5A
SOFT-START WAVEFORMSMAX1951 toc10
1ms/div
VCOMP
2V/div
OUTPUT VOLTAGE
0.5V/div
VIN = VCC = 3.3V
VOUT = 0.8V
SHUTDOWN WAVEFORMSMAX1951 toc11
20μs/divVCOMP
2V/div
VLX
5V/div
OUTPUT VOLTAGE
1V/div
VIN = VCC = 3.3V
VOUT = 2.5V
ILOAD = 1.5A
MAX1951/MAX1952
1MHz, All-Ceramic, 2.6V to 5.5V Input,
2A PWM Step-Down DC-to-DC Regulators
Detailed DescriptionThe MAX1951/MAX1952 high-efficiency switching regula-
tors are small, simple, DC-to-DC step-down converters
capable of delivering up to 2A of output current. The
devices operate in pulse-width modulation (PWM) at a
fixed frequency of 1MHz from a 2.6V to 5.5V input voltage
and provide an output voltage from 0.8V to VIN, making
the MAX1951/MAX1952 ideal for on-board postregula-
tion applications. The high switching frequency allows
for the use of smaller external components, and internal
synchronous rectifiers improve efficiency and eliminate
the typical Schottky free-wheeling diode. Using the on-
resistance of the internal high-side MOSFET to sense
switching currents eliminates current-sense resistors,
further improving efficiency and cost. The MAX1951
total output error over load, line, and temperature (0°C
to +85°C) is less than 1%.
Controller Block FunctionThe MAX1951/MAX1952 step-down converters use a
PWM current-mode control scheme. An open-loop com-
parator compares 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, cur-
rent ramps up through the inductor, sourcing current to
the output and storing energy in the inductor. The current-
mode feedback system regulates the peak inductor cur-
rent as a function of the output voltage error signal. Since
the average inductor current is nearly the same as the
peak inductor current (<30% ripple current), the circuit
acts as a switch-mode transconductance amplifier. 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 p-channel MOSFET turns off,
and the internal low-side n-channel MOSFET turns on.
The inductor releases the stored energy as its current
ramps down while still providing current to the output. The
output capacitor stores charge when the inductor current
exceeds the load current, and discharges when the
inductor current is lower, smoothing the voltage across
the load. Under overload conditions, when the inductor
current exceeds the current limit (see the Current Limit
section), the high-side MOSFET does not turn on at the
rising edge of the clock and the low-side MOSFET
remains on to let the inductor current ramp down.
Current SenseAn internal current-sense amplifier produces a current
signal proportional to the voltage generated by the
high-side MOSFET on-resistance and the inductor cur-
rent (RDS(ON) x ILX). The amplified current-sense signal
and the internal slope compensation signal are
summed together into the comparator’s inverting input.
The PWM comparator turns off the internal high-side
MOSFET when this sum exceeds the output from the
voltage-error amplifier.
Current LimitThe internal high-side MOSFET has a current limit of 3.1A
(typ). If the current flowing out of LX exceeds this limit,
the high-side MOSFET turns off and the synchronous
rectifier turns on. This lowers the duty cycle and causes
the output voltage to droop until the current limit is no
longer exceeded. A synchronous rectifier current limit of
-0.6A (typ) protects the device from current flowing into
LX. If the negative current limit is exceeded, the synchro-
nous rectifier turns off, forcing the inductor current to flow
Pin Description
PINNAMEFUNCTION1VCCSupply Voltage. Bypass VCC with 0.1µF
capacitor to ground and 10Ω resistor to IN.REFReference Bypass. Bypass REF with 0.1µF
capacitor to ground.GNDGround
4FB
Feedback Input. Connect FB to the output to
regulate using the internal feedback resistor
string (MAX1952). Connect an external resistor-
divider from the output to FB and GND to set
the output to a voltage between 0.8V and VIN
(MAX1951).COMP
Regulator Compensation. Connect series RC
network from COMP to GND. Pull COMP below
0.17V to shut down the regulator. COMP =
GND when VIN is less than 2.25V (see the
Compensation and Shutdown Mode section)PGND
Power Ground. Internally connected to GND.
Keep power ground and signal ground planes
separate.
7LXInductor Connection. Connect an inductor
between LX and the regulator output.
8IN
Power-Supply Voltage. Input voltage range
from 2.6V to 5.5V. Bypass IN with a 10µF (min)
ceramic capacitor to GND and a 10Ω resistor
to VCC.
MAX1951/MAX1952
1MHz, All-Ceramic, 2.6V to 5.5V Input,
2A PWM Step-Down DC-to-DC Regulatorsthrough the high-side MOSFET body diode, back to the
input, until the beginning of the next cycle or until the
inductor current drops to zero. The MAX1951/MAX1952
utilize a pulse-skip mode to prevent overheating during
short-circuit output conditions. The device enters pulse-
skip mode when the FB voltage drops below 300mV, lim-
iting the current to 3A (typ) and reducing power
dissipation. Normal operation resumes upon removal of
the short-circuit condition.
VCCDecouplingDue to the high switching frequency and tight output
tolerance (1%), decouple VCCwith a 0.1µF capacitor
connected from VCCto GND, and a 10Ωresistor con-
nected from VCCto IN. Place the capacitor as close to
VCCas possible.
Soft-StartThe MAX1951/MAX1952 employ digital soft-start circuitry
to reduce supply inrush current during startup conditions.
When the device exits undervoltage lockout (UVLO), shut-
down mode, or restarts following a thermal-overload
event, or the external pulldown on COMP is released, the
digital soft-start circuitry slowly ramps up the voltages at
REF and FB (see the Soft-Start Waveforms in theTypical
Operating Characteristics).
Undervoltage LockoutIf VCC drops below 2.25V, the UVLO circuit inhibits
switching. Once VCCrises above 2.35V, the UVLO
clears, and the soft-start sequence activates.
Compensation
and Shutdown ModeThe output of the internal transconductance voltage
error amplifier connects to COMP. The normal operation
voltage for COMP is 1V to 2.2V. To shut down the
MAX1951/MAX1952, use an NPN bipolar junction
transistor or a very low output capacitance open-drain
MOSFET to pull COMP to GND. Shutdown mode causes
the internal MOSFETs to stop switching, forces LX to a
high-impedance state, and shorts REF to GND.
Release COMP to exit shutdown and initiate the soft-
start sequence.
Thermal-Overload ProtectionThermal-overload protection limits total power dissipation
in the device. When the junction temperature exceeds TJ
= +160°C, a thermal sensor forces the device into shut-
down, allowing the die to cool. The thermal sensor turns
the device on again after the junction temperature cools
by 15°C, resulting in a pulsed output during continuous
overload conditions. Following a thermal-shutdown condi-
tion, the soft-start sequence begins.
MAX1951
VCC
COMP
CURRENT SENSE
SLOPE
COMP
ERROR
SIGNAL
CLOCK
POSITIVE AND NEGATIVE CURRENT LIMITS
GND
REF
PGND
DAC
SOFT-START/
UVLO
REF
PWM
CONTROL
THERMAL
SHUTDOWN
BANDGAP
REF
1.25V
CLAMP
OSC
RAMP GEN
Figure 1. Functional Diagram
