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MAX1843EGI-T-MAX1843ETI+-MAX1843ETI+T
2.7A, 1MHz, Low-Voltage, Step-Down Regulator with Internal Synchronous Rectification in TQFN Package
MAX1843
2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Internal Synchronous Rectification in TQFN Package19-1986; Rev 2; 4/06
General DescriptionThe MAX1843 constant-off-time, pulse-width modulated
(PWM) step-down DC-DC converter is ideal for use in 5V
and 3.3V to low-voltage conversion necessary in note-
book and subnotebook computers. This device features
an internal PMOS power switch and internal synchronous
rectification for high efficiency and reduced component
count. An external Schottky diode is not required. The
internal 90mΩpower switch and 70mΩnMOS synchro-
nous-rectifier switch easily deliver continuous load cur-
rents up to 2.7A. The MAX1843 produces a preset +2.5V,
+1.8V, or +1.5V output voltage or an adjustable output
from +1.1V to VIN. It achieves efficiencies as high as
95%.
The MAX1843 uses a unique current-mode, constant-off-
time, PWM control scheme, which includes Idle Mode™
to maintain high efficiency during light-load operation.
The programmable constant-off-time architecture sets
switching frequencies up to 1MHz, allowing the user to
optimize performance trade-offs between efficiency, out-
put switching noise, component size, and cost. The
MAX1843 features an adjustable soft-start to limit surge
currents during startup, a 100% duty-cycle mode for low
dropout operation, and a low-power shutdown mode that
disconnects the input from the output and reduces sup-
ply current below 1µA. The MAX1843 is available in a 28-
pin TQFN package with an exposed backside pad.
Applications5V or 3.3V to Low-Voltage Conversion
CPU I/O Ring
Chipset Supplies
Notebook and Subnotebook Computers
Features±1% Output AccuracyUp to 1MHz Switching Frequency95% EfficiencyInternal pMOS/nMOS Switches
90mΩ/70mΩOn-Resistance at VIN= +4.5V
110mΩ/80mΩOn-Resistance at VIN= +3VOutput Voltage
+2.5V, +1.8V, or +1.5V Pin Selectable
+1.1V to VINAdjustable+3V to +5.5V Input Voltage Range350µA Operating Supply Current< 1µA Shutdown Supply CurrentProgrammable Constant-Off-Time OperationIdle Mode Operation at Light LoadsThermal Shutdown Adjustable Soft-Start Inrush Current Limiting100% Duty Cycle During Low-Dropout OperationOutput Short-Circuit Protection28-Pin TQFN Package
Ordering InformationIdle Mode is a trademark of Maxim Integrated Products, Inc.
MAX18432534567
COMP
N.C.LXPGNDV
FBSELPGNDPGND
TQFNTOP VIEW
N.C.
161718192021
REF
GND
N.C.
N.C.
N.C.
TOFF
N.C.
N.C.
N.C.
SHDN
N.C.
Pin ConfigurationTOFF
COMP
VCC
FBSELSHDN
PGND
GND
REFMAX1843
OUTPUT
+1.1V TO
VIN
INPUT
+3V TO
+5.5V
0.01µF
1µF
2.2µF470pF
10Ω
Typical Configuration
PARTTEMP
RANGE
PIN-
PACKAGE
PKG
CODEMAX1843ETI+-40°C to +85°C28 TQFNT2855-6
+Denotes lead-free package.
MAX1843
2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Synchronous Rectification in TQFN Package
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS (VIN= VCC= +3.3V, FBSEL = GND, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +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.
VCC, IN to GND........................................................-0.3V to +6V
IN to VCC.............................................................................±0.3V
GND to PGND.....................................................................±0.3V
All Other Pins to GND.................................-0.3V to (VCC+ 0.3V)
LX Current (Note 1).............................................................±4.7A
REF Short Circuit to GND Duration............................Continuous
ESD Protection.....................................................................±2kV
Continuous Power Dissipation (TA= +70°C)
28-Pin TQFN (derate 20mW/°C above +70°C, part mounted
on 1in2of 1oz copper)......................................................1.6W
Operating Temperature Range...........................-40°C to +85°C
Storage Temperature Range.............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s)................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSInput VoltageVIN, VCC3.05.5V
TA = +25°C
to +85°C2.5002.5252.550
FBSEL = VCC
TA = 0°C to
+85°C2.4872.5252.563
TA = +25°C
to +85°C1.5001.5151.530
FBSEL =
unconnectedTA = 0°C to
+85°C1.4921.5151.538
TA = +25°C
to +85°C1.8001.8181.836
FBSEL = REF
TA = 0°C to
+85°C1.7911.8181.845
TA = +25°C
to +85°C1.0891.1001.111
Preset Output VoltageVOUT
VIN =
+3V to
+5.5V
ILOAD =
0 to 2.5A
VFB =
VOUT
FBSEL = GND
TA = 0°C to
+85°C1.0841.1001.117
Adjustable Output Voltage
RangeVIN = VCC = +3V to +5.5V, FBSEL = GNDVREFVINV
AC-Load Regulation Error2%
DC-Load Regulation Error0.4%
Dropout VoltageVDOVIN = VCC = +3V, ILOAD = 1A250mV
TA = +25°C to +85°C1.0891.1001.111Reference VoltageVREFTA = 0°C to +85°C1.0841.1001.117V
Reference Load RegulationΔVREFIREF = -1µA to +10µA0.52mV
VIN = +4.5V90200pMOS Switch On-ResistanceRON,PILX = 0.5AVIN = +3V110250mΩ
VIN = +4.5V70150nMOS Switch On-ResistanceRON,NILX = 0.5AVIN = +3V80200mΩ
Current-Limit ThresholdILIMIT3.13.64.1A
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.
MAX1843
2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Synchronous Rectification in TQFN Package
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSIdle-Mode Current Threshold0.30.60.9A
Switching Frequencyf(Note 2)1MHz
No-Load Supply CurrentIIN + ICCVFB = 1.2V350600µA
Shutdown Supply CurrentIIN + ICCSHDN = GND, includes pMOS leakage<115µA
Thermal Shutdown ThresholdTSHDNHysteresis = 15°C160°C
Undervoltage LockoutVUVLOVIN falling, hysteresis = 90mV2.52.62.7V
FB Input Bias CurrentVFB = 1.2V060250nA
RTOFF = 110kΩ0.91.001.1
RTOFF = 30.1kΩ0.240.300.37Off-TimetOFF
RTOFF = 499kΩ3.84.55.2
Off-Time Startup PeriodFB = GND4 tOFFµs
On-TimetON(Note 2)0.4µs
SS Source CurrentISS456µA
SS Sink CurrentISSVSS = 1V100µA
SHDN Input CurrentISHDNVSHDN = 0 to VCC-11µAHD N Log i c Inp ut Low V ol tag eVIL0.8VHD N Log i c Inp ut H i g h V ol tag eVIH2.0V
FBSEL Input CurrentIFBVFBSEL = 0 to VCC-44µA
FBSEL = GND0.2
FBSEL = REF0.91.3
FBSEL = unconnected0.7VCC
- 0.2
0.7VCC
+ 0.2FBSEL Logic Thresholds
FBSEL = VCCVCC
- 0.2axi m um O utp ut RM S C ur r ent3.1ARMS
ELECTRICAL CHARACTERISTICS(VIN= VCC= +3.3V, FBSEL = GND, TA
= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 3)
PARAMETERSYMBOLCONDITIONSMINMAXUNITSInput VoltageVIN, VCC3.05.5V
FBS E L = V C C 2.4752.576
FBS E L = unconnected 1.4851.545
FBS E L = RE F1.7821.854Preset Output VoltageVOUT
VIN = +3V to + 5.5V,
ILOAD = 0 to 2.5A,FB = V OU TFBS E L = GN D 1.0781.122
Adjustable Output Voltage
RangeVIN = VCC = +3V to +5.5V, FBS E L = GN D VREFVINV
Reference VoltageVREF1.0781.122V
VIN = +4.5V200pMOS Switch On-ResistanceRON,PILX = 0.5AmΩ
ELECTRICAL CHARACTERISTICS (continued)(VIN= VCC= +3.3V, FBSEL = GND, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
Typical Operating Characteristics(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT
(VIN = +5.0V, L = 2.5µH)
MAX1843 toc03
OUTPUT CURRENT (A)
VOUT = +1.5V, RTOFF = 1OOkΩ,
fPWM = 770kHz
VOUT = +1.8V, RTOFF = 75kΩ,
fPWM = 910kHz
VOUT = +2.5V, RTOFF = 47kΩ,
fPWM = 1070kHz
EFFICIENCY (%)
EFFICIENCY vs. OUTPUT CURRENT
(VIN = +3.3V, L = 1.5µH)
MAX1843 toc04
OUTPUT CURRENT (A)
VOUT = +2.5V, RTOFF = 56kΩ,
fPWM = 1000kHz
VOUT = +2.5V, RTOFF = 39kΩ,
fPWM = 610kHz
VOUT = +1.8V, RTOFF = 43kΩ,
fPWM = 1050kHz
EFFICIENCY (%)
EFFICIENCY vs. OUTPUT CURRENT
(fPWM = 270kHz)
MAX1843 toc05
IOUT (A)
VIN = +3.3V, VOUT = +1.8V,
L = 4.7µH, RTOFF = 160kΩ
EFFICIENCY (%)
VIN = +5V, VOUT = +1.8V, L = 5.6µH,
RTOFF = 240kΩ
NORMALIZED OUTPUT ERROR
vs. OUTPUT CURRENTMAX1843 toc06
OUTPUT CURRENT (A)
VIN = +3.3V, VOUT = +1.5V, L = 1.5µH
VIN = +5V, VOUT = +1.5V, L = 2.5µH
NORMALIZED OUTPUT ERROR (%)
PARAMETERSYMBOLCONDITIONSMINMAXUNITSVIN = +4.5V150nMOS Switch On-ResistanceRON,NILX = 0.5AVIN = +3V200mΩ
Current-Limit ThresholdILIMIT2.94.3A
Idle-Mode Current Threshold0.21.0A
No-Load Supply CurrentIIN + ICCVFB = 1.2V600µA
FB Input Bias CurrentIFBVFB = 1.2V0300nA
Off-TimetOFFRTOFF = 110kΩ0.851.15µs
MAX1843
2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Synchronous Rectification in TQFN Package
ELECTRICAL CHARACTERISTICS (continued)(VIN= VCC= +3.3V, FBSEL = GND, TA
= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 3)
Note 2:Recommended operating frequency, not production tested.
Note 3:Specifications from 0°C to -40°C are guaranteed by design, not production tested.
MAX1843
2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Synchronous Rectification in TQFN PackageSUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX1843 toc01
VIN (V)
NO-LOAD SUPPLY CURRENT, I
+ I
CC
SHUTDOWN SUPPLY CURRENT, I
+ I
CC
(nA)
NO LOAD
SHUTDOWN
ypical Operating Characteristics (continued)(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
OFF-TIME vs. RTOFF
MAX1843 toc02
RTOFF (kΩ)
tOFF
LOAD-TRANSIENT RESPONSEVOUTPUT
50mV/div
2A/div
MAX1843 toc09
10µs/div
LINE-TRANSIENT RESPONSEVINPUT
2V/div
VOUTPUT
20mV/div
AC-COUPLED
MAX1843 toc10
20µs/div
IOUT = 2.5A, VOUT = +1.5V
SWITCHING FREQUENCY
vs. OUTPUT CURRENT
MAX1843 toc07
OUTPUT CURRENT (A)
FREQUENCY (kHz)
VIN = +5V, VOUT = +2.5V, L = 2.5µH
VIN = +3.3V, VOUT = +1.5V, L = 1.5µH
VIN = +5V, VOUT = +1.5V, L = 2.5µH
STARTUP AND SHUTDOWNVSS
2V/div
MAX1843 toc08
VSHDN
5V/div
ROUT = 0.5Ω, RTOFF = 56kΩ
VIN = +3.3V, VOUT = +1.5V
IINPUT
1A/div
VOUTPUT
1V/div
1ms/div
