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MAX8581ETB+T-MAX8582ETB+
2.5MHz/1.5MHz Step-Down Converters with 60mΩ Bypass in TDFN for CDMA PA Power
General DescriptionThe MAX8581/MAX8582 high-frequency step-down con-
verters are optimized for dynamically powering the power
amplifier (PA) in CDMA handsets. They integrate a high-
efficiency PWM step-down converter for medium- and
low-power transmission and a 60mΩ(typ) bypass mode
to power the PA directly from the battery during high-
power transmission. They use an analog input driven by
an external DAC to control the output voltage linearly for
continuous PA power adjustment. The MAX8581/
MAX8582 use an internal feedback network, and the
switchingfrequency is internally set to 2.5MHz and
1.5MHz, respectively.
Fast switching (up to 2.5MHz) and fast soft-start allow
the use of ceramic 2.2µF input and output capacitors
while maintaining low voltage ripple. The small 1.5µH to
3.3µH inductor size can be optimized for efficiency.
The MAX8581/MAX8582 are available in 10-pin, 3mm x
3mm TDFN packages (0.8mm max height).
ApplicationsWCDMA/NCDMA Cell Phones
Wireless PDAs, Smartphones
Features600mA Step-Down Converter60mΩ(typ) Bypass Mode with Integrated FETDynamically Adjustable Output from 0.4V to VIN2.5MHz and 1.5MHz Switching FrequencySmall LC Components: 1.5µH to 3.3µH and 2.2µFUp to 94% EfficiencyLow Output Ripple at All Loads2.7V to 5.5V Input0.1µA Shutdown ModeOutput Short-Circuit ProtectionThermal Shutdown10-Pin, 3mm x 3mm TDFN Packages
MAX8581/MAX8582
2.5MHz/1.5MHz Step-Down Converters
with 60mΩBypass in TDFN for CDMA PA PowerTOP VIEW
OUT2OUT
SHDN
GND4
MAX8581/
MAX8582987
REFIN+
Pin Configuration
Ordering InformationINPUT
Li+ BATTERY
2.2μF
GND
SHDN
REFIN
OUTFORCED BYPASS
OUTPUT
0.4V TO VBATT
1.5μH OR 3.3μH
2.2μF
ON/OFF
ANALOG
CONTROL
MAX8581
MAX8582
Typical Operating Circuit19-0593; Rev 1; 1/07
*All devices are specified in the -40°C to +85°C extended
temperature range.
**EP = Exposed pad.
+Denotes a lead-free package.
EVALUATION KIT
AVAILABLE
PART* PIN-
PACKAGE
TOP
MARK
PKG
CODE
MAX8581ETB+10 TDFN-EP**ACTT1033-1
MAX8582ETB+10 TDFN-EP**ACUT1033-1
MAX8581/MAX8582
2.5MHz/1.5MHz Step-Down Converters
with 60mΩBypass in TDFN for CDMA PA Power
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VIN= VSHDN= 3.6V, VREFIN= 0.9V, VHP= VIC= 0V, TA= -40°C to +85°C, typical values are at TA= +25°C, unless otherwise
noted.) (Note 1)
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.
IN, SHDN, HP, REFIN to GND...............................-0.3V to +6.0V
LX, OUT, IC to GND.....................................-0.3V to (VIN+ 0.3V)
OUT Short Circuit to GND..........................................Continuous
LX Current......................................................................0.7ARMS
IN, OUT Current..............................................................2.5ARMS
Continuous Power Dissipation (TA= +70°C)
10-Pin TDFN (derate 24.4mW/°C above +70°C).........1951mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
SUPPLYSupply Voltage RangeVIN2.75.5V
UVLO ThresholdUVLOVIN rising, 180mV hysteresis2.552.632.70V
ILOAD = 0A, switching at 1.5MHz4000
Shutdown, TA = +25°C0.110Supply CurrentIIN
Shutdown, TA = +85°C1.0
OUTVIN = 4.2V, VREFIN = 1.7V3.333.403.47
VREFIN = 0.9V1.751.801.85OUT Voltage AccuracyVOUTVIN = 3.6VVREFIN = 0.4V0.750.800.85
MAX8581360OUT Input ResistanceROUTVLX = VOUTMAX8582558kΩ
REFINREFIN Common-Mode Range02.2V
REFIN to OUT Gain2.00V/V
REFIN Input Resistance518kΩ
REFIN Dual Mode ThresholdVREFIN rising, 77mV hysteresis0.45 x
VIN
0.463 x
VIN
0.475 x
VINV
LOGIC INPUTSVIHVIN = 2.7V to 5.5V1.4Logic Input LevelVILVIN = 2.7V to 5.5V0.4V
TA = +25°C0.011Logic Input Bias CurrentIIH, IILVINPUT = 0V or VINTA = +85°C0.1µA
Dual Mode is a trademark of Maxim Integrated Products, Inc.
MAX8581/MAX8582
2.5MHz/1.5MHz Step-Down Converters
with 60mΩBypass in TDFN for CDMA PA Power
Note 1:All devices are 100% production tested at TA= +25°C. Limits over the operating temperature range are guaranteed by design.
ELECTRICAL CHARACTERISTICS (continued)(VIN= VSHDN= 3.6V, VREFIN= 0.9, VHP= VIC= 0V, TA= -40°C to +85°C, typical values are at TA= +25°C, unless otherwise noted.)
(Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSRONPp-channel MOSFET switch, ILX = -40mA0.20.4On-ResistanceRONNn-channel MOSFET rectifier, ILX = 40mA0.180.35Ω
TA = +25°C0.15LX Leakage CurrentILXLKGVIN = 5.5V,
LX = GNDTA = +85°C1µA
p-Channel MOSFET Peak
Current LimitILIMP70010771400mA
n-Channel MOSFET Valley
Current LimitILIMN7909851150mA
tON(MIN)70114150Minimum On- and Off-TimestOFF(MIN)70112150ns
tON/tOFF RatiotON(MIN) / tOFF(MIN)0.901.021.13 s/s
MAX85812.5Switching FrequencyMAX85821.5MHz
BYPASSp-channel MOSFET bypass,
IOUT = -400mA, TA = +25°C0.060.1On-ResistanceRONBYP
p-channel MOSFET bypass, IOUT = -400mA0.12
Bypass Current Limit1.02.1A
Step-Down Current Limit in
Bypass70010771400mA
GENERALThermal Shutdown+160°C
Thermal-Shutdown Hysteresis20°C
Power-Up DelayVSHDN rising to VLX rising50130µs
MAX8581/MAX8582
2.5MHz/1.5MHz Step-Down Converters
with 60mΩBypass in TDFN for CDMA PA Power
Typical Operating Characteristics(VIN= 3.6V, VOUT= 1.2V, MAX8582 EV Kit, TA= +25°C, unless otherwise noted.)
BYPASS MODE DROPOUT VOLTAGE
vs. LOAD CURRENTMAX8581/2 toc01
LOAD CURRENT (A)
DROPOUT VOLTAGE (V
- V
OUT
) (V)
VOUT = 3.2V
VOUT = 3.6V
EFFICIENCY vs. OUTPUT VOLTAGEMAX8581/2 toc02
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
RLOAD = 7.5Ω
EFFICIENCY
vs. LOAD CURRENT (VOUT = 1.8V)MAX8581/2 toc03
LOAD CURRENT (mA)
EFFICIENCY (%)
EFFICIENCY
vs. LOAD CURRENT (VOUT = 1.2V)
MAX8581/2 toc04
LOAD CURRENT (mA)
EFFICIENCY (%)
EFFICIENCY
vs. LOAD CURRENT (VOUT = 0.6V)
MAX8581/2 toc05
LOAD CURRENT (mA)
EFFICIENCY (%)
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX8581/2 toc06
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX8581/2 toc07
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE vs. REFIN VOLTAGE
MAX8581/2 toc08
REFIN VOLTAGE (V)
OUTPUT VOLTAGE V
OUT
(V)
VIN = 4.2V
VIN = 3.6V
VIN = 3.0V
RLOAD = 7.5Ω
MAX8581/MAX8582
2.5MHz/1.5MHz Step-Down Converters
with 60mΩBypass in TDFN for CDMA PA Power
Typical Operating Characteristics (continued)(VIN= 3.6V, VOUT= 1.2V, MAX8582 EV Kit, TA= +25°C, unless otherwise noted.)
LIGHT-LOAD SWITCHING WAVEFORMSMAX8581/2 toc09
200ns/div
ILX
VLX
VOUT
100mA/div
20mV/div
AC-COUPLED
2V/div
ILOAD = 50mA
HEAVY-LOAD SWITCHING WAVEFORMSMAX8581/2 toc10
200ns/div
ILX
VLX
VOUT
600mA
400mA
200mA
20mV/div
AC-COUPLED
2V/div
ILOAD = 500mA
SOFT-START WAVEFORMSMAX8581/2 toc11
20μs/div
ILX
IIN
VOUT
2V/div
1V/div
100mA/div
500mA/div
VSHDN
LINE-TRANSIENT WAVEFORMSMAX8581/2 toc12
20μs/div
ILX
VIN
VOUT
50mV/div
AC-COUPLED
200mA/div
RLOAD = 7.5Ω
LOAD TRANSIENTMAX8581/2 toc13
20μs/div
VOUT
IOUT
50mV/div
AC-COUPLED
100mA/div
REFIN TRANSIENT RESPONSEMAX8581/2 toc14
20μs/div
ILX
VREFIN
VOUT
0.5V
200mA/div
RLOAD = 7.5Ω
REFIN TRANSIENT WITH AUTOBYPASSMAX8581/2 toc15
20μs/div
ILX
VREFIN
VOUT
IOUT
2V/div
1V/div
500mA/div
500mA/div
RLOAD = 7.5Ω
HP TRANSIENT RESPONSE
WITH FORCED AUTOBYPASSMAX8581/2 toc16
20μs/div
ILX
VHP
VOUT
IOUT
2V/div
1V/div
500mA/div
500mA/div
RLOAD = 7.5Ω
VREFIN = 0.6V
MAX8581/MAX8582
2.5MHz/1.5MHz Step-Down Converters
with 60mΩBypass in TDFN for CDMA PA Power
Detailed DescriptionThe MAX8581/MAX8582 step-down converters deliver
over 600mA to dynamically power the PA in CDMA
handsets. The hysteretic PWM control scheme switches
with nearly fixed frequency at 1.5MHz (MAX8582) to
2.5MHz (MAX8581), allowing efficiency and tiny external
components. A 60mΩbypass mode connects the PA
directly to the battery during high-power transmission.
Control SchemeA hysteretic PWM control scheme ensures high effi-
ciency, fast switching, fast transient response, low out-
put ripple, and physically tiny external components.
This control scheme is simple: When the output voltage
is below the regulation voltage, the error comparator
begins a switching cycle by turning on the high-side
switch. This switch remains on until the minimum on-
time expires and the output voltage is in regulation or
the current-limit threshold is exceeded. Once off, the
high-side switch remains off until the minimum off-time
expires and the output voltage falls out of regulation.
During this period, the low-side synchronous rectifier
turns on and remains on until the high-side switch turns
on again. The internal synchronous rectifier eliminates
the need for an external Schottky diode.
Voltage-Positioning Load RegulationThe MAX8581/MAX8582 utilize a unique feedback net-
work. By taking feedback from the LX node, the usual
phase lag due to the output capacitor is removed, mak-
ing the loop exceedingly stable and allowing the use of
very small ceramic output capacitors. This configura-
tion yields load regulation equal to half the inductor’s
series resistance multiplied by the load current. This
voltage-positioning load regulation greatly reduces
overshoot during load transients or when changing
VOUTfrom one voltage to another. However, when cal-
culating REFIN voltage, the load regulation should be
considered. Because inductor resistance is typically
well specified and the typical PA is a resistive load, the
VREFINto VOUTgain is slightly less than 2V/V for the
MAX8581/MAX8582.
Bypass ModeDuring high-power transmission, the bypass mode’s
low on-resistance provides low dropout, long battery
life, and high output-current capability. Bypass mode
connects IN directly to OUT with the internal 60mΩ
(typ) bypass FET, while the step-down converter is
forced into 100% duty-cycle operation to slightly lower
total on-resistance to less than 60mΩ(typ).
Pin Description
PINNAMEFUNCTIONGNDGround
2, 3INSupply Voltage Input. 2.7V to 5.5V. Bypass with a 2.2µF ceramic capacitor as close as possible to IN
and GND.SHDNActive-Low Shutdown Input. Connect to IN or logic-high for normal operation. Connect to GND or
logic-low for shutdown mode.
5HPHigh-Power Mode Set Input. Drive HP high to invoke bypass mode. Bypass mode connects IN
directly to OUT with the internal bypass MOSFET.REFINDAC-Controlled Input. Output regulates to 2 x VREFIN for the MAX8581 and MAX8582. Dual-mode
threshold at 0.465 VIN enables bypass mode.
7ICInternally Connected. Connect to ground.
8, 9OUTOutput Voltage Connection for Bypass Mode. Internally connected to IN using the internal bypass
MOSFET during bypass mode. Connects to the internal feedback network.LXInductor Connection. Connect inductor to the drains of the internal p-channel and n-channel
MOSFETs. Connects to the internal feedback network.
—EPExposed Paddle. Connect to GND.