MAX8545EUB+T ,Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current LimitMAX8545/MAX8546/MAX854819-2795; Rev 2; 6/07Low-Cost, Wide Input Range, Step-DownControllers with Fo ..
MAX8546EUB ,Low-Cost / Wide Input Range / Step-Down Controllers with Foldback Current Limitapplications. It drives low-cost N-channel MOSFETs for both the high-side switch and synchronous re ..
MAX8546EUB ,Low-Cost / Wide Input Range / Step-Down Controllers with Foldback Current Limit MAX8546EUB Rev. A RELIABILITY REPORT FOR MAX8546EUB PLASTIC ENCA ..
MAX8546EUB ,Low-Cost / Wide Input Range / Step-Down Controllers with Foldback Current LimitTable of Contents I. ........Device Description V. ........Quality Assurance Information II ..
MAX8546EUB+ ,Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current LimitApplicationsMAX8548 100 -320Set-Top Boxes Notebook DockingStation SuppliesGraphic Card and VideoTyp ..
MAX8546EUB+T ,Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limitapplications.♦ No Additional Bias Supply NeededThey drive low-cost n-channel MOSFETs for both thehi ..
MB8264A-10 , MOS 65536-BIT DYNAMIC RANDOM ACCESS MEMORY
MB8264A-10 , MOS 65536-BIT DYNAMIC RANDOM ACCESS MEMORY
MB8264A-10 , MOS 65536-BIT DYNAMIC RANDOM ACCESS MEMORY
MB82D01171A-80LLPBN , 16 Mbit (1 M word x 16 bit) Mobile Phone Application Specific Memory
MB82D01171A-80LLPBN , 16 Mbit (1 M word x 16 bit) Mobile Phone Application Specific Memory
MB82D01171A-90LLPBT , 16 Mbit (1 M word x 16 bit) Mobile Phone Application Specific Memory
MAX8545EUB+T-MAX8546EUB+-MAX8546EUB+T-MAX8546EUB-T-MAX8548EUB+T
Low-Cost, Wide Input Range, Step-Down Controllers with Foldback Current Limit
General DescriptionThe MAX8545/MAX8546/MAX8548 are voltage-mode
pulse-width-modulated (PWM), step-down DC-DC con-
trollers ideal for a variety of cost-sensitive applications.
They drive low-cost n-channel MOSFETs for both the
high-side switch and synchronous rectifier, and require
no external current-sense resistor. These devices can
supply output voltages as low as 0.8V.
The MAX8545/MAX8546/MAX8548 have a wide 2.7V to
28V input range, and do not need any additional bias
voltage. The output voltage can be precisely regulated
from 0.8V to 0.83 x VIN. These devices can provide effi-
ciency up to 95%. Lossless short-circuit and current-limit
protection is provided by monitoring the RDS(ON)of the
low-side MOSFET. The MAX8545 and MAX8548 have a
current-limit threshold of 320mV, while the MAX8546 has
a current-limit threshold of 165mV. All devices feature
foldback-current capability to minimize power dissipation
under short-circuit condition. Pulling the COMP/EN pin
low with an open-collector or low-capacitance, open-
drain device can shut down all devices.
The MAX8545/MAX8546 operate at 300kHz and the
MAX8548 operates at 100kHz. The MAX8545/MAX8546/
MAX8548 are compatible with low-cost aluminum elec-
trolytic capacitors. Input undervoltage lockout prevents
proper operation under power-sag operations to prevent
external MOSFETs from overheating. Internal soft-start is
included to reduce inrush current. These devices are
offered in space-saving 10-pin µMAX®packages.
Applications
Features2.7V to 28V Input RangeFoldback Short-Circuit ProtectionNo Additional Bias Supply Needed0.8V to 0.83 x VINOutputUp to 95% EfficiencyLow-Cost External ComponentsNo Current-Sense ResistorAll n-Channel MOSFET DesignAdaptive Gate Drivers Eliminate Shoot-ThroughLossless Overcurrent and Short-Circuit
Protection300kHz Switching Frequency
(MAX8545/MAX8546)100kHz Switching Frequency (MAX8548)Pin-Compatible with the MAX1967Thermal Shutdown
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current LimitMAX8545
MAX8546
MAX8548
OFF
OPTIONAL
BSTVIN
COMP/VCC
GND
INPUT
2.7V TO 28V
OUTPUT
0.8V TO
0.9 x VIN
UP TO 6A
Typical Operating Circuit
Ordering Information
Pin Configuration appears at end of data sheet.19-2795; Rev 2; 6/07
PARTTEMP RANGE
PIN-
PACKAGE
PKG
CODE
MAX8545EUB-40°C to +85°C10 µMAXU10-2
MAX8545EUB+-40°C to +85°C10 µMAXU10-2
MAX8546EUB-40°C to +85°C10 µMAXU10-2
MAX8546EUB+-40°C to +85°C10 µMAXU10-2
MAX8548EUB-40°C to +85°C10 µMAXU10-2
MAX8548EUB+-40°C to +85°C10 µMAXU10-2
Selector Guide
PART
SWITCHING
FREQUENCY
(kHz)
CURRENT-LIMIT
THRESHOLD
(mV)MAX8545300-320
MAX8546300-165
MAX8548100-320Set-Top Boxes
Graphic Card and Video
Supplies
Desktops and Desknotes
PCIExpress Power
Supplies
Telecom Power Supplies
Notebook Docking
Station Supplies
Cable Modems and
Routers
Networking Power
Supplies
+Denotes a lead-free package.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VIN= VL = VCC= 5V, TA= -40°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.
(All voltages referenced to GND unless otherwise noted.)
VINto GND ............................................................-0.3V to +30V
VCCto GND .............................-0.3V, lower of 6V or (VL + 0.3V)
FB to GND................................................................-0.3V to +6V
BST to GND............................................................-0.3V to +36V
VL, DL, COMP to GND ..............................-0.3V to (VCC+ 0.3V)
BST to LX..................................................................-0.3V to +6V
DH to LX....................................................-0.3V to (VBST+ 0.3V)
VL Short to GND ......................................................................5s
LX to GND ................................................................-1V to +30V
Input Current (any pin).....................................................±50mA
Continuous Power Dissipation (TA= +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C)..........444mW
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
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSVCC = VL, VIN separate from VCC4.928.0VIN Operating RangeVINVIN = VL = VCC2.75.5V
VIN Undervoltage Lockout
(UVLO) Trip LevelRising and falling edge, hysteresis = 2%2.352.502.66V
VIN Operating Supply CurrentVFB = 0.88V (no switching)0.71.2mA
VL Output Voltage5.5V < VIN < 28V, VCC = VL,
1mA < ILOAD < 25mA4.755.3V
Thermal ShutdownRising temperature, typical
hysteresis = 10°C (Note 1)+160°C
OSCILLATORMAX8545, MAX8546250300360FrequencyfOSCMAX854880100120kHz
DH output, MAX8545, MAX85465Minimum Duty CycleDCMINMAX854810%
DH output, MAX8545, MAX85468386Maximum Duty CycleDCMAXMAX85489095%
SOFT-STARTMAX8545, MAX85466.6Digital Ramp PeriodMAX854810.2ms
MAX8545, MAX8546VOUT / 64Soft-Start LevelsMAX8548VOUT / 32V
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
ELECTRICAL CHARACTERISTICS (continued)(VIN= VL = VCC= 5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
ERROR AMPLIFIER2.7V < VCC < 5.5V, 0°C to +85°C0.7870.8000.815FB Regulation Voltage2.7V < VCC < 5.5V, -40°C to +85°C0.7820.8000.815V
FB to COMP/EN Gain4000V / V
FB to COMP/EN
Transconductance-5µA < ICOMP/EN < +5µA70108160µS
FB Input Bias CurrentVFB = 0.88V12µA
COMP/EN Source CurrentVCOMP/EN = 0V1546100µA
LX to GND, MAX8545, MAX8548,
VFB = 0.8V-355-320-280Current-Limit Threshold Voltage
(Across Low-Side MOSFET)
LX to GND MAX8546, VFB = 0.8V-185-165-140
LX to GND, VFB = 0V,
MAX8545, MAX8548-105-75-45Foldback Current-Limit Threshold
Voltage (Across Low-Side
MOSFET) When Output is ShortMAX8546, LX to GND, VFB = 0-53-38-22
MOSFET DRIVERSRising edge, DH going low to DL going high96Break-Before-Make TimeFalling edge, DL going low to DH going high28ns
DH On-Resistance in Low State1.64Ω
DH On-Resistance in High State2.55.5Ω
DL On-Resistance in Low State1.12.5Ω
DL On-Resistance in High State2.55.5Ω
BST Leakage CurrentVBST = 33V, VLX = 28V, VFB = 0.88V050µA
LX Leakage CurrentVBST = 33V, VLX = 28V, VFB = 0.88V33100µA
Note 1:Thermal shutdown disables the buck regulator when the die reaches this temperature. Soft-start is reset but the VL regulator
remains on.
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
Typical Operating Characteristics(VIN= VL = VCC= 5V, typical values are at TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENTMAX8545/46/48 toc01
LOAD CURRENT (A)
(CIRCUIT OF FIGURE 1; TABLE 1a)
EFFICIENCY (%)0.1
VIN = 3.3V
VOUT = 1.2V
EFFICIENCY vs. LOAD CURRENTMAX8545/46/48 toc02
LOAD CURRENT (A)
(CIRCUIT OF FIGURE 1; TABLE 1a)
EFFICIENCY (%)0.1
VIN = 5V
VOUT = 1.8V
VOUT = 3.3V
EFFICIENCY vs. LOAD CURRENTMAX8545/46/48 toc03
LOAD CURRENT (A)
(CIRCUIT OF FIGURE 2; TABLE 2a)
EFFICIENCY (%)0.1
VOUT = 1.8V
VOUT = 3.3V
VIN = 12V
EFFICIENCY vs. LOAD CURRENTMAX8545/46/48 toc04
LOAD CURRENT (A)
(CIRCUIT OF FIGURE 2; TABLE 2a)
EFFICIENCY (%)0.1
VIN = 17V
VOUT = 3.3V
VOUT = 1.8V
EFFICIENCY vs. LOAD CURRENTMAX8545/46/48 toc05
LOAD CURRENT (A)
EFFICIENCY (%)0.1
VOUT = 1.8V
VOUT = 1.2V
VIN = 3.3V
(CIRCUIT OF FIGURE 1; TABLE 1b)
EFFICIENCY vs. LOAD CURRENTMAX8545/46/48 toc06
LOAD CURRENT (A)
EFFICIENCY (%)0.1
VOUT = 3.3V
VOUT = 2.5V
VOUT = 1.8V
VOUT = 1.2V
VIN = 5V
(CIRCUIT OF FIGURE 1; TABLE 1b)
EFFICIENCY vs. LOAD CURRENTMAX8545/46/48 toc07
LOAD CURRENT (A)
EFFICIENCY (%)0.1
VOUT = 3.3V
VOUT = 2.5V
VOUT = 1.8V
VOUT = 1.2V
VIN = 12V
(CIRCUIT OF FIGURE 2; TABLE 2b)
EFFICIENCY vs. LOAD CURRENTMAX8545/46/48 toc08
LOAD CURRENT (A)
EFFICIENCY (%)0.1
VOUT = 3.3V
VOUT = 2.5VVOUT = 1.8V
VOUT = 1.2V
VIN = 17V
(CIRCUIT OF FIGURE 2; TABLE 2b)
CHANGE IN OUTPUT VOLTAGE
vs. LOAD CURRENTMAX8545/46/48 toc09
LOAD CURRENT (A)
OUTPUT VOLTAGE (V)432
VOUT = 2.5V
VIN = 12V
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
CHANGE IN OUTPUT VOLTAGE
vs. INPUT VOLTAGEMAX8545/46/48 toc10
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
ILOAD = 6A
CHANGE IN OUTPUT VOLTAGE
vs. INPUT VOLTAGEMAX8545/46/48 toc11
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)202224161412
ILOAD = 6A
FREQUENCY vs. INPUT VOLTAGEMAX8545/46/48 toc12
INPUT VOLTAGE (V)
FREQUENCY (kHz)
VOUT = 2.5V
NO LOAD
MAX8545/
MAX8546
FREQUENCY vs. TEMPERATUREMAX8545/46/48 toc13
TEMPERATURE (°C)
FREQUENCY (kHz)
VIN = 12V
VOUT = 2.5V
NO LOAD
MAX8545/
MAX8546
VOUT
AC COUPLED
100mV/div
IOUT
5A/div
40μs/div
LOAD TRANSIENT RESPONSEMAX8545 toc14
VIN = 17V
VOUT = 2.5V
ypical Operating Characteristics (continued)(VIN= VL = VCC= 5V, typical values are at TA = +25°C, unless otherwise noted.)
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limitypical Operating Characteristics (continued)(VIN= VL = VCC= 5V, typical values are at TA = +25°C, unless otherwise noted.)
VOUT
1V/div
VIN
5V/div
INDUCTOR
CURRENT
5A/div
1ms/div
STARTUP WAVEFORMMAX8545 toc15
ILOAD = 3A
VOUT
1V/div
VIN
5V/div
INDUCTOR
CURRENT
2A/div
2ms/div
SHUTDOWN WAVEFORMMAX8545 toc16
ILOAD = 3A
VOUT
2V/div
VIN
5V/div
IIN
10A/div
IOUT
5A/div
SHORT-CIRCUIT WAVEFORMMAX8545 toc18
VOUT
2V/div
VIN
20V/div
IIN
2A/div
INDUCTOR
CURRENT
5A/div
1ms/div
SHORT-CIRCUIT WAVEFORMMAX8545 toc17
GAIN AND PHASE vs. FREQUENCYMAX8545/46/48 toc19
FREQUENCY (kHz)
GAIN (dB)
PHASE (DEGREES)1
VIN = 17V, VOUT = 2.5V
ILOAD = 6A
GAIN
PHASE
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
Pin Description
PINNAMEFUNCTIONCOMP/ENCompensation Input. Pull COMP/EN low with an open-collector or open-drain device to turn
off the output.FBFeedback Input. Connect a resistive-divider network to set VOUT. FB threshold is 0.8V.
3VCCInternal Chip Supply. Connect VCC to VL through a 10Ω resistor. Bypass VCC to GND with at
least a 0.1µF ceramic capacitor.
4VINPower Supply for LDO Regulator for VIN > 5.5V, and Chip Supply for VIN < 5.5V. Bypass VIN with
at least a 1µF ceramic capacitor to GND.
5VLOutput of Internal 5V LDO. Connect VL to VIN for VIN < 5.5V. Bypass VL with at least a 1µF ceramic
capacitor to GND.DLLow-Side External MOSFET Gate-Driver Output. DL swings from VL to GND.GNDGround and Negative Current-Sense InputLXInductor Switching Node. LX is used for both current limit and the return supply of the DH driver.DHHigh-Side External MOSFET Gate-Driver Output. DH swings from BST to LX.BSTPositive Supply of DH Driver. Connect a 0.1µF ceramic capacitor between BST and LX.
VIN
BST
VCC
COMP/EN
5V LINEAR
REGULATOR
RAMP
GENERATOR
MAX8545
MAX8546
MAX8548
PWM COMP
ERROR
AMPLIFIER
800mV
REFSOFT-START
INTERNAL
CHIP SUPPLY
100kHz/
300kHz*
CLOCK
GENERATOR
*SEE SELECTOR GUIDE
CONTROL
LOGIC
TEMPERATURE
SHUTDOWN
GND
FOLD-
BACKFB
CURRENT-LIMIT
COMPARATOR
Functional Diagram
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
Detailed DescriptionThe MAX8545/MAX8546/MAX8548 are BiCMOS switch-
mode power-supply controllers designed to implement
simple, buck-topology regulators in cost-sensitive
applications. The main power-switching circuit consists
of two n-channel MOSFETs, an inductor, and input/out-
put filter capacitors. An all n-channel synchronous-rec-
tified design provides high efficiency at reduced cost.
These devices have an internal 5V linear regulator that
steps down the input voltage to supply the IC and the
gate drivers. The low-side-switch gate driver is directly
powered from the 5V regulator (VL), while the high-
side-switch gate driver is indirectly powered from VL
plus an external diode-capacitor boost circuit.
Current-Limit and
Short-Circuit ProtectionThe MAX8545/MAX8546/MAX8548 employ a valley cur-
rent-sensing algorithm that uses the RDS(ON)of the low-
side n-channel MOSFET to sense the current. This
eliminates the need for an external sense resistor usually
placed in series with the output. The voltage measured
across the low-side MOSFET’s RDS(ON)is compared to
a fixed -320mV reference for the MAX8545/MAX8548
and a fixed -165mV reference for the MAX8546. The cur-
rent limit is given by the equations below:
Aside from current limiting, these devices feature fold-
back short-circuit protection. This feature is designed
to reduce the current limit by 80% as the output voltage
drops to 0V.
MOSFET Gate DriversThe DH and DL drivers are optimized for driving n-chan-
nel MOSFETs with low gate charge. An adaptive dead-
time circuit monitors the DL output and prevents the
high-side MOSFET from turning on until the low-side
MOSFET is fully off. There must be a low-resistance,
low-inductance connection from the DL driver to the
MOSFET gate for the adaptive dead-time circuit to work
properly. Otherwise, the sense circuitry in the MAX8545/
MAX8546/MAX8548 may detect the MOSFET gate as off
while there is actually charge left on the gate. Use very
short, wide traces measuring no less than 50mils to 100
mils wide if the MOSFET is 1in away from the MAX8545/
MAX8546/MAX8548. The same type of adaptive dead-
time circuit monitors the DH off edge. The same recom-
mendations apply for the gate connection of the
high-side MOSFET.
The internal pulldown transistor that drives DL low is
robust, with a 1.1Ω(typ) on-resistance. This helps pre-
vent DL from being pulled up due to capacitive cou-
pling from the drain to the gate of the low-side
synchronous-rectifier MOSFET during the fast rise time
of the LX node.
Soft-StartThe MAX8545/MAX8546/MAX8548 feature an internally
set soft-start function that limits inrush current. It accom-
plishes this by ramping the internal reference input to the
controller’s transconductance error amplifier from 0 to
the 0.8V reference voltage. The ramp time is 1024 oscil-
lator cycles for the MAX8548 and 2048 oscillator cycles
for the MAX8545/MAX8546. At the nominal 100kHz and
300kHz switching rate, the soft-start ramp is approxi-
mately 10.2ms and 6.8ms, respectively.
High-Side Gate-Drive Supply (BST)A flying-capacitor boost circuit generates gate-drive volt-
age for the high-side n-channel MOSFET. The flying
capacitor is connected between the BST and LX nodes.
On startup, the synchronous rectifier (low-side MOSFET)
forces LX to ground and charges the boost capacitor to
VL. On the second half-cycle, the MAX8545/MAX8546/
MAX8548 turn on the high-side MOSFET by closing an
internal switch between BST and DH. This provides the
necessary gate-to-source voltage to drive the high-side
MOSFET gate above its source at the input voltage.
Internal 5V Linear RegulatorAll MAX8545/MAX8546/MAX8548 functions are internally
powered from an on-chip, low-dropout 5V regulator (VL).
These devices have a maximum input voltage (VIN) of
28V. Connect VCCto VL through a 10Ωresistor and
bypass VCCto GND with a 0.1µF ceramic capacitor. The
VIN-to-VL dropout voltage is typically 140mV, so when VIN
is less than 5.5V, VL is typically VIN- 140mV.
The internal linear regulator can source a minimum of
25mA and a maximum of approximately 40mA to supply
power to the IC low-side and high-side MOSFET drivers.
Duty-Cycle Limitations for
Low VOUT/VINRatiosThe MAX8545/MAX8546/MAX8548s’ output voltage is
adjustable down to 0.8V. However, the minimum duty
cycle can limit the ability to supply low-voltage outputsmVMAXLIMITDSON1658546()mVMAXMAXLIMITDSON32085458548)
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limitfrom high-voltage inputs. With high input voltages, the
required duty factor is approximately:
where RDS(ON)x ILOADis the voltage drop across the
synchronous rectifier. Therefore, the maximum input
voltage (VIN(DFMAX)) that can supply a given output
voltage is:
If the circuit cannot attain the required duty cycle dic-
tated by the input and output voltages, the output volt-
age still remains in regulation. However, there may be
intermittent or continuous half-frequency operation as
the controller attempts to lower the average duty cycle
by deleting pulses. This can increase output voltage
ripple and inductor current ripple, which increases
noise and reduces efficiency. Furthermore, circuit sta-
bility is not guaranteed.
Applications Information
Design Procedures1)
Input Voltage Range. The maximum value(VIN(MAX)) must accommodate the worst-case high
input voltage. The minimum value (VIN(MIN)) must
account for the lowest input voltage after drops due
to connectors, fuses, and switches are considered.
In general, lower input voltages provide the best
efficiency.
2)
Maximum Load Current. There are two currentvalues to consider. Peak load current (ILOAD(MAX))
determines the instantaneous component stresses
and filtering requirements and is key in determining
output capacitor requirements. ILOAD(MAX)also
determines the required inductor saturation rating.
Continuous load current (ILOAD) determines the
thermal stresses, input capacitor, and MOSFETs,
as well as the RMS ratings of other heat-contribut-
ing components such as the inductor.
3)
Inductor Value. This choice provides tradeoffsbetween size, transient response, and efficiency.
Higher inductance value results in lower inductor
ripple current, lower peak current, lower switching
losses, and, therefore, higher efficiency at the cost
of slower transient response and larger size. Lower
inductance values result in large ripple currents,
smaller size, and poor efficiency, while also provid-
ing faster transient response.
Setting the Output VoltageAn output voltage between 0.8V and (0.83 x VIN) can
be configured by connecting FB to a resistive divider
between the output and GND (see Figures 1 and 2).
Select resistor R4 in the 1kΩto 10kΩrange. R3 is then
given by:
where VFB= +0.8V.
Inductor SelectionDetermine an appropriate inductor value with the fol-
lowing equation:
where LIR is the ratio of inductor ripple current to aver-
age continuous maximum load current. Choosing LIR
between 20% to 40% results in a good compromise
between efficiency and economy. Choose a low-core-
loss inductor with the lowest possible DC resistance.
Ferrite-core-type inductors are often the best choice for
performance; however, the MAX8548’s low switching
frequency also allows the use of powdered iron core
inductors in ultra-low-cost applications where efficiency
is not critical. With any core material, the core must be
large enough not to saturate at the peak inductor cur-
rent (IPEAK):
Setting the Current LimitThe MAX8545/MAX8546/MAX8548 provide valley cur-
rent limit by sensing the voltage across the external
low-side MOSFET. The minimum current-limit threshold
voltage is -280mV for the MAX8545/MAX8548 and
-140mV for the MAX8546. The MOSFET on-resistance
required to allow a given peak inductor current is:
where IVALLEY= ILOAD(MAX)x (1 - LIR / 2), and
RDS(ON)MAXis the maximum on-resistance of the low-
side MOSFET at the maximum operating junction
temperature.VfortheMAXDSONMAX
VALLEY. ( )≤0148546VfortheMAXMAXDSONMAX
VALLEY. ( /)≤02885458548LIRIPEAKLOADMAXLOADMAX=+⎛⎝⎜⎞⎠⎟×()()2VVfLIRIOUTINOUTOSCLOADMAX−()×()V
OUT341=−⎡⎢⎤⎥DCVRIINDFMAXMINOUTDSONLOAD()()≤+×()()1I
OUTDSONLOAD()()
