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MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
General Description
The MAX77324 is a single channel high-efficiency synchronous step-down (buck) converter capable of delivering up to 1.5A of current. With a 6.89mm2 total solution
size, up to 93% efficiency, and 40µA quiescent current,
it is optimized for portable space constrained batteryoperated applications.
The device operates over a 2.5V to 4.8V input voltage
range to support Li+ battery powered applications. The
output voltage is adjustable from 0.6V to 2V, with a better than 2% accuracy over the whole temperature range.
The device uses constant-on-time PWM control scheme.
A nominal 2MHz switching frequency reduces the overall solution footprint by use of small 0603 inductor. An
automatic SKIP mode is also implemented to improve
the light-load efficiency. The device provides low output
voltage ripple, excellent line and load regulation, and transient response. A dedicated enable pin allows for simple
hardware control.
Built-in undervoltage lockout (UVLO), soft-start, active
output discharge, cycle-by-cycle short-circuit, and thermal
shutdown protections insure safe operations under abnormal operating conditions.
The device is available in a space-saving 1.22mm x
0.85mm, 6-bump wafer-level package (WLP).
Benefits and Features
●● 1.5A Output Current Step-down Converter
●● 2.5V to 4.8V VIN Range
●● 0.6V to 2V Adjustable VOUT Range, ±2% Accuracy
●● 93% Peak Efficiency (3.8VIN, 1.8VOUT)
• SKIP Mode for Higher Light-Load Efficiency
• 40μA Quiescent Current
• 1μA Shutdown Current
●● 2MHz Nominal Switching Frequency
●● Enable Pin for Direct Hardware Control
●● Cycle-by-Cycle Inductor Current Limit
●● UVLO, Soft-Start, Active Output Discharge,
Short-Circuit, and Thermal Shutdown Protections
●● 1.22mm x 0.85mm, 6-Bump WLP
• 6.89mm2 Total Solution Area
• Uses Small 0603 0.47μH Inductor
Applications
●● 1-Cell Battery Powered Equipment
●● Portable/Wearables
●● Internet of Things (IoT) Devices
●● Space Constrained Equipment
Ordering Information appears at end of data sheet.
1-Cell to Core Voltage Buck Converter Application Circuit
ENABLE
MAX77324
EN
AGND
RTOP*
CTOP
220pF
COUT
22μF
L
CIN
FB
PGND
RBOT
30.1kΩ, 1%
CTOP
CIN
10μF
LX
COUT
IN
VOUT
0.6V TO 2.0V
3.25 mm
2.5V TO 4.8V
DC SOURCE
6.89mm2 SOLUTION SIZE
L
0.47μH
RBOT
RTOP
2.12mm
*CHOOSE RTOP VALUE BASE ON VOUT, REFER TO TABLE 1
19-100206; Rev 1; 3/18
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
Absolute Maximum Ratings
VIN to PGND...........................................................-0.3V to 5.5V
EN to AGND................................................... -0.3V to VIN +0.3V
PGND to AGND.....................................................-0.3V to +0.3V
FB to AGND................................................... -0.3V to VIN +0.3V
LX Continuous Current (Note 1)....................................1.6ARMS
Continuous Power Dissipation (Multilayer Board,
TA = +70°C) (derate 10.51mW/°C above +70°C)........841mW
Operating Temperature Range............................ -40°C to +85°C
Junction Temperature.......................................................+150°C
Storage Temperature Range............................. -40°C to +150°C
Soldering Temperature (reflow)........................................+260°C
Note 1: LX has internal clamp diodes to PGND and VIN. Applications that forward bias these diodes should not exceed the ICs
package power dissipation limits.
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.
Package Information
6 WLP
Package Code
W60H1+1
Outline Number
21-100206
Land Pattern Number
Refer to Application Note 1891
Thermal Resistance, Four-Layer Board:
Junction to Ambient (θJA)
95.15°C/W
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
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 www.maximintegrated.com/thermal-tutorial.
Electrical Characteristics
(VIN = 3.8V, VFB = 0.6V, typicals are at TA = +25°C. Limits are 100% production tested at TA = +25°C. Limits over the operating
temperature range (TA = -40°C to +85°C) are guaranteed by design and characterization, unless otherwise noted.)
PARAMETER
Input Voltage Range
Input Undervoltage
Lockout
Shutdown Supply
Current
Supply Quiescent
Current
SYMBOL
MIN
TYP
2.5
MAX
UNITS
4.8
V
VIN_UVLO_R
VIN rising
2.605
2.65
2.695
VIN_UVLO_F
VIN falling
2.25
2.3
2.35
ISHDN_85C
EN = LOW, TA = -40°C to +85°C
ISHDN_25C
EN = LOW, TA = +25°C
-1
+0.1
IQ_SKIP
FB Voltage Accuracy
VFB
FB Input Current
IFB
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CONDITIONS
VIN
1
No switching, no load, leakage from EN
is not included
No load, PWM mode
+1
40
0.588
-0.7
0.6
V
µA
µA
0.612
V
+0.7
μA
Maxim Integrated │ 2
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
Electrical Characteristics (continued)
(VIN = 3.8V, VFB = 0.6V, typicals are at TA = +25°C. Limits are 100% production tested at TA = +25°C. Limits over the operating
temperature range (TA = -40°C to +85°C) are guaranteed by design and characterization, unless otherwise noted.)
PARAMETER
Output Voltage Ripple
SYMBOL
CONDITIONS
MIN
TYP
VOUT_PP_SKIP
COUT = 8μF (derated capacitance), skip region
of operation VOUT = 1.2V (Note 2)
20
VOUT_PP_PWM
COUT = 8μF (derated capacitance), PWM
region of operation (Note 2)
10
Line Regulation
VLINE
VIN = 2.5V to 4.8V
Load Regulation
VLOAD
(Note 2)
MAX
UNITS
mV
0.2
%/V
0.185
%/A
Line Transient Response
VOS1, VUS1
IOUT = 750mA, VIN changes from 3.4V to 2.9V
in 25µs (20mV/µs), L = 0.47µH, COUT_NOM =
22µF (Note 2)
30
mV
Load Transient
Response
VOS2, VUS2
IOUT changes from 0A to 750mA in 6µs,
L = 0.47µH, COUT_NOM = 22µF (Note 2)
30
mV
2.34
mV/µs
Regulated at FB pin, VOUT = 0.6V, see the
Soft-Start section for more details (Note 2)
Soft-Start Slew Rate
Peak Current Limit
ILIM_PEAK
Valley Current Limit
ILIM_VALLEY
2.63
3.00
3.37
A
1.1
A
Skip region of operation
30
mA
NMOS Zero-Crossing
Threshold
IZX
High-Side PMOS ON
Resistance
RDSON-HS
IN to LX, ITEST = -150mA
100
mΩ
Low-Side NMOS ON
Resistance
RDSON_LS
LX to PGND, ITEST = 150mA
50
mΩ
Switching Frequency
fSW
VOUT = 1V, IOUT = 1A
2
MHz
Turn-On Delay Time
tON_DLY
220
µs
Minimum Effective
Output Capacitance
CEFF_MIN
0mA ≤ IOUT ≤ 1.5A (Note 2)
Output Active Discharge
Resistance
RDISCHG
Resistance from LX to PGND, EN = 0V
From EN asserting to LX switching (Note 2)
ILK_25C
VLX = 0V or 4.8V, TA = +25°C
ILK_85C
VLX = 0V or 4.8V, TA = +85°C (Note 3)
TSHDN
Rising, 15°C hysteresis
EN Logic High Threshold
VEN_HI
TA = +25°C
EN Logic Low Threshold
VEN_LO
TA = +25°C
EN Pulldown Resistance
RPD
LX Leakage Current
Thermal Shutdown
Pulldown resistance from EN to AGND
8
µF
100
-1
0.1
Ω
+1
1
165
°C
1.2
250
µA
V
500
0.4
V
1000
kΩ
Note 2: Guaranteed by design. Not production tested.
Note 3: Guaranteed by ATE characterization. Not directly tested in production.
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Maxim Integrated │ 3
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
Typical Operating Characteristics
(VIN = +3.8V, TA = +25°C, unless otherwise noted. Inductor part number: GLULKR4701A.
toc 01
3.0
EN = VIN FOR IQ
70
2.5
60
2.0
SUPPLY CURRENT (µA)
50
40
VOUT = 1.8V
VOUT = 1.2V
VOUT = 1.0V
VOUT = 0.6V
30
20
10
0
2
4
5
TA = +85°C
TA = +25°C
TA = -40°C
1.0
0.5
85
80
75
0.0
2
3
4
5
65
0.001
6
EFFICIENCY vs. LOAD
1.2V OUTPUT
EFFICIENCY vs. LOAD
1.8V OUTPUT
95
toc 05
95
85
85
VIN = 3.0V
VIN = 3.8V
VIN = 4.5V
L = 0.47µH
RBOT = 30.1kΩ
RTOP = 20kΩ
CTOP = 220pF
70
0.01
0.1
80
VIN = 3.0V
VIN = 3.8V
VIN = 4.5V
75
L = 0.47µH
RBOT = 30.1kΩ
RTOP = 30.1kΩ
CTOP = 220pF
70
65
0.001
1
0.01
IOUT (A)
toc 07
1.02
0.61
toc 08
0.59
VIN = 3.0V
VIN = 3.8V
VIN = 4.5V
0.0
0.5
1.22
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0.99
0.96
1
toc 09
L = 0.47µH
RBOT = 30.1kΩ
RTOP = 30.1kΩ
CTOP = 220pF
1.23
1.00
VIN = 3.0V
VIN = 3.8V
VIN = 4.5V
0.97
1.5
0.1
1.21
0.98
1.0
IOUT (A)
0.01
LOAD REGULATION
1.2V OUTPUT
1.24
VOUT (V)
VOUT (V)
0.60
0.57
L = 0.47µH
RBOT = 30.1kΩ
RTOP = 60.4kΩ
CTOP = 220pF
IOUT (A)
1.01
0.58
75
65
0.001
L = 0.47µH
RBOT = 30.1kΩ
RTOP = 20kΩ
CTOP = 220pF
1.03
toc 06
VIN = 3.0V
VIN = 3.8V
VIN = 4.5V
70
1
LOAD REGULATION
1.0V OUTPUT
1.04
L = 0.47µH
RBOT = OPEN
RTOP = 0Ω
CTOP = OPEN
0.62
0.1
80
IOUT (A)
LOAD REGULATION
0.6V OUTPUT
0.63
0.56
1
EFFICIENCY vs. LOAD
1.0V OUTPUT
85
0.64
0.1
IOUT (A)
90
65
0.001
0.01
SUPPLY VOLTAGE (V)
90
75
L = 0.47µH
RBOT = OPEN
RTOP = 0Ω
CTOP = OPEN
70
90
80
VIN = 3.0V
VIN = 3.8V
VIN = 4.5V
SUPPLY VOLTAGE (V)
toc 04
toc 03
90
1.5
-1.0
6
EFFICIENCY (%)
EFFICIENCY (%)
3
EFFICIENCY vs. LOAD
0.6V OUTPUT
95
-0.5
95
VOUT (V)
toc 02
EFFICIENCY (%)
SUPPLY CURRENT (µA)
80
SHUTDOWN CURRENT
EFFICIENCY (%)
QUIESCENT CURRENT
0.0
0.5
1.19
VIN = 3.0V
VIN = 3.8V
VIN = 4.5V
1.18
1.17
1.0
IOUT (A)
1.20
1.5
1.16
0.0
0.5
1.0
1.5
IOUT (A)
Maxim Integrated │ 4
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
Typical Operating Characteristics (continued)
(VIN = +3.8V, TA = +25°C, unless otherwise noted. Inductor part number: GLULKR4701A.
LOAD REGULATION
1.8V OUTPUT
1.84
toc 10
0.620
L = 0.47µH
RBOT = 30.1kΩ
RTOP = 60.4kΩ
CTOP = 220pF
1.83
1.82
0.615
0.610
1.79
1.78
1.77
0.0
0.5
1.0
0.595
0.580
1.5
2
3
toc 14
1.19
3.5
3
4
1.80
1.79
5
1.76
2
VIN (V)
SWITCHING FREQUENCY vs.
OUTPUT VOLTAGE
3
4
2.5
2.0
1.5
0.5
5
0.0
0.6
0.8
1.0
VIN (V)
STARTUP WAVEFORMS
EN
1.2
1.4
1.6
1.8
2.0
VOUT (V)
LOAD TRANSIENT RESPONSE
0.6V OUTPUT
toc 16
toc 17
2V/div
2V/div
VOUT
toc 15
VIN = 3.8V
IOUT = 750mA
1.0
IOUT = 500mA
IOUT = 750mA
IOUT = 1.5A
1.77
4
5
3.0
1.78
1.18
4.0
FREQUENCY (MHz)
1.82
3
2
VIN (V)
1.81
2
0.97
5
L = 0.47µH
RBOT = 30.1kΩ
RTOP = 60.4kΩ
CTOP = 220pF
1.83
1.20
1.17
4
LINE REGULATION
1.8V OUTPUT
1.84
VOUT (V)
VOUT (V)
toc 13
L = 0.47µH
RBOT = 30.1kΩ
RTOP = 30.1kΩ
CTOP = 220pF
1.21
IOUT = 500mA
IOUT = 750mA
IOUT = 1.5A
0.98
VIN (V)
LINE REGULATION
1.2V OUTPUT
1.22
1.00
0.99
IOUT = 500mA
IOUT = 750mA
IOUT = 1.5A
IOUT (A)
1.23
1.01
0.600
toc 12
L = 0.47µH
RBOT = 30.1kΩ
RTOP = 20kΩ
CTOP = 220pF
1.02
PWM
0.585
LINE REGULATION
1.0V OUTPUT
1.03
SKIP
0.590
VIN = 3.0V
VIN = 3.8V
VIN = 4.5V
toc 11
VOUT (V)
1.80
1.76
L = 0.47µH
RBOT = OPEN
RTOP = 0Ω
CTOP = OPEN
0.605
VOUT (V)
VOUT (V)
1.81
LINE REGULATION
0.6V OUTPUT
VOUT
50mV/div
IOUT
500mA/div
VOUT = 1.8V
2V/div
VLX
ILX
1A/div
100µs/div
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100µs/div
Maxim Integrated │ 5
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
Typical Operating Characteristics (continued)
(VIN = +3.8V, TA = +25°C, unless otherwise noted. Inductor part number: GLULKR4701A.
LOAD TRANSIENT RESPONSE
1.0V OUTPUT
LOAD TRANSIENT RESPONSE
1.8V OUTPUT
toc 18
toc 19
VOUT
50mV/div
VOUT
50mV/div
IOUT
500mA/div
IOUT
500mA/div
100µs/div
100µs/div
LINE TRANSIENT RESPONSE
0.6V OUTPUT
LINE TRANSIENT RESPONSE
1.0V OUTPUT
toc 21
toc 20
VIN
500mV/div
VIN
500mV/div
VOUT
20mV/div
VOUT
20mV/div
100µs/div
LINE TRANSIENT RESPONSE
1.8V OUTPUT
100µs/div
SWITCHING WAVEFORM
toc 22
VIN
500mV/div
VOUT
20mV/div
100µs/div
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toc 23
VIN = 3.8V
VOUT = 1.0V
IOUT = 1.0A
VLX
100ns/div
Maxim Integrated │ 6
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
Typical Operating Characteristics (continued)
(VIN = +3.8V, TA = +25°C, unless otherwise noted. Inductor part number: GLULKR4701A.
OUTPUT VOLTAGE RIPPLE
1.0V OUTPUT
OUTPUT VOLTAGE RIPPLE
1.0V OUTPUT
toc 24
IOUT = 0A
toc 25
IOUT = 1.5A
20mV/div
VOUT
VLX
10mV/div
VOUT
VLX
2V/div
2V/div
200ns/div
400ns/div
SHORT-CIRCUIT HICCUP AND RECOVERY
1.0V OUTPUT
SHORT APPLIED
RECOVERY
toc 26
VOUT
500mV/div
HICCUP/RETRY
ILX
1A/div
100µs/div
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Maxim Integrated │ 7
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
Pin Configuration
TOP VIEW
(BUMP SIDE DOWN)
1
2
3
A
IN
LX
PGND
B
EN
AGND
FB
+
6-BUMP WLP, 0.4mm PITCH
Pin Description
PIN
NAME
FUNCTION
A1
IN
Power Input. Bypass to PGND with a 10µF ceramic capacitor.
A2
LX
Buck Switching Node
A3
PGND
B1
EN
B2
AGND
B3
FB
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Power Ground. Connect to AGND on the PCB.
Active-High Buck Enable Input. An 500kΩ internal pulldown resistance to AGND. Drive EN low to disable
the device. Drive EN high to enable the device.
Analog Ground. Connect to PGND on the PCB.
Feedback Input. Connect FB to the center tap of an external resistor-divider from the output to AGND to
set the output voltage. See the Setting the Output Voltage section for more details.
Maxim Integrated │ 8
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
Simplified Block Diagram
IN
LX
UVLO
HIGH-SIDE
CURRENT
SENSE
ILIM_PEAK
OCP
FB
0.6V REF
EN
SOFT
START
LOGIC
CONTROL
EAMP
TSHDN
AGND
Detailed Description
The MAX77324 is a high-efficiency synchronous stepdown converter with integrated MOSFETs that operates
over a 2.5V to 4.8V input voltage range. The device supports up to 1.5A of load current. The device uses external
feedback resistors to set the output between 0.6V to 2.0V.
The device automatically transitions between PWM and
SKIP modes of operation when the load condition changes. SKIP mode improves system light-load efficiency,
while PWM mode maintains a constant-on-time switching.
In SKIP mode, the device draws only 40μA of quiescent
current from the supply input. In shutdown mode, the current consumption is reduced to less than 1μA.
An internal synchronous rectifier improves efficiency and
eliminates the need for an external Schottky freewheeling
diode. On-chip current sensing uses the on-resistance of
the internal MOSFETs, eliminating current-sensing resistors and improving efficiency.
A soft-start voltage ramp reduces inrush current during
startup. The enable (EN) pin turns on/off the device.
Buck Converter Control Scheme
The device uses Maxim’s proprietary Quick-PWM™
quick-response, constant-on-time PWM control scheme.
This control scheme handles wide input/output voltage
ratios with ease and provides immediate response to load
transients, while maintaining a pseudo constant switching
frequency.
ILIM_VALLEY
LOW-SIDE
CURRENT
SENSE
ACTIVE
DISCHARGE
PGND
During the first half of the switching cycle (on-time), current ramps up through the inductor, sourcing current to
the output, and storing energy in a magnetic field.
During the second half of the switching cycle (off-time),
the internal high-side MOSFET turns off and the internal
low-side MOSFET turns on. The inductor releases the
stored energy as its current ramps down and provides
current to the output. The output capacitor stores a
charge when the inductor current exceeds the load current and discharges when the inductor current is lower
than load current, smoothing the voltage across the load.
Enable Control (EN)
Raise EN above VEN_HI (1.2V min) to enable the buck
converter. Lower EN below VEN_LO (0.4V max) to disable the buck.
Whenever the buck is enabled and VIN is higher than
VIN_UVLO_R, the output voltage soft-starts. Soft-start
avoids excessive supply inrush current and prevents supply voltage drop.
Driving EN low disables the switching and the output is
discharged with a typical discharge resistor of 100Ω from
FB pin to PGND. The same happens when the device
gets disabled by thermal shutdown or when input UVLO
triggers.
Quick-PWM is a trademark of Maxim Integrated Products, Inc.
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Maxim Integrated │ 9
MAX77324
Shutdown Mode
Pulling the EN pin low causes the device to enter shutdown mode. In this mode, the device consumes less
than 1µA. In shutdown mode, the LX pin is tied to PGND
through the 100Ω active discharge resistor.
Current Sense and Current Limit
The current-sense circuit amplifies the current-sense voltage generated by the high-side MOSFET’s on-resistance
and the inductor current (RDS(ON) x IL).
The internal high-side MOSFET has a current limit of 3A
(typ). If the current flowing out of LX exceeds this maximum, the high-side MOSFET turns off and the low-side
MOSFET turns on. This lowers the duty cycle and causes
the output voltage to droop until the current limit is no
longer exceeded. There is also a low-side MOSFET zerocrossing current threshold of 30mA (typ) under skip region
of operation, to protect the device from current flowing
into LX. If the current in the low-side MOSFET falls below
30mA, the low-side MOSFET turns off, and the inductor
current continues to flow through 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.
SKIP/PWM Operation
The device automatically transitions from SKIP to fixed
frequency operation as load current increases.
In the PWM region of operation, the device operates
with a nominal switching frequency of 2MHz. In the SKIP
region, the device skip pulses at light loads for high
efficiency. The advantage of the SKIP mode is higher
efficiency at light loads because of the lower quiescent
current drawn from the supply.
Protection Features
Undervoltage Lockout (UVLO)
The device supports an UVLO feature that prevents operations in case of low input voltage conditions. Regardless
of the EN pin status, the device is disabled until the input
voltage VIN rises above the VIN_UVLO_R threshold or VIN
falls below the VIN_UVLO_F threshold.
Operations are halted until this condition is resolved.
Soft-Start
When starting up the device, the bias circuitry must
be enabled and provided with adequate time to settle.
The bias circuitry is guaranteed to settle within 220µs,
then the BUCK converter's soft-start operation begins.
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4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
During the soft-start period, the ramping-up slew rate is
regulated at the FB pin (typical 2.34mV/µs). To calculate
the soft-start slew rate at VOUT, use the following equation:
=
S R SS_VO UT
R TOP + R BOT
× S R SS _FB
R BOT
To calculate the soft-start time, use the following equation:
t SS =
VOUT
SR SS _ VOUT
The soft-start feature limits the inrush current during
startup.
Pre-Bias Output Startup
The device supports starting up into a pre-biased output.
If the output is at a pre-biased voltage, which is less than
the target output voltage, the device ramps up the output
voltage monotonically at the preset 2.34mV/µs (typ) FB
slew-rate from the pre-biased level to the target level. If
the output is at a pre-biased voltage which exceeds the
target output voltage, no switching happens during the
soft-start period.
Output Active Discharge
The device provides an internal 100Ω resistor from LX to
PGND for output active discharge function. The internal
resistor discharges the energy stored in the output capacitor to GND whenever the converter is disabled.
Over-Current Protection (OCP)
The device features a robust OCP scheme that protects the device and inductor under overload and output
short-circuit conditions. A cycle-by-cycle peak current
limit turns off the high-side MOSFET and turns on the
low-side MOSFET whenever the high-side MOSFET current exceeds the internal peak current limit. The low-side
MOSFET remains on until the inductor current reduces to
the valley current limit. After that, the high-side MOSFET
is turned on again and the cycle repeats.
The buck stops switching if eight consecutive on-times
are ended by current limit. After switching stops, the buck
waits for 8µs before attempting to soft-start again. This
prevents inductor current from increasing uncontrollably
due to the short-circuited output.
Maxim Integrated │ 10
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
Thermal Shutdown
Thermal protection limits total power dissipation and
protects the device from damage in case of an overload
or short-circuit condition. The device has a thermal protection circuit which monitors temperature on the die. If
the die temperature exceeds 165°C (TSHDN), a thermal
shutdown event is initiated and the buck is disabled. The
active discharge resistor is enabled when the device is
disabled through thermal shutdown. After the thermal
shutdown, if the die temperature reduces by 15°C, the
buck is re-enabled.
Applications Information
The device uses resistors to set the output voltage
between 0.6V and 2V. Connect a resistor divider between
VOUT, FB, and AGND as shown in Figure 1. Choose
RBOT (FB to AGND) to be less than or equal to 30kΩ. One
percent accuracy resistors are highly recommended to
keep the accuracy of VOUT. Calculate the value of RTOP
(VOUT to FB) for a desired output voltage with Equation 1.
Equation 1:
[
VOUT
VFB
−1
]
where VFB is 0.6V and VOUT is the desired output voltage.
CTOP is to maintain the stability of the device. Suggest
CTOP to be 220pF for the full operation range of the
device.
Enable the Device
The device is enabled by raising EN above VEN_HI
(1.2V min).
Table 1. Set the Output Voltage
V OUT (V)
R TOP (kΩ)
R BOT (kΩ)
C TOP (PF)
0.6
Short
Open
Open
0.85
12.4
30.1
220
0.9
15
30.1
220
0.95
17.8
30.1
220
1.0
20
30.1
220
1.1
24.8
30.1
220
1.2
30.1
30.1
220
1.35
37.4
30.1
220
1.5
45.3
30.1
220
1.8
60.4
30.1
220
2.0
69.8
30.1
220
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MAX77324
RTOP
CTOP
FB
RBOT
Figure 1. Setting the Output Voltage for MAX77324
Self-Enabled Operations
Setting the Output Voltage
RTOP = RBOT ×
VOUT
Automatic self-enabling operation is possible with the
device. Tying the EN pin directly to VIN enables the device
as soon as VIN reaches the UVLO rising threshold, at
which point the internal bias circuitry is initialized, and
soft-start is initiated.
Input and Output Capacitor Selection
Choose CIN to be a 10μF nominal capacitor. Larger values improve the decoupling for the buck converter, but
increase inrush current from the voltage supply when
connected. CIN reduces the current peaks drawn from the
input power source during buck operation and reduces
switching noise in the system. The ESR/ESL of CIN and
its series PCB traces should be very low (i.e., < 15mΩ + <
2nH) for frequencies up to 2MHz. Ceramic capacitors with
X5R or X7R dielectric are highly recommended due to their
small size, low ESR, and small temperature coefficients.
Choose the CIN capacitor voltage rating to be greater
than the expected input voltage of the system.
Choose the output bypass capacitance (COUT) to be
22μF. Larger values of COUT improve load transient
performance, but increase the input surge currents during soft-start and output voltage changes. The output
filter capacitor must have low enough ESR to meet output ripple and load transient requirements. The output
capacitance must be high enough to absorb the inductor
energy while transitioning from full-load to no load conditions. When using high-capacitance, low-ESR capacitors,
the filter capacitor’s ESR dominates the output voltage
ripple in continuous conduction mode. Therefore, the size
of the output capacitor depends on the maximum ESR
required to meet the output voltage ripple (VRIPPLE(P-P))
specifications:
VRIPPLE(P − P) = ESR × ILOAD × LIR
where LIR is the inductor's ripple current to average current ratio. Compute LIR with Equation 2.
Maxim Integrated │ 11
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
PCB Layout Guidelines
LIR
=
VOUT ×
(VIN
)
− VOUT
VIN × fSW x ILOAD x L
Where ILOAD is the buck's output current in the particular
application (1.5A, max), VIN is the application's input voltage, and FSW is 2MHz. Ceramic capacitors with X5R or
X7R dielectric are highly recommended due to their small
size, low ESR, and small temperature coefficients.
All ceramic capacitors derate with DC bias voltage
(effective capacitance goes down as DC bias goes up).
Generally, small case size capacitors derate heavily compared to larger case sizes (0603 case size performs better than 0402). Consider the effective capacitance value
carefully by consulting the manufacturer's data sheet.
Inductor Selection
Select an inductor with a saturation current rating greater
than or equal to the maximum peak current limit (ILIMPEAK) of 3.37A. In general, inductors with lower saturation current and higher DCR ratings are physically small.
Higher values of DCR reduce buck efficiency. Choose the
RMS current rating of the inductor (the current at which
the temperature rises appreciably) based on the expected
load current.
The chosen inductor value should ensure that the peak
inductor ripple current (IPEAK) is below the high-side
MOSFET peak current limit (ILIM-PEAK) so that the buck
can maintain regulation. A 0.47μF value of inductor is
recommended through the operation range of the device.
Use Equation 3 and Equation 4 to compute IPEAK. If
IPEAK is greater than ILIM-PEAK, then increase the inductor value.
Equation 3:
Careful circuit board layout is critical to achieve lowswitching power losses and clean, stable operation.
Figure 2 shows an example PCB top-metal layout.
When designing the PCB, follow these guidelines:
1) The input capacitor should be placed immediately
next to the IN pin of the device. Since the device
operates at 2MHz switching frequency, this placement
is critical for effective decoupling of high-frequency
noise from the IN pin.
2) Place the inductor and output capacitor close to the
part and keep the loop area small.
3) Make the trace between LX and the inductor short
and wide. Do not take up an excessive amount of
area. The voltage on this node is switching very
quickly and additional area creates more radiated
emissions.
4) Connect PGND and AGND together to the common
ground on the second layer. Do not connect them
anywhere else.
5) Keep the power traces and load connections short
and wide. This practice is essential for high efficiency.
OUT
LX
LEGEND
L
IN
COUT
Equation 2:
CIN
0402
GND
+
(
VOUT × VIN − VOUT
VIN × fSW × L
)
GND
CTOP
EN
IP − P =
RBOT
0201
RTOP
0603
VIAs
Equation 4:
IPEAK = ILOAD +
IP − P
2
Figure 2. Example Layout
where ILOAD is the buck's output current in the particular
application (1.5A max), VIN is the application's largest
expected input voltage (4.8V max), fSW depends on
VOUT setting, see the Typical Operating Characteristics
to find fSW under various VOUT settings.
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Maxim Integrated │ 12
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
Typical Application Circuit
2.5V TO 4.8V
DC SOURCE
CIN
10μF
ENABLE
IN
LX
VOUT
0.6V TO 2.0V
L
0.47μH
MAX77324
CTOP
220pF
RTOP*
EN
COUT
22μF
FB
RBOT
30.1KΩ, 1%
AGND
PGND
* CHOOSE RTOP VALUE BASE ON VOUT, REFER TO TABLE 1
Suggested Inductors
PART NUMBER
DC
INDUCTA
RESISTANCE
NCE [µH]
[mΩ]
I RATING [A]
-30% (∆L/L)
I RATING [A]
∆T = 40°C
RISE
DIMENSIONS
LXWXH
[mm]
NOTE
GLULKR4701A
0.47
20
4.5
4.9
2.5 x 2.0 x 1.0
Optimize performance.
Default on evaluation
board.
DFE18SANR47MG0L
0.47
54
3.6
2.6
1.6 x 0.8 x 1.0
Optimize solution size.
Suggested Capacitors for both CIN and COUT
CAPACITANCE CAPACITANCE
[µF]
TOLERANCE
PART NUMBER
VOLTAGE
DIMENSIONS
TEMPERATURE
RATING
LXWXH
CHARACTERISTIC
[V]
[mm]
NOTE
C1608X5R0J226M080AC
22
±20%
6.3
X5R
1.6 x 0.8 x
0.8
Optimize
performance. Default
on evaluation board
CL05A226MQ5QUNC
22
±20%
6.3
X5R
1.0 x 0.5 x
0.8
Optimize solution size
(higher capacitance
derating).
Ordering Information
PART NUMBER
VOUT
PIN-PACKAGE
MAX77324EWTAD+
Adjustable from
0.6V to 2V
6 WLP
+Denotes a lead(Pb)-free/RoHS-compliant package.
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Maxim Integrated │ 13
MAX77324
4.8VIN, 1.5A High-Efficiency,
Ultra-Small Buck Converter
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
0
1/18
Initial release
1
3/18
Updated Application Circuit, corrected typos in the Package Information table, added
details in the Electrical Characteristics table, updated TOCs, added more information
to the Detailed Description and Application Information sections.
DESCRIPTION
—
1-6, 8-9,
11-12
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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