MAX20079EATPVY [MAXIM]
Automotive 36V 3.5A Buck Converter with 3.5μA Iq;
| 型号： | MAX20079EATPVY |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Automotive 36V 3.5A Buck Converter with 3.5μA Iq |
| 文件： | 总16页 (文件大小：1776K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
General Description
Benefits and Features
● Synchronous DC-DC Converter with Integrated FETs
The MAX20079 is a small, automotive grade synchronous
buck converter with integrated high-side and low-side
switches. The device is designed to deliver up to 3.5A with
input voltages from +3V to +36V while using only 3.5µA
quiescent current at no load. The MAX20079 provides an
accurate output voltage of ±2% within the normal opera-
tion input range of +6V to +18V. With 65ns minimum on-
time capability, the converter is capable of large input-to-
output conversion ratios. Voltage quality can be monitored
by observing the PGOOD signal. MAX20079 can operate
in drop-out by running at 99% duty cycle, making it ideal
for automotive and industrial applications. The IC offers
standard parts with fixed output voltages of 3.3V and 5V.
In addition, MAX20079 can be configured for output volt-
ages from 3V to 12V, using an external resistor divider.
Frequency is internally fixed at 2.1MHz, which allows for
small external components, reduces output ripple, and
guarantees there is no AM interference. A 400kHz option
is also offered to provide minimum switching losses and
maximum efficiency. MAX20079 automatically enters skip
mode at light loads with ultra-low quiescent current of
3.5µA at no load. It offers pin-enabled spread-spectrum
frequency modulation designed to minimize EMI-radiated
emissions due to the modulation frequency.
• 3.5A Output-Current Capability
• 3.5μA Quiescent Current in Standby Mode
● Small Solution Size Saves Space
• 65ns Minimum On-Time
• 2.1MHz or 400kHz Fixed Operating Frequency
Options
• Programmable 3V to 12V Output Voltage or
Fixed 5V/3.3V Options Available
• Fixed 3.5ms Internal Soft-Start
• Innovative Current-Mode-Control Architecture
Minimizes Total Board Space and BOM Count
● PGOOD Output and High-Voltage EN Input Simplify
Power Sequencing
● Protection Features and Operating Range Ideal for
Automotive Applications
• 3V to 36V Operating V Range
IN
• 40V Load-Dump Protection
• 99% Duty-Cycle Operation with Low Dropout
• -40°C to +125°C Automotive Temperature Range
• AEC-Q100 Qualified
Ordering Information appears at end of data sheet.
The MAX20079 comes in a small 4mm x 4mm 20-pin
SW-TQFN package and uses very few external compo-
nents. The intelligent package layout results in an extreme-
ly low-noise solution with superior EMI performance.
Applications
● Automotive
● Industrial
● High Voltage DC-DC Converters
19-100465; Rev 3; 7/19
MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Simplified Block Diagram
SPS
SYNC
REF
EN
BANDGAP
HVLDO
OSC
BST
SUP
BIAS
CLK
CURRENT SENSE
+
SOFTSTART
SLOPE COMP
LOGIC
LX
OUT
FB
CONTROL
BIAS
PWM
EAMP
COMP
FB
SW1
MAX20079
V/RESET
GND
SW2
PGOOD
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Absolute Maximum Ratings
SUP .......................................................................-0.3V to +40V
EN..........................................................................-0.3V to +40V
BST to LX..............................................................................+6V
BST........................................................................-0.3V to +45V
OUT Short-Circuit Duration .......................................Continuous
ESD Protection
Human Body Model.........................................................±2kV
Continuous Power Dissipation (T = +70°C)
A
FB.............................................................-0.3V to V
SYNC........................................................-0.3V to V
SPS ..........................................................-0.3V to V
OUT.........................................................................-0.3V to 13V
PGOOD.....................................................................-0.3V to 6V
PGND to AGND......................................................-0.3V to 0.3V
BIAS .....................................................................-0.3V to +6.0V
+ 0.3V
+ 0.3V
+ 0.3V
20-L SW TQFN
BIAS
BIAS
BIAS
(Derate 30.3 mW/°C above +70°C)......................2424.20mW
Operating Ambient Temperature Range .......... -40°C to +125°C
Operating Junction Temperature (Note 2)........ -40°C to +150°C
Storage Temperature Range ........................... -65°C to +150°C
Lead Temperature (Soldering 10s) .................................+300°C
Soldering Temperature (Reflow)......................................+260ºC
Note 1: LX has internal clamp diodes to PGND/AGND and SUP. Applications that forward bias these diodes should take care not to
exceed the IC’s package power dissipation limits.
Note 2: The device is designed for continuous operation up to T = +125°C for 95,000 hours and T = +150°C for 5,000 hours.
J
J
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.
Recommended Operating Conditions
PARAMETER
SYMBOL
CONDITION
TYPICAL
UNIT
Ambient Temperature Range
-40 to 125
°C
Package Information
20-Lead Side-Wettable TQFN Package
Package Code
T2044Y+5C
21-100318
90-0409
Outline Number
Land Pattern Number
Thermal Resistance, Single-Layer Board:
Junction to Ambient (θ
)
48
2
JA
Junction to Case (θ
)
JC
Thermal Resistance, Four-Layer Board:
Junction to Ambient (θ
)
33
2
JA
Junction to Case (θ
)
JC
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.
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Electrical Characteristics
(V
= V = 14V, V
EN
= 0V, T = -40°C to +150°C unless otherwise noted, V
= 5V, (Notes 3 and 4))
SUP
SYNC
J
OUT
PARAMETER
SYMBOL
CONDITIONS
MIN
3.5
TYP
MAX
36
UNITS
V
V
SUP
Supply Voltage Range
After start-up
t < 1s
3.0
36
V
40
SUP_MAX
I
V
= Low
1
5
μA
SUP_OFF
EN
Fixed V
(internal) = 3.3V,
OUT
I
3.5
8
SUP,3.3V
f
= 2.1MHz/400kHz, no load, no switching
SW
μA
μA
Fixed V
(internal) = 3.3V, f
=
OUT
SW
I
4.5
6
SUP_SW,3.3V
2.1MHz/400kHz, no load, switching (Note 5)
Supply Current
Fixed V
400kHz, no load, no switching
(internal) = 5V, f
= 2.1MHz/
= 2.1MHz/
SW
OUT
SW
I
10
SUP,5V
Fixed V (internal) = 5V, f
400kHz, no load, switching (Note 5)
OUT
I
7.5
μA
μA
SUP_SW,5V
LX Leakage
UV Lockout
I
V
= 36V, LX = 0V or 40V, T = +25°C
A
-1
1
LX,leak
SUP
UVLO
UVLO
V
rising
2.525
2.725
0.13
5
2.925
BIAS
V
V
Hysteresis
HYS
BIAS
BIAS Voltage
V
+5.5V ≤ VSUP ≤ +36V
BUCK CONVERTER
Skip mode
(Note 4)
4.85
4.93
3.2
5
5
5.06
5.07
3.37
Fixed V
(internal) = 5V,
OUT
V
OUT,5V
OUT,3.3V
OUT,3.395V
f
= 2.1MHz/400kHz
SW
PWM mode
Fixed V
(internal) = 3.3V,
Skip mode
(Note 4)
OUT
3.3
f
= 2.1MHz/400kHz
SW
Voltage Accuracy
V
V
Fixed V
(internal) = 3.3V,
OUT
PWM mode
3.25
3.3
3.35
f
= 2.1MHz/400kHz
SW
Skip mode
(Note 4)
3.293
3.345
3.395
3.395
3.465
3.445
Fixed V
(internal) = 3.395V,
OUT
V
f
= 2.1MHz
SW
PWM mode
Output Voltage
Range with External
Resistor-Divider
V
3
12
V
OUT
FB Voltage Accuracy
FB Current
V
0.985
1
1.015
V
FB
I
V
V
= 1V, T = +25°C
0.02
0.02
μA
FB
FB
A
FB Line Regulation
LR
= 6V to 36V
%/V
FB
SUP
High-Side Switch
ON Resistance
R
V
V
= 5V, I = 1A
70
70
125
125
5.3
mΩ
mΩ
A
ON,HS
BIAS
BIAS
LX
Low-Side Switch
ON Resistance
R
= 5V, I = 1A
LX
ON,LS
High-Side Current-Limit
Threshold
ILIM
4.1
4.7
PEAK
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Electrical Characteristics (continued)
(V
= V = 14V, V
= 0V, T = -40°C to +150°C unless otherwise noted, V
= 5V, (Notes 3 and 4))
SUP
EN
SYNC
J
OUT
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Low-Side Negative
Current-Limit Threshold
I
-1.2
A
NEG
I
f
f
= 2.1MHz
= 400KHz
3.5
5.5
65
5
Soft-Start Ramp Time
(Note 5)
SS,2M
SW
SW
ms
I
7.5
80
SS,400K
Minimum ON Time
T
ns
%
ON_MIN
Maximum Duty Cycle
DC
98
99
MAX
f
f
f
= 2.1MHz option
= 400kHz option
1.925
360
2.1
400
±3%
2.275
440
MHz
kHz
%
PWM Switching
Frequency
SW,2M
SW
SW
f
SW,400K
SS
Spread-Spectrum Range
V
= 5V
SPS
PGOOD
V
V
V
rising
falling
91
90
93
92
95
94
THR,PGD
OUT
OUT
PGOOD Threshold
PGOOD Debounce
%
V
THF,PGD
DEB_PWM,2M
T
PWM mode, f
= 2.1MHz option (Note 4)
60
μs
μs
μs
μs
SW
T
Skip mode, f
= 2.1MHz option (Note 4)
SW
90
DEB_SKIP,2M
T
PWM mode, f
= 400kHz option (Note 4)
80
DEB_PWM,400K
SW
T
Skip mode, f
= 400kHz option (Note 4)
SW
110
DEB_SKIP,400K
PGOOD High
Leakage Current
I
T
= +25°C
A
1
μA
LEAK,PGD
PGOOD Low Level
V
Sinking 1mA
0.4
V
OUT,PGD
LOGIC LEVELS
V
2.4
IH,EN
EN Level
V
V
0.6
1
IL,EN
IN,EN
EN Input Current
I
V
= V
= 36V, T = +25°C
μA
MHz
kHz
EN
SUP
A
FSYNC
f
= 2.1MHz option
= 400kHz option
1.7
325
1.4
2.6
500
External Input Clock
Frequency
2M,PEAK SW
FSYNC
f
SW
400K
V
IH,SYNC
SYNC Threshold
V
kΩ
V
V
0.4
0.4
IL,SYNC
SYNC Internal Pulldown
SPS Threshold
R
1000
1000
PD,SYNC
V
1.4
IH,SPS
V
IL,SPS
SPS Internal Pulldown
THERMAL PROTECTION
Thermal Shutdown
R
kΩ
PD,SPS
T
(Note 4)
(Note 4)
175
15
°C
°C
SHDN
Thermal Shutdown
Hysteresis
T
SHDN.HYS
Note 3: Limits are 100% tested at T = +25°C. Limits over the operating temperature range and relevant supply voltage are
A
guaranteed by design and characterization. Typical values are at T = +25°C.
A
Note 4: Guaranteed by design; not production tested.
Note 5: Soft-start time is measured as the time taken from EN going high to PGOOD going high.
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Typical Operating Characteristics
((V
= V
= +14V, T = +25°C, unless otherwise noted.))
SUP
EN A
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
(5VOUT, 2.1MHz)
toc04
10
VEN = 0
1
0.1
6
16
26
36
V
IN (V)
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Typical Operating Characteristics (continued)
((V
= V
= +14V, T = +25°C, unless otherwise noted.))
SUP
EN A
SHUTDOWN WAVEFORM
(5VOUT, 2.1MHz)
3A LOAD
STARTUP WAVEFORM
(5VOUT, 2.1MHz)
toc11
toc10
VEN
5V/div
5V/div
5V/div
VEN
5V/div
VPGOOD
VPGOOD
3V/div
IINDUCTOR
3A/div
3V/div
VOUT
VOUT
100µs/div
1ms/div
STEADY STATE SWITCHING WAVEFORM
(5VOUT, 2.1MHz)
SHORT-CIRCUIT RESPONSE
(5VOUT, 2.1MHz)
NO LOAD
toc12
toc13
600mA/div
5V/div
IINDUCTOR
2A/div
IINDUCTOR
VPGOOD
VLX
5V/div
5V/div
5V/div
VBIAS
VOUT
5V/div
VOUT
10µs/div
200ns/div
SLOW VIN RAMP
COLD CRANK
(5VOUT, 2.1MHz)
(5VOUT, 2.1MHz)
toc14
toc15
100mA Load
100mA Load
16V
5V/div
5V/div
3.5V
VIN
5V/div
5V/div
VIN
VPGOOD
VPGOOD
5V/div
5V/div
VBIAS
VOUT
VBIAS
VOUT
5V/div
5V/div
5s/div
10ms/div
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Typical Operating Characteristics (continued)
((V
= V
= +14V, T = +25°C, unless otherwise noted.))
SUP
EN A
LOAD-DUMP TEST
(5VOUT, 2.1MHz)
LOAD-TRANSIENT RESPONSE
(5VOUT, 2.1MHz)
toc16
toc17
40V
100mA LOAD
5V/div
2A/div
16V
VPGOOD
VIN
10V/div
ILOAD
5V/div
5V/div
VBIAS
VOUT
100mV/div
(AC
COUPLED)
VOUT
100ms/div
100µs/div
LOAD-TRANSIENT RESPONSE
(5VOUT, 400kHz)
toc18
5V/div
VPGOOD
200mV/div
(AC
COUPLED)
VOUT
2A/div
ILOAD
100µs/div
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Pin Configuration
TOP VIEW
15
14
13
12
11
NC 16
10
9
PGND
LX
17
18
19
20
SYNC
PGOOD
NC
MAX20079
8
LX
7
PGND
NC
+
6
SPS
1
2
3
4
5
20-L SWTQFN
(4mm x 4mm)
Pin Description
PIN
NAME
EN
FUNCTION
1
2
High-Voltage-Compatible Enable Input. If this pin is low, the part is off.
Bootstrap pin for HS driver. It is recommended to use 0.1μF from BST to LX.
Supply Input. Connect a 4.7μF ceramic capacitor from SUP to ground.
BST
SUP
4, 5, 11
Buck Switching Node. Connect inductor between LX and OUT. See the Inductor Selection section.
If the part is off, this node is high impedance.
8, 9
LX
Feedback pin. Connect a resistor-divider from the buck output to FB to ground for external
adjustment of the output voltage. Connect FB to BIAS for internal fixed voltages.
13
15
17
18
FB
BIAS
5V Internal BIAS supply. Connect a 1μF (minimum) ceramic capacitor to ground.
Sync Input. If connected to ground or left floating, skip-mode operation is enabled under light loads.
If connected to BIAS, forced PWM mode is enabled. This pin has a 1MΩ internal pulldown.
SYNC
PGOOD
NC
Open-Drain Reset Output. External pullup required.
No Connect
3, 6,
16, 19
Spread-Spectrum Enable. Connect logic-high to enable spread spectrum of internal oscillator,
or logic-low to disable spread spectrum. This pin has a 1MΩ internal pulldown.
20
SPS
7, 10
12
PGND
AGND
OUT
Power Ground.
Analog Ground.
14
Buck Regulator Output-Voltage-Sense Input. Bypass OUT to PGND with ceramic capacitors.
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Oscillator/Synchronization and
Efficiency (SYNC)
Detailed Description
The MAX20079 family of small, current-mode-controlled
buck converters features synchronous rectification and
requires no external compensation network. MAX20079 is
designed for 3.5A output current and can stay in dropout
by running at 99% duty cycle. Each device provides an
accurate output voltage of ±2% within the 6V to 18V input
range. Voltage quality can be monitored by observing
the PGOOD signal. The devices operate at 2.1MHz (typ)
frequency, which allows for small external components,
reduces output ripple, and guarantees there is no AM-band
interference. The devices are also available at 400kHz (typ)
for minimum switching losses and maximum efficiency.
Each device has an on-chip oscillator that provides a
2.1MHz (typ) or 400kHz (typ) switching frequency. There
are two modes of operation, depending on the condition
of SYNC. If SYNC is unconnected or at AGND, the device
operates in highly efficient pulse-skipping mode. If SYNC
is connected to BIAS or has a clock applied to it, the
device is in forced-PWM mode (FPWM). The device can
be switched during operation between FPWM mode and
skip mode by switching SYNC.
Skip-Mode Operation
Skip mode is entered when the SYNC pin is connected
to ground or is unconnected and the peak load current is
less than 600mA (typ). In this mode, the HSFET is turned
on until the inductor current ramps up to 600mA (typ) peak
value and the internal feedback voltage is above the regu-
lation voltage (1.0V, typ). At this point, both the HSFETs
and low-side FETs (LSFETs) are turned off. Depending on
the choice of the output capacitor and the load current,
the HSFET turns on when OUT (valley) drops below the
1.0V (typ) feedback voltage.
Each device features an ultra-low 3.5μA (typ) quiescent
supply current in standby mode. The device enters
standby mode automatically at light loads if the high-side
FET (HSFET) does not turn on for eight consecutive clock
cycles. The devices operate from a 3.5V to 36V supply
voltage and can tolerate transients up to 40V, making
them ideal for automotive applications. The devices are
available in factory-trimmed output voltages (3.3V and
5V) and are programmable with an external resistor-
divider. For fixed-output voltages outside of 3.3V and 5V,
contact factory for availability.
When the device is in skip mode, the internal high-voltage
LDO is turned off to save current. V
is supplied by the
BIAS
The symmetrical design of the 4mm x 4mm 20-pin side-
wettable TQFN package enables a design with extremely
low noise, high efficiency, and superior EMI performance.
output after the soft-start is completed.
Achieving High Efficiency at Light Loads
Each device operates with very low-quiescent current at
light loads to enhance efficiency and conserve battery
life. When the device enters skip mode, the output current
is monitored to adjust the quiescent current. The lowest
quiescent-current standby mode is only available for fac-
tory-trimmed devices between 3.0V and 5.5V output volt-
ages. When the output current is less than approximately
5mA, the device operates in the lowest quiescent-current
mode, also called standby mode. In this mode, the major-
ity of the internal circuitry in the device (excluding what
is necessary to maintain regulation) is turned off to save
current. Under no load and with skip mode enabled, the
device typically draws 6μA for the 3.3V parts, and 6μA for
the 5.0V parts. For load currents greater than 5mA, the
device enters normal skip mode and still maintains very
high efficiency.
Enable Input (EN)
Each device is activated by driving EN high. EN is com-
patible from a 3.3V logic level to automotive battery
levels. EN can be controlled by microcontrollers and
automotive KEY or CAN inhibit signals. The EN input has
no internal pullup/pulldown current, minimizing the over-
all quiescent supply current. To realize a programmable
undervoltage-lockout level, use a resistor-divider from
SUP to EN to AGND.
Bias/UVLO
Each device features undervoltage lockout. When the
device is enabled, an internal bias generator turns on. LX
begins switching after V
has exceeded the internal
BIAS
undervoltage-lockout level, V
= 2.73V (typ).
UVLO
Soft-Start
Output-Voltage Overshoot Protection
Each device features an internal soft-start timer. The out-
put voltage soft-start time is 3.5ms (typ), which includes
the delay in PGOOD. If a short circuit or undervoltage is
encountered after the soft-start timer has expired, the device
is disabled for 7ms (typ) and then reattempts soft-start. This
pattern repeats until the short circuit has been removed.
In dropout, the output voltage closely follows the input
voltage, but is below the regulation point. The device runs
at maximum duty cycle to satisfy the loop, and the internal
error-amplifier output is railed high. When the input volt-
age rises above the output, the device exits dropout, but
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
the internal error-amplifier output takes some time to get
back to steady state. This causes an overshoot in the out-
put voltage. To limit this overshoot, the device clamps the
output of the error amplifier while exiting dropout, causing
it to discharge faster and limiting the output-voltage over-
shoot. The actual value of the overshoot depends on the
output capacitor, inductor, and load.
output voltage is below 92% (typ) of its nominal value.
PGOOD is high impedance when the output voltage is
above 93% (typ) of its nominal value. Connect a 10kΩ
(typ) pullup resistor to an external supply, or to the on-chip
BIAS output.
Overcurrent Protection
Each device limits the peak output current to 4.7A (typ).
The accuracy of the current limit is ±12%, making selec-
tion of external components very easy. To protect against
short-circuit events, the device shuts off when OUT is
Controlled EMI with Forced-Fixed Frequency
In FPWM mode, the device attempts to operate at a con-
stant switching frequency for all load currents. For tight-
est frequency control, apply the operating frequency to
SYNC. The advantage of FPWM is a constant switching
frequency, which improves EMI performance; the disad-
vantage is that considerable current can be discarded. If
the load current during a switching cycle is less than the
current flowing through the inductor, the excess current is
diverted to AGND.
below 50% of V
and an overcurrent event is detected.
OUT
The device attempts a soft-start restart every 7ms and
remains off if the short circuit has not been removed.
When the current limit is no longer present, it reaches the
output voltage by following the normal soft-start sequence.
If the device’s die reaches the thermal limit of 175°C (typ)
during the current-limit event, it immediately shuts off.
Extended Input Voltage Range
Thermal-Overload Protection
In some cases, the device is forced to deviate from its
operating frequency, independent of the state of SYNC.
For input voltages above 18V (for MAX20079BATP/
VY+), the required duty cycle to regulate its output may
be smaller than the minimum on-time (65ns, typ). In this
event, the device is forced to lower its switching frequency
by skipping pulses.
Each device features thermal-overload protection. The
device turns off when the junction temperature exceeds
+175°C (typ). Once the device cools by 15°C (typ), it turns
back on with a soft-start sequence.
Applications Information
Setting the Output Voltage
If the input voltage is reduced and the device approaches
dropout, it continuously tries to turn on the HSFET. To
maintain gate charge on the HSFET, the BST capacitor
must be periodically recharged. To ensure proper charge
on the BST capacitor when in dropout, the HSFET is
turned off every 20μs and the LSFET is turned on for
approximately 200ns. This gives an effective duty cycle
of greater than 99%, and a switching frequency of 50kHz
when in dropout.
Connect FB to BIAS for a fixed +5V/3.3V output voltage.
To set the output to other voltages between 3V and 12V,
connect a resistive divider from output (OUT) to FB to
AGND (see Figure 1). Select R
(FB to AGND resistor)
FB2
≤ 500kΩ. Calculate R
(OUT to FB resistor) with the
FB1
following equation:
Equation 1:
V
OUT
R
=
R
−
1
FB1
FB2
V
FB
Spread-Spectrum Option
where V = 1V (see the Electrical Characteristics table).
FB
Each device has an optional spread spectrum enabled by
the SPS pin. If SPS is pulled high, the internal operating
frequency varies by ±3% relative to the internally gener-
ated operating frequency. Spread spectrum is offered to
improve EMI performance of the device.
V
OUT
R
R
FB1
MAX20079
The internal spread spectrum does not interfere with the
external clock applied on the SYNC pin. It is active only
when the device is running with an internally generated
switching frequency.
FB
FB2
Power-Good (PGOOD)
Each device features an open-drain power-good output.
PGOOD is an active-high output that pulls low when the
Figure 1. Adjustable Output-Voltage Setting
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
A large inductor reduces the ripple, but increases the
size and cost of the solution and slows the response.
Table 1 provides optimized inductor values for respective
switching frequency. The nominal standard value selected
should be within ±50% of the specified inductance.
Input Capacitor
The discontinuous input current of the buck converter
causes large input-ripple current. Switching frequency,
peak inductor current, and the allowable peak-to-peak
input-voltage ripple dictate the input-capacitance require-
ment. Increasing the switching frequency or the inductor
value lowers the peak-to-average current ratio, yielding a
lower input-capacitance requirement.
Output Capacitor
Output capacitance is selected to satisfy the output load-
transient requirements. During a load step, the output
current changes almost instantaneously, whereas the
inductor is slow to react. During this transition time, the
load-charge requirements are supplied by the output
capacitor, which causes an undershoot/overshoot in the
output voltage. For a buck converter that is controlled by
peak-current, as employed in MAX20079, output capaci-
tance also affects the control-loop stability.
MAX20079 incorporates a symmetrical pinout that can
be leveraged for better EMI performance. Connect two
high-frequency 0603 or smaller capacitors on two SUP
pins on either side of the package for good EMI perfor-
mance. Connect a high-quality, 4.7μF low-ESR ceramic
capacitor—or equivalent value in capacitance—on the
SUP pin for low-input voltage ripple.
The input ripple is primarily composed of ΔV (caused
Q
Based on internal-compensation design of MAX20079,
for optimal phase margin (> 60°, typ), the recommended
output capacitances are shown in Table 2. Recommended
values are the actual capacitances, after accounting for
voltage derating. If a lower or higher output capacitance
is required for the application, contact the factory for an
optimized solution.
by the capacitor discharge) and ΔV
(caused by the
ESR
ESR of the input capacitor). The total voltage ripple is the
sum of ΔV and ΔV . Assume that input-voltage ripple
Q
ESR
from the ESR and the capacitor discharge is equal to 50%
each. The following equations show the ESR and capaci-
tor requirement for a target voltage ripple at the input:
Equations 2:
The allowable output-voltage ripple and the maximum
deviation of the output voltage during step-load currents
determine the output capacitance and its ESR. The output
ΔV
ESR
ESR =
I
+ (ΔI
2)
/
OUT
P−P
ripple comprises ΔV (caused by the capacitor discharge)
Q
and ΔV
(caused by the ESR of the output capacitor).
ESR
I
×
D(1 − D)
OUT
Use low-ESR ceramic or aluminum electrolytic capaci-
tors at the output. For aluminum electrolytic capacitors,
C
=
IN
ΔV × f
Q
sw
the entire output ripple is contributed by ΔV
. Use
ESR
where:
and:
(V − V
) × V
IN
OUT
OUT
Equation 2 to calculate the ESR requirement and choose
the capacitor accordingly. If using ceramic capacitors,
assume the contribution to the output-ripple voltage
from the ESR and the capacitor discharge to be equal.
ΔI
=
P − P
V
× f × L
IN sw
V
OUT
D =
V
IN
Table 1. Inductor Selection
where I
is the output current, D is the duty cycle,
is the switching frequency. Use additional input
OUT
PART
RECOMMENDED INDUCTANCE (μH)
and f
SW
capacitance at lower input voltages to avoid possible
undershoot below the UVLO threshold during transient
loading.
f
= 2.1MHz
= 400kHz
2.2
10
SW
f
SW
Inductor Selection
Table 2. Output-Capacitance Selection
Inductor design is a compromise between the size,
efficiency, control-loop bandwidth, and stability of the
converter. Insufficient inductance value would increase
the inductor current ripple, causing higher conduction
losses and higher output voltage ripple. Since the slope
compensation is fixed internally for MAX20079, it might
also cause current-mode-control instability to appear.
NOMINAL OUTPUT MINIMUM OUTPUT
PART
CAPACITANCE
CAPACITANCE
(μF)
(µF)
f
= 2.1MHz
= 400kHz
35
44
25
34
SW
f
SW
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
The following equations show the output capacitance and
ESR requirement for a specified output-voltage ripple.
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching-
power losses and clean, stable operation. Use a multi-
layer board whenever possible for better noise immunity.
The package for MAX20079 offers a unique symmetrical
design, which helps cancel the magnetic field generated
in the opposite direction. Adhere the following guidelines
to ensure a low-noise PCB layout:
Equations 3:
ΔV
ESR
ESR =
ΔI
P_P
ΔI
P−P
C
=
OUT
8 × ΔV × f
Q
SW
● Place two high-frequency ceramic capacitors (C ) on
IN
two SUP pins, on opposite sides of the IC and close
to the device. High-frequency AC current flows on
the loop formed by the input capacitor and the half-
bridge MOSFETs internal to the device (see Figure
2). A small loop would reduce the radiating effect of
high switching currents and improve EMI functional-
ity. Two capacitors placed on opposite sides create
current loops in the opposite direction, which cancels
the magnetic field to reduce radiated EMI.
(V − V
IN
) × V
OUT
× f
OUT
× L
where
ΔI
=
P − P
V
IN SW
and
= ΔV
V
+ ΔV
Q
OUT_RIPPLE
ESR
ΔI
P-P
is the peak-to-peak inductor current as calculated
above, and f
is the converter’s switching frequency.
SW
● Solder the exposed pad to a large copper-plane area
under the device. To effectively use this copper area
as a heat exchanger between the PCB and ambient
environment, expose the copper area on the top and
bottom. Add a few small vias (or one large via) on the
copper pad for efficient heat transfer.
The allowable deviation of the output voltage during fast
transient loads also determines the output capacitance
and its ESR. The output capacitor supplies the step-load
current until the converter responds with a greater duty
cycle. The resistive drop across the output capacitor’s
ESR and the capacitor discharge causes a voltage droop
during a step load. Use a combination of low-ESR tanta-
lum and ceramic capacitors for better transient-load and
ripple/noise performance. Keep the maximum output-
voltage deviations below the tolerable limits of the elec-
tronics being powered. When using a ceramic capacitor,
assume an 80% and 20% contribution from the output-
capacitance discharge and the ESR drop, respectively.
Use the following equations to calculate the required ESR
and capacitance value:
● Connect PGND andAGND pins directly to the exposed
pad under the IC. This ensures the shortest connec-
tion path between AGND and PGND.
● Keep the power traces and load connections short.
This practice is essential for high efficiency. Use a
thick copper PCB to enhance full-load efficiency and
power-dissipation capability.
● Using internal PCB layers as ground planes helps to
improve the EMI functionality, as ground planes act as
a shield against radiated noise. Spread multiple vias
around the board, especially near the ground connec-
tions, for better overall ground connection.
Equations 4:
ΔV
ESR
ESR
=
OUT
I
STEP
● Keep the bias capacitor (C ) close to the device
BIAS
to reduce the bias current loop. This helps to reduce
noise on the bias for smooth operation.
● Place output capacitors (C
) symmetrically on the
OUT
opposite sides of the inductor. This further reduces the
radiated noise.
where I
is the load step and t
is the delay for
DELAY
STEP
the PWM mode, the worst-case delay would be (1 - D)
t
when the load step occurs immediately after a turn-
SW
on cycle. This delay is greater in skip mode.
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Figure 2
GROUND
MAX20079
SUP
C
IN
C
IN
SUP
VIAS
HF1
HF2
LX
INDUCTOR
C
C
OUT
OUT
GROUND
VIAS
OUT
GROUND
GROUND
Figure 2. Recommended PCB Layout for MAX20079
Typical Application Circuits
C
1µF
SYNC
PGOOD
SPS
BIAS
FB
EN
BIAS
SUP
MAX20079
SUP
C
IN2
C
IN1
2.2µF
2.2µF
NH
NL
OUT
BST
AGND
PGND
PGND
C
BST
0.1µF
LX
L
V
OUT
2.2µH
3.3V/5V
C
OUT
35µF
Figure 3. 2.1MHz, 5V/3.3V Fixed Output in 20-Pin Side-Wettable TQFN Package
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Typical Application Circuits (continued)
Figure 4. 400kHz, 5V/3.3V Fixed Output in 20-Pin Side-Wettable TQFN Package
Ordering Information
PART NUMBER
MAX20079AATP/VY+
MAX20079BATP/VY+*
MAX20079DATP/VY+*
MAX20079EATP/VY+*
MAX20079FATP/VY+
V
f
PACKAGE
T2044Y+5C
T2044Y+5C
T2044Y+5C
T2044Y+5C
T2044Y+5C
I
(A)
OUT
OUT
SW
5.0V (fixed), or 3V to 12V using external divider
3.3V (fixed), or 3V to 12V using external divider
5.0V (fixed), or 3V to 12V using external divider
3.3V (fixed), or 3V to 12V using external divider
3.395V (fixed), or 3V to 12V using external divider
2.1MHz
2.1MHz
400kHz
400kHz
2.1MHz
3.5
3.5
3.5
3.5
3.5
Note: All part numbers are OTP versions, no metal mask differences.
/V Denotes an automotive qualified part
+ Denotes a lead(Pb)-free/RoHS-compliant package
* Future Product - Contact factory for availability
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MAX20079
Automotive 36V 3.5A Buck Converter with 3.5μA Iq
Revision History
REVISION REVISION
PAGES
DESCRIPTION
CHANGED
NUMBER
DATE
0
1/19
Initial release
—
Updated General Description, Benefits and Features, Absolute Maximum Ratings,
Electrical Characteristics, Applications Information, and Ordering Information.
1, 3, 4, 11, 12,
15
1
3/19
2
3
4/19
7/19
Updated the PN (**) on three variants for intro in the Ordering Information
Updated Electrical Characteristics
15
4
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
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.
2019 Maxim Integrated Products, Inc.
│ 16
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