EVALUATION KIT AVAILABLE
Click here to ask about the production status of specific part numbers.
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
General Description
The MAX77597 is a small, synchronous buck converter
with integrated switches. The device is designed to
deliver up to 300mA with input voltages from 3.5V to
36V, while using only 1.1µA quiescent current at no load
(fixed-output version). Voltage quality can be monitored
by observing the RESET signal. The device can operate
near dropout by running at 98% duty cycle, making it ideal
for battery-powered applications.
The device offers fixed 3.3V. Frequency is fixed at
1.7MHz, which allows for small external components and
reduced output ripple. The device offers both forced-PWM
and skip modes of operation, with ultra-low quiescent current of 1.1µA in skip mode.
The MAX77597 is available in a small (2mm x 2.5mm)
10-pin TDFN package and operates across the -40°C to
+85°C temperature range.
Applications
●
●
●
Portable Devices Powered from 2s, 3s,
or 4s Li+ Batteries
USB Type-C Devices
Point-of-Load Applications
Ordering Information appears at end of data sheet.
19-100785; Rev 1; 4/20
Benefits and Features
● Flexible Power for Systems That Require a Wide
Input Voltage Range
• VIN Range: 3.5V to 36V
• Up to 300mA Output Current
• Fixed 3.3V, Output Voltage
• 98% (Max) Duty Cycle Operation with Low
Dropout
• Operates from 5V, 12V, or 20V USB Type-C Input
Power
• Operates from 2S, 3S, or 4S Li-Ion Battery
● Minimizes Power Consumption and Extends Battery
Life
• 1.1µA Quiescent Current (3.3V Fixed Output
Voltage)
• 86% Peak Efficiency at 12VIN, 3.3 VOUT
● Minimizes Solution Size
• 1.7MHz Operating Frequency
• Small 2.0mm x 2.5mm x 0.75mm 10-Pin TDFN
Package
● Robust Solution
• Short-Circuit, Thermal Protections
• 6.67ms Internal Soft-Start Minimizes Inrush Current
• Current-Mode Control Architecture
• Up to 42V Input Voltage Tolerance
MAX77597
Absolute Maximum Ratings
36V, 300mA, Buck Converter with 1.1µA IQ
(Voltages Referenced to PGND)
SUP........................................................................-0.3V to +42V
EN..............................................-0.3V to MIN (24V, VSUP + 0.3V)
BST to LX...............................................................................+6V
BST.........................................................................-0.3V to +47V
MODE, OUT/FB, RESET.......................... -0.3V to VBIAS + 0.3V
AGND....................................................................-0.3V to +0.3V
BIAS......................................................................-0.3V to +6.0V
www.maximintegrated.com
OUT/FB Short-Circuit Duration..................................Continuous
Continuous Power Dissipation (TA = +70°C)
(derate 9.8mW/°C above +70°C).................................784mW
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
Soldering Temperature (reflow)........................................+260°C
Maxim Integrated │ 2
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Package Information
20-TDFN
PACKAGE CODE
T102A2+1C
Outline Number
21-100013
Land Pattern Number
—
Thermal Resistance:
Junction to Ambient (θJA)
102ºC/W
Junction to Case (θJC)
2.9ºC/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.
www.maximintegrated.com
Maxim Integrated │ 3
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Electrical Characteristics
(VSUP = VEN = 14V, VMODE = 0V, TA = TJ = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C, unless
otherwise noted.) (Note 1)
PARAMETER
SYMBOL
Supply Voltage
VSUP
Supply Voltage
VSUP
Supply Current
ISUP
UV Lockout
VUVLO
BIAS Regulator Voltage
VBIAS
CONDITIONS
MIN
TYP
3.5
t < 500ms (Note 2)
MAX
UNITS
36
V
42
V
Shutdown (VEN = 0V)
0.75
3.0
No load, fixed 3.3V VOUT
1.1
3.0
VMODE = VBIAS , no load, FPWM,
no switching
0.5
1
1.5
VBIAS rising
3.0
3.2
3.4
Hysteresis
0.4
VSUP = 5.5V to 36V
BIAS Current Limit
5
µA
mA
V
V
10
mA
BUCK CONVERTER
Voltage Accuracy
VOUT,3.3V
VOUT = 3.3V, 6V ≤ VSUP ≤ 36V,
ILOAD = 0 to 300mA
3.1
3.3
3.4
V
High-Side DMOS RDSON
RON,HS
VBIAS = 5V, ILX = 200mA
1000
2200
mΩ
Low-Side DMOS RDSON
RON,LS
VBIAS = 5V, ILX = 200mA
500
1200
mΩ
DMOS High-Side Current-Limit
Threshold
IMAX
425
500
575
mA
DMOS High-Side Skip-Mode
Peak-Current Threshold
ISKIP
70
100
130
mA
DMOS Low-Side Zero-Crossing
Threshold
DMOS Low-Side Negative
Current-Limit Threshold
Soft-Start Ramp Time
IZX
INEG
tSS
LX Rise Time
tRISE,LX
Minimum On-Time
tON_MIN
Maximum Duty Cycle
DCMAX
PWM Switching Frequency
FPWM mode
(Note 2)
40
mA
-320
mA
6.67
ms
6
ns
34
ns
98
fSW
%
1.58
1.7
1.82
MHz
RESET OUTPUT (RESET)
RESET Threshold
RESET Debounce
VTHR_RES
VOUT rising
88
92
96
VTHF_RES
VOUT falling
86
90
94
tDEB
12
%VOUT
µs
RESET High Leakage Current
ILEAK,RES
TA = +25°C
1
µA
RESET Low Level
VOUT,RES
Sinking 1mA
0.4
V
www.maximintegrated.com
Maxim Integrated │ 4
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Electrical Characteristics (continued)
(VSUP = VEN = 14V, VMODE = 0V, TA = TJ = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C, unless
otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
LOGIC LEVELS
EN Input High Threshold
VIH,EN
EN Input Low Threshold
VIL,EN
EN Input Current
2.4
IIN,EN
MODE Input High Threshold
VIH,MODE
MODE Input Low Threshold
VIL,MODE
MODE Internal Pulldown
RPD,MODE
V
0.4
0.1
V
µA
1.4
V
0.4
V
1000
kΩ
THERMAL PROTECTION
Thermal Shutdown
Thermal-Shutdown Hysteresis
TSHDN
(Note 2)
+175
°C
TSHDN,HYS
(Note 2)
+15
°C
Note 1: Limits are 100% tested at TA = +25°C. Limits over the operating temperature range and relevant
supply voltage range are guaranteed by design and characterization.
Note 2: Guaranteed by design; not production tested.
www.maximintegrated.com
Maxim Integrated │ 5
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Typical Operating Characteristics
(VSUP = VEN = 12V, TA = +25°C, unless otherwise noted.)
3.0
2.5
3.0
SUPPLY CURRENT (μA)
2.5
2.0
1.5
1.0
1.5
1.0
0
10
20
30
40
-40 -20
0
20
toc04
EFFICIENCY (%)
EFFICIENCY (%)
80
70
60
FPWM
80
SKIP
70
60
FPWM
50
20
0.001
0.01
100
1
10
20
0.001
100
90
toc08
OUTPUT VOLTAGE (V)
SKIP
60
FPWM
40
3.30
1
10
OUTPUT CURRENT (mA)
www.maximintegrated.com
100
100
toc09
SKIP
3.28
FPWM
3.26
3.22
0.1
10
3.32
3.24
0.01
1
VSUP = 12V
SKIP
3.30
3.28
FPWM
3.26
3.24
30
20
0.001
0.1
LOAD REGULATION
3.3V FIXED-OUTPUT
3.34
VSUP = 5V
3.32
80
50
0.01
OUTPUT CURRENT (mA)
LOAD REGULATION
3.3V FIXED-OUTPUT
3.34
toc07
VSUP = 36V
70
FPWM
50
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
EFFICIENCY vs. LOAD
3.3V FIXED-OUTPUT
0.1
80 100 120 140
SKIP
60
30
100
60
70
30
10
40
VSUP = 20V
90
40
1
20
toc06
100
30
0.1
0
EFFICIENCY vs. LOAD
3.3V FIXED-OUTPUT
40
0.01
-40 -20
TEMPERATURE (°C)
40
20
0.001
EFFICIENCY (%)
0
80 100 120 140
VSUP = 12V
90
SKIP
50
60
toc05
100
VSUP = 5V
80
0.8
EFFICIENCY vs. LOAD
3.3V FIXED-OUTPUT
EFFICIENCY vs. LOAD
3.3V FIXED-OUTPUT
90
1.2
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
100
40
EFFICIENCY (%)
0
1.6
0.4
0.5
0.5
0.0
2.0
2.0
OUTPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
3.5
VOUT = 3.3V
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX77596 toc03
toc01
VOUT = 3.3V
SUPPLY CURRENT (μA)
4.0
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE (SKIP MODE)
MAX77596 toc02
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
(FIXED-OUTPUT, SKIP MODE)
0
50
100
150
200
OUTPUT CURRENT(mA)
250
300
3.22
0
50
100
150
200
250
300
OUTPUT CURRENT (mA)
Maxim Integrated │ 6
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Typical Operating Characteristics (continued)
(VSUP = VEN = 12V, TA = +25°C, unless otherwise noted.)
LOAD REGULATION
3.3V FIXED-OUTPUT
3.34
toc10
3.40
VSUP = 20V
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
3.28
SKIP
3.26
toc11
FPWM
VEN
3.34
5V/div
3.32
3.9V
ISUP
3.30
0.1A/div
3.28
VBIAS
SKIP
3.26
3.3V
5V/div
3.24
3.24
3.22
3.22
toc12
24V
3.36
FPWM
STARTUP WAVEFORM
3.3V ADJUSTABLE-OUTPUT
(SKIP, 0mA LOAD)
VSUP = 36V
3.38
3.32
3.30
LOAD REGULATION
3.3V FIXED-OUTPUT
0
50
100
150
200
250
VOUT
1V/div
3.20
300
0
OUTPUT CURRENT (mA)
200
0V
300
1ms/div
OUTPUT CURRENT (mA)
LINE REGULATION
3.3V FIXED-OUTPUT
3.40
100
LOAD TRANSIENT RESPONSE
3.3V FIXED-OUTPUT (SKIP)
toc13
VSUP = 12V
3.35
OUTPUT VOLTAGE (V)
toc14
IOUT = 100mA
3.30
3.25
IOUT = 300mA
IOUT
200mA/div
VOUT
100mV/div
(3.3V offset)
3.20
3.15
3.10
0
10
20
30
40
100us/div
SUPPLY VOLTAGE (V)
LOAD TRANSIENT RESPONSE
3.3V FIXED-OUTPUT (FPWM)
LOAD TRANSIENT RESPONSE
3.3V FIXED-OUTPUT (SKIP)
toc15
VSUP =V12V
SUP = 12V
IOUT
200mA/div
VOUT
100mV/div
(3.3V offset)
100us/div
www.maximintegrated.com
toc16
VSUP = 36V
IOUT
200mA/div
VOUT
100mV/div
100µs/div
Maxim Integrated │ 7
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Typical Operating Characteristics (continued)
(VSUP = VEN = 12V, TA = +25°C, unless otherwise noted.)
LOAD TRANSIENT RESPONSE
3.3V FIXED-OUTPUT (FPWM)
LOAD TRANSIENT RESPONSE
3.3V ADJUSTABLE-OUTPUT (SKIP)
toc17
VSUP = 36V
toc18
VSUP = V12V
SUP = 12V
IOUT
200mA/div
VOUT
100mV/div
IOUT
200mA/div
VOUT
100mV/div
(3.3V offset)
100µs/div
100us/div
LINE TRANSIENT RESPONSE
(3.3V FIXED-OUTPUT, 100mA LOAD, SKIP)
3.3V FIXED-OUTPUT VSUP ON/OFF
RESPONSE (FPWM, 300mA LOAD)
toc19
toc20
24V
VSUP
10V/div
3.9V
VOUT
2V/div
VSUP
10V/div
VBIAS
5V/div
VOUT
50mV/div
(3.3V
OFFSET)
VLX
10V/div
40ms/div
200µs/div
3.3V FIXED-OUTPUT SLOW VSUP
RESPONSE (FPWM, NO LOAD)
SHORT-CIRCUIT RESPONSE (SKIP)
toc21
VSUP
10V/div
toc22
24V
VLX
10V/div
3.9V
VOUT
2V/div
ILX
0.5A/div
VBIAS
5V/div
VOUT
2V/div
VLX
10V/div
10s/div
www.maximintegrated.com
4ms/div
Maxim Integrated │ 8
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Pin Configuration
TOP VIEW
EN
10
OUT BIAS MODE RESET
9
8
7
6
MAX77597
EP*
+
1
2
BST
SUP
3
4
5
LX PGND AGND
TDFN
*EXPOSED PAD
Pin Description
PIN
NAME
FUNCTION
1
BST
High-Side Driver Supply. Connect a 0.1µF bootstrap capacitor between LX and BST.
2
SUP
IC Supply Input. Connect a minimum of 4.7µF ceramic capacitor from SUP to PGND.
3
LX
4
PGND
Power Ground. Connect to AGND under the device in a star configuration.
5
AGND
Analog Ground. Connect to PGND under the device in a star configuration.
6
RESET
Open-Drain Reset Output. An external pullup resistor is required.
7
MODE
Mode Switch-Control Input. Connect to ground or leave open to enable skip-mode operation under light loads.
Connect to BIAS to enable forced-PWM mode. MODE has a 1MΩ internal pulldown.
8
BIAS
5V Internal Logic Supply. Connect a 1µF ceramic capacitor to AGND. Do not load this pin externally.
9
OUT
MAX77597ETBB+ (Fixed Output): Buck Regulator Voltage-Sense Input. Bypass OUT to PGND with a minimum
22µF X5R ceramic capacitor.
10
EN
Enable Input. Drive EN low to disable the device. Drive EN high to enable the device.
—
EP
Exposed Pad. Connect EP to a large copper ground plane for effective power dissipation. Do not use EP as the
only IC ground connection. EP must be connected to PGND.
Buck Switching Node. LX is high impedance when the device is off.
www.maximintegrated.com
Maxim Integrated │ 9
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Block Diagram
MODE
EN
HVLDO
BANDGAP
REF
OSC
BST
BIAS
MAX77597
SOFTSTART
OUT
OR
FB
OUT/FB
OUT
EAMP
FB
SW1
PWM
LOGIC
CONTROL
PGND
RESET
www.maximintegrated.com
LX
BIAS
VGOOD COMP
SW2
NOTE:
SUP
CLK
CURRENT SENSE
+
SLOPE COMP
AGND
FOR INTERNAL FEEDBACK VERSION, SW1 IS OPEN AND SW2 CLOSED.
EXTERNAL PIN IS CALLED OUT.
Maxim Integrated │ 10
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Detailed Description
The MAX77597 is a small, current-mode buck converter
that features synchronous rectification and requires no
external compensation network. The device operates
from a 3.5V to 36V supply voltage and can deliver up
to 300mA output current. Frequency is fixed at 1.7MHz,
which allows for small external components and reduced
output ripple.
The device offers fixed 3.3V output Voltage quality can
be monitored by observing the RESET signal. The device
offers both forced-PWM and skip mode, with ultra-lowquiescent current of 1.1µA in skip mode.
DC-DC Converter Control Architecture
The step-down converter uses a PWM peak current-mode
control scheme with a load-line architecture. Peak currentmode control provides several advantages over voltagemode control, including precise control of the inductor current on a cycle-by-cycle basis, simpler compensation, and
inherent compensation for line voltage variation.
An internal transconductance amplifier establishes an
integrated error voltage. The heart of the PWM controller is an open-loop comparator: one input is the integrated voltage-feedback signal; the other consists of the
amplified current-sense signal plus slope-compensation
ramp. Integrated high-side current sensing is used, which
reduces component count and layout risk by eliminating
the need to carefully route sensitive external signals.
Error-amplifier compensation is also integrated, once
again simplifying the power-supply designer’s task while
eliminating external components.
The controller features a load-line architecture. The output voltage is positioned slightly above nominal regulation at no load and slightly below nominal regulation at
full load. As output load changes, a small but controlled
amount of load regulation (“load-line”) error occurs on
the output voltage. This voltage positioning architecture
allows the output voltage to respond to sudden load
transients in a critically damped manner, and effectively
reduces the amount of output capacitance needed when
compared to classical integrating controllers. See the
Typical Operating Characteristics section of the data
sheet for information about the converter’s typical voltage
regulation behavior versus load.
www.maximintegrated.com
The device can operate in either forced-PWM or skip
mode. In forced-PWM mode, the converter maintains a
constant switching frequency, regardless of load, to allow
for easier filtering of the switching noise. The device
includes proprietary circuitry that dramatically reduces
quiescent current consumption in skip mode, improving
light-load efficiency. See the Forced PWM/Skip Modes
section for further details.
System Enable (EN)
An enable control input (EN) activates the device from its
low-power shutdown mode. EN is compatible with inputs
from levels down to 2.4V. EN can be connected directly
to SUP for voltage level up to 24V. For self-enable operations with SUP voltages above 24V, connect EN using an
external resistor divider to maintain EN below 24V.
Linear Regulator Output (BIAS)
The device includes a 5V linear regulator output (BIAS)
that provides power to the internal circuit blocks. Connect
a 1µF ceramic capacitor from BIAS to AGND. Do not load
this pin externally.
Undervoltage Lockout
When VBIAS drops below the undervoltage-lockout
(UVLO) level of VUVLO = 2.8V (typ), the device assumes
that the supply voltage is too low for proper operation, so
the UVLO circuitry inhibits switching. When VBIAS rises
above the UVLO rising threshold, the controller enters the
startup sequence and then resumes normal operation.
Startup and Soft-Start
The device features an internal soft-start timer. The
output-voltage soft-start ramp time is 6.67ms (typ). If a
short circuit or undervoltage is encountered after the softstart timer has expired, the device is disabled for 16.5ms
(typ) and then reattempts soft-start again. This pattern
repeats until the short circuit has been removed.
RESET Output
The device features an open-drain RESET output to
monitor the output voltage. The RESET output requires
an external pullup resistor. RESET goes high (high
impedance) after the regulator output increases above
92% of the nominal regulated voltage. RESET goes low
when the regulator output drops to below 90% of the
nominal regulated voltage.
Maxim Integrated │ 11
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Forced PWM/Skip Modes
The device features a logic-level input (MODE) to switch
between forced-PWM and skip modes. Connecting MODE
to BIAS enables the forced-PWM operation. Connecting
MODE to ground, or leaving unconnected, enables skipmode operation with ultra-low-quiescent current of 1.1µA.
In skip-mode operation, the converter’s switching frequency is load dependent until the output load reaches the skip
threshold. At higher load current, the switching frequency
does not change and the operating mode is similar to the
forced-PWM mode. Skip mode helps improve efficiency
in light-load applications by allowing the converter to turn
on the high-side switch only when the output voltage falls
below a set threshold. As such, the converter does not
switch the MOSFETs on and off as often as is the case
in the forced-PWM mode. Consequently, the gate charge
and switching losses are much lower in skip mode.
output voltage, and selected LIR then determines the
inductor value as follows:
L=
VOUT × ( VSUP − VOUT )
VSUP × f SW × I OUT × LIR
where VSUP, VOUT, and IOUT are typical values (so that
efficiency is optimum for typical conditions). The switching
frequency is 1.7MHz. Table 1 lists some of the inductor values for 300mA output current and several output voltages.
Table 1. Inductor Values for 300mA
Output Current
VSUP/VOUT (V)
14V/3.3V
INDUCTOR (µH) ILOAD = 300mA
10µH (typ)
22µH (max)
Current Limit /Short-Circuit Protection
The device has fault protection designed to protect itself
from abnormal conditions. If the output is soft shorted
(meaning the output is overloaded but over 25% of
regulation), cycle-by-cycle current limit limits how high
the inductor current goes for any cycle. If the output is
hard shorted to ground and the output falls to less than
25% of regulation, the part goes into a mode where it
switches until 15 cycles are ended by current limit, then
waits for 16.5ms before trying to soft-start again. This
mode of operation limits the amount of power dissipated
by the device under these conditions. The device also
has overtemperature protection. If the die temperature
exceeds approximately 175°C, the device stops switching
until the die temperature drops by approximately 15°C
and then resumes operation, including going through
soft-start again.
Applications Information
Inductor Selection
Three key inductor parameters must be specified for
operation with the device: inductance value (L), inductor
saturation current (ISAT), and DC resistance (RDCR). To
select inductance value, the ratio of inductor peak-topeak AC current to DC average current (LIR) must be
selected first. A good compromise between size and loss
is a 30% peak-to-peak ripple current to average current
ratio (LIR = 0.3). The switching frequency, input voltage,
www.maximintegrated.com
Input Capacitor
The input filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on the input caused by the circuit’s switching.
The input capacitor RMS current requirement (IRMS) is
defined by the following equation:
IRMS = ILOAD(MAX)
VOUT × (VSUP − VOUT )
VSUP
IRMS has a maximum value when the input voltage
equals twice the output voltage (VSUP = 2VOUT), so
IRMS(MAX) = ILOAD(MAX) /2.
Choose an input capacitor that exhibits less than +10°C
self-heating temperature rise at the RMS input current for
optimal long-term reliability.
The input voltage ripple is composed of ΔVQ (caused
by the capacitor discharge) and ΔVESR (caused by the
ESR of the capacitor). Use low-ESR ceramic capacitors
with high ripple current capability at the input. Assume
the contribution from the ESR and capacitor discharge
equal to 50%. Calculate the input capacitance and ESR
required for a specified input voltage ripple using the
following equations:
ESR IN =
∆VESR
∆I
I OUT + L
2
Maxim Integrated │ 12
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
PCB Layout Guidelines
where:
(V
− VOUT ) × VOUT
∆IL = SUP
VSUP × f SW × L
and:
=
C IN
I OUT × D(1 − D)
VOUT
=
and D
∆VQ × f SW
VSUP
where IOUT is the maximum output current and D is the
duty cycle.
Output Capacitor
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 noload conditions. When using high-capacitance, low-ESR
capacitors, the filter capacitor’s ESR dominates the output voltage ripple. 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(MAX) × LIR
The actual capacitance value required relates to the
physical size needed to achieve low ESR, as well as to
the chemistry of the capacitor technology. Therefore, the
capacitor is usually selected by ESR and voltage rating
rather than by capacitance value.
When using low-capacity filter capacitors, such as ceramic capacitors, size is usually determined by the capacity
needed to prevent voltage droop and voltage rise from
causing problems during load transients. Generally, once
enough capacitance is added to meet the overshoot
requirement, undershoot at the rising-load edge is no
longer a problem.
www.maximintegrated.com
Careful PCB layout is critical to achieve low-switching
power losses and clean, stable operation. Use a multilayer board whenever possible for better noise immunity
and power dissipation. Follow these guidelines for good
PCB layout:
1) The input capacitor (4.7µF, see Figures 3 and 4) should
be placed immediately next to the SUP pin of the
device. Since the device operates at 1.7MHz switching frequency, this placement is critical for effective
decoupling of high-frequency noise from the SUP pin.
2) Solder the exposed pad to a large copper plane area
under the device. To effectively use this copper area as
heat exchanger between the PCB and ambient, expose
the copper area on the top and bottom sides. Add a
few small vias or one large via on the copper pad for
efficient heat transfer. Connect the exposed pad to
PGND, ideally at the return terminal of the output
capacitor.
3) Isolate the power components and high-current path
from the sensitive analog circuitry. Doing so is essential
to prevent any noise coupling into the analog signals.
4) Keep the high-current paths short, especially at the
ground terminals. This practice is essential for stable,
jitter-free operation.
5) Connect PGND and AGND together at the return
terminal of the output capacitor. Do not connect them
anywhere else.
6) Keep the power traces and load connections short.
This practice is essential for high efficiency.
7) Place the BIAS capacitor ground next to the AGND pin
and connect with a short and wide trace.
Maxim Integrated │ 13
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Typical Application Circuits
VBAT
CIN1
4.7µF
MAX77597
SUP
BST
CIN2
0.1µF
LX
CBST
0.1µF
L
10µH
NH
MODE
VOUT
3.3V
OUT
EN
NL
BIAS
RESET
AGND
CL
1µF
COUT
22µF
PGND
Figure 1. MAX77597ETBB+, Fixed Output Voltage (3.3V), 10-Pin TDFN
Ordering Information
PART
MAX77597ETBB+
VOUT
PIN-PACKAGE
Fixed 3.3V
10 TDFN-EP*
*EP = Exposed pad.
+Denotes a lead(Pb)-free/RoHS-compliant package.
www.maximintegrated.com
Maxim Integrated │ 14
MAX77597
36V, 300mA, Buck Converter with 1.1µA IQ
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
DESCRIPTION
0
4/20
Initial release
—
1
4/20
Updated the Detailed Description section
11
For information on other Maxim Integrated products, 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.
© 2020 Maxim Integrated Products, Inc. │ 15
工商网监
湘ICP备2023018690号
