EVALUATION KIT AVAILABLE
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
General Description
Benefits and Features
The device offers fixed 3.3V and 5V output versions, as
well as an adjustable version. The adjustable version
allows the user to program the output voltage between 1V
and 10V by using a resistor-divider. 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.
● Minimizes Power Consumption and Extends Battery
Life
• 1.1µA Quiescent Current (3.3V Fixed Output
Voltage)
• 86% Peak Efficiency at 12VIN, 3.3 VOUT
The MAX77596 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
24V, 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 MAX77596 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
19-7733; Rev 1; 3/16
● Flexible Power for Systems That Require a Wide
Input Voltage Range
• VIN Range: 3.5V to 24V
• Up to 300mA Output Current
• Fixed 3.3V, 5V, or Programmable 1V to 10V
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 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
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
Absolute Maximum Ratings
(Voltages Referenced to PGND)
SUP........................................................................-0.3V to +42V
EN...............................................................-0.3V to 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
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
Package Thermal Characteristics (Note 1)
TDFN
Junction-to-Ambient Thermal Resistance (BJA).........102°C/W
Junction-to-Case Thermal Resistance (BJC)...................2.9°C/W
Note 1: 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 Characteristic
(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 2)
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 3)
MAX
UNITS
24
V
42
V
Shutdown (VEN = 0V)
0.75
3.0
No load, fixed 3.3V VOUT
1.1
3.0
No load, fixed 5.0V VOUT
1.8
5.0
32
70
No load, adjustable
VOUT
TA = +25°C
TA = -40°C to +85°C
80
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 24V (MAX77596ETBC+)
BIAS Current Limit
µA
5
mA
V
V
10
mA
BUCK CONVERTER
VOUT,3.3V
VOUT = 3.3V, 6V ≤ VSUP ≤ 24V,
ILOAD = 0 to 300mA
3.1
VOUT,5.0V
VOUT = 5.0V, 6V ≤ VSUP ≤ 24V,
ILOAD = 0 to 300mA
4.8
Voltage Accuracy
Output Voltage Range
VOUT
Adjustable output versions
FB Voltage Accuracy
VFB
Adjustable output versions,
3.5V ≤ VSUP ≤ 24V, ILOAD = 300µA
FB Input Current
IFB
VFB = 1V
FB Load Regulation
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ΔVLOAD
ILOAD = 0.3mA to 300mA
3.3
3.4
V
5.0
1
0.98
1.0
5.15
10
V
1.03
V
0.02
µA
2
%
Maxim Integrated │ 2
MAX77596
24V, 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 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
FB Line Regulation
ΔVLINE
6V ≤ VSUP ≤ 24V
0.02
%/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 3)
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
90
92
94
VTHF_RES
VOUT falling
88
90
92
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
LOGIC LEVELS
EN Input High Threshold
VIH,EN
EN Input Low Threshold
VIL,EN
EN Input Current
IIN,EN
MODE Input High Threshold
VIH,MODE
MODE Input Low Threshold
VIL,MODE
MODE Internal Pulldown
RPD,MODE
2.4
V
0.4
0.1
V
µA
1.4
V
0.4
V
1000
kΩ
THERMAL PROTECTION
Thermal Shutdown
Thermal-Shutdown Hysteresis
TSHDN
(Note 3)
+175
°C
TSHDN,HYS
(Note 3)
+15
°C
Note 2: 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 3: Guaranteed by design; not production tested.
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Maxim Integrated │ 3
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
Typical Operating Characteristics
(VSUP = VEN = 12V, TA = +25°C, unless otherwise noted.)
2.5
3
SUPPLY CURRENT (μA)
SUPPLY CURRENT (μA)
VOUT = 3.3V
2
1
2.0
2.0
1.5
1.0
5
10
15
20
0
25
-40 -20
0
EFFICIENCY vs. LOAD
3.3V FIXED-OUTPUT
toc04
60
0
80 100 120 140
80
70
60
FPWM
80
SKIP
70
FPWM
50
30
20
0.001
100
OUTPUT CURRENT (mA)
0.01
0.1
1
10
20
0.001
100
80
1
10
LOAD REGULATION
3.3V FIXED-OUTPUT
3.34
toc07
100
toc08
VSUP = 5V
VSUP = 12V
3.32
SKIP
70
60
FPWM
50
40
SKIP
3.30
3.28
FPWM
3.26
3.24
30
20
0.001
0.1
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
90
0.01
OUTPUT CURRENT (mA)
EFFICIENCY vs. LOAD
5V FIXED-OUTPUT
100
FPWM
50
30
10
80 100 120 140
SKIP
60
30
1
60
70
40
0.1
40
VSUP = 20V
90
60
20
toc06
100
40
0.01
0
EFFICIENCY vs. LOAD
3.3V FIXED-OUTPUT
40
20
0.001
-40 -20
TEMPERATURE (°C)
VSUP = 12V
90
SKIP
50
40
toc05
100
VSUP = 5V
EFFICIENCY (%)
EFFICIENCY (%)
80
0.8
EFFICIENCY vs. LOAD
3.3V FIXED-OUTPUT
EFFICIENCY (%)
90
1.2
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
100
20
EFFICIENCY (%)
0
1.6
0.4
0.5
0
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX77596 toc03
3.0
VOUT = 3.3V
SUPPLY CURRENT (μA)
toc01
4
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE (SKIP MODE)
MAX77596 toc02
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
(FIXED-OUTPUT, SKIP MODE)
3.22
0.01
0.1
1
10
OUTPUT CURRENT (mA)
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100
0
50
100
150
200
250
300
OUTPUT CURRENT(mA)
Maxim Integrated │ 4
MAX77596
24V, 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
toc09
LOAD REGULATION
3.3V FIXED-OUTPUT
3.34
VSUP = 12V
3.32
3.28
FPWM
3.26
3.24
toc11
VSUP = 12V
VSUP = 20V
SKIP
5.05
FPWM
3.30
OUTPUT VOLTAGE (V)
3.30
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
5.10
toc10
3.32
SKIP
3.22
LOAD REGULATION
5V FIXED-OUTPUT
3.28
SKIP
3.26
5.00
FPWM
4.95
3.24
0
50
100
150
200
250
300
3.22
0
50
OUTPUT CURRENT (mA)
100
150
200
250
150
200
250
300
toc13
IOUT = 100mA
3.3
OUTPUT VOLTAGE (V)
3.9V
ISUP
VBIAS
3.3V
5V/div
VOUT
100
LINE REGULATION
3.3V FIXED-OUTPUT
3.32
0.1A/div
1V/div
50
OUTPUT CURRENT (mA)
3.34
toc12
24V
5V/div
0
OUTPUT CURRENT (mA)
STARTUP WAVEFORM
3.3V ADJUSTABLE-OUTPUT
(SKIP, 0mA LOAD)
VEN
4.90
300
3.28
3.26
3.24
IOUT = 300mA
3.22
3.2
0V
3.18
1ms/div
0
5
10
15
20
25
SUPPLY VOLTAGE (V)
LOAD TRANSIENT RESPONSE
3.3V FIXED-OUTPUT (SKIP)
LOAD TRANSIENT RESPONSE
3.3V FIXED-OUTPUT (FPWM)
toc14
toc15
VSUP = V12V
SUP = 12V
VSUP = 12V
IOUT
200mA/div
IOUT
200mA/div
VOUT
100mV/div
(3.3V offset)
VOUT
100mV/div
(3.3V offset)
100us/div
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100us/div
Maxim Integrated │ 5
MAX77596
24V, 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 ADJUSTABLE-OUTPUT (SKIP)
LOAD TRANSIENT RESPONSE
5V FIXED-OUTPUT (SKIP)
toc16
VSUP = V12V
SUP = 12V
toc17
VSUP = 12V
VSUP = 12V
IOUT
200mA/div
IOUT
200mA/div
VOUT
100mV/div
(3.3V offset)
VOUT
100mV/div
(5V offset)
100us/div
100µs/div
LOAD TRANSIENT RESPONSE
5V FIXED-OUTPUT (FPWM)
LINE TRANSIENT RESPONSE
(3.3V FIXED-OUTPUT, 100mA LOAD, SKIP)
toc18
toc19
VSUP = 12V
VSUP = 12V
24V
IOUT
200mA/div
VOUT
100mV/div
(5V offset)
3.9V
VSUP
10V/div
VOUT
50mV/div
(3.3V
OFFSET)
100µs/div
200µs/div
3.3V FIXED-OUTPUT VSUP ON/OFF
RESPONSE (FPWM, 300mA LOAD)
5V FIXED VSUP ON/OFF
RESPONSE (SKIP, NO LOAD)
MAX77596 toc20
MAX77596 toc21
VSUP
10V/div
VSUP
10V/div
40ms/div
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VOUT
2V/div
VOUT
5V/div
VBIAS
5V/div
VBIAS
5V/div
VLX
10V/div
VLX
10V/div
40ms/div
Maxim Integrated │ 6
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
Typical Operating Characteristics (continued)
(VSUP = VEN = 12V, TA = +25°C, unless otherwise noted.)
5V FIXED-OUTPUT SLOW VSUP
RESPONSE (SKIP, NO LOAD)
3.3V FIXED-OUTPUT SLOW VSUP
RESPONSE (FPWM, NO LOAD)
MAX77596 toc23
MAX77596 toc22
VSUP
10V/div
VSUP
10V/div
VOUT
2V/div
VOUT
5V/div
VBIAS
5V/div
VBIAS
5V/div
VLX
10V/div
VLX
10V/div
10s/div
10s/div
SHORT-CIRCUIT RESPONSE (SKIP)
toc24
24V
VLX
10V/div
3.9V
ILX
0.5A/div
VOUT
2V/div
4ms/div
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Maxim Integrated │ 7
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
Pin Configuration
TOP VIEW
EN OUT/FB BIAS MODE RESET
10
9
8
7
6
MAX77596
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
Buck Switching Node. LX is high impedance when the device is off.
5V Internal Logic Supply. Connect a 1µF ceramic capacitor to AGND. Do not load this pin externally.
9
OUT/FB
MAX77596ETBA+/MAX77596ETBB+ (Fixed Output): Buck Regulator Voltage-Sense Input. Bypass OUT to
PGND with a minimum 22µF X5R ceramic capacitor.
MAX77596ETBC+ (Adjustable Output): Feedback Input. Connect FB to a resistive divider between the buck
output and AGND to set the output voltage.
10
EN
SUP Voltage-Compatible 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.
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Maxim Integrated │ 8
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
Block Diagram
MODE
EN
HVLDO
BANDGAP
REF
OSC
BST
BIAS
MAX77596
SOFTSTART
OUT
OR
FB
OUT/FB
OUT
EAMP
FB
SW1
PWM
SUP
CLK
CURRENT SENSE
+
SLOPE COMP
LOGIC
CONTROL
LX
BIAS
VGOOD COMP
SW2
PGND
RESET
AGND
NOTE 1: FOR INTERNAL FEEDBACK VERSION, SW1 IS OPEN AND SW2 CLOSED.
EXTERNAL PIN IS CALLED OUT.
NOTE 2: FOR EXTERNAL FEEDBACK VERSION, SW1 IS CLOSED AND SW2 OPEN.
EXTERNAL PIN IS CALLED FB.
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Maxim Integrated │ 9
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
Detailed Description
The MAX77596 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 24V 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, fixed 5V output, and
adjustable output options. The adjustable version can be
set between 1V and 10V by using an external resistive
divider. Voltage quality can be monitored by observing
the RESET signal. The device offers both forced-PWM
and skip mode, with ultra-low-quiescent 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
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Typical Operating Characteristics section of the data
sheet for information about the converter’s typical voltage
regulation behavior versus load.
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. The high-voltage compatibility
allows EN to be connected directly to SUP.
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
Maxim Integrated │ 10
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
when the regulator output drops to below 90% of the
nominal regulated voltage.
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.
V
R1 =
R2 × OUT − 1
V
FB
where VFB = 1V (see the Electrical Characteristics).
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,
output voltage, and selected LIR then determines the
inductor value as follows:
L=
VOUT × ( VSUP − VOUT )
VSUP × f SW × I OUT × LIR
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
Setting the Output Voltage
The device’s adjustable output-voltage version (see the
Selector Guide for more details) allows the user to set
the output to any voltage between 1V and 10V. Connect
a resistive divider from output (VOUT) to FB to AGND to
set the output voltage (Figure 1). Select R2 (FB to AGND
resistor) less than or equal to 100kΩ. Calculate R1 (VOUT
to FB resistor) with the following equation:
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VOUT
R1
MAX77596
FB
R2
Figure 1. Adjustable Output-Voltage Setting
Table 1. Inductor Values for 300mA
Output Current
VSUP/VOUT (V)
INDUCTOR (µH) ILOAD = 300mA
14V/5V
14V/3.3V
10µH (typ) 10µH (typ)
22µH (max) 22µH (max)
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.
Maxim Integrated │ 11
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
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
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:
www.maximintegrated.com
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.
PCB Layout Guidelines
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 │ 12
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
Typical Application Circuits
VBAT
CIN1
4.7µF
MAX77596
SUP
BST
CIN2
0.1µF
LX
CBST
0.1µF
L
10µH
NH
MODE
VOUT
3.3V/5V
OUT
EN
NL
BIAS
RESET
AGND
COUT
22µF
CL
1µF
PGND
Figure 2. MAX77596ETBA+/MAX77596ETBB+, Fixed Output Voltage (3.3V/5V), 10-Pin TDFN
VBAT
CIN1
4.7µF
MAX77596
SUP
BST
CIN2
0.1µF
LX
CBST
0.1µF
NH
MODE
L
10µH
VOUT
1V–10V
RTOP
VARIES
COUT
22µF
FB
EN
NL
RESET
AGND
BIAS
CL
1µF
RBOT
50kΩ
PGND
Figure 3. MAX77596ETBC+, Variable Output Voltage, 10-Pin TDFN
www.maximintegrated.com
Maxim Integrated │ 13
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
Ordering Information
PART
VOUT
PIN-PACKAGE
MAX77596ETBA+
Fixed 5V
10 TDFN-EP*
MAX77596ETBB+
Fixed 3.3V
10 TDFN-EP*
MAX77596ETBC+
Adjustable
10 TDFN-EP*
*EP = Exposed pad.
+Denotes a lead(Pb)-free/RoHS-compliant package.
www.maximintegrated.com
Maxim Integrated │ 14
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
Package Information
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 TYPE
PACKAGE CODE
OUTLINE NO.
LAND PATTERN NO.
10 TDFN
T102A2+1C
21-100013
—
www.maximintegrated.com
Maxim Integrated │ 15
MAX77596
24V, 300mA, Buck Converter with 1.1µA IQ
Revision History
REVISION
NUMBER
REVISION
DATE
0
10/15
Initial release
3/16
Updated General Description, Benefits and Features, Electrical Characteristics,
Typical Operating Characteristics, Block Diagram, Detailed Description, Figure 2
caption, Figure 3 , and Ordering Information
1
PAGES
CHANGED
DESCRIPTION
—
1, 4–7, 9,
10, 13, 14
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.
© 2016 Maxim Integrated Products, Inc. │ 16
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