MAX38888ATD+ [MAXIM]
Switching Regulator,;
| 型号： | MAX38888ATD+ |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Switching Regulator, 开关 |
| 文件： | 总13页 (文件大小：756K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Click here for production status of specific part numbers.
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
General Description
Benefits and Features
The MAX38888 is a storage capacitor or capacitor bank
backup regulator designed to efficiently transfer power
between a storage element and a system supply rail in
reversible buck and boost operations using the same
inductor.
When the main supply is present and above the
minimum system supply voltage, the regulator operates
in buck mode and charges the storage element at up to
500mA peak inductor current. Once the storage element
is charged, the circuit draws only 2.5µA of current while
it maintains the super capacitor or other storage element
in its ready state. When the main supply is removed,
the regulator operates in boost mode and prevents the
system from dropping below the minimum operating voltage,
discharging the storage element at up to 2.5A peak
inductor current.
● 2.5V to 5V System Output Voltage
● 0.8V to 4.5V Cap Voltage Range
● Up to 2.5A Peak Inductor Discharge Current
● Programmable Voltage and Current Thresholds
● ±2% Threshold Accuracy
● Up to 95% Efficiency, Charge or Discharge
● 2.5µA Ready Quiescent Current
● Small Solution Size
● 3mm x 3mm x 0.75mm TDFN Package
Ordering Information appears at end of data sheet.
The MAX38888 is externally programmable for minimum
and maximum voltage of the storage element, such as
super capacitor, minimum system voltage, and maximum
charge and discharge currents. The internal DC/DC
converter requires only a 1µH inductor.
Applications
● Handheld Industrial Equipment
● Portable Computers
● Portable Devices with a Removable Battery
Typical Application Circuit
CHARGE
DISCHARGE
L1
1µH
V
V
SYS
SYSTEM LOAD
3V (MIN)
SC
LX
CAP
SYS
FBS
2.7V (MAX)
1.5V (MIN)
10F
SUPER
CAP
R3
1.8M
R7
1M
R8
1M
R6
2.49M
MAIN
BATTERY
C2
C1
MAX38888
22µF
22µF
(REMOVEABLE)
FBCL
R2
402k
BACKUP
READY
BKUPB
RDY
FBCH
EN
ENABLE
INPUT
ISET
GND
R1
499k
R4
20k
R5
499k
19-100369; Rev 2; 10/18
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Absolute Maximum Ratings
CAP, EN, SYS, LX, BKUPB, RDY to GND..............-0.3V to +6V
FBCH, FBCL to GND ................................. -0.3V to CAP + 0.3V
FBS, ISET to GND ..................................... -0.3V to SYS + 0.3V
PGND to GND......................................................-0.3V to +0.3V
Operating Temperature Range......................... -40°C to +125°C
Storage Temperature Range............................ -65°C to +150°C
Maximum Junction Temperature .....................................+150°C
Lead Temperature (soldering, 10 seconds).....................+300°C
Continuous Power Dissipation (T = +70°C, TDFN,
LX RMS Current..........................................................±2.0A
A
RMS
derate 24.4mW/°C above +70°C)...........................1951.2mW
Output Short-Circuit Duration....................................Continuous
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
TDFN
Package Code
T1433+2C
21-0137
90-0063
Outline Number
Land Pattern Number
Thermal Resistance, Four-Layer Board:
Junction to Ambient (θ
)
41°C/W
8°C/W
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.
Maxim Integrated
│ 2
www.maximintegrated.com
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Electrical Characteristics
(V
= 3.7V, V
= 2.7V, T = -40°C to +125°C (typical values at T = 25°C), circuit of Figure 1, unless otherwise specified.)
SYS
CAP
J
J
PARAMETER
SYMBOL
CONDITIONS
MIN
2.5
TYP
MAX
5
UNITS
SYS Voltage Range
CAP Voltage Range
V
V
V
VSYS
V
0.8
4.5
1
VSC
EN = 0V, T = 25°C
0.01
0.1
A
SYS Shutdown Current
I
μA
SYS_SD
EN = 0V
SYS Charging Supply
Current
I
V
= 0.6V, V
= V = 0.485V
FBCL
1.5
mA
SYS_CHG
FBS
FBCH
V
T
= V
= 25°C
= V
= 0.515V,
FBS
FBCH
FBCL
35
35
65
SYS Backup Supply
Current
I
μA
A
SYS_BUP
V
V
= V
= V
= 0.515V
FBS
FBCH
FBCL
= 0.6V, V
= V
=
FBS
FBCH
FBCL
FBCL
2.5
5
1
SYS Ready Supply
Current
0.515V, T = 25°C
A
I
μA
μA
SYS_RDY
V
= 0.6V, V
= V
= 0.515V
2.5
0.01
0.1
FBS
FBCH
EN = 0V, T = 25°C
A
CAP Shutdown Current
I
CAP_SD
EN = 0V
UVLO Threshold
V
V
falling, 100mV typical hysteresis
1.7
1.8
1.9
V
V
UVLOF
VSYS
FBS Backup Voltage
V
FBS rising, when discharging stops
-2%
0.5
+2%
FBS
V
Above FBS Backup Voltage, when charging
begins, 30mV typical hysteresis
TH_FBS
_CHG
FBS Charging Threshold
FBCH Threshold
25
60
0.5
95
mV
V
FBCH rising, when charging stops,
25mV typical hysteresis
V
-2%
+2%
TH_FBCH
FBCL falling, when preserve mode starts,
25mV typical hysteresis
FBCL Threshold
V
-3.5%
225
0.475
+3.5%
V
TH_FBCL
V
When LX stops switching, EN falling
EN rising
600
660
IL
EN Threshold
mV
V
925
100
IH
ISET Resistor Range
R
Guaranteed by LX Peak Current Limits
20
kΩ
ISET
Circuit of Figure 1, V
= 2V,
CAP
2.0
2.5
0.50
500
100
3.0
V
= 2.9V, R
= 20kΩ
SYS
ISET
LX Peak Backup Current
Limit (Note 1)
I
A
DCHG
Circuit of Figure 1, V
= 2V,
CAP
V
= 2.9V, R
= 100kΩ
SYS
ISET
Circuit of Figure 1, V
= 3.7V,
SYS
400
-0.1
600
0.1
V
= 2V, R
= 20kΩ
CAP
ISET
LX Peak Charge Current
Limit (Note 1)
ICHG
mA
Circuit of Figure 1, V
= 3.7V,
SYS
V
V
V
= 2V, R
= 100kΩ
CAP
ISET
= 0.5V, T = 25°C
A
0.001
0.01
FBS/FBCH/FBCL
FBS/FBCH/FBCL
FBS/FBCH/FBCL Input
Bias Current
I
FBS/FBCH/
FBCL
μA
= 0.5V
Maxim Integrated
│ 3
www.maximintegrated.com
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Electrical Characteristics (continued)
(V
= 3.7V, V
= 2.7V, T = -40°C to +125°C (typical values at T = 25°C), circuit of Figure 1, unless otherwise specified.)
SYS
CAP
J
J
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
0.001
0.01
2
MAX
UNITS
0V < V
0V < V
< 5.5V, T = 25°C
A
-0.1
0.1
EN
EN Input Leakage Current
I
μA
EN
< 5.5V
EN
LX Switching Frequency
f
Delivering maximum current from CAP
MHz
SW
LX Low-Side FET
Resistance
R
V
= 3V, LX switched to GND
= 3V, LX switched to SYS
50
80
100
160
1
mΩ
LOW
SYS
LX High-Side FET
Resistance
R
V
V
mΩ
μA
HIGH
SYS
= 0V, V
= 5V, V = 0V/5V,
LX
EN
SYS
-1
T
= 25°C
A
LX Leakage Current
I
LX_LKG
V
= 0V, V
= 5V, V = 0V/5V
0.1
400
100
EN
SYS
LX
Maximum On-Time
t
Backup Mode, V
Backup Mode, V
= 0.485V
= 0.485V
320
80
480
120
ns
ns
ON
FBS
FBS
Minimum Off-Time
t
OFF
Overtemperature
Lockout Threshold
T
T rising, 15°C typical hysteresis
165
50
°C
OTLO
J
High-Side FET
Zero-Crossing (Note 1)
Circuit of Figure 1, V
= 2V,
CAP
I
25
75
mA
mA
ZXP
V
= 2.9V
SYS
Low-Side FET
Zero-Crossing (Note 1)
Circuit of Figure 1, V
= 3.7V,
SYS
I
25
-1
50
75
1
ZXN
V
V
V
V
= 2V
CAP
= 0V, V
= 0V, V
= 5V, T = 25°C
A
EN
EN
BKUPB
BKUPB Leakage Current
I
μA
BKUPB
= 5V
0.1
BKUPB
BKUPB Output Voltage
Low
= 0.48V, V
= 2mA
= V
= 0.515V,
FBS
FBCH
FBCL
V
0.4
1
V
BKUPB_L
I
SINK
V
V
V
= 0.54V, V
= 0.54V, V
= 5V, T = 25°C
A
-1
FBCH
RDY
RDY Leakage Current
I
μA
RDY
= 5V
0.1
FBCH
RDY
RDY Output Voltage Low
V
= 0V, I = 2mA
SINK
0.4
V
RDY_L
EN
Note 1: DC measurement, actual zero-crossing and peak current accuracy in circuit will be affected by the propagation delay time.
Maxim Integrated
│ 4
www.maximintegrated.com
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Typical Operating Characteristics
(MAX38888, V
= 3.6V, V
= 2.0V, C1 = 22µF, C2 = 22µF T = +25°C, unless otherwise noted.)
SYS
CAP , A
CAP PIN SHUTDOWN CURRENT
SYS BACKUP SUPPLY CURRENT
SYS PIN SHUTDOWN CURRENT
toc02
toc01
toc03
70
60
50
40
30
20
10
0
EN = 0V
VCAP = 2.7V
EN = 0V
VSYS = 3.6V
V
= V
= V = 0.515V
FBCL
FBS
FBCH
1000
100
10
1000
100
10
1
1
-40
10
60
110
-40 -20
0
20 40 60 80 100 120
-40
10
60
110
TEMPERATURE (ºC)
TEMPERATURE (ºC)
TEMPERATURE (ºC)
SWITCHING WAVEFORM
WHILE CHARGING
SYS READY SUPPLY CURRENT
toc04
toc05
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
V
= 0.54V, V
FBCH
= V = 0.515V
FBCL
FBS
VSYS
2V/div
2V/div
VCAP
500mA/div
IL
2V/div
VLX
-40 -20
0
20 40 60 80 100 120
2µs/div
SYS = 3.6V, VCAP = 0V
TEMPERATURE (ºC)
V
SWITCHING WAVEFORM HEAVY LOAD
POWER-UP
toc06
toc07
2V/div
2V/div
VSYS
VCAP
VSYS
1V/div
2V/div
2V/div
3V/div
1A/div
VCAP
EN
2V/div
VLX
VLX
IL
400µs/div
SYS = 3.6V, VCAP = 0V
1µs/div
SYS = 3.6V
V
V
Maxim Integrated
│ 5
www.maximintegrated.com
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Typical Operating Characteristics (continued)
(MAX38888, V
= 3.6V, V
= 2.0V, C1 = 22µF, C2 = 22µF T = +25°C, unless otherwise noted.)
SYS
CAP , A
EFFICIENCY DURING BOOST MODE
POWER-DOWN
EFFICIENCYDURING BUCK MODE
toc09
toc08
100
95
90
85
80
75
70
toc10
94
92
90
88
86
84
82
80
2.5V TO 4.2V
2.5V TO 3V
VSYS = 3.3V, VCAP = 2V
2V/div
VSYS
1.5V TO 4.2V
1.5V TO 3V
2V/div
2V/div
VCAP
EN
2V/div
VLX
1µs/div
SYS = 3.6V, VCAP = 2V
0
500
1000
ISYS (mA)
1500
0
50
100
150
V
ICAP(mA)
LOAD REGULATION DURING BOOST
ISYS MAX vs VCAP
toc12
toc11
1200
3.5
3% REGULATION VSYS
1000
800
600
400
200
0
3.0
2.5
2.0
1.5
1.0
VSYS = 3V
VCAP = 2.5V
VCAP = 1.5V
VSYS = 3V
3% REGULATION
VSYS = 4.2V
0.5
1
1.5
2
2.5
1
10
100
ISYS (mA)
1000
VCAP (V)
VSYS TRANSITION DURING BACKUP
toc13
2V/div
BKUPB
1V/div
800mV/div
VSYS
VCAP
5ms/div
VSYS = 3.3V to 3V DURING BACKUP
Maxim Integrated
│ 6
www.maximintegrated.com
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Pin Configuration
TOP VIEW
14 13 12 11 10
9
8
MAX38888
+
1
2
3
4
5
6
7
TDFN
(3mm x 3mm)
Pin Description
PIN
NAME
SYS
NC
FUNCTION
System Supply Rail. Connect to a system supply rail or removable battery between 2.5V and 5V and
bypass with a 22µF capacitor to GND.
1
2
No Connect.
Open-Drain Backup Indicator. BKUPB is held low when the part is in backup mode i.e. when
FBS < 0.5V and FBCL > 0.5V. BKUPB is released High when FBCL < 0.475V or FBS > 0.56V.
Connect to external pullup resistor.
3
BKUPB
Open-Drain Supercap Ready Indicator. RDY goes high when the supercap is fully charged (i.e., FBCH >
0.5V). RDY is pulled low when FBCL < 0.475V. Connect to an external pullup resistor.
4
5
RDY
ISET
Charge/Discharge Current Input. The peak discharge current is set by 50kV/R
charging current is 1/5 the discharging current.
while the peak
ISET
SYS Feedback. Connect to the center point of a resistor divider from SYS to GND.
6
7
8
FBS
GND
FBCL
SYS will boost to 0.5V x (1 + R
/R
) when V
< 0.5V.
FBS
STop SBot
Analog Ground.
CAP Feedback. Connect to the upper point of a resistor divider from CAP to GND.
Part enters preserve mode when V < 0.475V.
FBCL
CAP Feedback. Connect to the lower point of a resistor divider from CAP to GND.
CAP will charge to 0.5V x (1 + R /R ) when V > 0.56V.
9
FBCH
EN
CTop CBot
FBS
Enable Input. Force this pin high to enable the regulator or force pin low to disable the part and
enter shutdown. If not driven, tie it to the SYS rail.
10
11
12
CAP
LX
Super Cap. Connect to a super cap rated between 0.8V to 5V with a maximum voltage less than V
.
SYS
Inductor Switching Node. Connect a 1.0µH to 4.7uH inductor from LX to CAP.
13
NC
No Connect.
14, EP
PGND
Power Ground.
Maxim Integrated
│ 7
www.maximintegrated.com
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Functional Diagrams
CAP
SYS
BIAS
EN
LX
DRIVERS
CONTROL
ISET
PGND
RDY
BKUPB
MAX38888
FBS
MODE
SELECT
FBCH
FBCL
GND
Maxim Integrated
│ 8
www.maximintegrated.com
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Application Circuit
Detailed Description
The typical application of the MAX38888 is shown in
Figure 1.
The MAX38888 is a flexible storage capacitor or capaci-
tor bank backup regulator efficiently transferring power
between a storage element and a system supply rail.
Super Capacitor Voltage Configuration
When the main supply is present and its voltage above
the minimum system supply voltage, the regulator
operates in the charging mode of operation and charges
the storage element at up to 500mA peak inductor
current. Once the storage element is charged, the RDY
flag will assert and the circuit will draw only 2.5µA of current
while maintaining the storage element in its ready state.
The maximum super capacitor voltage is set using a resis-
tor divider from CAP to FBCH to GND. Recommended
value for R2 is 499kΩ. Because resistor tolerance will
have direct effect on voltage accuracy, these resistors
should have 1% accuracy or better.
R2 + R3 = R1 x ((V /0.5) -1)
CAP MAX
V
halts charging when V
reaches 0.5V. The
FBCH
CAP
When the main supply is removed, the regulator prevents
the system from dropping below the minimum operating
maximum super capacitor voltage is where the super
capacitor will remain after it is completely charged and
ready for backup.
voltage, boosting V
by discharging the storage
SYS
element at up to 2.5A peak inductor current. During this
backup mode of operation, the MAX38888 utilizes a
fixed on-time, current-limited, pulse-frequency-modulation
(PFM) control scheme. Once MAX38888 is in the backup
mode, the BKUPB flag is asserted.
The minimum super capacitor discharge voltage is set
using a resistor divider from CAP to FBCL to GND.
R3 = (R1 + R2) x ((V
/0.5) -1)
CAP MIN
FBCL prevents the super capacitor from further discharge
when V reaches 0.475V during a backup event in
order to preserve the remaining capacity for keeping alive
a real-time clock, memory, or other low-level function. In
this preserve mode, the IC disconnects all circuitry from
the super capacitor and draws 2.5µA current from it.
The external pins allow a wide range of system and
storage element, such as super capacitor voltage
settings, as well as charging and discharging peak inductor
current settings.
FBCL
The MAX38888 implements a true shutdown feature
disconnecting V
from V
as well as protecting
SYS
CAP
against a SYS short or if V
> V
.
CAP
SYS
CHARGE
DISCHARGE
L1
1µH
V
V
SYS
SYSTEM LOAD
3V (MIN)
SC
LX
CAP
SYS
FBS
2.7V (MAX)
1.5V (MIN)
10F
SUPER
CAP
R3
1.8M
R7
1M
R8
1M
R6
2.49M
MAIN
BATTERY
C2
C1
MAX38888
22µF
22µF
(REMOVEABLE)
FBCL
R2
402k
BACKUP
READY
BKUPB
RDY
FBCH
EN
ENABLE
INPUT
ISET
GND
R1
499k
R4
20k
R5
499k
Figure 1. Typical Application
Maxim Integrated
│ 9
www.maximintegrated.com
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
In applications where SYS voltage needs to be boosted to
higher levels, selecting V min has to take into account
to the maximum voltage set by FBCH and be ready for
backup. When the main battery is removed, V drops
CAP
FBS
duty cycle limitation of the boosting phase which is 80%.
to 0.5V and the SYS pin is regulated to the programmed
minimum voltage with up to 2A of CAP current.
MAX38888 detects when V falls below V . The
SYS
CAP
device will not enable if V
is below V
. Raising
SYS
CAP
Charge/Discharge Current Configuration
The peak inductor discharge current is set by placing a
V
SYS
above the backup threshold re-initiates charging
and backup.
resistor from ISET to GND. The values of R
is calculated by following formula:
resistor
ISET
System Voltage Configuration
The minimum system voltage is set using a resistor divider
from SYS to FBS to GND. Recommended value for R5 is
499kΩ. Because resistor tolerance will have direct effect
on voltage accuracy, these resistors should have 1%
accuracy or better.
I
= 2.5A x (20kΩ/R
)
ISET
DISCHARGE
The super capacitor charging current is internally set to
1/5 of the discharge current.
I
= 0.5A x (20kΩ/R
)
ISET
CHARGE
Value of
R
between 20kΩ and 100kΩ is recom-
ISET
R6 = R5 x ((V
/0.5) -1)
SYS MIN
mended to ensure accurate current compliance.
When V
is above 0.56V, the DC/DC regulator will draw
FBS
power from the SYS pin to charge the super capacitor
4V
3.36V
3.18V
VSYS
3V
0V
2.7V
1.42V
VCAP
0V
BKUPB
FBS ™" " 0.5V
0V
RDY
FBCH Ð""0.5V
FBCL < 0.475V
CHARGE
LOW CURRENT
BACKUP
PRESERVE
Figure 2. System Waveforms
Maxim Integrated
│ 10
www.maximintegrated.com
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
super capacitor where smaller current will be pulled out
System Waveforms
of the super capacitor near its maximum V
voltage.
CAP
The waveforms in Figure 2 represent system behavior of
However, current drawn from the super capacitor will
increase as it discharges to maintain constant power at
the load. The amount of energy required in the backup
mode will be the product of the constant back up power
MAX38888 in the Typical Application Circuits.
Applications Information
Capacitor Selection
and time defined as backup time, t
.
BACKUP
Capacitors at SYS and CAP pins reduce current
peaks and increase efficiency. Ceramic capacitors are
recommended because they have the lowest equivalent
series resistance (ESR), smallest size, and lowest cost.
Choose an acceptable dielectric such as X5R or X7R.
Due to ceramic capacitors' capacitance derating with DC
bias standard 22µF ceramic capacitors are recommended
at both pins for most applications.
The amount of energy available in the super capacitor is
calculated using the following formula:
2
2
E = 1/2 x C
x (V
- V
) (J)
SCAP
CAPMAX
CAPMIN
The amount of energy required to complete the backup
equals to:
E = V
x I
x t
) (J)
SYS
SYS
BACKUP
where, I
will be the system load during backup.
SYS
Super Capacitor Selection
When the power source supplying the V
Since energy required at the system side during the
backup event comes from available energy in the super
capacitor, and assuming conversion efficiency η, and
voltage is
SYS
removed, power to the output is provided by MAX38888
operating in the back-up or boost mode of operation using
the super capacitor as its source. In order to ensure the
supply voltage stays in regulation, the amount of power
the super capacitor can deliver at its minimal voltage
should be greater than that required by the system.
MAX38888 will present a constant power load to the
given t
, the required C
will be determined
BACKUP
SCAP
by the following equation:
2
C
= (2 x V
2
x I
x t
)/[(V
CAPMAX
–
SCAP
SYS
) x η] (F)
SYS
BACKUP
V
CAPMIN
VOLTAGE (V)
VSYS
4
3.36
3
VCAP
2.7
LOW IQ
1.5
0
IDLE
(NO SWITCHING)
BACKUP
(BOOST)
PRESERVE
(LOW CURRENT)
CHARGING CAP
(BUCK)
Figure 3. Charging/Discharging Waveforms
Maxim Integrated
│
11
www.maximintegrated.com
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
For example, in Figure 1 (Application Circuit), minimum
value of the super capacitor required for 1s backup time,
assuming 200mA system load and average efficiency of
93%, will be:
Enabling Device
MAX3888 has dedicated enable pin. The pin can either
be driven by a digital signal or pulled up or strapped to
the SYS rail.
2
2
C
≥ (2 x 3.0V x 0.2A x 1s)/[((2.7V) – (1.5V) ) x 0.93]
SCAP
PCB Layout Guidelines
= 256mF
Minimize trace lengths to reduce parasitic capacitance,
inductance and resistance, and radiated noise. Keep the
main power path from SYS, LX, CAP, and PGND as tight
and short as possible. Minimize the surface area used for
LX since this is the noisiest node. The trace between the
feedback resistor dividers should be as short as possible
and should be isolated from the noisy power path. Refer
to the EV kit layout for best practices.
Inductor Selection
MAX38888 works with 1µH inductor in most applications.
In applications where lower peak currents are desired,
larger inductance may be used in order to reduce the
ripple. Recommended inductance range is from 1µH to
4.7µH. Select 4.7µH for higher RISET value [100k]. 1µH
is not supported for 100k RISET value.
The PCB layout is important for robust thermal design.
The junction to ambient thermal resistance of the package
greatly depends on the PCB type, layout, and pad
connections. Using thick PCB copper and having the
SYS, LX, CAP, and PGND copper pours will enhance the
thermal performance. The TDFN package has a large
thermal pad under the package which creates excellent
thermal path to PCB. This pad is electrically connected
to PGND. Its PCB pad should have multiple thermal vias
connecting the pad to internal PGND plane. Thermal vias
should either be capped or have small diameter to
minimize solder wicking and voids.
Status Flags
MAX38888 has two dedicated pins to report the device
status to the host processor. Ready output (RDY) will
be high when the super capacitor is fully charged
(i.e., FBCH > 0.5V). RDY is pulled low when FBCL
< 0.475V. The other status flag is the Backup Output
(BKUPB), which will be held low when the part is in the
backup mode (i.e., when FBS < 0.5V and FBCL > 0.5V).
BKUPB is released high when FBCL < 0.475V or FBS >
0.56V. Both output pins are open-drain type and require
external pullup resistors. Recommended values for the
pullup resistors are 1MΩ. The pins should be pulled up
to the SYS rail.
Ordering Information
PART NUMBER
TEMP RANGE
PIN-PACKAGE
FEATURES
MAX38888ATD+
-40°C to +125°C
14 TDFN
Enable Input, Selectable Voltages and Currents
+ Denotes a lead(Pb)-free/RoHS-compliant package.
T Denotes tape-and-reel.
Maxim Integrated
│ 12
www.maximintegrated.com
MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Revision History
REVISION REVISION
PAGES
DESCRIPTION
CHANGED
NUMBER
DATE
0
1
6/18
Initial release
—
7/18
Updated General Description and Benefits and Features
1
Update General Description, Benefits and Features section, Electrical Characteristics
table, Typical Operating Characteristics, Detailed Description
10/18
2
1, 3–6, 9–12
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.
2018 Maxim Integrated Products, Inc.
│ 13
相关型号：
MAX388CPN+
Single-Ended Multiplexer, 1 Func, 8 Channel, CMOS, PDIP18, ROHS COMPLIANT, PLASTIC, DIP-18
MAXIM
MAX388CWG+T
Single-Ended Multiplexer, 1 Func, 8 Channel, CMOS, PDSO24, ROHS COMPLIANT, SOIC-24
MAXIM
MAX388EPN+
Single-Ended Multiplexer, 1 Func, 8 Channel, CMOS, PDIP18, ROHS COMPLIANT, PLASTIC, DIP-18
MAXIM
©2020 ICPDF网 联系我们和版权申明