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MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
General Description
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.
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
Benefits and Features
● 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.
VSC
2.7V (MAX)
1.5V (MI N)
C HAR GE
D ISCH ARGE
L1
10F
SUPER
CAP
C2
22µF
R3
1.8M
R2
40 2k
EN ABLE
IN PUT
R1
49 9k
1µH
CAP
LX
SYS
MAX38888
FBCL
FBS
FBCH
EN
BKUPB
R DY
GND ISET
VSY S
SYSTEM LOAD
R7 R8 R6 C1 MAI N 3V (MI N)
1M
1M
2.49M
22µF
BATTERY
(R EMOVEABL E)
BAC KUP
R EADY
R4 R5
20k 499k
19-100369; Rev 2; 10/18

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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
Continuous Power Dissipation (TA = +70°C, TDFN,
derate 24.4mW/°C above +70°C)............................1951.2mW
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
LX RMS Current...........................................................±2.0ARMS
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
Outline Number
Land Pattern Number
Thermal Resistance, Four-Layer Board:
Junction to Ambient (θJA)
Junction to Case (θJC)
T1433+2C
21-0137
90-0063
41°C/W
8°C/W
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board.
For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.
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Maxim Integrated 2

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MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Electrical Characteristics
(VSYS = 3.7V, VCAP = 2.7V, TJ = -40°C to +125°C (typical values at TJ = 25°C), circuit of Figure 1, unless otherwise specified.)
PARAMETER
SYS Voltage Range
CAP Voltage Range
SYS Shutdown Current
SYS Charging Supply
Current
SYS Backup Supply
Current
SYS Ready Supply
Current
CAP Shutdown Current
UVLO Threshold
FBS Backup Voltage
FBS Charging Threshold
FBCH Threshold
FBCL Threshold
EN Threshold
ISET Resistor Range
LX Peak Backup Current
Limit (Note 1)
LX Peak Charge Current
Limit (Note 1)
FBS/FBCH/FBCL Input
Bias Current
SYMBOL
VVSYS
VVSC
ISYS_SD
ISYS_CHG
ISYS_BUP
ISYS_RDY
ICAP_SD
VUVLOF
VFBS
VTH_FBS
_CHG
VTH_FBCH
VTH_FBCL
VIL
VIH
RISET
IDCHG
ICHG
IFBS/FBCH/
FBCL
CONDITIONS
EN = 0V, TA = 25°C
EN = 0V
MIN
2.5
0.8
VFBS = 0.6V, VFBCH = VFBCL = 0.485V
VFBS = VFBCH = VFBCL = 0.515V,
TA = 25°C
VFBS = VFBCH = VFBCL = 0.515V
VFBS = 0.6V, VFBCH = VFBCL =
0.515V, TA = 25°C
VFBS = 0.6V, VFBCH = VFBCL = 0.515V
EN = 0V, TA = 25°C
EN = 0V
VVSYS falling, 100mV typical hysteresis
FBS rising, when discharging stops
Above FBS Backup Voltage, when charging
begins, 30mV typical hysteresis
FBCH rising, when charging stops,
25mV typical hysteresis
FBCL falling, when preserve mode starts,
25mV typical hysteresis
When LX stops switching, EN falling
EN rising
Guaranteed by LX Peak Current Limits
Circuit of Figure 1, VCAP = 2V,
VSYS = 2.9V, RISET = 20kΩ
Circuit of Figure 1, VCAP = 2V,
VSYS = 2.9V, RISET = 100kΩ
Circuit of Figure 1, VSYS = 3.7V,
VCAP = 2V, RISET = 20kΩ
Circuit of Figure 1, VSYS = 3.7V,
VCAP = 2V, RISET = 100kΩ
VFBS/FBCH/FBCL = 0.5V, TA = 25°C
VFBS/FBCH/FBCL = 0.5V
1.7
-2%
25
-2%
-3.5%
225
20
2.0
400
-0.1
TYP
0.01
0.1
1.5
35
35
2.5
2.5
0.01
0.1
1.8
0.5
60
0.5
0.475
600
660
2.5
0.50
500
100
0.001
0.01
MAX
5
4.5
1
65
5
1
1.9
+2%
95
+2%
+3.5%
925
100
3.0
600
0.1
UNITS
V
V
μA
mA
μA
μA
μA
V
V
mV
V
V
mV
A
mA
μA
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Maxim Integrated 3

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MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Electrical Characteristics (continued)
(VSYS = 3.7V, VCAP = 2.7V, TJ = -40°C to +125°C (typical values at TJ = 25°C), circuit of Figure 1, unless otherwise specified.)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX UNITS
EN Input Leakage Current
LX Switching Frequency
LX Low-Side FET
Resistance
IEN
fSW
RLOW
0V < VEN < 5.5V, TA = 25°C
0V < VEN < 5.5V
Delivering maximum current from CAP
VSYS = 3V, LX switched to GND
-0.1 0.001 0.1
0.01
2
50 100
μA
MHz
LX High-Side FET
Resistance
RHIGH
VSYS = 3V, LX switched to SYS
80 160
LX Leakage Current
Maximum On-Time
Minimum Off-Time
Overtemperature
Lockout Threshold
ILX_­LKG
tON
tOFF
TOTLO
VEN = 0V, VSYS = 5V, VLX = 0V/5V,
TA = 25°C
VEN = 0V, VSYS = 5V, VLX = 0V/5V
Backup Mode, VFBS = 0.485V
Backup Mode, VFBS = 0.485V
TJ rising, 15°C typical hysteresis
-1 1
0.1
320 400 480
80 100 120
165
μA
ns
ns
°C
High-Side FET
Zero-Crossing (Note 1)
IZXP
Circuit of Figure 1, VCAP = 2V,
VSYS = 2.9V
25 50 75
mA
Low-Side FET
Zero-Crossing (Note 1)
IZXN
Circuit of Figure 1, VSYS = 3.7V,
VCAP = 2V
25 50 75
mA
BKUPB Leakage Current
IBKUPB
VEN = 0V, VBKUPB = 5V, TA = 25°C
VEN = 0V, VBKUPB = 5V
-1 1
0.1
μA
BKUPB Output Voltage
Low
VBKUPB_L
VFBS = 0.48V, VFBCH = VFBCL = 0.515V,
ISINK = 2mA
0.4 V
RDY Leakage Current
IRDY
VFBCH = 0.54V, VRDY = 5V, TA = 25°C
VFBCH = 0.54V, VRDY = 5V
-1 1
0.1
μA
RDY Output Voltage Low
VRDY_L
VEN = 0V, ISINK = 2mA
0.4 V
Note 1: DC measurement, actual zero-crossing and peak current accuracy in circuit will be affected by the propagation delay time.
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Maxim Integrated 4

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MAX38888
2.5V–5.0V, 0.5A/2.5A Reversible Buck/Boost
Regulator for Backup Power Applications
Typical Operating Characteristics
(MAX38888, VSYS = 3.6V, VCAP = 2.0V, C1 = 22µF, C2 = 22µF, TA = +25°C, unless otherwise noted.)
SYS PIN SHUTDOWN CURRENT
toc01
EN = 0V
1000 VSYS = 3.6V
100
10
1
-40 10 60 110
TEMPERATURE (ºC)
CAP PIN SHUTDOWN CURRENT
toc02
EN = 0V
1000 VCAP = 2.7V
100
10
1
-40 10 60 110
TEMPERATURE (ºC)
SYS READY SUPPLY CURRENT
4.5 toc04
4.0 VFBS = 0.54V, VFBCH = VFBCL = 0.515V
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-40 -20 0
20 40 60 80 100 120
TEMPERATURE (ºC)
SWITCHING WAVEFORM HEAVY LOAD
toc06
VSYS
VCAP
VLX
IL
1µs/div
VSYS = 3.6V
2V/div
2V/div
3V/div
1A/div
VSYS
VCAP
IL
VLX
VSYS
VCAP
EN
VLX
SYS BACKUP SUPPLY CURRENT
70 toc03
VFBS = VFBCH = VFBCL = 0.515V
60
50
40
30
20
10
0
-40 -20
0 20 40 60 80 100 120
TEMPERATURE (ºC)
SWITCHING WAVEFORM
WHILE CHARGING
toc05
2V/div
2V/div
500mA/div
2µs/div
VSYS = 3.6V, VCAP = 0V
2V/div
POWER-UP
toc07
2V/div
1V/div
2V/div
2V/div
400µs/div
VSYS = 3.6V, VCAP = 0V
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Maxim Integrated 5