19-2902; Rev 0; 7/03
SOT23 Dual-Input USB/AC Adapter 1-Cell Li+
Battery Chargers
General Description
The MAX1551/MAX1555 charge a single-cell lithium-ion
(Li+) battery from both USB* and AC adapter sources.
They operate with no external FETs or diodes, and
accept operating input voltages up to 7V.
On-chip thermal limiting simplifies PC board layout and
allows optimum charging rate without the thermal limits
imposed by worst-case battery and input voltage. When
the MAX1551/MAX1555 thermal limits are reached, the
chargers do not shut down, but progressively reduce
charging current.
The MAX1551 includes a
POK
output to indicate when
input power is present. If either charging source is
active,
POK
goes low. The MAX1555 instead features a
CHG
output to indicate charging status.
With USB connected, but without DC power, charge cur-
rent is set to 100mA (max). This allows charging from
both powered and unpowered USB hubs with no port
communication required. When DC power is connected,
charging current is set at 280mA (typ). No input-blocking
diodes are required to prevent battery drain.
The MAX1551/MAX1555 are available in 5-pin thin SOT23
packages and operate over a -40°C to +85°C range.
o
Charge from USB or AC Adapter
o
Automatic Switchover when AC Adapter is
Plugged In
o
On-Chip Thermal Limiting Simplifies Board
Design
o
Charge Status Indicator
o
5-Pin Thin SOT23 Package
o
Protected by U.S. Patent #6,507,172
Features
MAX1551/MAX1555
Ordering Information
PART
MAX1551EZK-T
MAX1555EZK-T
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
5 Thin SOT23-5
5 Thin SOT23-5
Selector Guide
PART
MAX1551EZK
MAX1555EZK
TOP MARK
ADRT
ADRU
FEATURES
POK
Output
CHG
Output
Applications
PDAs
Wireless Appliances
Cell Phones
Digital Cameras
Pin Configuration
TOP VIEW
USB
1
5
BAT
AC ADAPTER
3.7V TO 7V
DC
Typical Operating Circuit
BAT
TO SYSTEM
LOAD
Li+
GND
2
MAX1551
(MAX1555)
4
DC
USB
3.7V TO 6V
USB
CHARGE
CONTROL
TO LOGIC RAIL
POK
3
(CHG)
LOGIC
CONTROL
POK
(CHG)
THIN SOT23
MAX1551
(MAX1555)
GND
*Protected
by U.S. Patent #6,507,172.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
SOT23 Dual-Input USB/AC Adapter 1-Cell Li+
Battery Chargers
MAX1551/MAX1555
ABSOLUTE MAXIMUM RATINGS
DC to GND......................................................................0 to +8V
DC to BAT .......................................................................0 to +7V
BAT,
CHG, POK,
USB to GND .................................-0.3V to +7V
Continuous Power Dissipation (T
A
= +70°C)
5-Pin Thin SOT23 (derate 9.1mW/°C above +70°C) ....727mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature Range ............................-40°C to +150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
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.
ELECTRICAL CHARACTERISTICS
(V
DC
= 5V, V
USB
= 0, I
BAT
= 0, C
BAT
= 1µF,
T
A
= 0°C to +85°C,
unless otherwise noted.)
PARAMETER
DC
DC Voltage Range
DC to BAT Voltage Range
DC Undervoltage Lockout
Threshold
DC Supply Current
DC to BAT On-Resistance
DC to BAT Dropout Voltage
USB
USB Voltage Range
USB Undervoltage Threshold
USB Supply Current
USB to BAT On-Resistance
USB to BAT Dropout Voltage
BAT
BAT Regulation Voltage
DC Charging Current
USB Charging Current
BAT Prequal Threshold
Prequalification Charging Current
BAT Leakage Current
POK, CHG,
AND THERMAL LIMIT
CHG
Threshold
CHG, POK
Logic-Low Output
CHG, POK
Leakage Current
Thermal-Limit Temperature
Charge current where
CHG
goes high,
I
BAT
falling, 50mA hysteresis
I
CHG
, I
POK
= 10mA
V
CHG
, V
POK
= 6V, T
A
= +25°C
Charge current reduced by 17mA/°C above this
temperature
25
50
150
0.001
+110
100
300
1
mA
mV
µA
°C
V
DC
or V
USB
= 5V
V
BAT
= 3.3V, V
USB
= 0, V
DC
= 5V
V
BAT
= 3.3V, V
DC
= 0, V
USB
= 5V
V
BAT
rising, 100mV hysteresis
V
BAT
= 2.8V
V
DC
= V
USB
= 0, V
BAT
= 4.2V
4.158
220
80
2.9
20
4.2
280
90
3
40
4.242
340
100
3.1
80
5
V
mA
mA
V
mA
µA
(Note 1)
Input rising, 430mV hysteresis, V
DC
= 0,
V
BAT
= 3V (Note 1)
V
USB
= 5V, V
DC
= 0
V
USB
= 3.7V, V
BAT
= 3.6V, V
DC
= 0
When charging stops, V
BAT
= 4V,
USB falling, 200mV hysteresis, V
DC
= 0
3.7
3.75
3.95
1.65
2
30
60
6.0
4.15
3
4
90
V
V
mA
Ω
mV
V
DC
= 3.7V, V
BAT
= 3.6V
When charging stops, V
BAT
= 4V,
DC falling, 200mV hysteresis
30
Input rising, 430mV hysteresis, V
BAT
= 3V (Note 1)
(Note 1)
3.7
0.1
3.75
3.95
1.75
1
60
7.0
6.0
4.15
3
2
90
V
V
V
mA
Ω
mV
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
SOT23 Dual-Input USB/AC Adapter 1-Cell Li+
Battery Chargers
ELECTRICAL CHARACTERISTICS
(V
DC
= 5V, V
USB
= 0, I
BAT
= 0, C
BAT
= 1µF,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
DC
DC Voltage Range
DC to BAT Voltage Range
DC Undervoltage Lockout
Threshold
DC Supply Current
DC to BAT On-Resistance
DC to BAT Dropout Voltage
USB
USB Voltage Range
USB Undervoltage Lockout
Threshold
USB Supply Current
USB to BAT On-Resistance
USB to BAT Dropout Voltage
BAT
BAT Regulation Voltage
DC Charging Current
USB Charging Current
BAT Prequal Threshold
Prequalification Charging Current
BAT Leakage Current
POK, CHG
CHG
Threshold
CHG, POK
Logic-Low Output
CHG, POK
Leakage Current
Charge current where
CHG
goes high,
I
BAT
falling, 50mA hysteresis
I
CHG
, I
POK
= 10mA
V
CHG
, V
POK
= 6V, T
A
= +25°C
25
100
300
1
mA
mV
µA
V
DC
or V
USB
= 5V
V
BAT
= 3.3V, V
USB
= 0, V
DC
= 5V
V
BAT
= 3.3V, V
DC
= 0, V
USB
= 5V
V
BAT
rising, 100mV hysteresis
V
BAT
= 2.8V
V
DC
= V
USB
= 0, V
BAT
= 4.2V
4.141
220
80
2.9
20
4.259
340
100
3.1
80
5
V
mA
mA
V
mA
µA
(Note 1)
Input rising, 430mV hysteresis, V
DC
= 0, V
BAT
= 3V
(Note 1)
V
USB
= 5V, V
DC
= 0
V
USB
= 3.7V, V
BAT
= 3.6V, V
DC
= 0
When charging stops, V
BAT
= 4V, USB falling, 200mV
hysteresis, V
DC
= 0
30
3.7
3.75
6.0
4.15
3
4
95
V
V
mA
Ω
mV
V
DC
= 3.7V, V
BAT
= 3.6V
When charging stops, V
BAT
= 4V, DC falling, 200mV
hysteresis
30
Input rising, 430mV hysteresis, V
BAT
= 3V (Note 1)
(Note 1)
3.7
0.1
3.75
7.0
6.0
4.15
3
2
95
V
V
V
mA
Ω
mV
CONDITIONS
MIN
MAX
UNITS
MAX1551/MAX1555
Note 1:
The input undervoltage lockout has 430mV of hysteresis. The charger turns on when an input rises to 3.95V (typ), and turns
off when it falls below 3.52V.
Note 2:
Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
3
SOT23 Dual-Input USB/AC Adapter 1-Cell Li+
Battery Chargers
MAX1551/MAX1555
Typical Operating Characteristics
(V
DC
= 5V, V
USB
= 0, I
BAT
= 0, C
BAT
= 1µF, T
A
= +25°C, unless otherwise noted.)
CHARGE CURRENT
vs. DC VOLTAGE HEADROOM
MAX1551/55 toc01
CHARGE CURRENT
vs. USB VOLTAGE HEADROOM
MAX1551/55 toc02
DC CHARGE CURRENT
vs. BATTERY VOLTAGE
MAX1551/55 toc03
300
250
CHARGE CURRENT (mA)
200
150
100
50
0
V
BAT
= 3.8V, V
DC
FALLING
-50
0
0.1
0.2
0.3
0.4
100
80
CHARGE CURRENT (mA)
60
40
20
0
V
DC
= 0, V
BAT
= 3.8V, V
USB
FALLING
-20
300
250
DC CHARGE CURRENT (mA)
200
150
100
50
0
-50
0.5
0
0.1
0.2
0.3
0.4
0.5
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
BATTERY VOLTAGE (V)
DC VOLTAGE HEADROOM (V
DC
- V
BAT
) (V)
USB VOLTAGE HEADROOM (V
USB
- V
BAT
) (V)
USB CHARGE CURRENT
vs. BATTERY VOLTAGE
MAX1551/55 toc04
DC CHARGE CURRENT
vs. AMBIENT TEMPERATURE
MAX1551/55 toc05
BATTERY TERMINATION VOLTAGE
vs. TEMPERATURE
BAT OPEN
BATTERY TERMINATION VOLTAGE (V)
4.21
MAx1551/55 toc06
100
80
60
40
20
0
-20
0
300
250
DC CHARGE CURRENT (mA)
THERMAL LIMIT ACTIVATED
200
150
100
50
0
V
BAT
= 3.8V, V
DC
= 5V
-50
4.22
USB CHARGE CURRENT (mA)
4.20
4.19
4.18
25
35
45
55
65
75
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
BATTERY VOLTAGE (V)
OFF-BATTERY LEAKAGE CURRENT
vs. DC INPUT VOLTAGE
OFF-BATTERY LEAKAGE CURRENT (µA)
V
DC
= 0, SWEEPING USB
0 TO 5V OR V
USB
= 0,
SWEEPING DC 0 TO 5V
V
BAT
= 4.2V
1.5
0V
1.0
0V
MAX1551/55 toc07
USB-TO-DC TRANSITION WAVEFORM
MAX1551/55 toc08
2.5
2.0
BATTERY
CURRENT
200mA/div
0A
V
USB
5V/div
0.5
V
POK
2V/div
V
DC
5V/div
400ms/div
0
0
1
2
3
4
5
DC OR USB INPUT VOLTAGE (V)
0V
4
_______________________________________________________________________________________
SOT23 Dual-Input USB/AC Adapter 1-Cell Li+
Battery Chargers
Pin Description
PIN
1
2
NAME
USB
GND
POK
3
CHG
FUNCTION
USB Port Charger Supply Input. USB draws up to 100mA to charge the battery. Decouple USB with a 1µF
ceramic capacitor to GND.
Ground
Power-OK Active-Low Open-Drain Charger Status Indicator.
POK
pulls low when either charger source is
present (MAX1551 only).
Active-Low Open-Drain Charge Status Indicator.
CHG
pulls low when the battery is charging.
CHG
goes to a
high-impedance state, indicating the battery is fully charged, when the charger is in voltage mode and
charge current falls below 50mA.
CHG
is high impedance when both input sources are low (MAX1555 only).
DC Charger Supply Input for an AC Adapter. DC draws 280mA to charge the battery. Decouple DC with a
1µF ceramic capacitor to GND.
Battery Connection. Decouple BAT with a 1µF ceramic capacitor to GND.
MAX1551/MAX1555
4
5
DC
BAT
Detailed Description
The MAX1551/MAX1555 charge a single-cell Li+ bat-
tery from both USB and AC adapter sources, enabling
portable users to forgo carrying a wall cube. These
devices operate with no external FETs or diodes, and
accept operating input voltages up to 7V.
An internal thermal control loop simplifies PC board lay-
out and allows optimum charging rate without the ther-
mal limits imposed by worst-case battery and input
voltage. When the MAX1551/MAX1555 thermal limits
are reached, the chargers do not shut down, but simply
reduce charging current by 17mA/°C above a die tem-
perature of +110°C.
With USB connected, but without DC power, the charge
current is set to 100mA (max). This allows charging
from both powered and unpowered USB hubs with no
port communication required. When DC power is con-
nected, charging current is set at 280mA (typ). The
MAX1551/MAX1555 do not feature an enable input.
Once power is connected to USB and/or DC, the
charger is on.
When input power is removed, battery leakage current
is less than 5µA. No input-blocking diodes are required
to prevent battery drain. Insert a diode at DC (the
adapter input) if protection from negative voltage inputs
(reversed-polarity adapter plugs) is required.
USB to Adapter Power Handoff
The MAX1551/MAX1555 can charge from either the
USB input or the DC input. The battery does not charge
from both sources at the same time. The MAX1551/
MAX1555 automatically detect the active input and
charge from that. If both power sources are active, the
DC input takes precedence. The switchover between
DC and USB is detailed in Table 1.
MAX1551 Power-OK (
POK
)
The MAX1551’s
POK
is an active-low, open-drain out-
put that goes low when V
DC
or V
USB
is above 3.95V.
POK
can be used as a logic output or can drive an
LED.
POK
indicates the charger is connected to input
power and is charging.
MAX1555 Charge Status (
CHG
)
The MAX1555’s
CHG
is an active-low, open-drain
charge status indicator.
CHG
pulls low when the battery
is charging (whenever USB or DC are powered) and
charge current is greater than 50mA.
CHG
indicates
when the battery is fully charged by going high imped-
ance when the charger is in voltage mode
and
charge
current falls below 50mA. Charging does not stop when
CHG
goes high.
CHG
is low in precharge mode.
Table 1. USB and DC Input Selection
V
DC
> 7V OR V
USB
> 6V
Exceeds operating input range. Not allowed. See the
Absolute Maximum Ratings
section.
V
DC
> 3.95V AND
V
USB
DON’T CARE
280mA (typ)
charging from DC
V
DC
< 3.52V AND
3.95V < V
USB
< 6V
100mA (max)
charging from USB
V
DC
AND V
USB
< 3.52V
Undervoltage lockout
(V
DC
takes precedence when both inputs are present.)
_______________________________________________________________________________________
5
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