LINEAR TECHNOLOGY LTC4160 Technical data
L DESIGN IDEAS
V
BUS
CURRENT (mA)
0
V
BUS
(V)
4.5
5.0
5.5
4.0
3.5
3.0
200
400
600100
300
500
700
V
BUS
= 4.75V
I
VBUS
= 500mA
V
OUT
= BAT = 3.8V
USB 2.0 SPECIFICATIONS
REQUIRE THAT HIGH
POWER DEVICES NOT
OPERATE IN THIS REGION
LOAD CURRENT (mA)
0
CURRENT (mA)
250
500
750
800
0
–250
–500
200
400
600
1000
V
BUS
CURRENT
BATTERY CURRENT
(CHARGING)
V
BUS
= 5V
BAT = 3.8V
5x MODE
BATTERY CURRENT
(DISCHARGING)
V
BUS
USB
USB
ON-THE-GO
3.3µH
10µF
0.1µF
3.01k 1k
CLPROG PROG
LTC4160/
LTC4160-1
SW
V
OUT
BAT
Li-Ion
+
OVGATE
OVSENS
OPTIONAL
OVERVOLTAGE
PROTECTION
SYSTEM
LOAD
6.2k
10µF
Bidirectional Power Manager Provides
Efficient Charging and Automatic USB
On-The-Go with a Single Inductor
by Sauparna Das
Introduction
Imagine that your car won’t start—the
battery is dead, the kids are getting
fussy, you’re stranded in the middle
of nowhere, and your cell phone won’t
turn on because you forgot to charge it.
What do you do now? Fortunately, you
remember that your new camera is in
the car, and it has a fully charged battery. Even better, this camera supports
USB On-The-Go using a bidirectional
power manager. You connect a USB
micro-AB cable between the cell phone
and camera and instantly start charging your phone. The phone powers up
and you’re able to call for help.
The LTC4160 is a versatile, high
efficiency power manager and battery
charger that incorporates a bidirectional switching regulator, full featured
battery charger, an ideal diode (with a
controller for an optional external ideal
diode), and an optional overvoltage
protection circuit. The bidirectional
switching regulator is able to power a
portable system and charge its battery
or provide a 5V output for USB OnThe-Go using a single inductor (Figure
1). This reduces component count and
board space, key attributes for a power
management IC in today’s feature rich
portable devices. In shutdown, the
part only draws 8µA of current, thus
maximizing battery life.
Bidirectional Switching Power
Path for USB On-The-Go
The LTC4160 contains a bidirectional
switching regulator between V
and V
V
BUS
a step down converter and provides
power to the application and battery
charger (Figure 1). The switching
regulator includes a precision average
input current limit with multiple settings. Two of the settings correspond to
the USB 100mA and 500mA limits.
The bidirectional switching
regulator is able to power a
portable system and charge
The voltage on V
ly 300mV above the battery when the
switcher is not in input current limit
and the battery voltage is above 3.3V.
This technique, known as Bat-Track
output control, provides very efficient
charging, which minimizes loss and
heat and eases thermal constraints.
For battery voltages below 3.3V, V
regulates to 3.6V when the switcher
. When power is applied to
OUT
,the switching regulator acts as
its battery or provide a 5V
output for USB On-The-Go
using a single inductor.
is approximate-
OUT
is not in input current limit. This
instant-on feature provides power to
the system even when the battery is
BUS
completely discharged.
prioritized over charging the battery. If
the combined system load and charge
current exceed the current available at
the input, the battery charger reduces
its charge current to maintain power
to the application. If the load alone
exceeds the input current limit, then
additional current is supplied by the
battery via the ideal diode(s).
the bidirectional switching regulator
steps up the voltage on V
5V on V
ing regulator is capable of delivering
at least 500mA. Power to V
from the battery via the ideal diode(s).
A precision output current limit circuit, similar to the one in step-down
mode, prevents a load on V
drawing more than 680 mA (Figure 1).
The switching regulator also features
true output disconnect which prevents
body diode conduction of the PMOS
switch. This allows V
volts during a short circuit condition
or while shut down, drawing zero current from the battery. When V
OUT
3.2V, the LTC4160 allows a portable
Power to the application is always
For USB On-The-Go applications,
to produce
. In this mode the switch-
BUS
OUT
OUT
BUS
to go to zero
BUS
OUT
comes
from
is ≥
Figure 1. The LTC4160 provides bidirectional power transfer. Left plot: V
currents vs load current when input power is available.
28
28
voltage vs V
BUS
current in On-The-Go mode. Right plot: battery and V
BUS
Linear Technology Magazine • June 2009
BUS
DESIGN IDEAS L
TO µC
15
16
6
7
ENCHARGER
ENOTG
19
NTCBIAS
I
LIM0
I
LIM1
5
ID
TO USB
TRANSCEIVER
J1
MICRO-AB
V
BUS
USB
ON-THE-GO
L1
3.3µH
M1
C3
22µF
0805
C2
0.1µF
0402
17 8
13
1
2
3.01k 1k
CLPROG
20
NTC PROG
LTC4160/LTC4160-1
SW
9
3
VBUSGD
CHRG
4
FAULT
V
OUT
IDGATE
BAT
V
BUS
D
–
D
+
ID
GND
LDO3V3
RTC
SYSTEM
LOAD
14
12
GND
21
10
11
18
Li-ion
+
1µF
OVGATE
OVSENS
C1, C3: TAYIO YUDEN JMK212BJ226MG
J1: HIROSE ZX62-AB-5PA
L1: COILCRAFT LPS4018-332LM
M1: FAIRCHILD FDN372S
M2: SILICONIX Si2333DS
R1: 1/10 WATT RESISTOR
V
BUS
POWERS UP WHEN ID PIN HAS
LESS THAN 10Ω TO GND
(MICRO-A PLUG CONNECTED)
R1
6.2k
10k
10k
10k
C1
22µF
0805
TO µC
M2
product to meet the specification for
a high power USB device by maintaining V
above 4.75V for currents up
BUS
to 500mA.
Automatic USB On-The-Go
When two On-The-Go devices are
connected, one is the A-device and
the other is the B-device, depending
on the orientation of the cable, which
has a micro-A and a micro-B plug.
The A-device provides power to the
B-device and starts as the host. MicroA/micro-B cables include an ID pin
in addition to the four standard pins
(V
, D–, D+, and GND)—the micro-
BUS
A plug has its ID pin shorted to GND
while on the micro-B plug the ID pin
is floating. The impedance on the ID
pin allows the USB power manager to
determine whether it receives power
from an external device or whether it
should power up V
to an external device.
Step-up mode can be enabled by
either the ENOTG pin or the ID pin.
The ENOTG pin can be connected to
a microcontroller. The ID pin, on the
other hand, is designed to be connected
directly to the ID pin of a micro-AB
receptacle. The pin is active low and
contains an internal 2.5µA pull up
current source. When the ID pin is
floating or a micro-B plug is connected
to the AB receptacle, the internal current source pulls ID up to the max of
V
, V
BUS
and BAT. When a micro-A
OUT
to provide power
BUS
plug is connected to the receptacle,
the short between ID and ground in
the micro-A plug overrides the pull-up
current source and pulls the ID pin
on the LTC4160 down to ground. This
activates the bidirectional switching
regulator in step-up mode and powers up V
. A complete application
BUS
schematic is shown in Figure 2.
Other Features
The LTC4160 also includes a battery charger featuring programmable
charge current (1.2A max), cell preconditioning with bad cell detection
and termination, CC-CV charging,
C/10 end of charge detection, safety
timer termination, automatic recharge
and a thermistor signal conditioner for
temperature qualified charging. For
the LTC4160, the nominal float voltage is 4.2V. The LTC4160-1 provides
a nominal float voltage of 4.1V.
The overvoltage protection circuit
can be used to protect the low voltage USB/Wall adapter input from the
inadvertent application of high voltage
or a failed wall adapter. This circuit
controls the gate of an external high
voltage N-channel MOSFET, and in
conjunction with an external 6.2k
resistor, can provide protection up
to 68V.
The LTC4160 includes an integrated
ideal diode and a controller for an
optional external ideal diode. This
provides a low loss power path from
the battery to V
when input power
OUT
is limited or unavailable. When input
power is removed, the ideal diode(s)
prevent V
from collapsing, with
OUT
only the output capacitor required for
the switching regulator.
Conclusion
The LTC4160 is a feature rich power
manager that is especially suited for
USB On-The-Go applications, enabling
bidirectional USB power transfer between portable devices. The part can
directly detect the impedance on the ID
pin of a micro-AB receptacle to automatically tell the internal bidirectional
switching regulator to provide a 5V
output on V
The switching regulator can supply at
least 500mA and comes with a current limit of 680mA. In addition, the
LTC4160 can efficiently take power
from 5V inputs (USB, Wall adapter,
etc.) to power a portable application
and charge its battery using a single
inductor. Its unique switching architecture and Bat-Track output control
provides fast and efficient charging.
Furthermore, an optional overvoltage
protection circuit can provide protection against voltages of up to 68V on
the V
pin. The combination of bi-
BUS
directional power transfer, automatic
USB On-The-Go functionality and high
voltage protection make the LTC4160
a must have for today’s high end portable devices.
for USB On-The-Go.
BUS
L
Linear Technology Magazine • June 2009
Figure 2. LTC4160 with automatic USB On-The-Go
2929
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