Linear Technology LTC3455EUF-1 User manual

LTC3455EUF-1
1
DESCRIPTION
Demonstration circuit 1448 is a Dual DC/DC Converter
with USB Power Manager and Li-Ion Battery Charger
featuring the LTC3455EUF-1. Power may be received
from the USB input, a Wall Adapter, or a battery. DC1448
provides the following functions; 700mA CC/CV timer
terminated charger suitable for Li-ion cells, USB power
manager that ensures compliance with the USB power
specification, two 1.5MHz synchronous step down con-
verters and reset and power button status outputs for
interface with a microprocessor.
The LTC3455EUF-1 is available in a 4mm x 4mm 24-
pin exposed-pad QFN package.
Design files for this circuit board are available. Call
the LTC factory.
L, LTC, and Burst Mode are registered trademarks of Linear Technology Corporation. Hot
Swap is a trademark of Linear Technology Corporation. Other product names may be trade-
marks of the companies that manufacture the products.
PERFORMANCE SUMMARY Specifications are at T
A
= 25°C
PARAMETER CONDITIONS MIN TYP MAX UNITS
Wall Adapter Input Voltage Range 4.75 5.5
V
USB Input Voltage Range 4.20 5.5
V
Battery Charger
Iout Vin = 5V, VBat = 3.6V 585 690 795 m
A
Float Voltage Vin = 5V 4.058 4.142
V
Trickle Charge Threshold Vin = 5V (Battery voltage rising) 2.85
V
Recharge Threshold V
BAT(REGULATED)
- V
RECHARGE
150 m
V
USB Current
Input Current 500mA Mode Vin = 5V; USB Active 500mA Mode 440 500 m
A
Input Current 100mA Mode Vin = 5V; USB Active 100mA Mode 60 100 m
A
Input Current Suspend Mode Vin = 5V; USB Suspend 4 20 u
A
Buck Converters
Switcher 1 1.72 1.86
V
Switcher 2 3.02 3.27
V
Hot Swap Output VBat 3.6V 3.02 3.27
V
OPERATING PRINCIPLES
Demo Circuit 1448 manages the power supplies that
would be typical for a USB powered device. Power is in-
put from either the USB cable or an adapter to an inter-
mediate voltage bus. This intermediate voltage is then
used to charge a Li-ion battery and to generate two low
voltage outputs via high efficiency step down converters.
The intermediate voltage bus is preferentially powered
from the Wall Adapter, then from the USB input, and fi-
nally from the battery via an ideal diode. The battery
charger is a CC/CV timer terminated type capable of
DEMO CIRCUI
T
1448
QUICK START GUIDE
LTC3455EUF-1
Dual DC/DC Converter with USB
Power Manager and Li-Ion Battery
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charge currents of up to 800mA. The two step down
converters are high efficiency synchronous Bucks with
outputs set at 1.8V and 3.15V. Other output settings are
possible by altering the feedback resistor ratios. The chip
is normally ON if either USB or Wall Adapter is present. If
the battery is the only source of power then the circuit
must be turned on by pressing the ON button and can be
turned off by depressing the OFF button. The OFF button
will only function when in battery power mode. The
LTC3455-1 provides a reset signal for 200msec after
power up. The ON pin is designed to interface to a push
button while the PBSTAT reports the button status to
allow the host microprocessor to shut down. Additionally
there is an uncommitted op-amp which is used on the
demo board as a low battery detector. Another possible
use for the uncommitted op-amp would be as an LDO
controller to generate an additional output or to augment
the peak current capability of one of the existing outputs.
QUICK START PROCEDURE
Demonstration circuit 1448 is easy to set up to evaluate
the performance of the LTC3455EUF-1. Refer to Figure 1
for proper measurement equipment setup and follow the
procedure below:
NOTE. When measuring the input or output voltage ripple, care must be
taken to avoid a long ground lead on the oscilloscope probe. Measure the
input or output voltage ripple by touching the probe tip directly across the
VIN or VOUT and GND terminals. See Figure 2 for proper scope probe
technique.
1. With power off, connect input power supplies, meters,
battery simulator, and output loads as shown in Figure
1.
2. Set the Jumpers on Demo Circuit 1448 as shown be-
low:
JP1. MODE jumper to CONTINUOUS MODE position.
JP3. HOT SWAP OUTPUT jumper to ON position.
JP4. USB CURRENT jumper to 500mA position.
JP5. USB SUSPEND jumper to USB ACTIVE position.
JP6. 3.15V ON/OFF jumper to ON position.
USB Charging
3. Set the battery simulator voltage to zero; slowly raise
the USB input voltage. When the supply voltage ex-
ceeds 4.1V the charger should activate and the charge
LED will illuminate. Continue increasing the USB input
voltage to 5.0V. The battery will be in trickle charge
mode. Slowly increase the battery voltage. At voltages
above 2.85V the battery charge current will increase to
approximately 400mA. Continue increasing the battery
voltage to 3.6V. Note that the input current from the
USB does not exceed the USB spec of 500mA.
4. Increase the loads on the outputs. Note that as the
output load is increased the charging current is de-
creased and the USB current remains within the
500mA limit.
5. Place the USB Current jumper, JP4, in the 100mA po-
sition and note that USB input current falls to maintain
compliance with the USB input current specification.
Also note that as the external load is increased the
battery will start to discharge to power the VMAX in-
termediate voltage bus, illustrating the ideal diode
function of the LTC3455EUF-1
6. Place the USB Suspend jumper, JP5, in the SUSPEND
position and note that the USB current falls to under
100uA to comply with the suspend mode current.
Adapter Charging
7.
Ramp up the wall adapter voltage. When the wall
adapter exceeds 4.7V the LTC3455EUF-1 will cease
drawing current from the USB and switch over to the
wall adapter.
8. Note that the charge current to the battery has in-
creased to approximately 690mA.
9. Increase the battery voltage to 4.1V and note that the
charge current falls to 0. This illustrates the constant
voltage portion of the charging characteristic.
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Battery Powered Operation
10. Set Both USB input voltage and the adapter input
voltage to zero. The battery will now support the op-
eration of the demo board.
11. In battery mode operation the OFF pushbutton is
now active. Push the OFF button and note battery cur-
rent draw falls to less than 10uA.
12. Now restart the converter using the ON pushbutton.
Note that the Reset LED goes on for 200ms. This
simulates the Reset signal that the LTC3455EUF-1
provides to the processor upon initial power up.
13. Set the MODE jumper, JP1, to the BURST MODE
position. Observe with an oscilloscope that the buck
converter outputs will operate in Burst Mode while in
light loads.
Other
14. Set the HOT SWAP OUTPUT jumper, JP3, to the OFF
position. Observe that the hot swap output shuts off.
15. Set the 3.15V ON/OFF jumper, JP6, to the OFF posi-
tion. Observe that the 3.15V output shuts off.
Figure 1. Proper Measurement Equipment Setup
VIN GND
Figure 2. Measuring Input or Output Ripple
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LTC3455EUF-1
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