LTC4088-2
1
DESCRIPTION
Demonstration circuit 1377A is a High Efficiency Battery
Charger/USB Power Manager with Regulated Output
Voltage featuring the LTC4088-2. The LTC4088-2 in-
cludes a synchronous switching input regulator, a full-
featured battery charger and an ideal diode. Designed
specifically for USB applications, the LTC4088-2’s
switching regulator automatically limits the input current
to a maximum of 100mA or 500mA for USB applications,
or 1A for wall-powered applications via logic control.
The switching input stage provides power to VOUT
where power sharing between the application circuit and
the battery charger is managed. Charge current is auto-
matically reduced to maintain a regulated 3.6V VOUT
during low battery conditions. As the battery is charged,
VOUT tracks BAT for high efficiency charging. This fea-
ture allows the LTC4088-2 to provide more power to the
application and eases thermal issues in constrained ap-
plications.
An ideal diode ensures that system power is available
from the battery when the input current limit is reached
or if the USB or wall supply is removed.
The external P-
channel MOSFET supplements the internal ideal diode
by reducing RON and increasing efficiency.
A CHRG LED indicates four possible states of the bat-
tery charger. Charging is indicated when the LED is
steady-ON. Not charging is indicated by a steady-OFF.
an NTC fault is indicated by a slow blinking rate
(1.5Hz) and a bad battery is indicated by a fast blink-
ing rate (6.1Hz).
The LTC4088-2 is available in a low profile 14-Lead 4mm
×
3mm
×
0.75mm DFN surface mount package.
Design files for this circuit board are available. Call
the LTC factory.
L, LTC, LT, and PowerPath are registered trademarks of Linear Technology Corporation.
Other product names may be trademarks of the companies that manufacture the products.
PERFORMANCE SUMMARY
Specifications are at T
A
= 25°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
BUS
Input Supply Range
4.35 5.5
V
V
OUT
Output Voltage Range V
BUS
= 5V, 1x, 5x, 10x Modes, 0V < BAT
≤
4.2V
V
BUS
= 5V, USB Suspend Modes, I
OUT
= 250μA
3.5
4.5
BAT+0.3
4.6
4.7
4.7
V
V
V
FLOAT
BAT Regulated Output Voltage
4.179 4.2 4.221
V
I
CHRG
Constant-Current Mode Charge Current V
BUS
= 5V, R
PROG
= 2K,
BAT
= 3.8V 490 515 540 m
A
I
C/X
Battery Charge Current at Programmed End of
Charge Indication
V
BUS
= 5V, R
C/X
= 2K 42.5 50 57.5 m
V
OPERATING PRINCIPLES
This demo circuit is designed to demonstrate the full ca-
pability of the LTC4088-2 High Efficiency Battery
Charger. Not all components are required in all applica-
tions. The critical circuit components are on the top of
the demo board near the IC and listed in the Required
Circuit Components section of the Bill-of-Materials.
The input RC network of C6 and R13 is used to dampen
source lead inductances that commonly are present in
DEMO CIRCUI
T
1377A
QUICK START GUIDE
LTC4088-2
High Efficiency Battery
Charger/USB Power Manager
with Regulated Output Voltage
LTC4088-2
laboratory setups with twisted leads and a bench power
supply. When using a USB cable or adaptor cable this
input damping network will likely not be required. Please
note that the in-circuit capacitance of the 10uF, 0805 ce-
ramic capacitor specified for C2 and C6 is approximately
5uF each at a VBUS greater than 4.25 Volts.
The LTC4088-2 requires a minimum of 10uF on the
VOUT pin in 10X mode for voltage loop stability. As an
alternative to using two smaller X5R capacitors, one lar-
ger X5R ceramic capacitor would be acceptable, pro-
vided that the actual in-circuit capacitance with 4.6 Volts
applied is greater than 10uF.
The RC network of C4 and R8, R9, and R12 is included
to simulate a low impedance battery. It is especially help-
ful when testing the demo circuit with a battery simulator
comprised of a standard power supply with a 3.6 Ohm
power resistor across it. The leads connecting the power
supply to the demo circuit should be a twisted pair to
minimize lead inductance; although, even twisted pairs
can introduce enough inductance into the circuit to cause
instability in the battery charger section without the pres-
ence of C4. If desired, it is possible to use a ceramic ca-
pacitor in series with a low valued resistor to stabilize the
battery charger when no battery is present. Please refer
to the datasheet for the suggested capacitor and resis-
tance range.
QUICK START PROCEDURE
Demonstration circuit 1377A is easy to set up to evaluate
the performance of the LTC4088-2. Refer to the Per-
formance Summary for a listing of the inputs and out-
puts of the 1377A Demo Circuit. Demo Circuit 1377A is
best evaluated using a Li-Ion/Polymer battery. When us-
ing a battery simulator for evaluation, oscillations must
be verified with a real battery at the same conditions
because it is difficult to match the impedance of a real
battery.
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
VBUS or VOUT and GND terminals. See
Figure 2 for proper scope probe
technique.
1.
If using an external supply, connect a 0 to 6V, 1.5A
supply with voltage adjusted to 0V between the
VBUS and GND terminals. Connect a Voltmeter
across the VBUS and GND terminals. If using the
USB input option, have the cable ready to plug in
when all loads and jumpers are set.
Do not use the
USB input and an external supply at the same time.
2.
Set JP1, NTC jumper, to INT to use the demo board
resistor. To use an external 100kOhm NTC resistor,
connect the NTC resistor between J2-3 and the
GND terminal. Then set the NTC jumper to EXT.
3.
Use Table 1 to set JP2, JP3, and JP4 (D0, D1, and
D2 respectively) to select the desired input current
limit and charger status.
TABLE 1. Controlled Input Current Limit
D0 D1 D2 CHARGER I
BUS(LIM)
0 0 0 ON 100mA(1x)
0 0 1 OFF 100mA(1x)
0 1 0 ON 500mA(5x)
0 1 1 OFF 500mA(5x)
1 0 0 ON 1A(10x)
1 0 1 OFF 1A(10x)
1
1 0 OFF
500uA
(
Susp
Low)
1
1 1 OFF
2.
5mA
(
Susp
high)
4.
Connect a 0 to 2A adjustable load in series with an
ammeter between the VOUT terminal and the GND
terminal. Connect a Voltmeter between the VOUT
and GND terminals.
5.
Connect a partially charged (~3.6V) Lithium ion
battery with the positive lead to the BAT terminal
and the negative lead to a GND terminal. Connect
the positive lead of a Voltmeter to the BAT terminal
and the negative lead to the GND terminal. Connect
2
LTC4088-2
3
the positive terminal of a Voltmeter to PROG and
the negative terminal to GND to measure the cur-
rent flowing into the battery. The voltage on PROG
will read 1 Volt when the maximum charge current
is reached. Observe VOUT.
NOTE.
Make sure that the BAT voltage does not exceed 7V.
1031
R
V
I PROG
PROG
BAT •=
6.
If using the USB input, plug in the USB cable and
observe the battery charge current and VOUT. If us-
ing an external power supply, slowly increase the
supply and observe that the LTC4088-2 starts to
use the VBUS input power as VBUS reaches 4.35V.
Connect a Voltmeter between the CLPROG terminal
and the GND terminal. The voltage on CLPROG will
read 1.188 Volts when the input current limit is
reached.
NOTE.
Make sure that the VBUS voltage does not exceed 7V.
See the datasheet for the proper values of I
BUSQ
and
h
CLPROG
in 1X, 5X and 10X modes.
7.
Discharge the battery to 2.5 volts. If Charger mode
is on, observe it is charging in trickle charge mode
and the charge current is 50mA. As the battery
voltage increases above 2.85V observe that the
charger goes into full constant current mode. Ob-
serve that VOUT stays above 3.6V when the input
current limit is not exceeded. Remove the NTC
jumper on JP1. Observe the CHRG LED slow blink-
ing rate. Also observe the 35KHz pulse width vary-
ing duty cycle between 4.7% and 95.3% on the
CHRG terminal with an oscilloscope. Reinstall the
NTC jumper.
8.
Increase the VOUT load and observe when the input
current starts to limit (VCLPROG=1.188 V). As the in-
put current limit is reached, VOUT gradually drops
from 300mV above the BAT voltage to 15mV below
the BAT voltage and the additional load transitions
to the battery through the ideal diode. Due to the
high efficiency of the switching regulator, the sum
of the charge and load current may be significantly
above the input current depending on the voltage
on the BAT pin.
9.
Repeat step 8 with different current limit modes.
10.
Set the VBUS input supply to 5V. Observe the bat-
tery current as the battery voltage increases above
4.1V. The charge current starts to decrease as the
battery voltage increases towards 4.2V.
See the latest LTC4088-1/LTC4088-2 datasheet for
more information on how this part performs.
()
1 h
R
V
I I CLPROG
CLPROG
CPROG
BUSQVBUS +•+=
LTC4088-2
4
Figure 1.
Proper Measurement Equipment Setup
VIN
GND
Figure 2.
Measuring Input or Output Ripple
LTC4088-2
5
LTC4088-2
6
