DC1276B - Demo Manual

DEMO CIRCUIT 1276B
QUICK START GUIDE
LTC3558EUD: Linear USB
Battery Charger with Buck and
Buck-Boost Regulators
DESCRIPTION
Demonstration Circuit DC1276B is a Linear USB Battery Charger with Buck and Buck-Boost Converters
featuring the LTC®3558EUD. The LTC3558EUD is a
linear battery charger IC for Li-Ion/polymer battery applications, with a general purpose synchronous stepdown switching regulator and a general purpose buckboost regulator. For USB powered applications, the
battery charge current can be limited to 500mA, by
setting RPROG to 1.74 kΩ. For non-USB powered applications, the charge current can be set as high as
950mA, by simply changing RPROG. The buck and the
buck-boost switching regulators can deliver up to
400mA load current, each. The LTC3558EUD is available in 20-pin (3mm × 3mm) QFN surface mount
package.
Design files for this circuit board are available, call the
LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation. PowerPath is a
trademark of Liner Technology Corporation.
PERFORMANCE SUMMARY Specifications are at TA = 25°C
SYMBOL
VCC
VFLOAT
IBAT
PARAMETER
Input voltage range
BAT float voltage
Battery charge current
VOUT1
VOUT2
Buck regulator output voltage
Buck-Boost regulator output voltage
CONDITIONS
Constant Voltage mode
Constant current mode, RPROG = 1.74kΩ,
HPWR=HI
IOUT1 ≤ 400mA
IOUT2 ≤ 400mA
MIN
4.35
4.15
0.46
1.17
3.27
TYP
MAX
5.5
4.23
0.5
UNITS
V
V
A
1.23
3.33
V
V
QUICK START PROCEDURE
Demo Circuit DC1276B is best evaluated using a LiIon or Li-Polymer battery. When using 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.
Capacitor C10 was added to simulate the low impedance of a real battery. It will allow proper operation
of the demo circuit with or without a battery and
even with a battery simulator consisting of a power
supply in parallel with a 3.6 Ohm resistor.
Refer to Figure 1 for the proper measurement equipment setup and jumper settings 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 VCC or VOUT(x) and GND terminals.
See Figure 2 for proper scope probe technique.
1. Set PS1 to 5.0V, and PS2 to 3.6V.
2. Observe AM1, AM4, VM2, VM3, VM4, VM5, and
VM6.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC1276B
HIGH EFFICIENCY USB POWER MANAGER WITH BUCK AND BUCK-BOOST
REGULATORS
LTC3558EUD
3. Set the HPWR jumper (JP1) to “20%”. Observe
AM1 and AM4.
4. Set the NTC jumper (JP3) to “EXT”. Observe
VM3. The “CHRG” LED (D1) should be blinking.
5. Set the HPWR jumper (JP1) to “100%”, the
SUSP jumper (JP2) to “OFF” and the NTC
jumper (JP3) to “INT”.
6. Set Ld1 to 400mA. Observe VM4 and AM2. Set
Ld1 to 0mA.
7. Set Ld2 to 400mA. Observe VM5 and AM3. Set
Ld2 to 0mA.
ments a charge termination timeout of 4 hours, and a
bad cell charging timeout of 30 minutes. An NTC input
is used to determine if the battery temperature is suitable for charging, too hot or too cold.
The state of charge, as well as any faults, is signaled
with the CHRG pin.
Buck Regulator
The general purpose 400mA buck regulator is implemented as a current mode, synchronous rectifier regulator, operating at 2.25MHz. Step response is excellent
and output ripple is very low.
8. Set EN1 (JP4) and EN2 (JP5) to “OFF”. Observe
VM4 and VM5.
OPERATING PRINCIPLES
The LTC3558 is composed of 3 major functional blocks
working together: Battery Charger, Buck Regulator, and
Buck-Boost Regulator.
The Battery Charger
The battery charger is a linear Li-Ion battery charger
that operates in constant current mode, until the battery
voltage rises to approximately the FLOAT voltage, of
4.2V, and then the charger switches to constant voltage
mode.
The charge current is programmed by the PROG (R6)
resistor, and has been set to 500mA, on DC1276B, with
a 1.74kΩ resistor. The HPWR pin is used to select
20% or 100% of the programmed charge current. The
charge current delivered is nominally the programmed
current, so if the application requires compliance with
the USB specification of presenting a 100mA/500mA or
less load, the nominal charge current must be set to
accommodate the full distribution of actual charge currents.
The battery charger implements trickle charging, for
initial battery voltages less than 2.9V. It also imple-
Buck-Boost Regulator
The general purpose 400mA buck-boost regulator is
implemented as a voltage mode regulator, operating at
2.25MHz. A type three compensation is recommended
for this regulator to achieve the best performance.
APPLICATION INFORMATION
This demo circuit is designed to demonstrate the full
capability of the device. Not all components are required in all applications. The critical circuit components are on the top of the board near the IC.
The VCC input capacitor network of C1 and R1 is
used to dampen input source inductances that
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC1276B
HIGH EFFICIENCY USB POWER MANAGER WITH BUCK AND BUCK-BOOST
REGULATORS
LTC3558EUD
commonly occur in 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 incircuit capacitance of the specified 10uF, 0603 ceramic capacitor for C1 is approximately 5uF each at
5V.
Capacitor C9 is included to simulate a low impedance battery. It is especially helpful when testing the
demo circuit with a battery simulator comprised of a
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 turn
on overshoot without damping resistor R17.
Power dissipation
The LTC3558 implements a linear battery charger
with no pre-regulator. The battery charge current
can be set as high as 0.95A, by choosing the appropriate PROG (R6) resistor.
For a typical application of USB charging of a battery,
VCC = 5V, BAT = 3V. The θJA of the package is
68°C/W, and the maximum TJ is 125°C. Thus, for
TA(max) = 50°C the maximum charge current without thermal regulation can be as high as 550mA.
If a higher charge current is desired, the PROG resistor (R6) can be changed. If the resultant power dissipation exceeds the package dissipation rating the
LTC3558 will go into thermal regulation, and reduce
charge current to an acceptable level.
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC1276B
HIGH EFFICIENCY USB POWER MANAGER WITH BUCK AND BUCK-BOOST
REGULATORS
LTC3558EUD
VM3
+
-
+
+
VM2
PS1
2A
-
Ld1
0V - 5V
-
1
2A
+
+
+
4.35V - 5.5V supply
+
AM2
VM4
-
AM1
-
-
+
-
-
VM1
VM5
-
+
+
-
+
2A
+
+A
VM6
Ld2
0V - 5V
AM3
AM4
3.6Ω
-
PS2
0V - 5V supply
+
5A
Note: All connections from equipment should be Kelvin connected directly to the board
pins which the are connected on this diagram and any input or output leads should be
twisted pair.
Figure 1. Proper Measurement Equipment Setup for DC1276B
GND
VIN
Figure 2: Measuring Input or Output Ripple
4
GND
JP2
SUSP
20%
JP1
HPWR
E10
E9
0
JP6
MODE
OFF
JP5
EN2
OFF
1
ON
ON
BAT
0
INT
0
100K
JP4
EN1
R5
R4
EXT
OFF
100%
R1
1.0
5%
C1
10
6.3V
0603
R3
E6
E8
MODE
EN2
5
4
3
TP1
DTP2
D+
TP3
ID
CHARGER
ON
GND
ID
D+
D-
2
1
R2
100K
R9
1.0M
R8
1.0M
R7
1.0M
VCC
JP3
NTC
E5
E7
PROG
EN1
E3
E2
E4
NTC
SUSP
HPWR
GND
USB
VBUS
E1
VCC
4.35V - 5.5V
J1
ENTC
R6
1.74K
3
15
5
18
17
12
16
MODE
EN2
EN1
PROG
NTC
SUSP
HPWR
20
VCC
21
GND
LTC3558EUD
U1
1
VC2
GND
FB2
SWCD2
SWAB2
VOUT2
FB1
SW1
PVIN2
PVIN1
BAT
CHRG
14
13
10
9
11
4
6
8
7
2
19
C10
1
10V
330pF
C3
C2
10pF
15k
R10
R16
324K
R12
324k
C8
22
6.3V
0805
L2
2.2uH
1072AS-2R2M
1098AS-4R7M
L1
4.7uH
R18
1k
5%
0603
D1
CHRG
GREEN
R11
105k
R13
121k
C4
33pF
R14
20
5%
R15
649K
ENTC
CHRG
BAT
GND
ENTC
E11
GND
E12
VOUT2
3.3V
400mA
GND
VOUT1
1.2V
400mA
E13
E14
E15
GND
DF3-3P-2DSA
1
2
3
E16
BAT
FLOAT=4.2V
0.5A
J2
OPT
E17
Unless noted:
Resistors: Ohms, 0402, 1%, 1/16W
Capacitors: uF, 0402, 10%, 50V
JP6 settings
BUCK
BUCK-BOOST
BURST
BURST
PULSE SKIP
PWM
C5
22
6.3V
0805
C7
10
6.3V
0603
R17
1.0
5%
C9
4.7
6.3V
0603
MODE
1
0
TP4
C6
22pF
BAT
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC1276B
HIGH EFFICIENCY USB POWER MANAGER WITH BUCK AND BUCK-BOOST
REGULATORS
LTC3558EUD
Figure 3: Circuit Schematic
5
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC1276B
HIGH EFFICIENCY USB POWER MANAGER WITH BUCK AND BUCK-BOOST
REGULATORS
LTC3558EUD
Figure 4: Bill of Materials
6
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