QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1138A-A/B
USB POWER MANAGER WITH Li-ION CHARGER AND TRIPLE BUCK REGULATORS
LTC3557/LTC3557-1 + LT3505
1
DESCRIPTION
The DC1138A-A/B contains the
LTC3557/LTC3557-1 Power Management Inte-
grated Circuit (PMIC) plus the LT3505EDD high
voltage buck controller. The LTC3557/LTC3557-1
is a highly integrated power management IC that
includes a PowerPath controller, battery charger,
an ideal diode, an always-on LDO, three synchro-
nous step-down switching regulators as well as a
buck regulator VC controller. Designed specifically
for USB applications, the PowerPath controller
incorporates a precision input current limit which
communicates with the battery charger to ensure
that the input current does not violate the USB
specification. The ideal diode from BAT to VOUT
guarantees that ample power is always available
to VOUT even if there is insufficient or absent
power at VBUS.
The LTC3557/LTC3557-1 also has the ability to
receive power from a wall adapter or other non-
current-limited power source. Such a power sup-
ply can be connected to the VOUT pin of the
LTC3557/LTC3557-1 through an external device
such as a power Schottky diode or MOSFET, Q1,
as shown in the demo board circuit schematic,
Figure 4. The LTC3557/LTC3557-1 has the
unique ability to use the output, which is powered
by an external supply, to charge the battery while
providing power to the load. A comparator on the
WALL pin is configured to detect the presence of
the wall adapter and shut off the power connection
between VOUT and the USB input. This prevents
reverse conduction from VOUT to VBUS when a
wall adapter is present.
The LTC3557/LTC3557-1 provides a VC output
pin which can be used to drive the VC pin of an
external high voltage buck switching regulator
such as the LT3480, LT3481, or LT3505 to provide
power to the VOUT pin. The VC control circuitry
adjusts the regulation point of the switching regu-
lator such that VOUT equals the greater of BAT
plus 300mV or 3.6 Volts. This control method pro-
vides a high input voltage, high efficiency battery
charger and PowerPath function. An always-on
LDO provides a regulated 3.3V from VOUT. This
LDO will be on at all times and can be used to
supply up to 25mA.
The LTC3557/LTC3557-1 includes three 2.25MHz
constant frequency current mode step-down
switching regulators providing 400mA, 400mA and
600mA. All step-down switching regulators can be
programmed for a minimum output voltage of 0.8V
and can be used to power a microcontroller core,
I/O, memory or other logic circuitry. All step-down
switching regulators support 100% duty cycle op-
eration and are capable of operating in Burst
Mode operation for highest efficiencies at light
loads (Burst Mode operation is pin selectable). No
external compensation components are required
for the switching regulators.
The LTC3557/LTC3557-1 is available in a 28-
pin low profile (4mm x 4mm x 0.75mm) QFN
package.
Design files for this circuit board are avail-
able by calling the LTC factory.
L
, LTC, LT and Burst Mode are registered trademarks of Linear Technol-
ogy Corporation. PowerPath is a trademark of LinearTechnology Corpora-
tion. Other product names may be trademarks of the companies that manu-
facture the products.
Figure 1. LTC3557/LTC3557-1 Simplified Typical
Application
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1138A-A/B
USB POWER MANAGER WITH Li-ION CHARGER AND TRIPLE BUCK REGULATORS
LTC3557/LTC3557-1 + LT3505
2
Table 1. Typical Specifications (25
°
C)
PARAMETER RANGE
VBUS 4.35V to 5.5V
5V ADAPTER 4.5V to 5.5V
HVIN 8V to 36V
VOUT 2.9V – 5.5V, 1.2A
VOUT1 3.3V, 600mA
VOUT2 1.2V, 400mA
VOUT3 1.8V, 400mA
LDO3V3 3.3V, 25mA
Battery Float Voltage in Constant Voltage Mode LTC3557EUF = 4.2V (DC1138A-A),
LTC3557EUF-1 = 4.1V (DC1138A-B)
Battery Charge Current in Constant Current Mode 500mA (RPROG = 2K Ohms)
QUICK START PROCEDURE
Demo Circuit 1138 is best evaluated using a
lithium ion battery. The test set-up in Figure 2
shows a battery simulator, consisting of PS4
and a 3.6 Ohm power resistor. Since the
demo circuit is designed to possibly be used
with a battery simulator, it includes a capacitor
between the BAT and GND terminals with
some series resistance. Please see the Ap-
plications Section below for a detailed discus-
sion of selecting the proper bypass capacitor
and series resistance for the BAT terminal.
Refer to Figure 2 for the proper measurement
and equipment setup and follow the proce-
dure below.
1. Set all Power Supplies to zero volts and all
loads to zero amps and then connect the
test equipment as shown in Figure 2. If
using the USB input option, have cable
ready to plug in for when all loads and
jumpers are set. Do not use the USB in-
put and an external supply at the same
time.
2. Set the NTC jumper to INT to use the
demo board resistors. To use an external
NTC resistor, connect an NTC resistor be-
tween J2-3 (ENTC) and GND. Then set
the NTC jumper to EXT.
3. Use Table 2 to set ILIM1 and ILIM0 to se-
lect the desired input current limit.
Table 2. Maximum Current Limit Settings
ILIM1 ILIM0 MAXIMUM INPUT CURRENT LIMIT
0 0 100mA
011A
1 0 SUSPEND
1 1 500mA
4. Set EN1, EN2 and EN3 to ON.
5. Set PS4 to 3.6 Volts. Alternatively, PS4
and the Power resistor could be replaced
with a lithium ion battery conditioned to 3.6
Volts. Observe VOUT, VOUT1, VOUT2,
VOUT3 and LDO3V3 outputs.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1138A-A/B
USB POWER MANAGER WITH Li-ION CHARGER AND TRIPLE BUCK REGULATORS
LTC3557/LTC3557-1 + LT3505
3
6. If using the USB input, plug in the USB
cable and observe the charge current and
VOUT. If using an external VBUS power
supply slowly increase PS3, and observe
that the LTC3557/LTC3557-1 starts to use
the VBUS input power as the device
reaches 3.9 Volts. Increase the VBUS
supply until it reaches 5.0 Volts.
7. Discharge the battery voltage to 2.6 Volts
and then reconnect the battery or reduce
PS4 to 2.6 Volts to observe that the
LTC3557/LTC3557-1 is now charging in
trickle charge mode and the charge cur-
rent is 1/10th of the maximum pro-
grammed charge current. As the battery
voltage increases above 2.85 Volts ob-
serve that the charge current increases to
the maximum programmed value.
8. Remove the NTC jumper on JP9. Observe
the CHRG LED slow blinking rate. Also
observe the 35KHz pulse-width varying
duty cycle between 4.7% and 95.3% on
the
CHRG
terminal with an oscilloscope.
Reinstall the NTC jumper to INT and ob-
serve the solid CHRG LED.
9. Increase the VOUT load and observe
when the input current starts to limit. When
the VOUT load exceeds the input current
limit, additional load smoothly transitions
to the battery through the ideal diode and
VOUT drops to the battery voltage minus
the voltage drop across the ideal diode
(~15mV).
10. Repeat step 9 with different ILIM1 and
ILIM0 settings.
11. With the VBUS input supply, PS3, equal to
5 Volts. Observe the battery current as the
battery voltage increases above 4.05
Volts. The charge current starts to de-
crease as the battery voltage approaches
50mV less than the float voltage.
12. Vary PS3 and observe the reduction of
charge current as VBUS is decreased be-
low 5.0 Volts.
13. Set PS3 to 5.0 Volts. Set LOAD1, LOAD2
and LOAD3 for the intended application to
test various operating conditions of the in-
tended application. Observe
RST2
going
high as VOUT2 comes into regulation.
14. Verify that jumper JP10 is set to HV
BUCK. Slowly increase PS1 to 8 Volts
and observe that the current through PS3
is reduced to zero amps as the HV BUCK
voltage reaches 4.5 Volts. Continue to in-
crease PS1 to 12 Volts.
15. Observe VOUT as the BAT voltage varies.
VOUT will now track the battery voltage
with a constant 300mV offset, which re-
duces power dissipation in the battery
charger.
16. Disconnect the positive lead of the battery
from the BAT terminal and observe the
float voltage of the battery charger.
VFLOAT = 4.2V for LTC3557EUF (DC1138A-A)
VFLOAT = 4.1V for LTC3557EUF-1 (DC1138A-B)
See the LTC3557 data sheet for additional in-
formation about how this part performs.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1138A-A/B
USB POWER MANAGER WITH Li-ION CHARGER AND TRIPLE BUCK REGULATORS
LTC3557/LTC3557-1 + LT3505
4
APPLICATION INFORMATION
This demonstration circuit is designed to dem-
onstrate 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 input capacitor network of C6 and R25 is
used to dampen input source inductances that
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 in-circuit capacitance of the
specified 10uF, 0805 ceramic capacitor for C6
and C7 is approximately 5uF each at applied
voltage.
Capacitor C18 in series with R24 are included to
simulate a low impedance battery. They are es-
pecially 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 short twisted pair to
minimize lead inductance. Capacitor C18 and
R24 will also provide proper operation of the cir-
cuit without a battery present.
Capacitor C18
and R24 are a 100uF OSCON capacitor in
series with a zero Ohm jumper from the BAT
terminal to GND. When measuring the BAT
discharge current or for an application circuit,
it is recommended that this OSCON capacitor
be replaced with a 100uF, ceramic capacitor
and R24 be changed to between 250 and 350
mOhms. The ceramic capacitor used must
maintain at least 47uF of real capacitance
with 4.5 Volts DC applied.
Please contact the factory if you would like to
use the SHDN function of the LT3505EDD
high voltage buck. The circuit as configured
will operate properly with HVIN either present
or not present, but the SHDN pin on the
LT3505 does not shut down the part when the
VC pin of the LT3505 is connected directly to
the VC pin of the LTC3557/LTC3557-1.
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1138A-A/B
USB POWER MANAGER WITH Li-ION CHARGER AND TRIPLE BUCK REGULATORS
LTC3557/LTC3557-1 + LT3505
5
Figure 2. Proper Equipment Setup for DC1138A-A/B
VIN
GND
Figure 3. Measuring Input or Output Ripple
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1138A-A/B
USB POWER MANAGER WITH Li-ION CHARGER AND TRIPLE BUCK REGULATORS
LTC3557/LTC3557-1 + LT3505
6
Figure 4. Circuit Schematic for DC1138A-A/B
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1138A-A/B
USB POWER MANAGER WITH Li-ION CHARGER AND TRIPLE BUCK REGULATORS
LTC3557/LTC3557-1 + LT3505
7
