DC1376A-B - ANALOG DEVICES - Datasheet.Directory

LTC3555-1 AND LTC3555-3

DESCRIPTION

Demonstration circuits 1376A-A and 1376A-B are High

Efficiency USB Power Manager + Triple Step Down

DC/DC featuring the LTC3555-1 and LTC3555-3 respec-

tively. The LTC

3555-1/LTC3555-3 are highly integrated

power management and battery charger ICs for Li-

Ion/polymer battery applications. It includes a high effi-

ciency current limited switching PowerPath manager

with automatic charge current reduction, a battery

charger, an ideal diode and three general purpose syn-

chronous step-down switching regulators. Designed

specifically for USB applications, the LTC3555-

1/LTC3555-3’s switching power manager automatically

limits input current to a maximum of either 100mA or

500mA for USB applications or 1A for AC-powered appli-

cations. Unlike linear PowerPath controllers, the

LTC3555-1/LTC3555-3’s switching input stage transmits

nearly all of the 2.5W available from the USB port to the

system load with minimal power wasted as heat. This

feature allows the LTC3555-1/LTC3555-3 to provide

more power to the application and eases the constraint

of thermal budgeting in small spaces. Two of the three

general purpose switching regulators can provide up to

400mA and the third can deliver 1A. The entire product

can be started from an external push button and subse-

quently controlled via I

C. The LTC3555-1/LTC3555-3 is

available in the 28-pin (4mm × 5mm × 0.75mm) QFN

surface mount package.

Design files for this circuit board are available. Call

the LTC factory.

L, LTC, LTM, LT, Burst Mode, are registered trademarks of Linear Technology Corporation.

PowerPath are trademarks of Linear Technology Corporation. Other product names may be

trademarks of the companies that manufacture the products.

PERFORMANCE SUMMARY

Specifications are at T

= 25°C

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VBUS

Input Supply Range

4.35 5.5

VOUT

VOUT Output Voltage Mode and load dependant 3.4 Bat + 0.3 4.7

LDO3V3

LDO3V3 Output Voltage Load and VOUT dependant 3.3

FLOAT

BAT Regulated Output Voltage LTC3555-1

LTC3555-3

4.179

4.079

4.2

4.1

4.221

4.121

BAT

Constant Current Mode Charge Current R

PROG

= 2K

460 511 532 m

VOUT1

VOUT1 Output Voltage

3.3

VOUT2 VOUT2 Output Voltage Servo Voltage = 0.8 3.0

VOUT3 VOUT3 Output Voltage Servo Voltage = 0.8 1.5

QUICK START PROCEDURE

Demonstration circuits 1376A-A and 1376A-B are easy

to set up to evaluate the performance of the LTC3555-1

and LTC3555-3. These circuits are best evaluated using

a Li-Ion 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. Ca-

pacitor C15 in combination with R9, R10, and R11 were

added to simulate the low impedance of a real battery.

It will allow proper operation of the demo circuit with or

without a battery, or a battery simulator consisting of a

power supply in parallel with a 3.6 Ohm resistor.

Demo Circuit1376A-A/-B

QUICK START GUIDE

LTC3555-1 and LTC3555-

High Efficiency USB Power Manage

+ Triple Step Down DC/D

LTC3555-1 AND LTC3555-3

Complete the Quick Start Procedure outlined in the

Quick Start Guide for Demo Circuit 590 available from

the Linear Technology Web Site, prior to proceeding.

Refer to

Figure 2 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(x) and GND terminals. See

Figure 3 for proper scope probe

technique.

After following the software installation procedure

in the DC590 Quick Start Guide, connect the

DC1376A, the DC590 and the Host PC as shown in

Figure 2.

NOTE.

If using the DC590B board, a specific DVCC voltage level may be

selected. This is done by setting the VCCIO jumper on the DC590

board to one of the following settings: 3.3V, 5V, removed for 2.7V or

set to external if an external supply is desired to be used.

Run the QuikEval.exe software. The QuikEval soft-

ware detects the DC1376A-A or the DC1376A-B

demo board and the LTC3555 Graphical User Inter-

face (GUI), shown in

Figure 1, will pop-up.

Figure 1.

Graphical User Interface Demonstration Software for

DC1376A-A and DC1376A-B.

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, plug in the USB cable after all

loads and jumpers are set. Connect the positive ter-

minal of a voltmeter to CLPROG and the negative

terminal to GND to measure the average input cur-

rent. The voltage on CLPROG will reach 1.188V when

the average input current limit is reached.

Do not

use the USB input and an external supply at the

same time

Set JP1, (NTC) to “INT” to use the demo board re-

sistor network. To use an external NTC resistor, con-

nect the external NTC resistor between the J2-3 ter-

minal and the GND terminal. Then set the NTC

jumper to “EXT”.

Set JP2 and JP3 (ILIM0 and ILIM1 respectively) to

“LO”. At Power-up, the average input current setting

will be equal to the value set by the position of JP2

and JP3 until an I

C command is received and over-

writes that default value.

TABLE 1. Input Current Limit Settings

ILIM1 ILIM0 CURRENT LIMIT

0 0 100mA (1X)

0 1 1A (10X)

1 0 0.5mA (SUSP)

1 1 500mA (5X)

Connect a 0 to 25mA adjustable load in series with

an ammeter between the LDO3V3 and GND termi-

nals. Connect a voltmeter between the LDO3V3 and

GND terminals.

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.

Connect a 0 to 400mA adjustable load in series with

an ammeter between the VOUT1 and GND terminals.

Connect a voltmeter between the VOUT1 and GND

terminals.

Connect a 0 to 400mA adjustable load in series with

an ammeter between the VOUT2 and GND terminals.

Connect a voltmeter between the VOUT2 and GND

terminals.

LTC3555-1 AND LTC3555-3

10.

Connect a 0 to 1.0A adjustable load in series with

an ammeter between the VOUT3 and GND terminals.

Connect a voltmeter between the VOUT3 and GND

terminals.

11.

Connect a Li-Ion or Li-Polymer 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 the positive terminal of

a voltmeter to PROG and the negative terminal to

GND to measure the current flowing into the battery.

The voltage on PROG will read 1 Volt when the

maximum charge current is reached. Observe VOUT

and the LDO3V3 output.

12.

If using the USB input, plug in the USB cable and

observe the charge current and the various output

voltages. If using an external power supply, slowly

increase the supply and observe that the LTC3555-

1/LTC3555-3 starts to use the VBUS input power as

VBUS reaches 4.35V.

13.

Set VBUS to 5V and set the CURRENT LIMIT

SETTING to 10X MODE (1A) on the LTC3555 GUI.

14.

Discharge the battery voltage 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 constant current mode. Ob-

serve charge current reduces when the VOUT load

increases while VOUT is at or below 3.6V in order to

keep VOUT from collapsing. When the input current

limit is exceeded, power is then drawn from the bat-

tery to supply VOUT.

15.

Remove the NTC jumper on JP1. Observe the

CHRG LED slow blinking rate (1.5Hz at 50% Duty

Cycle). Also observe the 35KHz pulse-width varying

duty cycle between 6.25% and 93.75% on the

CHR

terminal with an oscilloscope. Reinstall the NTC

jumper.

16.

Increase the VOUT load and observe when the input

current starts to limit. When input current limit is

reached, additional load smoothly transitions to the

battery through the ideal diode. Due to the high effi-

ciency 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.

17.

Repeat step 16 with different current limit modes.

18.

Observe the battery current as the battery voltage

increases above 4.1V for the LTC3555-1 or 4.0V for

the LTC3555-3. The charge current starts to de-

crease as the battery voltage increases towards 4.2V

for the LTC3555-1 or 4.1V for the LTC3555-3.

See the LTC3555/LTC3555-X data sheet for more in-

formation on how this part performs.

LTC3555-1 AND LTC3555-3

Figure 2.

Proper Measurement Equipment Setup

VIN

GND

Figure 3.

Measuring Input or Output Ripple

APPLICATION INFORMATION

This demo circuit is designed to demonstrate the full

capability of the device. Not all components are re-

quired in all applications. The critical circuit compo-

nents are on the top of the board near the IC.

The input RC network of C5 and R26 is used to dampen

input source inductances that commonly occur in labo-

ratory 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 speci-

fied 10uF, 0805 ceramic capacitor for C5 and C1 is ap-

proximately 5uF each at applied voltage.

The LTC3555-1/LTC3555-3 requires a minimum of

10uF on the VOUT pin in 10X mode for stability.

The RC network of C15 and R9, R10, and R11 is in-

cluded to simulate a low impedance battery. It is espe-

cially helpful when testing the demo circuit with a bat-

tery 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 cause instability in the battery charger section

without the presence of the C15 RC network. The C15

RC network will also provide proper operation of the

circuit without a battery present. Please refer to the

datasheet for the suggested capacitor and resistance

range.

LTC3555-1 AND LTC3555-3