Linear Technology LTC3554EPD User manual

DEMO CIRCUIT 1468

QUICK START GUID

LTC3554EPD

Micropower USB Power Manage

with Two Step-Down Regulators

DESCRIPTION

Demonstration Circuit DC1468A is a Micropower USB Power Manager with Two Step-Down Regulators featuring

the LTC®3554.

PERFORMANCE SUMMARY

Specifications are at T

= 25°C

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VBUS

Bus Input Voltage Range 4.35 6 V

V(BAT)

Battery Float Voltage Constant Voltage Mode 4.15 4.23 V

I(BAT)

Battery Charge Current Constant Current Mode, R

PROG

= 1.87k

420 500 mA

VOUT1

Output Voltage 1 I(VOUT1) ≤ 200mA 3.25 3.35 V

VOUT2

Output Voltage 2 I(VOUT2) ≤ 200mA 1.15 1.25 V

QUICK START PROCEDURE

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 VBUS or VOUT(x) and GND terminals.

See Figure 2 for proper scope probe technique.

1. Set PS1 = 0V, PS2 = 3.6V. Press “ON” button

for > 0.5s. Observe I(BAT) (AM2), VOUT1 (VM5)

and VOUT2 (VM6). The regulator ENable lines

are low. Pressing the “ON” button turns on the

regulators for 5s, via the pushbutton controller.

The regulator ENables are bootstrapped to the

outputs of the regulators, so regulators stay on

indefinitely. The STBY jumper is on, so the

LTC3554 draws only ~10μA from the battery.

2. Set STBY (JP4) to “OFF”, PS1 to 5V. Observe

I(VBUS) (AM1), I(BAT) (AM2) and VPROG

(VM2). The STBY jumper is off, and the battery

charger is trying to charge the battery at 500mA,

but the input current limit is keeping the charge

current at 100mA.

3. Set HPWR (JP2) to “500mA”. Observe I(VBUS)

(AM1), I(BAT) (AM2) and VPROG (VM2). The

input current limit is now 500mA, so the battery

charger is charging at 450mA, and the buck

regulators are unloaded.

4. Set LD2 to 200mA, LD3 to 200mA. Observe

VOUT1(VM5), VOUT2 (VM6) and I(BAT) (AM2).

The buck regulators are each loaded at 200mA.

These loads are reflected back to the VBUS input

by the ratio of their output voltage to the VOUT

Voltage. The buck regulators are higher priority

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LTC3554EPD

than the battery charger, so the charger is only

charging at the input current limit of 500mA mi-

nus the reflected buck regulator loads, ~200mA.

5. Set LD2 to 0A, LD3 to 0A. Press “OFF” button.

Observe VOUT1 (VM5) and VOUT2 (VM6). The

“OFF” button momentarily brings the ENable

lines low, shutting regulators off. The battery

charge current should now return to 450mA.

6. Reset the Jumpers to their default position.

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LTC3554EPD

Figure 1. Proper Measurement Equipment Setup for DC1468A

VIN

GND

Figure 2. Measuring Input or Output Ripple

PS1 +

4.35V - 5.5V supply

1A -

VM1

+ PS2

0V - 5V supply

1 1

3.6

Ω

VM4

+ -

AM2

VM3

+ -

AM1

Note: All connections from equipment should be Kelvin connected directly to the board

pins which they are connected on this diagram and any input or output leads should be

twisted pair.

VM5

+ -

+ LD2

0V - 5V

- 2

AM3

VM6

+ -

+ LD3

0V - 5V

- 2

AM4

VM2

Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.

LTC3554EPD

Figure 3. Circuit Schematic

Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.Downloaded from Arrow.com.

LTC3554EPD

Figure 4. Bill of Materials

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