Linear Technology LTC3554EPD Quick Start Manual

DESCRIPTION
Demonstration Circuit DC1468A is a Micropower USB Power Manager with Two Step-Down Regulators featuring
®
the LTC 3554.
PERFORMANCE SUMMARY
SYMBOL
VBUS
V(BAT)
I(BAT)
VOUT1
VOUT2
QUICK START PROCEDURE
Refer to Figure 1 for the proper measurement
equipment setup and jumper settings and follow the
procedure below.
When measuring the input or output voltage ripple, care
NOTE.
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.
LTC3554 draws only ~10μA from the battery.
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PARAMETER CONDITIONS
Bus Input Voltage Range
Battery Float Voltage Constant Voltage Mode
Battery Charge Current Constant Current Mode, R
Output Voltage 1 I(VOUT1) ≤ 200mA
Output Voltage 2 I(VOUT2) ≤ 200mA
The STBY jumper is on, so the
DEMO CIRCUIT 1468A
QUICK START GUIDE
Micropower USB Power Manager
with Two Step-Down Regulators
Specifications are at T = 25°C
A
MIN
4.35
4.15
= 1.87k 420
PROG
3.25
1.15
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
LTC3554EPD
TYP MAX UNITS
6 V
4.23 V
500 mA
3.35 V
1.25 V
1