DEMO CIRCUIT 1468A
QUICK START GUIDE
LTC3554EPD
Micropower USB Power Manager
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
A
= 25°C
SYMBOL
VBUS
V(BAT)
I(BAT)
VOUT1
VOUT2
PARAMETER
Bus Input Voltage Range
Battery Float Voltage
Battery Charge Current
Output Voltage 1
Output Voltage 2
CONDITIONS
Constant Voltage Mode
Constant Current Mode, R
PROG
= 1.87k
I(VOUT1) ≤ 200mA
I(VOUT2) ≤ 200mA
MIN
4.35
4.15
420
3.25
1.15
TYP
MAX
6
4.23
500
3.35
1.25
UNITS
V
V
mA
V
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
1
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.
2
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