Linear Technology LTC3554EPD User manual

1
DEMO CIRCUIT 1468
A
QUICK START GUID
E
LTC3554EPD
Micropower USB Power Manage
r
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 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
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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
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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
A
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
A
AM3
-
+
VM6
+ -
+ LD3
0V - 5V
- 2
A
AM4
-
+
VM2
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Figure 3. Circuit Schematic
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Figure 4. Bill of Materials
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