SC1404ITSTR View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SC1404ITSTR' PDF : 27 Pages View PDF
SC1404
POWER MANAGEMENT
PRELIMINARY
Overvoltage Test
Measuring the overvoltage trip point can be problematic. Any
buck converter with synchronous mosfets can act as a boost con-
verter, sending energy from output to input. In some cases the
energy sent to the input is enough to drive the input voltage be-
yond normal levels, causing input overvoltage. To prevent this,
enable the SC1404 PSAVE# feature, which effectively disables
the low side mosfet drive so that little energy, if any, is transferred
back to the input.
Typical Characteristics
3.3V Efficiency
100
90
6V
10V
19V
Semtech recommends the following circuit for measuring the ov-
ervoltage trip point. D1 prevents the output voltage from damag-
ing lab supply 1. R1 limits the amount of energy that can be cycled
from the output to the input. R2 absorbs the energy that might
flow from output to input, and D2 protects lab supply from pos-
sible damage. The ON5 signal is monitored to indicate when
overvoltage occurs.
Initial conditions:
Both lab supplies set to zero volts
No load connected to 3V or 5V
PSAVE# enabled (PSAVE# tied to GND)
ON5 enabled
ON3 enabled
DVMs monitoring ON5 and the output under test.
Oscilloscope probe connected to Phase Node
of the output under test (not strictly required).
80
70
60
50
0.01
0.1
1
10
Load Current (A)
5V Efficiency
6V
10V
19V
100
95
Set Lab Supply 2 to provide 10V at the SC1404 input. The phase
node of the output being tested should show some switching ac-
tivity. The ON5 pin should be above 4V.
Slowly increase Lab Supply 1 until the output under test rises
slightly above it’s normal DC level. As Lab Supply 1 increases,
switching activity at the phase node will cease. The ON5 pin should
remain above 4V.
Increase Lab Supply 1 in very small increments, monitoring both
ON5 and the output under test. The overvoltage trip point is the
highest voltage seen at the output before ON5 pulls low (approxi-
mately 0.3V). Do not record the voltage seen at the output after
ON5 has pulled low; when ON5 pulls low, the current flowing in D1
changes, corrupting the voltage seen at the output.
90
85
80
0.01
0.1
1
10
Load Current (A)
D1
e.g. 1N4004
Lab
Supply
2
R2
470
1/2W
Output
under
test
Vin
SC1404
Evaluation
Board
ON5
VL
1K
to DVM
D1
e.g. 1N4004
R1
75
1/2W
to DVM
Lab
Supply
1
2004 Semtech Corp.
18
www.semtech.com
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