SC1404ITSTR Semtech, SC1404ITSTR Datasheet - Page 18

• Manufacturer Part Number: SC1404ITSTR
• Description: IC, PWM CONTROLLER, 28-TSSOP
• Manufacturer: Semtech

Specifications of SC1404ITSTR

• Primary Input Voltage: 15V
• No. Of Outputs: 3
• Output Voltage: 5.25V
• Output Current: 1A
• No. Of Pins: 28
• Operating Temperature Range: -40°C To +85°C
• Peak Reflow Compatible (260 C): No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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.
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:
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.
POWER MANAGEMENT
Set Lab Supply 2 to provide 10V at the SC1404 input. The phase
2004 Semtech Corp.
Lab
Supply
2
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
D1
e.g. 1N4004
R2
470
1/2W
of the output under test (not strictly required).
Vin
SC1404
Evaluation
Board
ON5
Output
under
test
VL
1K
to DVM
to DVM
R1
75
1/2W
D1
e.g. 1N4004
Lab
Supply
1
18
Typical Characteristics
100
90
80
70
60
50
3.3V Efficiency
100
0.01
5V Efficiency
95
90
85
80
0.01
0.1
Load Current (A)
Load Current (A)
0.1
6V
1
1
6V
10V
PRELIMINARY
10V
SC1404
www.semtech.com
10
10
19V
19V