MCD10085 Rev. 1.1, 08-Jul-10 Page 7 of 30 www.power-one.com
SQM48 Series Data Sheet
SemiQ
TM
Family 25A DC-DC Converters
Start-up Information (using negative ON/OFF)
Scenario #1: Initial Start-up From Bulk Supply
ON/OFF function enabled, converter started via application of V
IN
.
See Figure E.
Time Comments
t
0
ON/OFF pin is ON; system front end power is toggled
on, V
IN
to converter begins to rise.
t
1
V
IN
crosses Under-Voltage Lockout protection circuit
threshold; converter enabled.
t
2
Converter begins to respond to turn-on command
(converter turn-on delay).
t
3
Converter V
OUT
reaches 100% of nominal value.
For this example, the total converter start-up time (t
3
- t
1
) is typically
3 ms.
Scenario #2: Initial Start-up Using ON/OFF Pin
With V
IN
previously powered, converter started via ON/OFF pin.
See Figure F.
Time Comments
t
0
V
INPUT
at nominal value.
t
1
Arbitrary time when ON/OFF pin is enabled (converter
enabled).
t
2
End of converter turn-on delay.
t
3
Converter V
OUT
reaches 100% of nominal value.
For this example, the total converter start-up time (t
3
- t
1
) is typically
3 ms.
Scenario #3: Turn-off and Restart Using ON/OFF Pin
With V
IN
previously powered, converter is disabled and then
enabled via ON/OFF pin. See Figure G.
Time Comments
t
0
V
IN
and V
OUT
are at nominal values; ON/OFF pin ON.
t
1
ON/OFF pin arbitrarily disabled; converter output falls
to zero; turn-on inhibit delay period (100 ms typical) is
initiated, and ON/OFF pin action is internally inhibited.
t
2
ON/OFF pin is externally re-enabled.
If (t
2
- t
1
) ≤ 100 ms, external action of ON/OFF pin
is locked out by start-up inhibit timer.
If (t
2
- t
1
) > 100 ms, ON/OFF pin action is internally
enabled.
t
3
Turn-on inhibit delay period ends. If ON/OFF pin is ON,
converter begins turn-on; if off, converter awaits
ON/OFF pin ON signal; see Figure F.
t
4
End of converter turn-on delay.
t
5
Converter V
OUT
reaches 100% of nominal value.
For the condition, (t
2
- t
1
) ≤ 100 ms, the total converter start-up
time (t
5
- t
2
) is typically 103 ms. For (t
2
- t
1
) > 100 ms, start-up will
be typically 3 ms after release of ON/OFF pin.
Fig. E: Start-up scenario #1.
ON/OFF
STATE
VOUT
t0 t1 t2 t3
ON
OFF
VIN
t
Fig. F: Start-up scenario #2.
ON/OFF
STATE
OFF
ON
V
OUT
t0 t2t1 t5
VIN
t
t4t3
100 ms
Fig. G: Start-up scenario #3.
VIN
ON/OFF
STATE
V
OUT
t
t
0 t1 t2 t3
ON
OFF
