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MCD10208 Rev. 1.0, 08-Jul-10
Page 4 of 33
www.power-one.com
SQM48T/S20 DC-DC Converter Data Sheet
36-75 VDC Input; 1.2-3.3 VDC @ 20A Outputs
current (originally obtained from the derating curves)
by the same percentage to ensure the converter’s
actual output power remains at or below the
maximum allowable output power.
Output Voltage Adjust /TRIM (Pin 6)
The output voltage can be adjusted up 10% or down
20% for Vout ≥ 1.5V, and ±10% for Vout = 1.2V
relative to the rated output voltage by the addition of
an externally connected resistor. For output voltage
3.3V, trim up to 10% is guaranteed only at Vin ≥ 40V,
and it is marginal (8% to 10%) at Vin = 36V
The TRIM pin should be left open if trimming is not
being used. To minimize noise pickup, a 0.1F
capacitor is connected internally between the TRIM
and SENSE(-) pins.
To increase the output voltage, refer to Fig. C. A trim
resistor, RT-INCR, should be connected between the
TRIM (Pin 6) and SENSE(+) (Pin 7), with a value of:
10.22
1.225Δ
626
Δ)V
5.11(100
R
NOM
O
INCR
T
[k
],
for 3.3 – 1.5V.
7.2
Δ
84.6
R INCR
T
[k
] (1.2V)
where,
INCR
T
R
Required value of trim-up resistor k
]
NOM
O
V
Nominal value of output voltage [V]
100
X
V
)
V
(V
Δ
NOM
-
O
NOM
-
O
REQ
-
O
[%]
REQ
O
V
Desired (trimmed) output voltage [V].
Rload
Vin
Vin (+)
Vin (-)
ON/OFF
Vout (+)
Vout (-)
TRIM
SENSE (+)
SENSE (-)
R T-INCR
(Top View)
Converter
Semi
QTM Family
Fig. C: Configuration for increasing output voltage.
When trimming up, care must be taken not to exceed
the converter‘s maximum allowable output power.
See previous section for a complete discussion of
this requirement.
To decrease the output voltage (Fig. D), a trim
resistor, RT-DECR, should be connected between the
TRIM (Pin 6) and SENSE(-) (Pin 5), with a value of:
10.22
Δ
511
R DECR
T
[k
] (3.3 – 1.5V)
15
Δ
700
R DECR
T
[k
] (1.2V)
where,
DECR
T
R
Required value of trim-down resistor [k
]
and Δ is defined above.
Note: The above equations for calculation of trim
resistor values match those typically used in
conventional industry-standard quarter bricks and
one-eighth bricks (except for 1.2V output).
Converters with output voltages 1.2V is available with
alternative trim feature to provide the customers with
the
flexibility
of
second
sourcing.
For
these
converters, the last character in the part number is
“T”. The trim equations of “T” version of converters
and more information can be found in Application
Note 103.
Rload
Vin
Vin (+)
Vin (-)
ON/OFF
Vout (+)
Vout (-)
TRIM
SENSE (+)
SENSE (-)
RT-DECR
(Top View)
Converter
Semi
QTM Family
Fig. D: Configuration for decreasing output voltage.
Trimming/sensing beyond 110% of the rated output
voltage is not an acceptable design practice, as this
condition could cause unwanted triggering of the
output over-voltage protection (OVP) circuit. The
designer should ensure that the difference between
the voltages across the converter’s output pins and its
sense pins does not exceed 10% of VOUT(NOM), or:
X
NOM
-
O
SENSE
OUT
10%
V
)]
(
V
)
(
[V
)]
(
V
)
(
[V
[V]
This equation is applicable for any condition of output
sensing and/or output trim.
Protection Features
Input Undervoltage Lockout
Input undervoltage lockout is standard with this
converter. The converter will shut down when the
input voltage drops below a pre-determined voltage.
The input voltage must be typically 34 V for the
converter to turn on. Once the converter has been
turned on, it will shut off when the input voltage drops
typically below 32 V. This feature is beneficial in
preventing deep discharging of batteries used in
telecom applications.