Technical Specification
Non-Isolated
SMT Converter
9.6 - 14.4V
16A
in
there is also no concern with operation or startup into large
capacitive loads. The voltage may rise slowly while charging
the output capacitance, but it will rise.
APPLICATION CONSIDERATIONS
Input Filtering/Capacitance/Damping: The filter circuit
of Figure C is often added to the converter's input to prevent
switching noise from reaching the input voltage bus.
There are also no problems starting into a load that has a resis-
tive V-I curve. As long as the load draws less than the current
limit value at 1/2 of the unit's setpoint voltage, proper startup
is ensured.
Internal Over-Voltage Protection: To fully protect from
excessive output voltage, the NQ12 series contains two levels
of Output Over-Voltage Shutdown circuitry.
The first type monitors the output at the load via the Sense+ pin
(or the output if Sense+ is left open). If the sensed voltage
exceeds the (optionally trimmed) setpoint by ~10% this protec-
tive circuit asserts the converter's low-side switch until the out-
put returns to normal. This circuit tracks the trimmed setpoint;
the +10% threshold is maintained over the wide trim range of
the T50 model. This circuit can also be benignly activated dur-
ing the response to a large, fast drop in load current. In this
instance the converter's normal transient response is momen-
tarily overridden by this OVP. The result is a slight asymmetry
in the converter's observed transient response.
Figure C: NQ12 converter with Input Filter
In the SMA16 (surface mount) converters Cin = 30µF and in the
VMA16 (SIP) converters Cin = 45µF of high quality ceramic
capacitors. With Lin of 1µH, Cd should be 100-200µF and Rd
should be 0.1-0.2Ω, in most applications. For more informa-
tion on designing the input filter and choosing proper values,
contact SynQor technical support.
With the values listed above, the ripple current in L1 will be
below 100mA RMS for all units. The full-load worst-case filter
operation is summarized in Table 1.
It should be noted that there is no limit on this OVP; if a pow-
erful external source attempts to raise the output of an NQ12
converter beyond 110% of its setpoint, the converter will sacri-
fice itself trying to draw down that external source and protect
its load from the overvoltage.
Vout
Model
0.9
1.0
1.2
1.5
1.8
2.0
2.5
Current
(A RMS)
5.2
5.5
6.0
6.7
7.4
7.8
8.8
Ripple
(V RMS)
0.06
0.07
0.08
0.09
0.11
0.11
0.13
Current in L1
(mA RMS)
Vp Ripple
(V RMS)
0.04
0.04
0.05
0.06
0.07
0.08
0.09
Current in L1
(mA RMS)
32
34
40
47
54
59
69
81
86
21
22
27
31
36
39
46
54
57
The second Output Over-Voltage Shutdown circuit indepen-
dently compares the voltage at the converter's output pin with
that of a redundant reference. If the output ever exceeds
~125% of nominal setpoint, both converter switches are dis-
abled. After the output voltage returns to normal, a softstart
cycle is initiated.
3.3
5.0
10.4
12.3
0.15
0.16
0.10
0.11
Table 1: Full Load Input Filter Performance, SMA16
Adding significant external pure ceramic capacitance directly
across the converter's input pins is not recommended. Parasitic
inductance associated with the input pin geometry and PCB
traces can create a high-Q CLC circuit with any external capac-
itors. Just a few nano-Henries of parasitic inductance can cre-
ate a resonance (or an overtone) near the converter's switching
This OVP is independent of the trimmed setpoint. As such, the
converter's load is protected from faults in the external trim cir-
cuitry (such as a trim pin shorted to ground). Since the setpoint
of this OVP does not track trim, it is set at 125% of 5.0V, or
6.2V, in the wide-trim T50 model.
frequency. Cin has a reactance of 10-20m
Ω at the 330kHz
switching frequency. To avoid this high-frequency resonance,
any external input filter should exhibit a net source impedance
Over-Temperature Shutdown: A temperature sensor on
the converter senses the average temperature of the module.
The thermal shutdown circuit is designed to turn the converter
off when the temperature at the sensed location reaches the
Over-Temperature Shutdown value. It will allow the converter to
turn on again when the temperature of the sensed location falls
by the amount of the Over-Temperature Shutdown Restart
Hysteresis value.
of at least 20m
Ω resistive through this frequency range. This
requirement is easily met with the damping elements discussed
above. Adding a small amount (a few µF) of high-frequency
external ceramic will not violate it.
If using converters at higher powers, do consider the ripple cur-
rent rating of Cd. Contact SynQor technical support for more
Product # NQ12T50SMA16
Phone 1-888-567-9596
Doc.# 005-2NS12TE Rev. A
5/28/04
Page 11
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