unr-1.8/10-d3t Murata Manufacturing Co., Ltd, unr-1.8/10-d3t Datasheet - Page 5

• Manufacturer Part Number: unr-1.8/10-d3t
• Description: Single Output, Non-isolated, 3.3vin To 1.5/1.8/2.5vout 8 And 10 Amp Dc/dc Converters
• Manufacturer: Murata Manufacturing Co., Ltd

www.murata-ps.com
When the output current of a thermally stabilized converter exceeds the
maximum rating (10A) by 40% (typical) to 80% (maximum), the internal over-
current detection circuit automatically shuts down the converter by discharg-
ing the soft-start circuit of the pulse width modulator (PWM). In this off state,
which is similar to that achieved by pulling the On/Off Control low, the output
voltage quickly drops as the output capacitors discharge into the load. Since
there is no longer any output current, the overcurrent detection circuit is
released, allowing the soft-start circuit to recharge and the converter to turn
on again. If the faulty load condition persists, the overcurrent detection circuit
will again discharge the soft-start circuit and shut down the converter. This
continuous on/off cycling of the converter is referred to as “hiccup mode.”
Once the overload condition is removed, the converter remains on, and the
output voltage is quickly restored to its regulated value.
The components used to sense the output current have large temperature
coefficients. Consequently, in a “cold-start” situation, the Overcurrent Detec-
tion Point may temporarily move to 80% to 120% above the rated current
specification. The device quickly heats up, particularly if an overload situation
exists, and restores the normal (40%) Overcurrent Detection Point. The
device easily survives starting up into an output-short-circuit condition.
The overcurrent detection circuitry helps keep internal current levels and
operating temperatures within safe operating limits. Nevertheless, sustained
operation at current levels above the rated output current (10 Amps) but
below the Overcurrent Detection Point (typically 14 Amps) may result in
permanent damage to the converter (unless active cooling keeps internal
temperatures below safe limits).
Output Voltage Trimming
For 2.5V
1.52V and 3.0V. For 1.5V
to any voltage between 1.28V and 3.0V. Trimming is accomplished with either
a trimpot or a single fixed resistor. The trimpot should be connected between
+Output and Output Return with its wiper connected to the Trim pin as shown
in Figure 3 below.
A trimpot can be used to determine the value of a single fixed resistor
which should be connected, as shown in Figure 4, between the Trim pin and
+Output to trim down the output voltage, or between the Trim pin and Output
Return to trim up the output voltage. Fixed resistors should be metal-film
types with absolute TCR’s less than 100ppm/ C to ensure stability.
The equations and look-up table below can be used as starting points for
selecting specific trim-resistor values. Recall that untrimmed devices are
guaranteed to be 1% accurate.
OUT
devices, the output can be trimmed to any voltage between
INPUT
RETURN
+INPUT
Figure 3. Trim Connections Using a Trimpot
OUT
and 1.8V
+OUTPUT
OUTPUT
RETURN
TRIM
OUT
devices, the output can be trimmed
20k
5-10
Turns
LOAD
Temperature Derating
The outstanding electrical efficiency of the UNR D3 Series' synchronous-
rectifier design and the excellent thermal conductivity of its encapsulated
metal package combine to eliminate the need for heat sinking or supplemen-
tal forced-air cooling in the majority of routine applications. As shown in
the derating curves on page 2, 2.5V
power (25 Watts) up to +55°C (ambient) and then derate linearly to +100°C.
1.8V
(ambient) and similarly derate linearly to +100°C.
When operated with 3.0V input voltages, all devices in the UNR D3 Series
are more efficient and can operate to +60°C and +55°C, respectively. At
3.6V
temperatures are reduced to +45°C and +50°C, respectively.
Trim-Resistor Equations for 2.5V
Trim-Resistor Equations for 1.8V
Trim-Resistor Look-Up Table for Common Output Voltages
Desired Output
Voltage (Volts)
OUT
IN
Trim Down
Trim Down
1.28
1.52
1.8
2.5
2.8
, devices operate less efficiently, and maximum full-load ambient
2
3
Trim Up
Trim Up
models deliver full rated output power (18 Watts) up to +50°C
Single Output, Non-Isolated, 3.3V
Note: Install either a fixed trim-up resistor or a fixed trim-down resistor
depending upon desired output voltage.
Figure 4. Trim Connections Using Fixed Resistors
Trim Resistor ( )
+INPUT
INPUT
RETURN
R
R
V
R
R
V
OUT
TRIM
TRIM
OUT
TRIM
TRIM
Technical enquiries email: [e-mail], tel:
2.07k
Open
16.9k
4.83k
3.38k
2.82k
= V
= V
0
(Ohms) =
(Ohms) =
(Ohms) =
(Ohms) =
1.8V
OUT
OUT
OUT
Desired
Desired
Models
+OUTPUT
OUTPUT
RETURN
2670 (V
7500 (V
Connect To
V
OUT
V
OUT
OUT
+Output
+Output
–Output
–Output
–Output
–Output
TRIM
OUT
OUT
Open
8 and 10 Amp DC/DC Converters
3380
9465
UNR D3 SERIES
Devices
Devices
1.8 – V
2.5 – V
models deliver full rated output
– 1.8
– 2.5
OUT
OUT
–1.267)
–1.267)
OUT
OUT
Trim Resistor ( )
Trim
Down
Trim Up
–1740
MDC_UNR15-25W Page 5 of 8
IN
17.15k
4.03k
9.35k
Open
29.7k
N.A.
0
to 1.5/1.8/2.5V
2.5V
OUT
LOAD
–1740
Models
[phone]
Connect To
+Output
+Output
+Output
–Output
–Output
Open
N.A.
OUT