LM4050/LM4051
50ppm/°C Precision Micropower Shunt Voltage
References with Multiple Reverse Breakdown Voltages
11
Maxim Integrated
Detailed Description
The LM4050/LM4051 shunt references use the
bandgap principle to produce a stable, accurate volt-
age. The device behaves similarly to an ideal zener
diode; a fixed voltage is maintained across its output
terminals when biased with 60µA to 15mA of reverse
current. The LM4050/LM4051 clamps to a voltage of
one diode drop below ground when biased with for-
ward currents up 10mA.
Figure 3 shows a typical operating circuit. The
LM4050/LM4051 are ideal for providing stable refer-
ences from a high-voltage power supply.
Applications Information
The LM4050/LM4051s’ internal pass transistors are used
to maintain a constant output voltage (VSHUNT) by sinking
the necessary amount of current across a source resistor.
The source resistance (RS) is determined from the load
current (ILOAD) range, supply voltage (VS) variations,
VSHUNT, and desired quiescent current.
Choose the value of RSwhen VSis at a minimum and ILOAD
is at a maximum. Maintain a minimum ISHUNT of 60µA at all
times. The RSvalue should be large enough to keep
ISHUNT less than 15mA for proper regulation when VSis
maximum and ILOAD is at a minimum. To prevent damage
to the device, ISHUNT should never exceed 20mA.
Therefore, the value of RSis bounded by the following
equation:
[VS(MIN) - VR] / [60µA + ILOAD(MAX)] > RS>
[VS(MAX) - VR] / [20mA + ILOAD(MIN)]
Choosing a larger resistance minimizes the total power dis-
sipation in the circuit by reducing the shunt current
(PD(TOTAL) = VSISHUNT). Provide a safety margin to
incorporate the worst-case tolerance of the resistor used.
Ensure that the resistor’s power rating is adequate, using
the following general power equation:
PDR= ISHUNT (VS(MAX) - VSHUNT)
Output Capacitance
The LM4050/LM4051 do not require external capacitors
for frequency stability and are stable for any output
capacitance.
Temperature Performance
The LM4050/LM4051 typically exhibit output voltage
temperature coefficients within ±15ppm/°C. The polari-
ty of the temperature coefficients may be different from
one device to another; some may have positive coeffi-
cients, and others may have negative coefficients.
High Temperature Operation
The maximum junction temperature of the LM4050/
LM4051 is +150°C. The maximum operating temperature
for the LM4050/LM4051_E_ is +125°C. At a maximum
load current of 15mA and a maximum output voltage of
5V, the parts dissipate 75mW of power. The power dissi-
pation limits of the 3-pin SC70 call for a derating value of
2.17mW/°C above +70°C and thus for 75mW of power
dissipation, the parts self-heat to 35.56°C above ambient
temperature. If the ambient temperature is +125°C, the
parts operate at 159.56°C, thereby exceeding the maxi-
mum junction temperature value of +150°C. For high-
temperature operation, care must be taken to ensure the
combination of ambient temperature, output power dissi-
pation, and package thermal resistance does not con-
spire to raise the device temperature beyond that listed
in the
Absolute Maximum Ratings
. Either reduce the out-
put load current or the ambient temperature to keep the
part within the limits.
Figure 3. Typical Operating Circuit