LM4040
Improved Precision Micropower Shunt Voltage
Reference with Multiple Reverse Breakdown Voltages
11
Maxim Integrated
Detailed Description
The LM4040 shunt references use the bandgap princi-
ple to produce a stable, accurate voltage. The device
behaves similarly to an ideal zener diode; a fixed volt-
age is maintained across its output terminals when
biased with 60µA to 15mA of reverse current. The
LM4040 behaves similarly to a silicon diode when
biased with forward currents up 10mA.
Figure 3 shows a typical operating circuit. The LM4040
is ideal for providing a stable reference from a high-
voltage power supply.
Applications Information
The LM4040’s internal pass transistor is used to maintain a
constant output voltage (V
SHUNT
) by sinking the necessary
amount of current across a source resistor. The source
resistance (R
S
) is determined from the load current (I
LOAD
)
range, supply voltage (V
S
) variations, V
SHUNT
, and desired
quiescent current.
Choose the value of R
S
when V
S
is at a minimum and I
LOAD
is at a maximum. Maintain a minimum I
SHUNT
of 60µA at all
times. The R
S
value should be large enough to keep
I
SHUNT
less than 15mA for proper regulation when V
S
is
maximum and I
LOAD
is at a minimum. To prevent damage
to the device, I
SHUNT
should never exceed 20mA.
Therefore, the value of R
S
is bounded by the following
equation:
[V
S(MIN)
- V
R
] / [60µA + I
LOAD(MAX)
] > R
S
>
[V
S(MAX)
- V
R
] / [20mA + I
LOAD(MIN)
]
Choosing a larger resistance minimizes the total power dis-
sipation in the circuit by reducing the shunt current
(P
D(TOTAL)
= V
S
I
SHUNT
). 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:
PD
R
= I
SHUNT
(V
S(MAX)
- V
SHUNT
)
Output Capacitance
The LM4040 does not require an external capacitor for fre-
quency stability and is stable for any output capacitance.
Temperature Performance
The LM4040 typically exhibits an output voltage tem-
perature coefficient within ±15ppm/°C. The polarity of
the temperature coefficient may be different from one
device to another; some may have positive coefficients,
and others may have negative coefficients.
High Temperature Operation
The maximum junction temperature of the LM4040 is
+150°C. The maximum operating temperature for the
LM4040_E_ is +125°C. At a maximum load current of 15mA
and a maximum output voltage of 5V, the part will dissipate
75mW of power. The power dissipation 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 part will self-
heat to 35.56°C above ambient temperature. If the ambient
temperature is +125°C, the part operates at 159.56°C,
thereby exceeding the maximum junction temperature
value of +150°C. For high-temperature operation, care must
be taken to ensure the combination of ambient temperature,
output power dissipation and package thermal resistance
does not conspire to raise the device temperature beyond
that listed in the
Absolute Maximum Ratings
. Either reduce
the output load current or the ambient temperature to keep
the part within the limits.
Figure 3. Typical Operating Circuit
