MAX6138
0.1%, 25ppm, SC70 Shunt Voltage Reference
with Multiple Reverse Breakdown Voltages
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Detailed Description
The MAX6138 shunt reference uses the bandgap prin-
ciple 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
MAX6138 behaves similarly to a silicon diode when
biased with forward currents up to 10mA.
Figure 3 shows a typical operating circuit. The
MAX6138 is ideal for providing a stable reference from
a high-voltage power supply.
Applications Information
The MAX6138’s internal pass transistor is used to main-
tain 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
dissipation in the circuit by reducing the shunt current
(P
D(TOTAL)
= V
S
X I
SHUNT
). Provide a safety margin to
incorporate the worst-case tolerance of the resistor
used. Ensure that the resistor’s power rating is ade-
quate, using the following general power equation:
PD
R
= I
SHUNT
✕
(V
S(MAX)
- V
SHUNT
)
Output Capacitance
The MAX6138 does not require an external capacitor
for operational stability and is stable for any output
capacitance.
Temperature Performance
The MAX6138 typically exhibits an output voltage tem-
perature coefficient within ±4ppm/°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.
Chip Information
TRANSISTOR COUNT: 70
PROCESS: BiCMOS
Pin Description
