TCN4040 Datasheet, PDF (8/9 Pages) TelCom Semiconductor, Inc – PRECISION MICROPOWER SHUNT VOLTAGE REFERENCE

PRELIMINARY INFORMATION
PRECISION MICROPOWER
SHUNT VOLTAGE REFERENCE
TCN4041
PIN DESCRIPTION
Pin No.
(SOT-23B-3)
1
Pin No.
TO-92
1
2
2
3
3
Pin No.
8-Pin SOIC
1
2
3
4
5
6
7
8
Symbol
NC
NC
NC
+
–
–
NC
NC
NC
+
Description
No connection
No connection
No connection
Positive terminal
Negative terminal
Negative terminal
No connection
No connection
No connection
Positive terminal
APPLICATIONS INFORMATION
Available in space-saving SOT-23B-3 surface
mount packages, the TCN4041 is a precision micro-power
curvature-corrected bandgap shunt voltage reference. It is
designed for stable operation without an external capacitor
connected between the “+” pin and the “-” pin. The TCN4041
also remains stable, however, if a bypass capacitor is used.
The device is available in either a fixed 1.2V or an adjustable
reverse breakdown voltage. The minimum operating cur-
rent is 60mA, and the maximum operating current is 12mA
for both options.
TCN4041s in the SOT-23 package have pin 1
connected as the (-) output. (Die attach interface contact).
Therefore, pin 1 of the TCN4041-1.2 must be left floating or
connected to pin 3, and pin 1 on the TCN4041-ADJ is the
(-) output.
In a conventional shunt regulator application, an
external series resistor (R_S) is connected between the
supply voltage and the TCN4041 (Figure 1). R_S determines
the current that flows through the load (I_L) and the TCN4041
(I_Q). Even when the supply voltage is at its minimum, and
the load current is at its maximum value, R_S should be small
enough to supply at least the minimum acceptable I_Q to the
TCN4041 since load current and supply voltage may vary.
Conversely, when the supply voltage is at its maximum and
I_L is at its minimum, R_S should be large enough that the
current flowing through the TCN4041 is less than 12mA.
R_S is determined by the supply voltage, (V_S), the
load and operating current, (I_L and I_Q), and the TCN4041’s
reverse breakdown voltage, V_R.
R_S =
V_S - V_R
I_L + I_Q
Output voltage on the TCN4041-ADJ can be adjusted to
any value between 1.24V and 10V. It is a function of the
internal reference voltage (V_REF) and the ratio of the external
feedback resistors (see Figure 2). The output can be found
with the equation (where V_OUT is the desired output voltage):
V_OUT = V_REF (R2/R1 + 1)
Equation 1.
The value of the internal V_REF is a function of V_O. The
“corrected” V_REF can be determined by (where V_O is the
desired output voltage):
V_REF’ = V_OUT ∆V_REF/∆V_OUT) +V_Y
Equation 2.
∆V_REF/∆V_OUT is typically -1.3mV/V, and V_Y = 1.240V.
Replace the value of V_REF’ in Equation 1 with the value
determined using Equation 2.
The actual output voltage can deviate from that pre-
dicted by the typical ∆V_REF/∆V_O in Equation 2. The worst
case ∆V_REF/∆V_OUT for C-grade parts is – 2.5mV/V and
V_Y = 1.246V; for D-grade, the worst case is – 3.0mV/V and
V_Y = 1.248V.
The difference in output voltage resulting from typical
worst case values are shown in the following example: Let
V_O = +9V. Using the typical value of ∆V_REF/∆V_OUT, V_REF is
1.228; choosing a value of R1 = 10kΩ, R2 = 63.272kW. The
output voltage, when using worst case ∆V_REF/∆V_OUT for
C-grade and D-grade parts, is 8.965V and 8.946V, respec-
tively. This could result in errors as large as 0.39% for
C-grade, and 0.59% for D-grade parts. However, resistor
values resulting from the typical value of ∆V_REF/∆V_OUT will
work most of the time, requiring no additional adjustments.
TCN4041-01 6/19/97
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