HIGH TEMPERATURE ADJUSTABLE
PRECISION ZENER SHUNT REGULATOR
ISSUE 1 JULY 1997
DEVICE DESCRIPTION
The ZHT2431 is a three terminal adjustable
shunt regulator offering excellent temperature
stability and output current handling capability
up to 25mA. The output voltage may be set to
any chosen voltage between 1.24 and 15 volts
by selection of two external divider resistors.
The devices can be used as a replacement for
zener diodes in many applications requiring an
improvement in zener performance.
The ZHT2431 is particularly used in the
feedback control loop of switch mode power
supplies. In this application the device 1.24 volt
reference enables the generation of low
voltage supplies, typically 3.3 volts or 3 volts.
The ZHT2431 is intended for use over the
extended operating range of -55°C to 125°C.
ZHT2431
FEATURES
•
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•
•
•
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•
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Surface mount SOT23 package
TO92 package
2.5% tolerance
Average temperature coefficient 50 ppm/°C
Temperature compensated for operation
over the full temperature range
Programmable output voltage
100µA to 25mA current sink capability
Low output noise
-55° to 125° C operation
APPLICATIONS
Shunt regulator
Series regulator
Voltage monitor
Over voltage/ under voltage protection
Switch mode power supplies
SCHEMATIC DIAGRAM
V
Z
V
ref
G
nd
ZHT2431
Cathode Voltage (V
Z
)
15V
Cathode Current
50mA
Operating Temperature
-55 to 125°C
Storage Temperature
-55 to 125°C
Recommended Operating Conditions
Cathode Voltage (min)V
REF
to (max) 15V
Cathode Current (min) 100µA to (max) 25mA
ABSOLUTE MAXIMUM RATING
Power Dissipation (T
amb
=25°C, T
jmax
=150°C)
SOT23
330mW
TO92
780mW
ELECTRICAL CHARACTERISTICS
TEST CONDITIONS (Unless otherwise stated):T
amb
=25°C
PARAMETER
Reference Voltage
Deviation of Reference Input
Voltage over Temperature
SYMBOL MIN TYP MAX UNITS CONDITIONS
2.5% V
ref
V
dev
1.21 1.24 1.27 V
5.0
0.5
15.0 mV
2.0
I
L
=10mA (Fig1), V
Z
=V
ref
I
L
=10mA, V
Z
=V
ref
T
a
=full range (Fig1)
VALUE
Ratio of the change in
∆V
ref
Reference Voltage to the
∆V
Z
Change in Cathode Voltage
Reference Input Current
Deviation of Reference Input
Current over Temperature
Minimum Cathode Current
for Regulation
Off-state Current
Dynamic Output
Impedance
I
ref
∆
I
ref
I
Zmin
I
Zoff
R
Z
mV/V V
Z
from V
ref
to 10V
I
Z
=10mA (Fig2)
µA
µA
µA
µA
Ω
R1=10K, R2=O/C, l
L
=10mA
(Fig2)
R1=10K, R2=O/C, I
L
=10mA
T
a
=full range (Fig2)
V
Z
=15V, V
ref
=0V (Fig3)
V
Z
=V
ref
(Fig1), f=0Hz,
I
L
=10mA
0.02 0.11 0.4
0.02 0.2
30
10
100
30
0.25 2
Deviation of reference input voltage, V
dev,
is defined as the maximum variation of the
reference input voltage over the full temperature range.
The average temperature coefficient of the reference input voltage, V
ref
is defined as:
V
dev
x
1000000
V
ref
(
ppm
⁄
°C)=
Vmax
V
ref
(T1−T2)
The dynamic output impedance, Rz, is defined
∆V
Z
as:
R
Z
=
∆I
Z
When the device is programmed with two
external resistors, R1 and R2, (fig 2) , the
dynamic output impedance of the overall
circuit, R, is defined as:
R1
R
=
R
z
1+
Vmin
Vdev = Vmax - Vmin
R2
T1
Temperature
T2
With a capacitance of greater than 100pF
between cathode and anode, minimum
cathode current must be 0.2mA.
ZHT2431
TYPICAL CHARACTERISTICS
140
130
120
110
100
90
80
-50 -25
0
25
50
75 100 125
Vref = Vz
Iz=10mA
2
1
0
-1
-2
-3
-4
-5
0
5
10
Iz = 10mA
15
Temperature (°C)
Cathode Voltage (V)
Reference Current v Temperature
26
24
22
20
18
16
14
-50 -25
0
25
50
75
100 125
Change in V
ref
v Cathode Voltage
10
Vref = Vz
1mA
Vref = Vz
Ω
10mA
1
0.1
100
1k
10k
100k
Cathode Current v Temperature
1.244
1.242
1.240
1.238
1.236
Iz=10mA
Temperature (°C)
Dynamic Impedance vs. Frequency
1.0
Frequency (Hz)
0.5
TO92
SOT23
1.234
1.232
-50 -25
0
25
50
75
100 125
0
25
50
75
100
125
Reference Voltage v Temperature
Temperature (°C)
Power Dissipation Derating
Ambient Temperature (°C)
TYPICAL CHARACTERISTICS
60
50
40
30
20
10
0
100
1k
10k
100k
1M
Iz = 10mA
ZHT2431
I
Z
V
Z
240
Ω
47k
10
µ
F
+
47k
-
Frequency (Hz)
I
Z
= 10mA,
T
A
= 25°C
Gain v Frequency
2.0
1.0
0
5.0
2.5
0
0
100
200
INPUT
Single
Pulse
Vz
Repetitive
Pulse
Test Circuit for Open Loop Voltage Gain
Input Monitor
120
Ω
V
Z
Pulse
Generator
50
Ω
300
400
500
T
A
= 25°C
Time (us)
Pulse Response
Test Circuit for Pulse Response
V
ref
< V
Z
< 20, I
Z
= 10mA, T
A
= 25°C
30
25
20
15
10
5
0
10p
100p
1n
10n
.1µ
1µ
10µ
UNSTABLE
STABLE
STABLE
Input
150
Ω
V
Z
I
Z
10k
100µF
Stablity Boundary Conditions
Load Capacitance(F)
Test Circuit for Stability
Boundary Conditions
ZHT2431
APPLICATION CIRCUITS
V+
R1
Vref
R2
Vout
V+
Vout
R1
Vref
R2
Vout = 1 +
R1
R2
Vref
Vout = 1 +
R1
R2
Vref
SHUNT REGULATOR
HIGHER CURRENT SHUNT REGULATOR
V+
V+
ZSR***
In
Common
Vout
R1
Vref
R2
Vref
Vout
MIN
= Vref + Vreg
R1
Vout = 1 +
R2
R2
Vout
0.01µF
R1
Out
30
Vref
Vout = 1 +
OUTPUT CONTROL OF A
THREE TERMINAL FIXED REGULATOR
R1
R2
Vref
SERIES REGULATOR
V+
V+
INPUT
OUTPUT
V
on
2V
V
off
= V+
R1A
Vref
R2A
R1B
Vref
OUTPUT
V
TH
= 2.5V
R2B
Low limit =
High limit =
1+
1+
R1B
R2B
R1A
R2A
Vref
Vref
SINGLE SUPPLY COMPARATOR
WITH TEMPERATURE
COMPENSATED THRESHOLD
OVER VOLTAGE / UNDER VOLTAGE
PROTECTION CIRCUIT
Embedded System
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