CHERRY CS8271

CS8271
CS8271
Adjustable Micropower Low Dropout
Linear Regulator with ENABLE
Features
Description
The CS8271 is an adjustable micropower voltage regulator with very
low quiescent current (60µA typical
at 100µA load). The output supplies
100mA of load current with a maximum dropout voltage of only
600mV. Control logic includes
ENABLE . The combination of low
quiescent current, outstanding regulator performance and control
logic makes the CS8271 ideal for
any battery operated equipment.
The logic level compatible ENABLE
pin allows the user to put the regu-
lator into a shutdown mode where it
draws only 50µA of quiescent current.
The regulator is protected against
reverse battery, short circuit, over
voltage, and over temperature conditions. The device can withstand
60V load dump transients making it
suitable for use in automotive environments.
The CS8271 is pin compatible with
the National Semiconductor
LM2931.
■ Low Quiescent Current
■ Adjustable Output:
5V to 12V
■
ENABLE for Sleep Mode
Control
■ 100mA Output Current
Capability
■ Fault Protection
+60V Load Dump
-15V Reverse Voltage
Short Circuit
Thermal Shutdown
■ Low Reverse Current
(Output to Input)
Block Diagram
VOUT
VIN
Current Source
(Circuit Bias)
Package Options
Over
Voltage
Shutdown
8L SOIC & PDIP
ENABLE
Input
Current Limit
Sense
VOUT
Adj
+
Thermal
Shutdown
- Error
VIN
1
Gnd
NC
NC
NC
Adj
ENABLE
Amplifier
Bandgap
Reference
Gnd
Other Packages: Consult factory for
16L SO Batwing, 5L TO-220 and D2PAK.
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Email: [email protected]
Web Site: www.cherry-semi.com
Rev. 3/26/97
1
A
¨
Company
CS8271
Absolute Maximum Ratings
Power Dissipation.............................................................................................................................................Internally Limited
Transient Input Voltage ..................................................................................................................................................-50V, 60V
Reverse Battery..........................................................................................................................................................................-15V
Output Current .................................................................................................................................................Internally Limited
ESD Susceptibility (Human Body Model)..............................................................................................................................2kV
Junction Temperature .............................................................................................................................................-40¡C to 150¡C
Storage Temperature...............................................................................................................................................-55¡C to 150¡C
Lead Temperature Soldering
Wave Solder (through hole styles only) .....................................................................................10 sec. max, 260¡C peak
Reflow (SMD styles only) ......................................................................................60 sec. max above 183¡C, 230¡C peak
Adj and Enable Output ..................................................................................................................................................-0.3V, 10V
...........................................................................................................................................................................-0.3V, 20V
VOUT
Electrical Characteristics: VOUT + 1V ² VIN ² 30V, 5V ² VOUT ² 12V, IOUT = 10mA, -40¡ ² TA ² 125¡, -40¡ ² TJ ² 150¡,
VENABLE = 0V; unless otherwise specified.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
■ Output Voltage
Dropout Voltage
IOUT = 100µA, VDROP = (VIN Ð VOUT)
IOUT = 100mA, VDROP = (VIN Ð VOUT)
100
400
150
600
mV
mV
Load Regulation
Measure VOUT when
IOUT = 100µA, 100mA.
LDREG = ABS (ÆVOUT)
0.1
1.0
%VOUT
Line Regulation
IOUT = 1mA. Measure VOUT
when VIN = VOUT + 1V, 30V.
LNREG = ABS (ÆVOUT)
0.1
0.5
%VOUT
VIN = 6V, IOUT = 100µA,
VOUT setup for 5V. IQ = IVIN - IOUT
55
120
µA
VIN = 13V, IOUT = 100µA,
VOUT setup for 12V. IQ = IVIN - 100µA
130
200
µA
VIN = 30V, IOUT = 100µA,
VOUT setup for 5V, IQ = IVIN - 100µA
150
450
µA
VIN = 30V, IOUT = 100µA,
VOUT setup for 12V, IQ = IVIN - 100µA
200
500
µA
IOUT = 50mA, IQ = IVIN - 50mA
4
7
mA
IOUT = 100mA, IQ = IVIN - 100mA
12
21
mA
VIN = 6V, ENABLE = 2.5V,
IQSLEEP = IVIN
20
50
µA
VIN = 30V, ENABLE = 2.5V,
IQSLEEP = IVIN
75
350
µA
Quiescent Current, (IQ)
Active Mode
Quiescent Current, (IQ)
Sleep Mode
Ripple Rejection
f=120Hz, (Note 1)
60
75
Current Limit
VOUT = VOUT - 500mV, ILIM = IVOUT
105
200
300
mA
Short Circuit Output Current
VOUT=0V, ISHRT = IVOUT
15
100
215
mA
Thermal Limit
(Note 1)
150
180
210
¡C
Overvoltage Shutdown
Adjust VIN from 28V to 40V
until VOUT ² 1V
30
34
38
V
Reverse Current
VIN=0V, IREV = IVOUT, VOUT = 13.2V
100
200
µA
2
dB
CS8271
Electrical Characteristics: VOUT + 1V ² VIN ² 30V, 5V ² VOUT ² 12V, IOUT = 10mA, -40¡ ² TA ² 125¡, -40¡ ² TJ ² 150¡,
VENABLE = 0V; unless otherwise specified.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
■ ENABLE
Enable Threshold
1.15
VENABLE = 2.6V
VENABLE = 5V
Enable Input Current
■ Adjustment Pin
2.0
2.6
V
10
35
20
50
µA
µA
R1: Feedback resistor between VOUT and Adjust, R2: Adjust resistor to ground.
Reference Voltage
100µA ² IOU T² 100mA
VREF (VOUT - VREF)
IAdj =
R2
R1
Adjustment Pin Current
1.246
1.272
1.297
V
20
500
nA
Note 1: Guaranteed by design, not 100% tested in production.
Package Pin Description
PACKAGE PIN #
PIN SYMBOL
FUNCTION
8L SOIC & PDIP
1
VOUT
100mA output; adjustable from 5V to 12V.
2
Gnd
Ground.
3, 6, 7
NC
No Connection.
4
Adj
Resistor divider from VOUT to Adj, sets output voltage.
5
ENABLE
8
VIN
Logic level switch, when HIGH, regulator is in sleep mode.
Input voltage.
Circuit Description
Output Voltage Adjustment
The output voltage of the CS8271 is adjustable to any value
between the reference voltage on the Adj pin, (1.272V Typ.)
and the maximum input voltage minus the dropout voltage.
To adjust the output voltage, a pair of external resistors R1
and R2 are connected as shown in Figure 1.
The equation for the output voltage is
VOUT = VREF x
VOUT
CS8271
VOUT
R1
Adj
VREF
R2
( )
R1 + R2
+ IAdj x R1
R2
Figure 1: Output Voltage Adjustment.
where Vref is the typical reference voltage and IAdj is the
adjust pin bias current. This is usually 500nA maximum.
3
CS8271
Circuit Description: continued
Should the junction temperature of the power device exceed
180ûC (typ) the power transistor is turned off. Thermal shutdown is an effective means to prevent die overheating since
the power transistor is the principle heat source in the IC.
Output Stage Protection
The output stage is protected against overvoltage, short
circuit and thermal runaway conditions (Figure 2).
If the input voltage rises above 30V (e.g. load dump), the
output shuts down. This response protects the internal circuitry and enables the IC to survive unexpected voltage
transients up to 60V in magnitude.
Short circuit protection limits the amount of current the
output transistor can supply. In the case of a CS8271 under
a short circuit condition, the output transistor current is
limited to 100mA.
ENABLE
The ENABLE switches the output transistor. When the
voltage on the ENABLE pin exceeds 2.0V typ, the output
pass transistor turns off, leaving a high impedance facing
the load. The IC will remain in Sleep mode, drawing only
20µA (typ), until the voltage on the ENABLE pin drops
below the ENABLE threshold.
> 30V
VIN
VOUT
IOUT
Load
Dump
Thermal
Shutdown
Short
Circuit
Figure 2: Typical Circuit Waveforms for Output Stage Protection.
Application Notes
To determine an acceptable value for COUT for a particular
application, start with a tantalum capacitor of the recommended value and work towards a less expensive alternative part.
Step 1: Place the completed circuit with a tantalum capacitor of the recommended value in an environmental chamber at the lowest specified operating temperature. Monitor
the outputs on the oscilloscope. A decade box connected in
series with the capacitor will simulate the higher ESR of an
aluminum capacitor. (Leave the decade box outside the
chamber, the small resistance added by the longer leads is
negligible)
Step 2: With the input voltage at its maximum value,
increase the load current slowly from zero to full load
while observing the output for any oscillations. If no oscillations are observed, the capacitor is large enough to
ensure a stable design under steady state conditions.
Step 3: Increase the ESR of the capacitor from zero using
the decade box and vary the load current until oscillations
appear. Record the values of load current and ESR that
cause the greatest oscillation. This represents the worst
case load conditions for the regulator at low temperature.
Step 4: Maintain the worst case load conditions set in step
3 and vary the input voltage until the oscillations increase.
This point represents the worst case input voltage conditions.
Step 5: If the capacitor is adequate, repeat steps 3 and 4
with the next smaller valued capacitor. (A smaller capacitor will usually cost less and occupy less board space.) If
the capacitor oscillates within the range of expected operating conditions, repeat steps 3 and 4 with the next larger
standard capacitor value.
Selecting the Right Capacitor Value
The output compensation capacitor COUT, determines
three main characteristics of a linear regulator: start-up
delay, load transient response and loop stability.
The selection of a capacitor value and type should be
based on cost, availability, size and temperature constraints. A tantalum or aluminum electrolytic capacitor is
best, since a film or ceramic capacitor with almost zero
ESR, can cause instability. The aluminum electrolytic
capacitor is the least expensive solution, but, if the circuit
operates at low temperatures (-25¡C to -40¡C), both the
value and ESR of the capacitor will vary considerably. The
capacitor manufacturers data sheet usually provide this
information.
The value for the output compensation capacitor COUT
shown in Figure 3 should work for most applications, but it
is not necessarily the least expensive or the optimal solution.
VIN
VOUT
CIN
0.1mF
CS8271
COUT
10mF
RRST
Adj
ENABLE
RL
CAdj
(optional)
Figure 3: Test and application circuit showing an output compensation
capacitor.
4
Step 6: Test the load transient response by switching in
various loads at several frequencies to simulate its real
work environment. Vary the ESR to reduce ringing.
Step 7: Remove the unit from the environmental chamber
and heat the IC with a heat gun. Vary the load current as
instructed in step 5 to test for any oscillations.
Once the minimum capacitor value with the maximum
ESR is found, a safety factor should be added to allow for
the tolerance of the capacitor and any variations in regulator performance. Most good quality aluminum electrolytic
capacitors have a tolerance of ±20% so the minimum value
found should be increased by at least 50% to allow for this
tolerance plus the variation which will occur at low temperatures. The ESR of the capacitor should be less than
50% of the maximum allowable ESR found in step 3 above.
Capacitance on the Adjust pin combined with the feedback resistors R1 and R2 can affect loop stability and
should also be considered. The CS8271 internal circuitry
produces about 5pF to Ground on the Adjust pin. This
capacitance, plus any additional external capacitance on
the Adjust pin will create a pole when combined with the
resistive feedback network. The effect can be significant
when using large values for the feedback resistors to minimize quiescent current.
A capacitor connected from the Adjust pin to Ground provides additional means to compensate the regulator by
creating a pole. Alternately, a capacitor can be connected
from the Adjust pin to VOUT to create a zero.
where
VIN(max) is the maximum input voltage,
VOUT(min) is the minimum output voltage,
IOUT(max) is the maximum output current, for the application
IQ is the quiescent current the regulator consumes at
IOUT(max).
IIN
VIN
IOUT
Smart
Regulator
}
VOUT
Control
Features
IQ
Figure 4: Single output regulator with key performance parameters
labeled.
Once the value of PD(max) is known, the maximum permissible value of RQJA can be calculated:
RQJA =
150¡C - TA
PD
The value of RQJA can then be compared with those in
the package section of the data sheet. Those packages with
RQJA's less than the calculated value in equation 2 will keep
the die temperature below 150¡C.
Calculating Power Dissipation
in a Single Output Linear Regulator
The maximum power dissipation for a single output regulator (Figure 4) is
PD(max)={VIN(max)ÐVOUT(min)}IOUT(max)+VIN(max)IQ
(1)
In some cases, none of the packages will be sufficient to
dissipate the heat generated by the IC, and an external
heatsink will be required.
Application Diagram
VIN
VOUT
VOUT
CS8271
C 1*
0.1mF
(2)
R1
ENABLE
Adj
C2**
10mF
Vref
Gnd
R2
C1* Required if regulator is away from power supply filter.
C2** Required for output stability.
5
VOUT = Vref x
( )
R1 + R2
+ IAdj x R1
R2
CS8271
Application Notes: continued
CS8271
Package Specification
PACKAGE DIMENSIONS IN mm (INCHES)
Lead Count
8L SOIC
8L PDIP
Metric
Max
Min
5.00
4.80
10.16 9.02
PACKAGE THERMAL DATA
D
English
Max Min
.197 .189
.400 .355
Thermal Data
RQJC
RQJA
8L
SOIC
45
165
typ
typ
8L
PDIP
52
100
ûC/W
ûC/W
Surface Mount Narrow Body (D); 150 mil wide
4.00 (.157)
3.80 (.150)
6.20 (.244)
5.80 (.228)
0.51 (.020)
0.33 (.013)
1.27 (.050) BSC
1.75 (.069) MAX
1.57 (.062)
1.37 (.054)
1.27 (.050)
0.40 (.016)
0.25 (.010)
0.19 (.008)
0.25 (0.10)
0.10 (.004)
D
REF: JEDEC MS-012
Plastic DIP (N); 300 mil wide
7.11 (.280)
6.10 (.240)
8.26 (.325)
7.62 (.300)
1.77 (.070)
1.14 (.045)
2.54 (.100) BSC
3.68 (.145)
2.92 (.115)
.356 (.014)
.203 (.008)
0.39 (.015)
MIN.
.558 (.022)
.356 (.014)
REF: JEDEC MS-001
D
Some 8 and 16 lead
packages may have
1/2 lead at the end
of the package.
All specs are the same.
Ordering Information
Part Number
Description
CS8271YD8
8L SOIC
CS8271YDR8
8L SOIC (tape & reel)
CS8271YN8
8L PDIP
Rev. 3/26/97
Cherry Semiconductor Corporation reserves the
right to make changes to the specifications without
notice. Please contact Cherry Semiconductor
Corporation for the latest available information.
6
© 1999 Cherry Semiconductor Corporation