Page 1
Features
■ 1.25V to 5V V
OUT
at 7A
■ Dropout Voltage < 1.0V @ 7A
■ 1.5% Trimmed Reference
■ Fast Transient Response
■ Thermal Shutdown
■ Current Limit
■ Short Circuit Protection
■ Drop-In Replacement for
LT1584
Package Options
CS5207A-1
7A LDO 3-Pin Adjustable Linear Regulator
CS5207A-1
Description
The CS5207A-1 linear regulator provides 7A at adjustable voltages
from 1.25V to 5V. This adjustable
device requires two external resistors to set the output voltage and
provide the minimum load current
for proper regulation.
This regulator is intended for use as
a post regulator and microprocessor
supply. The fast loop response and
low dropout voltage make this regulator ideal for applications where
low voltage operation and good
transient response are
important.
The circuit is designed to operate
with dropout voltages as low as
1.0V at 7A.
This regulator is protected against
overload conditions with overcurrent and thermal shutdown
protection circuitry.
The CS5207A-1 is pin compatible
with the LT1584 family of linear
regulators but has lower dropout
voltage and faster transient
response.
This regulator is available in a
TO-220 package.
Applications Diagram
1
3 Lead TO-220
1
1. Adjust
2. V
OUT
3. V
IN
Tab = V
OUT
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Email: info@cherry-semi.com
Web Site: www.cherry-semi.com
A Company
¨
Rev. 6/11/97
5.0V
V
IN
CS5207A-1
V
OUT
3.3V @ 7A
100mF
Adj
0.1mF
124
200
Load
300mF
Page 2
Package Pin Description
PACKAGE PIN # PIN SYMBOL FUNCTION
Electrical Characteristics: 0¡C²TA= 70¡C, 0¡C²TJ= 150¡C, V
Adj
= 0V unless otherwise specified.
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
CS5207A-1
2
Absolute Maximum Ratings
Input Voltage...............................................................................................................................................................................6V
Operating Junction Temperature Range .........................................................................................................0¡C ² T
J
² 150¡C
Storage Temperature Range ..............................................................................................................................-65¡C to +150¡C
Lead Temperature Soldering
Wave Solder (through hole styles only)....................................................................................10 sec. max, 260¡C peak
ESD Damage Threshold ..........................................................................................................................................................2kV
3L TO-220
1 Adjust This pin is connected to the low side of the internally trimmed 1.5%
bandgap reference voltage and carries a bias current of about 70µA.
A resistor divider from Adj to V
OUT
and from Adj to ground sets the
output voltage. Also, transient response can be improved by adding
a small bypass capacitor from this pin to ground.
2V
OUT
This pin is connected to the emitter of the power pass transistor and
provides a regulated voltage capable of sourcing 7A of current.
3V
IN
This is the supply voltage for the regulator. For the device to regulate, this voltage should be between 1V and 1.25V (depending on the
output current) greater than the output voltage.
Reference voltage VIN=2.75V to 5.5V, I
OUT
=10mA to 7A 1.234 1.253 1.271 V
(-1.5%) (+1.5%)
Line Regulation VIN=2.75V to 5.5V, I
OUT
=10mA .02 .20 %
Load Regulation VIN=2.75V,I
OUT
=10mA to 7A .04 .50 %
Minimum Load Current VIN=5V, ÆV
OUT
=+1.5% 5 10 mA
(Note 1)
Adjust Pin Current VIN=2.75V,I
OUT
=10mA 70 120 µA
Current Limit VIN=2.75V,ÆV
OUT
= -1.5% 7.1 8.0 A
Short Circuit Current VIN=2.75V,V
OUT
=0V 5.0 9.0 A
Ripple Rejection VIN=3.25V, 60 80 dB
(Note 2) V
Ripple
=1V
P-P
@120Hz,
I
OUT
=4A,C
Adj
=0.1µF; C
OUT
= 22µF
Thermal Regulation (Note 2) 30ms Pulse, TA=25¡C 0.002 %/W
Dropout Voltage I
OUT
=100mA 0.92 1.15 V
(Minimum V
IN -VOUT
)I
OUT
=1A 0.93 1.15 V
(Note 3) I
OUT
=2.75A 0.94 1.15 V
I
OUT
=4A 0.95 1.15 V
I
OUT
=7A 0.96 1.25 V
RMS Output Noise Freq=10Hz to 10kHz, TA=25¡C 0.003 %V
OUT
Temperature Stability 0.5 %
Thermal Shutdown (Note 4) 150 180 210 ¡C
Thermal Shutdown Hysteresis 25 ¡C
(Note 4)
Note 1: The minimum load current is the minimum current required to maintain regulation. Normally the current in the resistor divider used to set
the output voltage is selected to meet the minimum load current requirement.
Note 2: This parameter is guaranteed by design and is not 100% production tested.
Note 3: Dropout voltage is defined as the minimum input/output voltage differential required to maintain 1.5% regulation.
Note 4: This parameter is guaranteed by design, but not parametrically tested in production. However, a 100% thermal shutdown functional test is
performed on each part.
Page 3
Typical Performance Characteristics
0 10 20 30 40 50 60 70 80 90 100 110 120 130
-0.150
-0.125
-0.100
-0.075
-0.050
-0.025
-0.000
0.025
0.050
0.075
0.100
TJ (°C)
Output Voltage Deviation (%)
IO=10mA
V
IN
=2.75V
Output Voltage Deviation (%)
Output Current (A)
0.000
0.0 7.06.0
5.04.03.02.01.0
T
Case
=0°C
0.200
0.025
0.050
0.075
0.100
0.125
0.150
0.175
T
Case
=25°C
T
Case
=125°C
0 10 20 30 40 50 60 70 80 90 100 110 120 130
60.00
65.00
70.00
75.00
80.00
85.00
90.00
T
Case
(°C)
Adjust Pin Current (mA)
IO=10mA
3
CS5207A-1
Block Diagram
V
Reference Voltage vs. Temperature Load Regulation vs. Output Current
Adjust Pin Current vs. Temperature
72.4
72.2
72.0
71.8
71.6
71.4
71.2
71.0
70.8
70.6
70.4
0.0 1.0 2.0 3.0 4.0 5.0 6.0
7.0
I
OUT
(A)
Adjust Pin Current (mA)
70.2
70.0
Adjust Pin Current vs. I
OUT
IN
BIAS
and
TSD
V
REF
-
EA
+
IA
+
-
V
OUT
Adj
Page 4
The CS5207A-1 linear regulator has a composite PNP-NPN
output stage that requires an output capacitor for stability.
A detailed procedure for selecting this capacitor is included in the Stability Considerations section.
Design Guidelines
This LDO adjustable regulator has an output voltage range
of 1.25V to 5V. An external resistor divider sets the output
voltage as shown in Figure 1. The regulatorÕs voltage sensing error amplifier maintains a fixed 1.25V reference
between the output pin and the adjust pin.
A resistor divider network R1and R2causes a fixed current
to flow to ground. This current creates a voltage across R
2
that adds to the 1.25V across R1and sets the overall output
voltage. The adjust pin current (typically 50µA) also flows
through R2and adds a small error that should be taken
into account if precise adjustment of Vout is necessary. The
output voltage is set according to the formula:
V
OUT
= V
REF
´ + R2´ I
Adj
The term I
Adj
´ R2represents the error added by the adjust
pin current.
R1is chosen so that the minimum load current is a least
10mA. R1and R2should be of the same composition for
best tracking over temperature. For best results, the divider
resistor should be placed near the regulator with a separate
metal trace connecting them to output.
R
1
+ R
2
R
1
Adjustable Operation
Theory of Operation
Application Notes
CS5207A-1
4
Dropout Voltage (V)
Output Current (A)
0.00
0.25
0.50
0.75
1.00
1.25
0.0 7.06.0
5.04.03.02.01.0
20.0
18.0
16.0
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Output Current (A)
VIN-V
OUT
(V)
4.0 4.5 5.0 5.5
Typical Performance Characteristics: continued
1.00
2.00 3.00
4.00 5.00
Minimum Load Current (mA)
VIN – V
OUT
(V)
0.80
0.82
0.88
0.90
0.98
1.00
T
CASE
= 23°C
0.84
0.86
0.92
0.94
0.96
T
CASE
= 125°C
T
CASE
= 0°C
Dropout Voltage vs. Output Current Short Circuit Current vs. VIN- V
OUT
Minimum Load Current vs. VIN- V
OUT
10
1
10
2
10
3
10
4
10
5
20.0
30.0
50.0
70.0
90.0
Frequency (Hz)
Ripple Rejection (dB)
80.0
60.0
40.0
10.0
VIN - V
OUT
= 2V
V
Ripple
= 1V
PP
I
OUT
= 4A
C
Adj
= 0.1mF
C
OUT
= 22mF
10
6
Ripple Rejection vs. Frequency
Page 5
CS5207A-1
Application Notes: continued
5
Figure 1.
While not required, a bypass capacitor connected between
the adjust pin and ground will improve transient response
and ripple rejection. A 0.1µF tantalum capacitor is recommended for Òfirst cutÓ design. Value and type may be varied to optimize performance vs. price.
The CS5207A-1 linear regulator has an absolute maximum
specification of 6V for the voltage difference between V
IN
and V
OUT
. However, the IC may be used to regulate voltages in excess of 6V. The main considerations in such a
design are power-up and short circuit capability.
In most applications, ramp-up of the power supply to V
IN
is fairly slow, typically on the order of several tens of milliseconds, while the regulator responds in less than one
microsecond. In this case, the linear regulator begins charging the output capacitor as soon as the VINto V
OUT
differential is large enough that the pass transistor conducts current. V
OUT
is essentially at ground, and VINis on the order
of several hundred millivolts, so the pass transistor is in
dropout. As V
IN
increases, the pass transistor will remain
in dropout, and current is passed to the load until V
OUT
is
in regulation. Further increase in VINbrings the pass transistor out of dropout. The result is that the output voltage
follows the power supply ramp-up, staying in dropout
until the regulation point is reached. In this manner, any
output voltage may be regulated. There is no theoretical
limit to the regulated voltage as long as the VINto V
OUT
differential of 6V is not exceeded.
However, maximum ratings of the IC will be exceeded in a
short circuit condition. Short circuit conditions will result
in the immediate operation of the pass transistor outside of
its safe operating area. Over-voltage stresses will then
cause destruction of the pass transistor before overcurrent
or thermal shutdown circuitry can become active.
Additional circuitry may be required to clamp VINto V
OUT
differential to less than 6V if failsafe operation is required.
One possible clamp circuit is illustrated below; however,
the design of clamp circuitry must be done on an application by application basis. Care must be taken to ensure the
clamp actually protects the design. Components used in
the clamp design must be able to withstand the short circuit conditions indefinitely while protecting the IC.
Figure 2.
The output compensation capacitor helps determine three
main characteristics of a linear regulator: start-up delay,
load transient response, and loop stability.
The capacitor value and type is 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.
However, when the circuit operates at low temperatures,
both the value and ESR of the capacitor will vary considerably. The capacitor manufacturerÕs data sheet provides this
information.
A 300µF tantalum capacitor will work for most applications, but with high current regulators such as the
CS5207A-1 the transient response and stability improve
with higher values of capacitance. The majority of applications for this regulator involve large changes in load current so the output capacitor must supply the instantaneous
load current. The ESR of the output capacitor causes an
immediate drop in output voltage given by:
ÆV = ÆI ´ ESR.
For microprocessor applications it is customary to use an
output capacitor network consisting of several tantalum and
ceramic capacitors in parallel. This reduces the overall ESR
and reduces the instantaneous output voltage drop under
transient load conditions. The output capacitor network
should be as close to the load as possible for the best results.
Protection Diodes
When large external capacitors are used with a linear regulator it is sometimes necessary to add protection diodes. If
the input voltage of the regulator gets shorted, the output
capacitor will discharge into the output of the regulator.
The discharge current depends on the value of the capacitor, the output voltage, and the rate at which VINdrops. In
the CS5207A-1 regulator, the discharge path is through a
large junction and protection diodes are not usually needed. If the regulator is used with large values of output
capacitance and the input voltage is instantaneously shorted to ground, damage can occur. In this case, a diode connected as shown in Figure 3 is recommended.
Stability Considerations
Other Adjustable Operation Considerations
V
IN
CS5207A-1
V
OUT
EXTERNAL SUPPLY
Adj
R1
R2
V
IN
V
OUT
V
Adj
Page 6
6
CS5207A-1
A rule of thumb useful in determining if a protection diode
is required is to solve for current
I = , where
I is the current flow out of the load capacitance when
V
IN
is shorted,
C is the value of the load capacitance,
V is the output voltage, and
T is the time duration required for VINto transition
from high to being shorted.
If the calculated current is greater than or equal to the typical short circuit current value provided in the specifications, serious thought should be given to including a protection diode.
Figure 3.
Current Limit
The internal current limit circuit limits the output current
under excessive load conditions, and protects the regulator.
Short Circuit Protection
The device includes foldback short circuit current limit that
clamps the output current at approximately two amperes
less than its current limit value.
Thermal Shutdown
The thermal shutdown circuitry is guaranteed by design to
become activated above a die junction temperature of
150¡C and to shut down the regulator output. This circuitry includes a thermal hysteresis circuit with 25¡C of typical
hysteresis, thereby allowing the regulator to recover from a
thermal fault automatically.
High power regulators such the CS5207A-1 usually operate
at high junction temperatures. Therefore, it is important to
calculate the power dissipation and junction temperatures
accurately to ensure that an adequate heat sink is used.
Since the package tab is connected to Vout on the
CS5207A-1, electrical isolation may be required for some
applications. Also, as with all high power packages, thermal compound is necessary to ensure proper heat flow. For
added safety, this high current LDO includes an internal
thermal shutdown circuit
The thermal characteristics of an IC depend on the following four factors. Junction temperature, ambient temperature, die power dissipation, and the thermal resistance
from the die junction to ambient air. The maximum junction temperature can be determined by:
T
J(max)
= T
A(max)
+ PD
(max)
´ R
QJA
The maximum ambient temperature and the power dissipation are determined by the design while the maximum
junction temperature and the thermal resistance depend on
the manufacturer and the package type. The maximum
power dissipation for a regulator is:
PD
(max)
= (V
IN(max)-VOUT(min))IOUT(max)
+ V
IN(max)
´ I
IN(max)
A heat sink effectively increases the surface area of the
package to improve the flow of heat away from the IC and
into the surrounding air. Each material in the heat flow
path between the IC and the outside environment has a
thermal resistance which is measured in degrees per watt.
Like series electrical resistances, these thermal resistances
are summed to determine the total thermal resistance
between the die junction and the surrounding air, R
QJA
.
This total thermal resistance is comprised of three components. These resistive terms are measured from junction to
case (R
QJC
), case to heat sink (R
QCS
), and heat sink to ambi-
ent air (R
QSA
). The equation is:
R
QJA
= R
QJC
+ R
QCS
+ R
QSA
R
QJC
is rated @ 1.4¡C/W for the CS5207A-1. For a high current regulator such as the CS5207A-1 the majority of heat is
generated in the power transistor section. The value for
R
QSA
depends on the heat sink type, while the R
QCS
depends on factors such as package type, heat sink interface (is an insulator and thermal grease used?), and the
contact area between the heat sink and the package. Once
these calculations are complete, the maximum
permissible value of R
QJA
can be calculated and the proper
heat sink selected. For further discussion on heat sink
selection, see our Cherry application note ÒThermal
Management for Linear Regulators.
Calculating Power Dissipation and Heat Sink Requirements
C ´ V
T
Application Notes: continued
Adj
V
OUT
V
IN
CS5207A-1
Page 7
CS5207A-1
7
Rev. 6/11/97 © 1999 Cherry Semiconductor Corporation
Thermal Data 3L
TO-220
R
QJC
typ 1.4 ûC/W
R
QJA
typ 50 ûC/W
Package Specification
PACKAGE DIMENSIONS IN mm (INCHES)
Cherry Semiconductor Corporation reserves the
right to make changes to the specifications without
notice. Please contact Cherry Semiconductor
Corporation for the latest available information.
PACKAGE THERMAL DATA
Ordering Information
Part Number Description
CS5207A-1GT3 3L TO-220 Straight
3 Lead TO-220 (T) Straight
5.33 (.210)
4.83 (.190)
2.79 (.110)
2.29 (.090)
1.02 (.040)
0.63 (.025)
0.56 (.022)
0.38 (.014)
1.40 (.055)
1.14 (.045)
4.83 (.190)
4.06 (.160)
6.17 (.243) REF
1.14 (.045)
1.52 (.060)
1.14 (.045)
1.40 (.055)
2.87 (.113)
2.62 (.103)
6.55 (.258)
5.94 (.234)
14.22 (.560)
13.72 (.540)
2.92 (.115)
2.29 (.090)
9.78 (.385)
10.54 (.415)
3.71 (.146)
3.96 (.156)
14.99 (.590)
14.22 (.560)
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