1
Features
s
Output Current to 5A
s
Output Trimmed to +/- 1%
s
Dropout Voltage
1.15V @ 5A
s
Fast Transient Response
s
Fault Protection Circuitry
Thermal Shutdown
Overcurrent Protection
Safe Area Protection
Package Options
3L TO-220
Tab (V
OUT
)
CS5205A-1
5A Adjustable Linear Regulator
1
CS5205A-1
The CS5205A-1 linear regulator
provides 5A at an adjustable volt-
age with an accuracy of 1%. Two
external resistors are used to set the
output voltage within a 1.25V to
13V range.
The regulator is intended for use as
a post regulator and microproces-
sor supply. The fast loop response
and low dropout voltage make this
regulator ideal for applications
where low voltage operation and
good transient response are impor-
tant.
The circuit is designed to operate
with dropout voltages as low as 1V
depending on the output current
level. The maximum quiescent cur-
rent is only 10mA at full load.
The regulator is fully protected
against overload conditions with
protection circuitry for Safe
Operating Area (SOA), overcurrent
and thermal shutdown.
The CS5205A-1 is pin compatible
with the LT1084 family of linear
regulators but has lower dropout
voltage.
The regulator is available in TO-220
and surface mount D
2
packages.
Block Diagram
1
Adj
2
V
OUT
3
V
IN
Error
Amplifier
+
Output
Current
Limit
-
V
IN
V
OUT
Adj
Thermal
Shutdown
Bandgap
Description
3L D
2
PAK
1
Rev. 7/8/97
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
2
CS5205A-1
Package Pin Description
PACKAGE PIN #
PIN SYMBOL
FUNCTION
Electrical Characteristics:
C
IN
= 10F, C
OUT
= 22F Tantalum, V
IN
V
OUT
=3V, V
IN
15V, 0C T
A
70C, T
J
+150C,
unless otherwise specified, I
full load
= 5A.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Absolute Maximum Ratings
Supply Voltage, V
CC
.....................................................................................................................................................................17V
Operating Temperature Range ..................................................................................................................................-40C to 70C
Junction Temperature ...............................................................................................................................................................150C
Storage Temperature Range .....................................................................................................................................-60C to 150C
Lead Temperature Soldering
Wave Solder (through hole styles only) ........................................................................................10 sec. max, 260C peak
Reflow (SMD styles only) .........................................................................................60 sec. max above 183C, 230C peak
s Adjustable Output Voltage
Reference Voltage
V
IN
V
OUT
=1.5V; V
Adj
= 0V
1.241
1.254
1.266
V
(Notes 1 and 2)
10mAI
OUT
5A
(-1%)
(+1%)
Line Regulation
1.5VV
IN
V
OUT
6V; I
OUT
=10mA
0.04
0.20
%
Load Regulation
V
IN
V
OUT
=1.5V;
0.08
0.4
%
(Notes 1 and 2)
10mAI
OUT
5A
Dropout Voltage (Note 3)
I
OUT
=5A; T
J
25C
1.15
1.25
V
Current Limit
V
IN
V
OUT
=3V; T
J
25C
5.5
8.5
A
V
IN
V
OUT
=9V
1.0
A
Minimum Load Current
V
IN
V
OUT
=7V
1.2
6
mA
Adjust Pin Current
50
100
A
Adjust Pin Current Change
1.5VV
IN
V
OUT
4V; 0.2
5.0
A
10mAI
OUT
5A
Thermal Regulation
30ms pulse; T
A
=25C
0.003
%W
Ripple Rejection
f=120Hz; C
Adj
=25F; I
OUT
=5A
82
dB
Temperature Stability
0.5
%
RMS Output Noise
10Hzf10kHz; T
A
=25C
0.003
%V
OUT
Thermal Shutdown
150
180
C
Thermal Shutdown Hysteresis
25
C
Note 1: Load regulation and output voltage are measured at a constant junction temperature by low duty cycle pulse testing. Changes in out-
put voltage due to thermal gradients or temperature changes must be taken into account separately.
Note 2: Specifications apply for an external Kelvin sense connection at a point on the output pin 1/4 from the bottom of the package.
Note 3: Dropout voltage is a measurement of the minimum input/output differential at full load.
D
2
PAK
3L TO-220
1
1
Adj
Adjust pin (low side of the internal reference).
2
2
V
OUT
Regulated output voltage (case).
3
3
V
IN
Input voltage.
CS5205A-1
3
Typical Performance Characteristics
Dropout Voltage vs. Output Current
Reference Voltage vs. Temperature
0.025
0.000
0.050
0.075
0.100
0.200
0
1
2
3
4
5
Output Current (A)
T
CASE
= 0
C
0.125
0.150
0.175
T
CASE
= 125
C
T
CASE
= 25
C
Output V
oltage Deviation (%)
0
10
130
-0.12
0.10
Output V
oltage Deviation (%)
T
J
(
C)
20
30
40
50
60
70
80
90 100 110 120
0.08
0.06
0.04
0.02
0.00
-0.02
-0.04
-0.06
-0.08
-0.10
Load Regulation vs. Output Current
0.85
0.70
0.90
0.95
1.00
1.10
1.15
1.20
1.25
T
CASE
= 0
C
T
CASE
= 125
C
T
CASE
= 25
C
0.75
Dropout V
oltage (V)
Output Current (A)
0
1
2
3
4
5
1.05
0.80
1
2
3
4
5
6
0.550
Minimum Load Current (mA)
V
IN
V
OUT
(V)
T
CASE
= 0
C
T
CASE
= 125
C
7
0.875
1.200
1.525
1.850
2.175
2.500
8
9
T
CASE
= 25
C
Minimum Load Current
0.0
10
1
Frequency (Hz)
Ripple Rejection (dB)
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
10
2
10
3
10
4
10
5
T
CASE
= 25
C
I
OUT
= 5A
(V
IN
V
OUT
) = 3V
V
RIPPLE
= 1.6V
PP
C
Adj
= 25
mF
Ripple Rejection vs. Frequency
4
CS5205A-1
The CS5205A-1 linear regulator provides an adjustable
voltage at currents up to 5A. The regulator is protected
against short circuit, and include thermal shutdown and
safe area protection (SOA) circuitry. The SOA protection
circuitry decreases the maximum available output current
as the input-output differential voltage increases.
The CS5205A-1 has a composite PNP-NPN output transis-
tor and requires an output capacitor for stability. A
detailed procedure for selecting this capacitor is included
in the Stability Considerations section.
The adjustable regulator (CS5205A-1) has an output volt-
age range of 1.25V to 13V. An external resistor divider sets
the output voltage as shown in Figure 1. The regulator
maintains a fixed 1.25V (typical) reference between the
output pin and the adjust pin.
A resistor divider network R1 and R2 causes a fixed cur-
rent to flow to ground. This current creates a voltage
across R2 that adds to the 1.25V across R1 and sets the
overall output voltage. The adjust pin current (typically
50A) also flows through R2 and adds a small error that
should be taken into account if precise adjustment of V
OUT
is necessary.
The output voltage is set according to the formula:
V
OUT
= V
REF
(
)
+ I
Adj
R2
The term I
Adj
R2 represents the error added by the adjust
pin current.
R1 is chosen so that the minimum load current is at least
10mA. R1 and R2 should be the same type, e.g. metal film
for best tracking over temperature. The adjust pin is
bypassed to improve the transient response and ripple
rejection of the regulator.
Figure 1. Resistor divider scheme for the adjustable version.
The output or 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 capaci-
tor with almost zero ESR, can cause instability. The alu-
minum electrolytic capacitor is the least expensive solu-
tion. However, when the circuit operates at low tempera-
tures, both the value and ESR of the capacitor will vary
considerably. The capacitor manufacturers data sheet pro-
vides this information.
A 22F tantalum capacitor will work for most applications,
but with high current regulators such as the CS5205A-1 the
transient response and stability improve with higher val-
ues of capacitor. The majority of applications for this regu-
lator 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:
V = I
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 load transient conditions. The output capacitor net-
work should be as close as possible to the load for the best
results.
When large external capacitors are used with a linear regu-
lator 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 capaci-
tor, the output voltage and the rate at which V
IN
drops. In
the CS5205A-1 linear regulator, the discharge path is
through a large junction and protection diodes are not usu-
ally needed. If the regulator is used with large values of
output capacitance and the input voltage is instantaneous-
ly shorted to ground, damage can occur. In this case, a
diode connected as shown in Figure2 is recommended.
Figure 2. Protection diode scheme for adjustable output regulator.
Since the CS5205A-1 is a three terminal regulator, it is not
possible to provide true remote load sensing. Load regula-
tion is limited by the resistance of the conductors connect-
ing the regulator to the load.
Output Voltage Sensing
V
OUT
V
IN
CS5205A-1
V
IN
Adj
R
1
R
2
C
1
V
OUT
C
2
C
Adj
IN4002 (optional)
Protection Diodes
Stability Considerations
V
OUT
V
IN
CS5205A-1
V
IN
Adj
R
1
R
2
C
1
V
OUT
C
2
V
REF
I
Adj
C
Adj
R1 + R2
R1
Adjustable Operation
Applications Information
5
Best load regulation occurs when R1 is connected directly
to the output pin of the regulator as shown in Figure 3. If
R1 is connected to the load, R
C
is multiplied by the divider
ratio and the effective resistance between the regulator and
the load becomes
R
C
(
)
R
C
= conductor parasitic resistance
Figure 3. Grounding scheme for the adjustable output regulator to min-
imize parasitics.
The CS5205A-1 linear regulator includes thermal shut-
down and safe operating area circuitry to protect the
device. High power regulators such as these usually oper-
ate at high junction temperatures so it is important to cal-
culate the power dissipation and junction temperatures
accurately to ensure that an adequate heat sink is used.
The case is connected to V
OUT
on the CS5205A-1, electrical
isolation may be required for some applications. Thermal
compound should always be used with high current regu-
lators such as these.
The thermal characteristics of an IC depend on the follow-
ing four factors:
1. Maximum Ambient Temperature T
A
(C)
2. Power dissipation P
D
(Watts)
3. Maximum junction temperature T
J
(C)
4. Thermal resistance junction to ambient R
QJA
(C/W)
These four are related by the equation
T
J
= T
A
+ P
D
R
QJA
(1)
The maximum ambient temperature and the power dissi-
pation 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:
P
D(max)
={V
IN(max)
V
OUT(min)
}I
OUT(max)
+V
IN(max)
I
Q
(2)
where
V
IN(max)
is the maximum input voltage,
V
OUT(min)
is the minimum output voltage,
I
OUT(max)
is the maximum output current, for the application
I
Q
is the maximum quiescent current at I
OUT
(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. Like series
electrical resistances, these resistances are summed to
determine R
QJA
, the total thermal resistance between the
junction and the surrounding air.
1. Thermal Resistance of the junction to case, R
QJC
(C/W)
2. Thermal Resistance of the case to Heat Sink, R
QCS
(C/W)
3. Thermal Resistance of the Heat Sink to the ambient air,
R
QSA
(C/W)
These are connected by the equation:
R
QJA
= R
QJC
+ R
QCS
+ R
QSA
(3)
The value for R
QJA
is calculated using equation (3) and the
result can be substituted in equation (1).
The value for R
QJC
is normally quoted as a single figure for
a given package type based on an average die size. For a
high current regulator such as the CS5205A-1 the majority
of the heat is generated in the power transistor section.
The value for R
QSA
depends on the heat sink type, while
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 per-
missible value of R
QJA
can be calculated and the proper
heat sink selected. For further discussion on heat sink
selection, see application note Thermal Management for
Linear Regulators.
Calculating Power Dissipation and Heat Sink Requirements
V
OUT
R
C
conductor parasitic
resistance
CS5205A-1
V
IN
Adj
R
LOAD
R
1
R
2
R1 + R2
R1
Applications Information: continued
CS5205A-1
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