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CS5257A-1
CS5257A-1
7 LDO 5-Pin Adjustable Linear Regulator A
Description
This new very low dropout regulator is designed to power the next generation of advanced microprocessors. To achieve very low dropout, the internal pass transistor is powered separately from the control circuitry. Furthermore, with the control and power inputs tied together, this device can be used in single supply configuration and still offer a better dropout voltage than conventional PNP-NPN based LDO regulators. In this mode the dropout is determined by the minimum control voltage. It is supplied in five-terminal TO-220 and D2PAK packages, allowing for the implementation of a remote-sense pin permitting very accurate regulation of output voltage directly at the load, where it counts, rather than at the regulator. This remote sensing feature virtually eliminates output voltage variations due to load changes and resistive voltage drops. Typical load regulation measured at the sense pin is 1mV for an output voltage of 2.5V with a load step of 10mA to 7A. The very fast transient loop response easily meets the needs of the latest microprocessors. In addition, a small capacitor on the Adjust pin will further improve the transient capabilities. Internal protection circuitry provides for Obust-proofO operation, similar to three-terminal regulators. This circuitry, which includes overcurrent, short circuit, supply sequencing and overtemperature protection will self protect the regulator under all fault conditions. The CS5257A-1 is ideal for generating a secondary 2-2.5V low voltage supply on a motherboard where both 5V and 3.3V are already available.
Features
s 1.25V to 5V VOUT at 7A s VPOWER Dropout < 0.35V @ 7A s VCONTROL Dropout < 1.10V @
7A
s 1.5% Trimmed Reference s Fast Transient Response s Remote Voltage Sensing s Thermal Shutdown s Current Limit s Short Circuit Protection s Drop-In Replacement for
LT1580
s Backwards Compatible with
3-pin Regulators
Package Options
5 Lead D2PAK
5 Lead TO-220 Applications Diagram
5.0V
VCONTROL
VOUT 2.5V @ 7A
1
CS5257A-1 3.3V VPOWER VSENSE Adjust 100mF 5V 0.1mF 5V
124 1% 124 Load 1% 300mF 5V
1. VSENSE 1 2. Adjust 3. VOUT 4. VCONTROL 5. VPOWER Tab = VOUT
10mF 10V
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
Rev. 4/5/99
1
A
Company
CS5257A-1
Absolute Maximum Ratings VPOWER Input Voltage .................................................................................................................................................................6V VCONTROL Input Voltage ...........................................................................................................................................................13V Operating Junction Temperature Range...........................................................................................................0C TJ 150C Storage Temperature Range ................................................................................................................................-65C 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 ESD Damage Threshold............................................................................................................................................................2kV
Electrical Characteristics: 0C TA 70C, 0C TJ 150C, VSENSE = VOUT and VAdj = 0V; unless otherwise specified.
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Reference Voltage Line Regulation Load Regulation (Note 3) Minimum Load Current (Note 1) Control Pin Current (Note 2)
VCONTROL = 2.75V to 12V, VPOWER = 2.05V to 5.5V, 10mA IOUT 7A VCONTROL = 2.5V to 12V, VPOWER = 1.75V to 5.5V, IOUT = 10mA VCONTROL = 2.75V, VPOWER = 2.05V, IOUT = 10mA to 7A, with remote sense VCONTROL = 5V, VPOWER = 3.3V, AEVOUT = +1% VCONTROL = 2.75V, VPOWER = 2.05V, IOUT = 100mA VCONTROL = 2.75V, VPOWER = 2.05V, IOUT = 4A VCONTROL = 2.75V, VPOWER = 1.75V, IOUT = 4A VCONTROL = 2.75V, VPOWER = 2.05V, IOUT = 7A VCONTROL = 2.75V, VPOWER = 2.05V, IOUT = 10mA VCONTROL = 2.75V, VPOWER = 2.05V, AEVOUT = -1.5% VCONTROL = 2.75V, VPOWER = 2.05V, VOUT = 0V VCONTROL = VPOWER = 3.25V, VRIPPLE = 1VP-P @ 120Hz, IOUT = 4A, CADJ = 0.1F 30ms Pulse, TA = 25C VPOWER = 2.05V, IOUT = 100mA VPOWER = 2.05V, IOUT = 1A VPOWER = 2.05V, IOUT = 2.75A VPOWER = 2.05V, IOUT = 4A VPOWER = 2.05V, IOUT = 7A VCONTROL = 2.75V, IOUT = 100mA VCONTROL = 2.75V, IOUT = 1A VCONTROL = 2.75V, IOUT = 2.75A VCONTROL = 2.75V, IOUT = 4A VCONTROL = 2.75V, IOUT = 7A Freq = 10Hz to 10kHz, TA = 25C
1.234 (-1.5%)
1.253 .02 .04 5 6 30 33 60 60
1.272 (+1.5%) .20 .20 10 10 60 70 180 120
V % % mA mA mA mA mA A A A dB %/W
Adjust Pin Current Current Limit Short Circuit Current Ripple Rejection (Note 3) Thermal Regulation VCONTROL Dropout Voltage (Minimum VCONTROL-VOUT) (Note 4)
7.1 5.0 60
10.0 9.0 80 0.002 1.00 1.00 1.00 1.00 1.10 .10 .15 .20 .26 .35 0.003 0.5 1.15 1.15 1.15 1.15 1.25 .15 .20 .30 .40 .65
V V V V V V V V V V %VOUT %
VPOWER Dropout Voltage (Minimum VPOWER-VOUT) (Note 4)
RMS Output Noise Temperature Stability Thermal Shutdown (Note 5) Thermal Shutdown Hysteresis VCONTROL Supply Only Output Current
150 VCONTROL = 13V, VPOWER not connected, VADJUST = VOUT = VSENSE = 0V
180
210 25 50
C C mA
2
CS5257A-1
Electrical Characteristics: 0C TA 70C, 0C TJ 150C, VSENSE = VOUT and VAdj = 0V unless otherwise specified.
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VPOWER Supply Only Output Current
Note 1: Note 2: Note 3: Note 4: Note 5:
VPOWER = 6V, VCONTROL not connected, VADJUST = VOUT = VSENSE = 0V
0.1
1
mA
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. The VCONTROL pin current is the drive current required for the output transistor. This current will track output current with roughly a 1:100 ratio. The minimum value is equal to the quiescent current of the device. This parameter is guaranteed by design and is not 100% production tested. Dropout is defined as either the minimum control voltage, (VCONTROL) or minimum power voltage (VPOWER) to output voltage differential required to maintain 1.5% regulation at a particular load current. This parameter is guaranteed by design, but not parametrically tested in production. However, a 100% thermal shutdown functional test is performed on each part.
Package Pin Description
PACKAGE PIN # PIN SYMBOL FUNCTION
5L TO-220 1 VSENSE This Kelvin sense pin allows for remote sensing of the output voltage at the load for improved regulation. It is internally connected to the positive input of the voltage sensing error amplifier. This pin is connected to the low side of the internally trimmed 1.5% bandgap reference voltage and carries a bias current of about 50A. A resistor divider from Adj to VOUT 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. This pin is connected to the emitter of the power pass transistor and provides a regulated voltage capable of sourcing 7A of current. This is the supply voltage for the regulator control circuitry. For the device to regulate, this voltage should be between 1V and 1.25V (depending on the output current) greater than the output voltage. The control pin current will be about 1% of the output current. This is the power input voltage. The pin is physically connected to the collector of the power pass transistor. For the device to regulate, this voltage should be between 0.1V and 0.65V greater than the output voltage, depending on output current. The output load current of 7A is supplied through this pin. Block Diagram
2
Adjust
3 4
VOUT VCONTROL
5
VPOWER
VPOWER VCONTROL
BIAS and TSD
VREF
+
EA
IA
+
-
VOUT VSENSE Adjust
3
CS5257A-1
Typical Performance Characteristics
Reference Voltage vs Temperature
0.100 0.090 0.080 Output Voltage Deviation (%) 0.070 0.060 0.050 0.040 0.030 0.020 0.010 0.000 VPOWER=2.05V VCONTROL=2.75V
Load Regulation vs Output Current
0.100 0.075 0.050
Output Voltage Deviation (%)
0.025 -0.000 -0.025 -0.050 -0.075 -0.100 -0.125 -0.150 0 10 20 30 40 50 60 70 80 90 100 110120130 TJ (C) I0=10mA VCONTROL=2.75V, VPOWER=2.05V
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
Output Current (A)
Transient Response
100
Output Voltage Deviation (mV)
Short Circuit Current vs VPOWER-VOUT
15.0 14.0 13.0 12.0 11.0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
50 0
Output Current (A)
VCONTROL=2.75V
-50 -100
COUT=330mF CPOWER=110mF CCONTROL=10mF CADJUST=0.1mF VCONTROL=5V VPOWER=3.3V VOUT=2.5V
Current (A)
7 0 0 0 1 2 3 Time (ms) 4 5
VPOWER-VOUT (V)
Adjust Pin Current vs Temperature
83.0
Minimum Load Current vs VCONTROL-VOUT
1200.000
81.0 Adjust Pin Current (mA)
1150.000 Minimum Load Current (mA)
79.0 77.0 75.0 73.0 71.0 69.0 67.0 65.0 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 Temperature (C)
VPOWER =3.3V D VOUT=+1%
1100.000 1050.000 1000.000 950.000 900.000 850.000 800.000
1.0 2.0
3.0
4.0
5.0 6.0 7.0 8.0 VCONTROL-VOUT (V)
9.0
10.0 11.0
4
CS5257A-1
Typical Performance Characteristics: continued
Adjust Pin Current vs VCONTROL-VOUT
75.00 VPOWER =2.05V IL=10mA 74.00
Ripple Rejection vs Frequency
90.0 80.0
Ripple Rejection (dB)
Adjust Pin Current (mA)
70.0 60.0 50.0 40.00 30.0 20.0
VIN-VOUT=2V IOUT=4A VRIPPLE=1VP-P COUT=22mF CADJ=0.1mF 101 102 103 104 105 106
73.00
72.00
71.00
70.00 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 VCONTROL-VOUT (V) 9.0 10.0 11.0
10.0
Frequency (Hz)
Adjust Pin Current vs VPOWER - VOUT
VCONTROL Dropout Voltage vs IOUT
75.00 VCONTROL=2.75V IL=10mA
VCONTROL Drop Out Voltage (V)
1.250
VPOWER=2.05V
74.00 Adjust Pin Current (mA)
1.000
73.00
0.750
72.00
0.500
71.00
0.250
70.00 0.50 1.50 2.50 VPOWER-VOUT (V) 3.50 4.50
0.00 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00
Output Current (A)
VPOWER Dropout Voltage vs IOUT
1.000 0.900 VPOWER Dropout Voltage (V) 0.800 0.700 0.600 0.500 0.400 0.300 0.200 0.100 0.000 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 Output Current (A) VCONTROL =2.75V
Minimum Load Current vs VPOWER-VOUT
916.400 916.300 Minimum Load Current (mA) 916.200 916.100 916.000 915.900 915.800 915.700 915.600 915.500 915.400 0.50 1.50 2.50 VPOWER-VOUT (V) 3.50 4.50 VCONTROL =5V D VOUT=+1%
5
CS5257A-1
Typical Performance Characteristics: continued
Adjust Pin Current vs Output Current
77.00
V POWER =2.05 V CONTROL =2.75V Adjust Pin Current (mA)
76.00
75.00
74.00
73.00
72.00
0.00 1.00 2.00 3.00 4.00 5.00 Output Current (A) 6.00 7.00 8.00
Application Notes
Theory of Operation Design Guidelines
The CS5257A-1 linear regulator provides adjustable voltages from 1.25V to 5V at currents up to 7A. The regulator is protected against short circuits, and includes a thermal shutdown circuit with hysteresis. The output, which is current limited, consists of a PNP-NPN transistor pair and requires an output capacitor for stability. A detailed procedure for selecting this capacitor is included in the Stability Considerations section. VPOWER Function The CS5257A-1 utilizes a two supply approach to maximize efficiency. The collector of the power device is brought out to the VPOWER pin to minimize internal power dissipation under high current loads. VCONTROL provides power for the control circuitry and the drive for the output NPN transistor. VCONTROL should be at least 1V greater than the output voltage. Special care has been taken to ensure that there are no supply sequencing problems. The output voltage will not turn on until both supplies are operating. If the control voltage comes up first, the output current will be typically limited to about 3mA until the power input voltage comes up. If the power input voltage comes up first the output will not turn on at all until the control voltage comes up. The output can never come up unregulated. The CS5257A-1 can also be used as a single supply device with the control and power inputs tied together. In this mode, the dropout will be determined by the minimum control voltage. Output Voltage Sensing The CS5257A-1 five terminal linear regulator includes a dedicated VSENSE function. This allows for true Kelvin sensing of the output voltage. This feature can virtually eliminate errors in the output voltage due to load regulation. Regulation will be optimized at the point where the sense pin is tied to the output.
Adjustable Operation 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 regulatorOs voltage sensing error amplifier maintains a fixed 1.253V reference between the output pin and the adjust pin. A resistor divider network R1 and R2 causes a fixed current to flow to ground. This current creates a voltage across R2 that adds to the 1.253V 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 VOUT is necessary. The output voltage is set according to the formula: VOUT = 1.253V R1+R2 R1 + R2 IADJ
The term IADJ R2 represents the error added by the adjust pin current. R1 is chosen so that the minimum load current is a least 10mA. R1 and R2 should be of the same composition for best tracking over temperature. The divider resistors should be placed physically as close to the load as possible.
VCONTROL
VOUT
CS5257A-1 VPOWER VSENSE Adjust R1 R2
Figure 1: An external resistor divider sets the value of VOUT. The 1.253V reference voltage drops across R1.
6
CS5257A-1
Application Notes: continued While not required, a bypass capacitor connected between the adjust pin and ground will improve transient response and ripple rejection. A 0.1F tantalum capacitor is recommended for Ofirst cutO design. Value and type may be varied to optimize performance vs. price. Other Adjustable Operation Considerations The CS5257A-1 linear regulator has an absolute maximum specification of 6V for the voltage difference between VIN and VOUT. However, the IC may be used to regulate voltages in excess of 6V. The two main considerations in such a design are the sequencing of power supplies and short circuit capability. Power supply sequencing should be such that the VCONTROL supply is brought up coincidentally with or before the VPOWER supply. This allows the IC to begin charging the output capacitor as soon as the VPOWER to VOUT differential is large enough that the pass transistor conducts. As VPOWER increases, the pass transistor will remain in dropout, and current is passed to the load until VOUT is in regulation. Further increase in the supply voltage brings the pass transistor out of dropout. In this manner, any output voltage less than 13V may be regulated, provided the VPOWER to VOUT differential is less than 6V. In the case where VCONTROL and VPOWER are shorted, there is no theoretical limit to the regulated voltage as long as the VPOWER to VOUT differential of 6V is not exceeded. There is a possibility of damaging the IC when VPOWER-VIN is greater than 6V if a short circuit occurs. 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 the VPOWER to VOUT differential to less than 6V if fail safe operation is required. One possible clamp circuit is illustrated in Figure 2; 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 condition indefinitely while protecting the IC.
External Supply
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 manufacturer's data sheet provides this information. A 300F tantalum capacitor will work for most applications, but with high current regulators such as the CS5257A-1 the transient response and stability improve with higher values of capacitor. 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: AEV = AEI 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 VCONTROL drops. In the CS5257A-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. Use of the diode has the added benefit of bleeding VOUT to ground if VCONTROL is shorted. This prevents an unregulated output from causing system damage.
VControl VPower
VSENSE VOUT
VCONTROL VOUT CS5257A-1 VPOWER VSENSE Adjust
VAdjust
Figure 2: Example clamp circuitry for VPOWER - VOUT > 6V.
Stability Considerations The output compensation capacitor helps determine three main characteristics of a linear regulator: start-up delay, load transient response, and loop stability. 7
Figure 3: Diode protection against VCONTROL short circuit conditions.
CS5257A-1
Application Notes: continued A rule of thumb useful in determining if a protection diode is required is to solve for current I= C V , where T I is the current flow out of the load capacitance when VCONTROL is shorted, C is the value of load capacitance V is the output voltage, and T is the time duration required for VCONTROL to 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 the use of a protection diode. Current Limit The internal current limit circuit limits the output current under excessive load conditions. Short Circuit Protection The device includes short circuit protection circuitry that clamps the output current at approximately two amperes less than its current limit value. This provides for a current foldback function, which reduces power dissipation under a direct shorted load. Thermal Shutdown The thermal shutdown circuitry is guaranteed by design to activate above a die junction temperature of approximately 150C and to shut down the regulator output. This circuitry has 25C of typical hysteresis, thereby allowing the regulator to recover from a thermal fault automatically. Calculating Power Dissipation and Heat Sink Requirements High power regulators such as the CS5257A-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 CS5257A-1, electrical isolation may be required for some applications. Also, as with all high power packages, thermal compound in 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: TJ(max) = TA(max) + PD(max) RQJA 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) = (VIN(max) -VOUT(min))IOUT(max) + VIN(max) IIN(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, RQJA. This total thermal resistance is comprised of three components. These resistive terms are measured from junction to case (RQJC), case to heat sink (RQCS), and heat sink to ambient air (RQSA). The equation is: RQJA = RQJC + RQCS + RQSA The value for RQJC is 1.4uC/watt for the CS5257A-1 in both the TO-220 and D2PAK packages. For a high current regulator such as the CS5257A-1 the majority of heat is generated in the power transistor section. The value for RQSA depends on the heat sink type, while the RQCS 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 RQJA can be calculated and the proper heat sink selected. For further discussion on heat sink selection, see our Cherry application note OThermal Management for Linear Regulators.O
8
CS5257A-1
Package Specification
PACKAGE DIMENSIONS IN mm (INCHES) PACKAGE THERMAL DATA
Thermal Data
5 Lead
10.31 (.406) 10.05 (.396)
D2PAK
(DP)
1.40 (.055) 1.14 (.045)
RQJC RQJA
typ typ
5L TO-220 1.4 50
5L D2PAK 1.4 10-50*
uC/W uC/W
1.68 (.066) 1.40 (.055)
*Depending on thermal properties of substrate. RqJA = RqJC + RqCA
8.53 (.336) 8.28 (.326) 15.75 (.620) 14.73 (.580) 2.74(.108) 2.49(.098) 0.91 (.036) 0.66 (.026) 2.79 (.110) 2.29 (.090) 1.70 (.067) REF .254 (.010) REF
4.57 (.180) 4.31 (.170)
0.10 (.004) 0.00 (.000)
5 Lead TO-220 (T) Straight
10.54 (.415) 9.78 (.385) 2.87 (.113) 6.55 (.258) 2.62 (.103) 5.94 (.234)
4.83 (.190) 4.06 (.160) 3.96 (.156) 3.71 (.146)
1.40 (.055) 1.14 (.045)
14.99 (.590) 14.22 (.560)
14.22 (.560) 13.72 (.540)
1.02 (.040) 0.76 (.030)
1.02(.040) 0.63(.025) 6.93(.273) 6.68(.263)
1.83(.072) 1.57(.062)
0.56 (.022) 0.36 (.014) 2.92 (.115) 2.29 (.090)
Ordering Information
Part Number CS5257A-1GT5 CS5257A-1GDP5 CS5257A-1GDPR5
Rev. 4/5/99
Description 5L TO-220 Straight 5L D2PAK 5L D2PAK (tape & reel) 9
Cherry Semiconductor Corporation reserves the right to make changes to the specifications without notice. Please contact Cherry Semiconductor Corporation for the latest available information.
(c) 1999 Cherry Semiconductor Corporation

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