September 2005 ET- AMS1084M-XX Inv № 400 LOW DROPOUT POSITIVE VOLTAGE REGULATOR DESCRIPTION The AMS1084M series of positive adjustable and fixed regulators are designed to provide 5A with high efficiency. All internal circuitry is designed to operate down to 1.3V input to output differential. On-chip trimming adjusts the reference voltage to 1%. APPLICATIONS • • • High Efficiency Linear Regulators Post Regulators for Switching Supplies Adjustable Power Supply FEATURES • • • • • • • Adjustable or Fixed Output Output Current of 5A Low Dropout, 1.5V max at 5A Output Current 0.04% Line Regulation 0.2 % Load Regulation 100% Thermal Limit Burn-In Fast Transient Response TYPICAL APPLICATION DATA 4.95V 4.8V AMS1085 AMS1084M AMS1084M-3.3 PIN DESCRIPTION Page 1 of 3 BEIJING ESTEK ELECTRONICS CO.,LTD ET- AMS1084M-XX ABSOLUTE MAXIMUM RATINGS SYMBOL PARAMETER VCC Power Dissipation VIN Input Voltage Operation Junction Temperature Range TJ Control Section Power Transistor TSTG Storage Temperature Range TLEAD Lead Temperature (Soldering 10 sec) VALUE Internally Limited 15 UNIT W V 0 to 125 0 to 150 -65 to +150 300 0 C 0 C C 0 ELECTRICAL CHARACTERISTICS ILOAD = 0mA and TJ = +25 0C (unless otherwise noted) PARAMETER DEVICE Reference Voltage Note 1 AMS1084M Output Voltage Note 1 Line Regulation Note 1 All fixed versions All Load Regulation Note 1 All Minimum Load Current AMS1084M All fixed versions Ground Pin Current Adjust Pin Current AMS1084M Current Limit All Ripple Rejection Note 2 All Dropout Voltage Note 1,3 All Temperature Coefficient All TEST CONDITIONS MIN. TYP. MAX. VIN =5V, ILOAD = 10mA VIN – VOUT = 1.5V to 10V, ILOAD = 10mA to 5A VIN – VOUT = 1.5V, Variator from nominal VOUT VIN – VOUT = 1.5V to 10V ILOAD = 0mA to 5A, Variator from nominal VOUT ILOAD = 10mA, VIN – VOUT = 1.5V to 10V 1.238 1.250 1.262 1.225 1.250 1.275 -1 - +1 * -2 - +2 * - 0.04 0.20 VIN – VOUT = 1.5V ILOAD = 10mA to 5A VIN =5V, VADJ = 0V VIN – VOUT = 1.5V ILOAD = 10mA to 5A VIN – VOUT = 1.5V to 10V ILOAD = 10mA VIN – VOUT = 1.5V VIN – VOUT = 3V ILOAD = 5A ILOAD = 5A VIN – VOUT = 1.5V, ILOAD = 10mA * UNIT V % % * - 0.2 0.40 * - 3 7 mA * - 7 10 mA * - 40 90 µA * 5 6.5 - A * 60 72 - dB * - 1.3 1.5 V * - 0.005 - %/0C The * denotes the specifications which apply over the full temperature range (see previous table, TJ) NOTES: 1: Low duty pulse testing with Kelvin connections required. 2: 120Hz input ripple (CADJ for ADJ = 25µF, COUT = 25µF) 3: ∆VOUT, ∆VREF = 1% APPLICATION INFORMATION The AMS1084M series of adjustable and fixed regulators are easy to use and have all the protection features expected in high performance voltage regulators: short circuit protection and thermal shut-down. Pin compatible with older three terminal adjustable regulators, these devices offer the advantage of a lower dropout voltage, more precise reference tolerance and improved reference stability with temperature. STABILITY The circuit design used in the AMS1084M series requires the use of an output capacitor as part of the device frequency compensation. The addition of 150µF aluminum electrolytic or a 22µF solid tantalum on the output will ensure stability for all operating conditions. When the adjustment terminal is bypassed with a capacitor to improve the ripple rejection, the requirement for an output capacitor increases. The value of 22µF tantalum or 150µF aluminum covers all cases of bypassing the adjustment terminal. Without bypassing the adjustment terminal smaller capacitors can be used with equally good results. Page 2 of 3 BEIJING ESTEK ELECTRONICS CO.,LTD ET- AMS1084M-XX To ensure good transient response with heavy load current changes capacitor values on the order of 100µF are used in the output of many regulators. To further improve stability and transient response of these devices larger values of output capacitor can be used. PROTECTION DIODES AMS1084M Unlike older regulators, the AMS1084M family does not need any protection diodes between the adjustment pin and the output and from the output to the input to prevent over-stressing the die. Internal resistors are limiting the internal current paths on the AMS1084M adjustment pin, therefore even with capacitors on the adjustment pin no protection diode is needed to ensure device safety under short-circuit conditions. Diodes between the input and output are not usually needed. Microsecond surge currents of 50A to 100A can be handled by the internal diode between the input and output pins of the device. In normal operations it is difficult to get those values of surge currents even with the use of large output capacitances. If high value output capacitors are used, such as 1000µF to 5000µF and the input pin is instantaneously shorted to ground, damage can occur. A diode from output to input is recommended, when a crowbar circuit at the input of the AMS1084M is used. Normal power supply cycling or even plugging and unplugging in the system will not generate current large enough to do any damage. The adjustment pin can be driven on a transient basis ±25V, with respect to the output without any device degradation. As with any IC regulator, none the protection circuitry will be functional and the internal transistors will break down if the maximum input to output voltage differential is exceeded. RIPPLE REJECTION The ripple rejection values are measured with the adjustment pin bypassed. The impedance of the adjust pin capacitor at the ripple frequency should be less than the value of R1 (normally 100Ω to 120Ω) for a proper bypassing and ripple rejection approaching the values shown. The size of the required adjust pin capacitor is a function of the input ripple frequency. If R1=100Ω at 120Hz the adjust pin capacitor should be 25µF. At 10kHz only 0.22µF is needed. The ripple rejection will be a function of output voltage, in circuits without an adjust pin bypass capacitor. The output ripple will increase directly as a ratio of the output voltage to the reference voltage (VOUT / VREF). OUTPUT VOLTAGE AMS1084M The AMS1084M series develops a 1.25V reference voltage between the output and the adjust terminal. Placing a resistor between these two terminals causes a constant current to flow through R1 and down through R2 to set the overall output voltage. This current is normally the specified minimum load current of 10mA. Because IADJ is very small and constant it represents a small error and it can usually be ignored. LOAD REGULATION AMS1084M True remote load sensing it is not possible to provide, because the AMS1084M is a three terminal device. The resistance of the wire connecting the regulator to the load will limit the load regulation. The data sheet specification for load regulation is measured at the bottom of the package. Negative side sensing is a true Kelvin connection, with the bottom of the output divider returned to the negative side of the load. The best load regulation is obtained when the top of the resistor divider R1 is connected directly to the case not to the load. If R1 were connected to the load, the effective resistance between the regulator and the load would be: Connected as shown Fig.3, RΡ is not multiplied by the divider ratio. Using 16-gauge wire the parasitic line resistance is about 0.004Ω per foot, translating to 4mV/ft at 1A load current. It is important to keep the positive lead between regulator and load as short as possible and use large wire or PC board traces. Page 3 of 3 BEIJING ESTEK ELECTRONICS CO.,LTD