Datasheet LT1529, LT1529-3.3, LT1529-5 (Analog Devices) - 8

LT1529 LT1529-3.3/LT1529-5
U U U PI FU CTIO S
function of voltage appears in the Typical Performance include a bypass capacitor in battery-powered circuits. A Characteristics. If the SHDN pin is not used it can be left bypass capacitor in the range of 1µF to 10µF is sufficient. open circuit. The device will be active, output on, if the The LT1529 is designed to withstand reverse voltages on SHDN pin is not connected. the VIN pin with respect to ground and OUTPUT pin. In the case of a reversed input, which can happen if a battery is
VIN (Pin 5):
Input Pin. Power is supplied to the device plugged in backwards, the LT1529 will act as if there is a through the VIN pin. The VIN pin should be bypassed to diode in series with its input. There will be no reverse ground if the device is more than six inches away from the current flow into the LT1529 and no reverse voltage will main input filter capacitor. In general, the output imped- appear at the load. The device will protect both itself and ance of a battery rises with frequency so it is advisable to the load.
O U U W U APPLICATI S I FOR ATIO
The LT1529 is a 3A low dropout regulator with mi- 5 1 VIN OUTPUT VOUT cropower quiescent current and shutdown capable of + VIN LT1529 R2 supplying 3A of output current at a dropout voltage of 4 2 SHDN SENSE 0.6V. The device operates with very low quiescent current GND R1 (50µA). In shutdown the quiescent current drops to only 3 LT1529 • F02 16µA. In addition to the low quiescent current the LT1529 incorporates several protection features which make it VOUT = 3.75V + (I 1 + R2 ADJ × R2) ( R1) ideal for use in battery-powered systems. The device is VADJ = 3.75V IADJ = 150nA AT 25°C protected against reverse input voltages. In battery backup OUTPUT RANGE = 3.3V TO 14V applications where the output can be held up by a backup
Figure 2. Adjustable Operation
battery when the input is pulled to ground, the LT1529 acts like it has a diode in series with its output and prevents reverse current flow. Bias Current vs Temperature appear in the Typical Perfor- mance Characteristics. The reference voltage at the ADJ
Adjustable Operation
pin has a positive temperature coefficient of approxi- mately 15ppm/°C. The ADJ pin bias current has a negative The adjustable version of the LT1529 has an output temperature coefficient. These effects will tend to cancel voltage range of 3.75V to 14V. The output voltage is set each other. by the ratio of two external resistors as shown in Figure 2. The device servos the output voltage to maintain the The adjustable device is specified with the ADJ pin tied to voltage at the ADJ pin at 3.75V. The current in R1 is then the OUTPUT pin. This sets the output voltage to 3.75V. equal to 3.75V/R1. The current in R2 is equal to the sum Specifications for output voltage greater than 3.75V will be of the current in R1 and the ADJ pin bias current. The ADJ proportional to the ratio of the desired output voltage to pin bias current, 150nA at 25°C, flows through R2 into the 3.75V (VOUT/3.75V). For example: load regulation for an ADJ pin. The output voltage can be calculated according output current change of 1mA to 3A is – 0.5mV typical at to the formula in Figure 2. The value of R1 should be less VOUT = 3.75V. At VOUT = 12V, load regulation would be: than 400k to minimize errors in the output voltage caused by the ADJ pin bias current. Note that in shutdown the ⎛ 12V ⎞ –0.5mV –1.6mV ⎜ ⎟ ( ) = ( ) output is turned off and the divider current will be zero. ⎝ 3.75V⎠ Curves of ADJ Pin Voltage vs Temperature and ADJ Pin 152935fb 8