Datasheet LTC1844 (Analog Devices) - 6

LTC1844 Series
W U TYPICAL PERFOR A CE CHARACTERISTICS RMS Output Noise vs Load Input Ripple Rejection Input Ripple Rejection Current (10Hz to 100kHz) vs Frequency vs Temperature
300 100 60 COUT = 10µF 90 CBYP = 1000pF 250 C I BYP = 0µF L = 100µA 50 80 ) RMS 70 200 µV 40 60 150 50 30 40 100 30 20 OUTPUT NOISE ( RIPPLE REJECTION (dB) C RIPPLE REJECTION (dB) BYP = 0.1µF 20 50 10 10 0 0 0 0.01 0.1 1 10 100 1000 10 100 1k 10k 100k 1M –50 –25 0 25 50 75 100 125 LOAD CURRENT (mA) FREQUENCY (Hz) TEMPERATURE (°C) 1844 G10 1844 G11 1844 G12
U U U PI FU CTIO S IN (Pin 1):
Power for LTC1844 and Load. Power is supplied
ADJ (Pin 4, Adjustable Devices):
Output Adjust. For the to the device through the IN pin. The IN pin should be adjustable versions of the LTC1844, this is the input to the locally bypassed to ground if the LTC1844 is more than a error amplifier. It has a typical bias current of 30nA flowing few inches away from another source of bulk capacitance. into the pin. The ADJ pin reference voltage is 1.25V In general, the output impedance of a battery rises with referenced to ground. The output voltage range is 1.25V to frequency, so it is usually advisable to include an input 6V and is typically set by connecting ADJ to a resistor bypass capacitor in battery-powered circuits. A capacitor divider from OUT to GND. See Figure 2. in the range of 0.1µF to 1µF is usually sufficient. The
BYP (Pin 4, Fixed/Pin 3, BYP Devices):
Noise Bypass. LTC1844 is designed to withstand reverse voltages on the The BYP pin is used to augment the internal noise filter to IN pin with respect to both ground and the output pin. In improve low noise performance. A small low leakage the case of a reversed input, which can happen if a battery bypass capacitor from this pin to ground will filter the input is plugged in backwards, the LTC1844 will act as if there of the error amplifier to lower the output voltage noise. is a large resistor in series with its input and only a small Any value may be used; larger values will result in lower amount of current will flow. output noise, but will increase initial power-up time.
GND (Pin 2):
Ground and Heat Sink. Solder to a ground Shutdown exit delay time after a brief shutdown (<10ms) plane or large pad to maximize heat dissipation. will not be affected. If not used, this pin must be left unconnected.
SHDN (Pin 3, Fixed and SD Devices):
Shutdown, Active Low. This pin is used to put the LTC1844 into shutdown.
OUT (Pin 5):
Voltage Regulated Output. The OUT pin The SHDN pin current is typically less than 10nA. The supplies power to the load. A minimum output capacitor of SHDN pin cannot be left floating and must be tied to the 1µF is required to ensure stability. Larger output capacitors input pin if not used. If reverse-battery protection is may be required for applications with large transient loads desired, the SHDN pin must be tied to the input pin through to limit peak voltage transients. See the Applications a large value resistor (10k to 1M). Information section for more information on output capacitance. 1844fa 6