Datasheet LT3582, LT3582-5, LT3582-12 (Analog Devices) - 10

LT3582/LT3582-5/LT3582-12
OPERATION
The LT3582 series are dual DC/DC converters, each contain- can be confi gured such that (1) they both rise simultane- ing both a Boost and an Inverting converter. Operation can ously, (2) VOUTP rises to regulation before VOUTN rises, (3) be best understood by referring to the Block Diagram. The VOUTN rises to regulation before VOUTP rises, or (4) neither Boost and Inverting converters each use a novel control output rises. The outputs of the LT3582-5 and LT3582-12 technique, which simultaneously varies both peak inductor are pre-confi gured to rise simultaneously. current and switch off time. This results in high effi ciency The ramp rates of the outputs are proportional to the ramp over a large load range and low output voltage ripple. In rates of their respective RAMP pins. A capacitor is placed addition, this technique further minimizes output ripple between each RAMP pin and ground. The RAMP pins are when the switching frequency is in the audio band. discharged during shutdown. Once enabled, confi gurable
Boost Converter:
The Boost converter uses a grounded (LT3582) or pre-confi gured (LT3582-5/LT3582-12) cur- source NMOS power transistor as the main switching ele- rents charge each RAMP pin in the desired sequence ment. The current in the NMOS is constantly monitored and causing the outputs to rise. controlled, along with the off-time of the switch to achieve
Output Power-Down Discharge:
The power-down dis- regulation of VOUTP. The VOUTP voltage is divided by the charge feature is permanently enabled on the LT3582-5 internal programmable (LT3582 only) resistor divider to and LT3582-12 and can be enabled or disabled through create FBP. The voltage on FBP is compared to an internal I2C on the LT3582. Upon SHDN falling, and when power- reference and amplifi ed, creating an error signal on the down discharge is enabled, internal transistors will acti- VCP node which commands the appropriate peak inductor vate to assist in discharging the outputs toward ground. current and off time for the subsequent switching cycle. When power-down discharge is disabled, the chip powers
Inverting Converter:
The Inverting converter uses a power down immediately after SHDN falls and the outputs will PMOS transistor with the source connected to VIN. This discharge on their own depending on their external load topology requires only one external inductor, instead of capacitances and currents. the normally required two inductors plus fl ying capacitor.
OTP Memory (LT3582 Only):
The LT3582 includes 22 bits Regulation is achieved in a similar manner as the Boost. of user programmable output settings and 1 programming
Output Power-Up Sequencing:
After an initial start-up lockout bit. Parameters such as positive and negative output delay (TSTART-UP = 64μs typical), the outputs VOUTP and voltages and power sequencing settings can be changed VOUTN rise (in magnitude) simultaneously with the LT3582-5/ in real time with the integrated I2C interface. Settings can LT3582-12 or in one of four selectable sequences with then be made permanent by programming to the on-chip the LT3582. Using the I2C interface, the LT3582 outputs non-volatile OTP (One Time Programmable) memory. 3582512fb 10