Datasheet LT8709 (Analog Devices)

ManufacturerAnalog Devices
DescriptionNegative Input Synchronous Multi-Topology DC/DC Controller
Pages / Page48 / 1 — FEATURES. DESCRIPTION. Wide Negative Input Range: –4.5V to –80V. …
File Size802 Kb

FEATURES. DESCRIPTION. Wide Negative Input Range: –4.5V to –80V. Rail-to-Rail Output Current Monitor and Control

Datasheet LT8709 Analog Devices

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LT8709 Negative Input Synchronous Multi-Topology DC/DC Controller
Wide Negative Input Range: –4.5V to –80V
The LT®8709 is a synchronous PWM controller for negative- n
Rail-to-Rail Output Current Monitor and Control
to-negative or negative-to-positive DC/DC conversion, n
Input Voltage Regulation for High Impedance Inputs
with rail-to-rail output current monitor and control. The n
Power Good Indication Pin
LT8709 is ideal for many local power supply designs. It n
MODE Pin for Forced CCM (Continuous Conduction
can be easily configured in buck, boost, buck-boost, and
Mode) or Pulse-Skipping/DCM (Discontinuous
inverting topologies with negative input voltages.
Conduction Mode) Operation
In addition, the LT8709’s rail-to-rail output current sense n Switching Frequency Up to 750kHz allows the part to be configured in current limited applica- n Easily Configurable as a Buck, Boost, Buck-Boost, or tions such as battery or capacitor charging. The PG pin Inverting Converter with a Single Feedback Pin is used for power good indication. n Can be Synchronized to an External Clock n High Gain EN/FBIN Pin Accepts Slowly Varying Input The LT8709’s switching frequency range can be set between Signals 100kHz and 750kHz. The part may be clocked internally n 20-Lead TSSOP Package at a frequency set by the resistor from the RT pin to the
–VIN pin, or it may be synchronized to an external clock. The LT8709 also features innovative EN/FBIN pin circuitry n High Power Negative Input, Negative Output Power that allows for slowly varying input signals and an adjust- Supplies able undervoltage lockout function. The pin is also used for n High Power Negative Input, Positive Output Power input voltage regulation to avoid collapsing a high imped- Supplies ance input supply. Additional features such as frequency n Telecom Equipment Power Supplies foldback, thermal shutdown and soft-start are integrated. n Cathodic Protection Power Supplies The LT8709 is available in a 20-lead TSSOP package. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION 250kHz, –16V to –30V Input to –12V/8.5A Output Buck
7.3µH 4mΩ VOUT
Efficiency and Power Loss
–12V 8.5A
vs Load Current (–VIN = –24V)
150µF + 100 4.5 10µF 2mΩ ×6 90 4.0 –VIN 22µF 80 3.5 ×3 2.2µF POWER LOSS (W) CSP CSN BG TG 70 3.0 GND ISN 33k 60 2.5 + 120µF 62.5k LT8709 ISP EN/FBIN 50 2.0 FBY EFFICIENCY (%) 10k 40 1.5 2.2µF 4.99k 30 1.0 INTVCC 100k MODE 20 0.5 BIAS PG 2.2µF 10 0 0 1 2 3 4 5 6 7 8 9 RT INTVEE 2.2µF LOAD CURRENT (A) SYNC VC 8709 TA01b 143k –V 5.9k IN IMON SS 100pF 2.2nF 68nF 470nF –VIN 8709 TA01a –16V TO –30V 8709fa For more information 1