LT8709_15 Datasheet, PDF (1/46 Pages) Linear Technology – Negative Input Synchronous Multi-Topology DC/DC Controller

LT8709
Features
Negative Input
Synchronous Multi-Topology
DC/DC Controller
Description
n _{Wide Negative Input Range: –4.5V to –80V}
n _{Rail-to-Rail Output Current Monitor and Control}
n _{Input Voltage Regulation for High Impedance Inputs}
n _{Power Good Indication Pin}
n _{MODE Pin for Forced CCM (Continuous Conduction}
Mode) or Pulse-Skipping/DCM (Discontinuous
Conduction Mode) Operation
n _{Switching Frequency Up to 750kHz}
n _{Easily Configurable as a Buck, Boost, Buck-Boost, or}
Inverting Converter with a Single Feedback Pin
n _{Can be Synchronized to an External Clock}
n _{High Gain EN/FBIN Pin Accepts Slowly Varying Input}
Signals
n _{20-Lead TSSOP Package}
Applications
n _{High Power Negative Input, Negative Output Power}
Supplies
n _{High Power Negative Input, Positive Output Power}
Supplies
n _{Telecom Equipment Power Supplies}
n _{Cathodic Protection Power Supplies}
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.
The LT^®8709 is a synchronous PWM controller for negative-
to-negative or negative-to-positive DC/DC conversion,
with rail-to-rail output current monitor and control. The
LT8709 is ideal for many local power supply designs. It
can be easily configured in buck, boost, buck-boost, and
inverting topologies with negative input voltages.
In addition, the LT8709’s rail-to-rail output current sense
allows the part to be configured in current limited applica-
tions such as battery or capacitor charging. The PG pin
is used for power good indication.
The LT8709’s switching frequency range can be set between
100kHz and 750kHz. The part may be clocked internally
at a frequency set by the resistor from the RT pin to the
–V_IN pin, or it may be synchronized to an external clock.
The LT8709 also features innovative EN/FBIN pin circuitry
that allows for slowly varying input signals and an adjust-
able undervoltage lockout function. The pin is also used as
input voltage regulation to avoid collapsing a high imped-
ance input supply. Additional features such as frequency
foldback, thermal shutdown and soft-start are integrated.
The LT8709 is available in a 20-lead TSSOP package.
Typical Application
250kHz, –16V to –30V Input to –12V/8.5A Output Buck
7.3µH
4mΩ
V_OUT
–12V
8.5A
10µF
×6
2.2µF
+ 120µF
62.5k
10k _2.2µF
100k
143k
–V_IN
–16V TO –30V
2mΩ
–V_IN
TG
CSP CSN
BG
GND
ISN
EN/FBIN ^LT8709
ISP
FBY
INTV_CC
MODE
PG
RT
SYNC
–V_IN
IMON
68nF
BIAS
INTV_EE
V_C
SS
470nF
150µF
22µF
×3
33k
4.99k
2.2µF
2.2µF
5.9k
100pF
2.2nF
8709 TA01a
For more information www.linear.com/LT8709
Efficiency and Power Loss
vs Load Current (–V_IN = –24V)
100
4.5
90
4.0
80
3.5
70
3.0
60
2.5
50
2.0
40
1.5
30
1.0
20
0.5
10
0
01 23456789
LOAD CURRENT (A)
8709 TA01b
8709f
1