LTC3850_15 Datasheet, PDF (9/38 Pages) Linear Technology – Dual, 2-Phase Synchronous Step-Down Switching Controller

LTC3850/LTC3850-1
PIN FUNCTIONS (GN/UF/UFD)
RUN1, RUN2 (Pins 1, 13/Pins 26, 9/Pins 27, 10): Run
Control Inputs. A voltage above 1.2V on either pin turns
on the IC. However, forcing either of these pins below 1.2V
causes the IC to shut down that particular channel. There
are 0.5µA pull-up currents for these pins. Once the RUN
pin rises above 1.2V, an additional 4.5µA pull-up current
is added to the pin.
SENSE1⁺, SENSE2⁺ (Pins 2, 12/Pins 27, 8/Pins 28, 9):
Current Sense Comparator Inputs. The (+) inputs to the
current comparators are normally connected to DCR sens-
ing networks or current sensing resistors.
SENSE1^–, SENSE2^– (Pins 3, 11/Pins 28, 7/Pins 1, 8):
Current Sense Comparator Inputs. The (–) inputs to the
current comparators are connected to the outputs.
TK/SS1, TK/SS2 (Pins 4, 10/Pins 1, 6/Pins 2, 7): Output
Voltage Tracking and Soft-Start Inputs. When one channel
is configured to be master of the two channels, a capaci-
tor to ground at this pin sets the ramp rate for the master
channel’s output voltage. When the channel is configured
to be the slave of two channels, the V_FB voltage of the
master channel is reproduced by a resistor divider and
applied to this pin. Internal soft-start currents of 1.3µA
charge the soft-start capacitors.
I_TH1, I_TH2 (Pins 5, 9/Pins 2, 5/Pins 3, 6): Current Control
Thresholds and Error Amplifier Compensation Points.
Each associated channels’ current comparator tripping
threshold increases with its I_TH control voltage.
V_FB1, V_FB2 (Pins 6, 8/Pins 3, 4/Pins 4, 5): Error Amplifier
Feedback Inputs. These pins receive the remotely sensed
feedback voltages for each channel from external resistive
dividers across the outputs.
SGND (Pin 7/Pin 29/Pin 29): Signal Ground. All small-
signal components and compensation components should
connect to this ground, which in turn connects to PGND
at one point. Pin 29 is the Exposed Pad, only available on
the UF package.
EXTV_CC (Pin 14, LTC3850-1 Only/Pin 11/Pin 12): External
Power Input to an Internal Switch Connected to INTV_CC.
This switch closes and supplies the IC power, bypassing
the internal low dropout regulator, whenever EXTV_CC is
higher than 4.7V. Do not exceed 6V on this pin and ensure
V_IN > V_EXTVCC at all times. On the GN package, EXTV_CC
is the optional bonding in place of I_LIM for LTC3850-1. In
the LTC3850-1, I_LIM will default to 50mV.
I_LIM (Pin 14, LTC3850 Only/Pin 10/Pin 11): Current
Comparator Sense Voltage Range Inputs. Tying this pin to
SGND, FLOAT or INTV_CC sets the maximum current sense
threshold to three different levels for each comparator.
PGOOD (Pin 15/Pin 12/Pin 13): Power Good Indicator
Output. Open-drain logic out that is pulled to ground when
either channel output exceeds the ±7.5% regulation window,
after the internal 17µs power bad mask timer expires.
PGND (Pin 19/Pin 16/Pin 17): Power Ground Pin. Connect
this pin closely to the sources of the bottom N-channel
MOSFETs, the (–) terminal of CV_CC and the (–) terminal
of C_IN.
INTV_CC (Pin 21/Pin 18/Pin 19): Internal 5V Regulator Output.
The control circuits are powered from this voltage.
Decouple this pin to PGND with a 4.7µF low ESR tantalum
or ceramic capacitor.
V_IN (Pin 22/Pin 19/Pin 20): Main Input Supply. Decouple
this pin to PGND with a capacitor (0.1µF to 1µF). For ap-
plications where the main input power is 5V, tie the V_IN
and INTV_CC pins together.
BG1, BG2 (Pins 23, 20/Pins 20, 17/Pins 21, 18): Bottom
Gate Driver Outputs. These pins drive the gates of the
bottom N-Channel MOSFETs and swings between PGND
and INTV_CC.
BOOST1, BOOST2 (Pins 24, 18/Pins 21, 15/Pins 22, 16):
Boosted Floating Driver Supplies. The (+) terminal of the
boost-strap capacitors connect to these pins. These pins
swing from a diode voltage drop below INTV_CC up to V_IN
+ INTV_CC.
TG1, TG2 (Pins 25, 17/Pins 22, 14/Pins 23, 15): Top Gate
Driver Outputs. These are the outputs of floating drivers
with a voltage swing equal to INTV_CC superimposed on
the switch nodes voltages.
SW1, SW2 (Pins 26, 16/Pins 23, 13/Pins 24, 14): Switch
Node Connections to Inductors. Voltage swing at these
pins are from a body diode voltage drop below ground
to V_IN.
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