Datasheet LTC3874-1 (Analog Devices) - 6

LTC3874-1
pin FuncTions I + + SENSE0 /ISENSE1 (Pin 1/Pin 6):
Current Sense Compara- is a three-state compatible output. To support three-state tor Inputs. The (+) inputs to the current comparators are mode, an external resistor divider is typically used from normally connected to DCR sensing networks. VCC0/VCC1 to ground.
I − − SENSE0 /ISENSE1 (Pin 2/Pin 5):
Current Sense Compara-
VCC0/VCC1(Pin 18/Pin 14):
PWM Pin Driver Supplies. tor Inputs. The (−) inputs to the current comparators are Decouple this pin to GND with a capacitor (0.1μF) to an connected to the outputs. external supply or tie this pin to the INTVCC pin. PWM0/
RUN0/RUN1 (Pin 3/Pin 4):
Enable Run Inputs. Logic high PWM1 signal swing is from ground to VCC0/VCC1. on the RUN pin enables the corresponding channel.
EXTVCC(Pin 15):
External Power Input to an Internal Switch
MODE0/MODE1(Pin 24/Pin 7):
DCM/CCM Mode Control Connected to INTVCC. The switch closes and supplies the Pins. Each channel runs in forced continuous mode if the IC power, bypassing the internal low dropout regulator, mode pin is logic high. There is an internal 500k pull-down whenever EXTVCC is higher than 4.7V and VIN is greater resistor on the mode pin. To select discontinuous conduc- than 7V. Do not exceed 6V on this pin. tion mode, float or pull down the mode pin.
INTVCC(Pin 16):
Internal 5.5V Regulator Output. The control
I
circuits are powered from this voltage. Decouple this pin
TH0/ITH1(Pin 23/Pin 8):
Current Control Threshold. Each associated channel’s current comparator tripping threshold to GND with a minimum of 4.7μF low ESR tantalum or increases with its I ceramic capacitor. TH voltage. These pins must be con- nected to the master controller’s ITH pins.
VIN (Pin 17):
Main Input Supply. Decouple this pin to GND
FREQ(Pin 9):
Frequency Set Pin. There is a precision with a capacitor (0.1μF to 1μF). 10µA current flowing out of this pin. A resistor to ground
FAULT0/FAULT1 (Pin 21/Pin 20):
Master Controller Fault sets a voltage which in turn programs the frequency. This Inputs. Connect these pins to the master chip fault indica- pin sets the default switching frequency when there is no tor pins to respond to the fault signals from the master external clock on the SYNC pin. See the application section controller. When a FAULT pin is floating or low, the PWM for detailed information. pin of the corresponding channel is in three-state. There
ILIM(Pin 10):
Current Comparators Sense Voltage Limit. is an internal 500k pull-down resistor on each FAULT pin. Program a DC voltage at this pin to set the maximum cur-
LOWDCR(Pin 22):
Sub-milliohm DCR Current Sensing rent sense threshold for the current comparators. Enable Pin. There is an internal 500k pull-up resistor
SYNC (Pin 11):
External Clock Synchronization Input. If an between the LOWDCR pin and INTVCC. Floating or pull- external clock is present at this pin, the switching frequency ing this pin logic high will enable the sub-milliohm DCR will be synchronized to the falling edge of external clock. current sensing. Pulling this pin logic low will disable the Tie this pin to GND if not used. sub-milliohm DCR current sensing.
PHASMD (Pin 12):
Phase Set Pin. This pin determines the
GND(Exposed Pad Pin 25):
Ground. Connect this pad, relative phases between the external clock on pin SYNC through vias, to a solid ground plane under the circuit. and the internal controllers. See Table 1 in the Operation The sources of the bottom N-channel MOSFETs, the (–) section for details. terminal of CINTVCC, and the (–) terminal of CIN should connect to this ground plane as closely as possible to
PWM0/PWM1(Pin 19/Pin 13):
(Top) Gate Signal Outputs. the IC. All small-signal components and compensation This signal goes to the PWM or top gate input of the exter- components should also connect to this ground plane. nal driver, integrated driver MOSFET or power block. This 38741f 6 For more information www.linear.com/LTC3874-1 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Block Diagram Operation Applications Information Typical Application Related Parts