Datasheet LTC3877 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | Dual Phase Step-Down Synchronous Controller with VID Output Voltage Programming and Low Value DCR Sensing |
| Pages / Page | 46 / 9 — pin FuncTions RUN (Pin 16):. VFB1 (Pin 6):. V + (Pin 10):. FB2. VID0, … |
| File Format / Size | PDF / 1.1 Mb |
| Document Language | English |
pin FuncTions RUN (Pin 16):. VFB1 (Pin 6):. V + (Pin 10):. FB2. VID0, VID1, VID2, VID3, VID4, VID5 (Pin 41, Pin 40,
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Text Version of Document
LTC3877
pin FuncTions RUN (Pin 16):
Run Control Input. A voltage above 1.22V
VFB1 (Pin 6):
Channel 1 Error Amplifier Feedback input. on this pin turns on the IC. However, forcing this pin below This pin receives the remotely sensed feedback voltage 1.14V causes the IC to shut down. There is a 1.0µA pull-up from the external resistive divider across the output. The current for this pin. Once the Run pin rises above 1.22V, error amp of channel 1 is disconnected from this pin when an additional 4.5µA pull-up current is added to the pin. It VID_EN is asserted. is highly recommended to have a resistor divider from VIN
V + (Pin 10):
Positive Input of Channel 2 Remote Sens- to SGND, and connect the center tap to RUN pin in order
FB2
ing Differential Amplifier. This pin receives the remotely not to turn on the IC until VIN is high enough. sensed feedback voltage from an external resistive divider
VID0, VID1, VID2, VID3, VID4, VID5 (Pin 41, Pin 40,
across the output. The Differential Amplifier output is con-
Pin 39, Pin 38, Pin 37, Pin 36):
Digital VID Inputs for nected directly to the Error Amplifier’s input inside the IC. Output Voltage Programming. There are internal 100kΩ
V – (Pin 11):
Negative Input of Channel 2 Remote Sens- pull-down resistors connected to these pins respectively.
FB2
ing Differential Amplifier. Connect this pin to the negative
VID_EN (Pin 35):
VID Enable Pin. When this pin is asserted, terminal of the output capacitors near the load when remote channel 1’s output will be programmed by the VID inputs sensing is desired. after startup is complete. If the LTC3877 is configured as
SNSA1+, SNSA2+ (Pin 1, Pin 12):
Positive Terminals of a dual-phase single-output controller with the CHL_SEL the AC Current Sense Comparator Inputs. The (+) input pin high, its output will be programmed through the VID to the AC current comparator is normally connected to pins after VID_EN is asserted. Before VID_EN is asserted, a DCR sensing network. When the respective channel’s channel 1’s output is set by an external resistor divider. SNSD+ pin is connected to this network, the channel’s There is an internal 100kΩ pull-down resistor connected AC ripple voltage seen by the IC is effectively increased to this pin. by a factor of 5.
CHL_SEL (Pin 34):
Channel Configuration Pin. When
SNSD1+, SNSD2+ (Pin 43, Pin 14):
Positive Terminals of this pin is asserted, the two channels are configured as a the DC Current Sense Comparator Inputs. The (+) input to dual-phase single-output regulator, and the output voltage the DC current comparator is normally connected to a DC can be programmed by VID inputs if VID_EN is asserted. current sensing network. When this pin is grounded, the When this pin is grounded, the two channels operate respective phase’s current limit is increased by a factor of 5. independently. Channel 1’s output can be programmed by VID inputs if VID_EN is high, but Channel 2’s output
SNS1–, SNS2– (Pin 44, Pin 13):
Negative Terminals of the must be set by an external resistor divider. There is an AC and DC Current Sense Comparator Inputs. The (–) inputs internal 100kΩ pull-down resistor connected to this pin. to the current comparators are connected to the output at the inductor (or current sense resistor, if one is used).
V + OSNS1 (Pin 3):
Positive Input of Channel 1 Remote Sens- ing Differential Amplifier. Connect this pin to the remote
ILIM (Pin 15):
Current Comparators' Sense Voltage Range load voltage directly. Input. A DC voltage applied to this pin programs the maximum current sense threshold to one of five different
V – OSNS1 (Pin 4):
Negative Input of Channel 1 Remote levels for the current comparators. Sensing Differential Amplifier. Connect this pin to the negative terminal of the output capacitors near the load.
ITH1, ITH2 (Pin 7, Pin 8):
Current Control Threshold and Error Amplifier Compensation Points. The current
DIFFOUT (Pin 5):
Output of Channel 1 Remote Sensing comparators' tripping thresholds increase with these Differential Amplifier. If remote sensing is used on chan- control voltages. nel 1, connect this pin to VFB1 through a resistor divider. 3877f For more information www.linear.com/LTC3877 9
pin FuncTions RUN (Pin 16):
Run Control Input. A voltage above 1.22V
VFB1 (Pin 6):
Channel 1 Error Amplifier Feedback input. on this pin turns on the IC. However, forcing this pin below This pin receives the remotely sensed feedback voltage 1.14V causes the IC to shut down. There is a 1.0µA pull-up from the external resistive divider across the output. The current for this pin. Once the Run pin rises above 1.22V, error amp of channel 1 is disconnected from this pin when an additional 4.5µA pull-up current is added to the pin. It VID_EN is asserted. is highly recommended to have a resistor divider from VIN
V + (Pin 10):
Positive Input of Channel 2 Remote Sens- to SGND, and connect the center tap to RUN pin in order
FB2
ing Differential Amplifier. This pin receives the remotely not to turn on the IC until VIN is high enough. sensed feedback voltage from an external resistive divider
VID0, VID1, VID2, VID3, VID4, VID5 (Pin 41, Pin 40,
across the output. The Differential Amplifier output is con-
Pin 39, Pin 38, Pin 37, Pin 36):
Digital VID Inputs for nected directly to the Error Amplifier’s input inside the IC. Output Voltage Programming. There are internal 100kΩ
V – (Pin 11):
Negative Input of Channel 2 Remote Sens- pull-down resistors connected to these pins respectively.
FB2
ing Differential Amplifier. Connect this pin to the negative
VID_EN (Pin 35):
VID Enable Pin. When this pin is asserted, terminal of the output capacitors near the load when remote channel 1’s output will be programmed by the VID inputs sensing is desired. after startup is complete. If the LTC3877 is configured as
SNSA1+, SNSA2+ (Pin 1, Pin 12):
Positive Terminals of a dual-phase single-output controller with the CHL_SEL the AC Current Sense Comparator Inputs. The (+) input pin high, its output will be programmed through the VID to the AC current comparator is normally connected to pins after VID_EN is asserted. Before VID_EN is asserted, a DCR sensing network. When the respective channel’s channel 1’s output is set by an external resistor divider. SNSD+ pin is connected to this network, the channel’s There is an internal 100kΩ pull-down resistor connected AC ripple voltage seen by the IC is effectively increased to this pin. by a factor of 5.
CHL_SEL (Pin 34):
Channel Configuration Pin. When
SNSD1+, SNSD2+ (Pin 43, Pin 14):
Positive Terminals of this pin is asserted, the two channels are configured as a the DC Current Sense Comparator Inputs. The (+) input to dual-phase single-output regulator, and the output voltage the DC current comparator is normally connected to a DC can be programmed by VID inputs if VID_EN is asserted. current sensing network. When this pin is grounded, the When this pin is grounded, the two channels operate respective phase’s current limit is increased by a factor of 5. independently. Channel 1’s output can be programmed by VID inputs if VID_EN is high, but Channel 2’s output
SNS1–, SNS2– (Pin 44, Pin 13):
Negative Terminals of the must be set by an external resistor divider. There is an AC and DC Current Sense Comparator Inputs. The (–) inputs internal 100kΩ pull-down resistor connected to this pin. to the current comparators are connected to the output at the inductor (or current sense resistor, if one is used).
V + OSNS1 (Pin 3):
Positive Input of Channel 1 Remote Sens- ing Differential Amplifier. Connect this pin to the remote
ILIM (Pin 15):
Current Comparators' Sense Voltage Range load voltage directly. Input. A DC voltage applied to this pin programs the maximum current sense threshold to one of five different
V – OSNS1 (Pin 4):
Negative Input of Channel 1 Remote levels for the current comparators. Sensing Differential Amplifier. Connect this pin to the negative terminal of the output capacitors near the load.
ITH1, ITH2 (Pin 7, Pin 8):
Current Control Threshold and Error Amplifier Compensation Points. The current
DIFFOUT (Pin 5):
Output of Channel 1 Remote Sensing comparators' tripping thresholds increase with these Differential Amplifier. If remote sensing is used on chan- control voltages. nel 1, connect this pin to VFB1 through a resistor divider. 3877f For more information www.linear.com/LTC3877 9
