Datasheet LT8636 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | 42V, 5A/7A Peak Synchronous Step-Down Silent Switcher with 2.5µA Quiescent Current |
| Pages / Page | 26 / 10 — PIN FUNCTIONS PG (Pin 1):. BST (Pin 7):. SW (Pins 8–10):. BIAS (Pin 2):. … |
| Revision | A |
| File Format / Size | PDF / 2.1 Mb |
| Document Language | English |
PIN FUNCTIONS PG (Pin 1):. BST (Pin 7):. SW (Pins 8–10):. BIAS (Pin 2):. EN/UV (Pin 14):. INTVCC (Pin 3):. SYNC/MODE (Pin 15):
Text Version of Document
link to page 13 link to page 11 LT8636
PIN FUNCTIONS PG (Pin 1):
The PG pin is the open-drain output of an
BST (Pin 7):
This pin is used to provide a drive voltage, internal comparator. PG remains low until the FB pin is higher than the input voltage, to the topside power switch. within ±8% of the final regulation voltage, and there are Place a 0.1µF boost capacitor as close as possible to no fault conditions. PG is also pulled low when EN/UV is the IC. below 1V, INTVCC has fallen too low, VIN is too low, or
SW (Pins 8–10):
The SW pins are the outputs of the inter- thermal shutdown. PG is valid when VIN is above 3.4V. nal power switches. Tie these pins together and connect
BIAS (Pin 2):
The internal regulator will draw current from them to the inductor. This node should be kept small on BIAS instead of VIN when BIAS is tied to a voltage higher the PCB for good performance and low EMI. than 3.1V. For output voltages of 3.3V to 25V this pin
EN/UV (Pin 14):
The LT8636 is shut down when this pin should be tied to VOUT. If this pin is tied to a supply other is low and active when this pin is high. The hysteretic than VOUT use a 1µF local bypass capacitor on this pin. threshold voltage is 1.00V going up and 0.96V going If no supply is available, tie to GND. However, especially down. Tie to V for high input or high frequency applications, BIAS should IN if the shutdown feature is not used. An external resistor divider from V be tied to output or an external supply of 3.3V or above. IN can be used to program a VIN threshold below which the LT8636 will shut down.
INTVCC (Pin 3):
Internal 3.4V Regulator Bypass Pin. The
SYNC/MODE (Pin 15):
For the LT8636, this pin programs internal power drivers and control circuits are powered four different operating modes: 1) Burst Mode operation. from this voltage. INTVCC maximum output current is Tie this pin to ground for Burst Mode operation at low 20mA. Do not load the INTVCC pin with external circuitry. output loads—this wil result in ultralow quiescent INTVCC current will be supplied from BIAS if BIAS > 3.1V, current. 2) Forced Continuous mode (FCM). This otherwise current will be drawn from VIN. Voltage on mode offers fast transient response and full frequency INTVCC will vary between 2.8V and 3.4V when BIAS is operation over a wide load range. Float this pin for FCM. between 3.0V and 3.6V. Place a low ESR ceramic capaci- When floating, pin leakage currents should be <1µA. tor of at least 1µF from this pin to ground close to the IC. See Block Diagram for internal pull-up and pull-down
GND (Pins 4, 13, Exposed Pad Pin 21):
Ground. Place resistance. 3) Spread spectrum mode. Tie this pin high the negative terminal of the input capacitor as close to to INTVCC (~3.4V) or an external supply of 3V to 4V the GND pins as possible. The exposed pads should be for forced continuous mode with spread-spectrum soldered to the PCB for good thermal performance. If modulation. 4) Synchronization mode. Drive this pin with necessary due to manufacturing limitations Pin 21 may a clock source to synchronize to an external frequency. be left disconnected, however thermal performance will During synchronization the part will operate in forced be degraded. continuous mode.
NC (Pins 5, 12):
No Connect. This pin is not connected
CLKOUT (Pin 16):
In forced continuous mode, spread to internal circuitry and can be tied anywhere on the PCB, spectrum, and synchronization modes, the CLKOUT pin typically ground. will provide a ~200ns wide pulse at the switch frequency.
V
The low and high levels of the CLKOUT pin are ground and
IN (Pins 6, 11):
The VIN pins supply current to the LT8636 internal circuitry and to the internal topside INTVCC respectively, and the drive strength of the CLKOUT power switch. The LT8636 requires the use of multiple pin is several hundred ohms. In Burst Mode operation, V the CLKOUT pin will be low. Float this pin if the CLKOUT IN bypass capacitors. Two small 1µF capacitors should be placed as close as possible to the LT8636, one capaci- function is not used. tor on each side of the device (CIN1, CIN2). A third capaci-
RT (Pin 17):
A resistor is tied between RT and ground to tor with a larger value, 2.2µF or higher, should be placed set the switching frequency. near CIN1 or CIN2. See Applications Information section for sample layout. Rev. A 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Typical Applications Related Parts
PIN FUNCTIONS PG (Pin 1):
The PG pin is the open-drain output of an
BST (Pin 7):
This pin is used to provide a drive voltage, internal comparator. PG remains low until the FB pin is higher than the input voltage, to the topside power switch. within ±8% of the final regulation voltage, and there are Place a 0.1µF boost capacitor as close as possible to no fault conditions. PG is also pulled low when EN/UV is the IC. below 1V, INTVCC has fallen too low, VIN is too low, or
SW (Pins 8–10):
The SW pins are the outputs of the inter- thermal shutdown. PG is valid when VIN is above 3.4V. nal power switches. Tie these pins together and connect
BIAS (Pin 2):
The internal regulator will draw current from them to the inductor. This node should be kept small on BIAS instead of VIN when BIAS is tied to a voltage higher the PCB for good performance and low EMI. than 3.1V. For output voltages of 3.3V to 25V this pin
EN/UV (Pin 14):
The LT8636 is shut down when this pin should be tied to VOUT. If this pin is tied to a supply other is low and active when this pin is high. The hysteretic than VOUT use a 1µF local bypass capacitor on this pin. threshold voltage is 1.00V going up and 0.96V going If no supply is available, tie to GND. However, especially down. Tie to V for high input or high frequency applications, BIAS should IN if the shutdown feature is not used. An external resistor divider from V be tied to output or an external supply of 3.3V or above. IN can be used to program a VIN threshold below which the LT8636 will shut down.
INTVCC (Pin 3):
Internal 3.4V Regulator Bypass Pin. The
SYNC/MODE (Pin 15):
For the LT8636, this pin programs internal power drivers and control circuits are powered four different operating modes: 1) Burst Mode operation. from this voltage. INTVCC maximum output current is Tie this pin to ground for Burst Mode operation at low 20mA. Do not load the INTVCC pin with external circuitry. output loads—this wil result in ultralow quiescent INTVCC current will be supplied from BIAS if BIAS > 3.1V, current. 2) Forced Continuous mode (FCM). This otherwise current will be drawn from VIN. Voltage on mode offers fast transient response and full frequency INTVCC will vary between 2.8V and 3.4V when BIAS is operation over a wide load range. Float this pin for FCM. between 3.0V and 3.6V. Place a low ESR ceramic capaci- When floating, pin leakage currents should be <1µA. tor of at least 1µF from this pin to ground close to the IC. See Block Diagram for internal pull-up and pull-down
GND (Pins 4, 13, Exposed Pad Pin 21):
Ground. Place resistance. 3) Spread spectrum mode. Tie this pin high the negative terminal of the input capacitor as close to to INTVCC (~3.4V) or an external supply of 3V to 4V the GND pins as possible. The exposed pads should be for forced continuous mode with spread-spectrum soldered to the PCB for good thermal performance. If modulation. 4) Synchronization mode. Drive this pin with necessary due to manufacturing limitations Pin 21 may a clock source to synchronize to an external frequency. be left disconnected, however thermal performance will During synchronization the part will operate in forced be degraded. continuous mode.
NC (Pins 5, 12):
No Connect. This pin is not connected
CLKOUT (Pin 16):
In forced continuous mode, spread to internal circuitry and can be tied anywhere on the PCB, spectrum, and synchronization modes, the CLKOUT pin typically ground. will provide a ~200ns wide pulse at the switch frequency.
V
The low and high levels of the CLKOUT pin are ground and
IN (Pins 6, 11):
The VIN pins supply current to the LT8636 internal circuitry and to the internal topside INTVCC respectively, and the drive strength of the CLKOUT power switch. The LT8636 requires the use of multiple pin is several hundred ohms. In Burst Mode operation, V the CLKOUT pin will be low. Float this pin if the CLKOUT IN bypass capacitors. Two small 1µF capacitors should be placed as close as possible to the LT8636, one capaci- function is not used. tor on each side of the device (CIN1, CIN2). A third capaci-
RT (Pin 17):
A resistor is tied between RT and ground to tor with a larger value, 2.2µF or higher, should be placed set the switching frequency. near CIN1 or CIN2. See Applications Information section for sample layout. Rev. A 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Typical Applications Related Parts
