Datasheet LTC3129-1 (Analog Devices) - 9

LTC3129-1
pin FuncTions (QFN/MSOP) BST1 (Pin 1/Pin 15):
Boot-Strapped Floating Supply for
VS3 (Pin 7/Pin 5):
Output Voltage Select Pin. Connect this High Side NMOS Gate Drive. Connect to SW1 through a pin to ground or VCC to program the output voltage (see 22nF capacitor, as close to the part as possible. The value Table 1). This pin should not float or go below ground. is not critical. Any value from 4.7nF to 47nF may be used. If this pin is externally driven above VCC, a 1M resistor
V
should be added in series.
IN (Pin 2/Pin 16):
Input Voltage for the Converter. Connect a minimum of 4.7µF ceramic decoupling capacitor from
VS2 (Pin 8/Pin 6):
Output Voltage Select Pin. Connect this this pin to the ground plane, as close to the pin as possible. pin to ground or VCC to program the output voltage (see
V
Table 1). This pin should not float or go below ground.
CC (Pin 3/Pin 1):
Output Voltage of the Internal Voltage Regulator. This is the supply pin for the internal circuitry.
VS1 (Pin 9/Pin 7):
Output Voltage Select Pin. Connect this Bypass this output with a minimum of 2.2µF ceramic ca- pin to ground or VCC to program the output voltage (see pacitor close to the pin. This pin may be back-driven by Table 1). This pin should not float or go below ground. an external supply, up to a maximum of 5.5V.
PWM (Pin 10/Pin 8):
Mode Select Pin.
RUN (Pin 4/Pin 2):
Input to the Run Comparator. Pull PWM = Low (ground): Enables automatic Burst Mode this pin above 1.1V to enable the VCC regulator and above operation. 1.28V to enable the converter. Connecting this pin to a resistor divider from VIN to ground allows programming a PWM = High (tie to VCC): Fixed frequency PWM VIN start threshold higher than the 1.8V (typical) VIN UVLO operation. threshold. In this case, the typical VIN turn-on threshold is This pin should not be allowed to float. It has internal 5M determined by VIN = 1.22V • [1+(R3/Pin R4)] (see Figure 2). pull-down resistor.
MPPC (Pin 5/Pin 3):
Maximum Power Point Control
PGOOD (Pin 11/Pin 9):
Open drain output that pulls to Programming Pin. Connect this pin to a resistor divider ground when FB drops too far below its regulated voltage. from VIN to ground to enable the MPPC functionality. Connect a pull-up resistor from this pin to a positive sup- If the VOUT load is greater than what the power source ply. This pin can sink up to the absolute maximum rating can provide, the MPPC will reduce the inductor current of 15mA when low. Refer to the Operation section of the to regulate VIN to a voltage determined by: VIN = 1.175V data sheet for more detail. • [1 + (R5/R6)] (see Figure 3). By setting the VIN regula- tion voltage appropriately, maximum power transfer from
VOUT (Pin 12/Pin 10):
Output voltage of the converter, set the limited source is assured. Note this pin is very noise by the VS1-VS3 programming pins according to Table 1. sensitive, therefore minimize trace length and stray capaci- Connect a minimum value of 4.7µF ceramic capacitor from tance. Please refer to the Applications Information section this pin to the ground plane, as close to the pin as possible. for more detail on programming the MPPC for different
BST2 (Pin 13/Pin 11):
Boot-Strapped Floating Supply for sources. If this function is not needed, tie the pin to VCC. High Side NMOS Gate Drive. Connect to SW2 through a
GND (Pin 6/Pin 4):
Signal Ground. Provide a short direct 22nF capacitor, as close to the part as possible. The value PCB path between GND and the ground plane where the is not critical. Any value from 4.7nF to 47nF may be used exposed pad is soldered.
SW2 (Pin 14/Pin 12):
Switch Pin. Connect to one side of the inductor. Keep PCB trace lengths as short and wide as possible to reduce EMI. 31291fc For more information www.linear.com/LTC3129-1 9