Datasheet LTC3422 (Analog Devices) - 6
| Fabricante | Analog Devices |
| Descripción | 1.5A, 3MHz Synchronous Step-Up DC/DC Converter with Output Disconnect |
| Páginas / Página | 16 / 6 — PI FU CTIO S. SW (Pin 1):. SHDN (Pin 5):. VIN (Pin 2):. FB (Pin 6):. … |
| Formato / tamaño de archivo | PDF / 271 Kb |
| Idioma del documento | Inglés |
PI FU CTIO S. SW (Pin 1):. SHDN (Pin 5):. VIN (Pin 2):. FB (Pin 6):. BURST (Pin 3):. VC (Pin 7):. T (Pin 8):. SYNC (Pin 9):
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LTC3422
U U U PI FU CTIO S SW (Pin 1):
Switch Pin for the Inductor Connection. The nominal soft-start charging current is 2.4µA. The active Minimize trace length between SW and inductor. For range of SS is from 0.8V to 1.6V. discontinuous inductor current, a controlled impedance is
SHDN (Pin 5):
Shutdown Input. Less than 250mV on SHDN internally connected from SW to VIN to eliminate high shuts down the LTC3422. Placing 1V or more on SHDN enables frequency ringing, reducing EMI radiation. the LTC3422. Once VOUT exceeds 2.2V, hysteresis is applied
VIN (Pin 2):
Input Supply Voltage. Connect VIN to the input to this pin (500nA exits the pin) allowing it to operate at a logic supply and decouple with a 4.7µF or larger ceramic high while the battery can drop to 500mV. capacitor as close to VIN as possible.
FB (Pin 6):
Feedback Input to Error Amplifier. Connect the VOUT
BURST (Pin 3):
Burst Mode Threshold Adjust. Automatic to ground resistor divider tap here. The output voltage can be Burst Mode Operation: A resistor/capacitor combination adjusted from 2.25V to 5.25V according to the formula: from BURST to ground programs the average load current at which automatic Burst Mode operation is exited, ac- R1 R2 VOUT = + 1.216 • cording to the formula: R2
VC (Pin 7):
Error Amp Output. A frequency compensation RB = 12 network is connected from V I C to ground to compensate the EXITBURST loop. See the section “Closing the Feedback Loop” for guide- where R lines. B is in kΩ and IEXITBURST is in amps
R
C V
T (Pin 8):
Frequency Adjust Input. Connect a resistor to ground C OUT OUT B ≥ • to program the oscillator frequency according to the formula: , 64 000 where CB(MIN) and COUT are in µF. fOSC = 28 RT Please refer to the Burst Mode Output Current Threshold vs R where f BURST Typical Performance Chacteristic curves. OSC is in MHz and RT is in kΩ. Note that during Burst Mode operation the peak inductor
SYNC (Pin 9):
Oscillator Synchronization Input. A clock pulse current will be approximately 600mA and return to zero on each width of 100ns to 2µs is required to synchronize the internal cycle. In Burst Mode operation the frequency is variable, oscillator. If not used, SYNC should be grounded. providing a significant efficiency improvement at light loads.
VOUT (Pin 10):
Output of the synchronous rectifier and The LTC3422 only allows Burst Mode operation to be entered bootstrapped power source for the LTC3422. A ceramic capaci- once VOUT exceeds approximately 2.2V. tor of at least 10µF is required and should be located as close to Manually Implementing Burst Mode Operation: Ground VOUT and the power ground plane as possible. BURST to force Burst Mode operation or connect it to VOUT to
Exposed Pad (Pin 11):
Signal and Power Ground for the force fixed frequency PWM mode. Note that BURST must not LTC3422. This pin MUST be soldered to the PCB ground plane be pulled higher than VOUT. for electrical contact and rated thermal performance.
SS (Pin 4):
Soft-Start. Connect a capacitor from SS to ground to set the soft-start time according to the formula: t(ms) = CSS(µF) • 320 3422fa 6
U U U PI FU CTIO S SW (Pin 1):
Switch Pin for the Inductor Connection. The nominal soft-start charging current is 2.4µA. The active Minimize trace length between SW and inductor. For range of SS is from 0.8V to 1.6V. discontinuous inductor current, a controlled impedance is
SHDN (Pin 5):
Shutdown Input. Less than 250mV on SHDN internally connected from SW to VIN to eliminate high shuts down the LTC3422. Placing 1V or more on SHDN enables frequency ringing, reducing EMI radiation. the LTC3422. Once VOUT exceeds 2.2V, hysteresis is applied
VIN (Pin 2):
Input Supply Voltage. Connect VIN to the input to this pin (500nA exits the pin) allowing it to operate at a logic supply and decouple with a 4.7µF or larger ceramic high while the battery can drop to 500mV. capacitor as close to VIN as possible.
FB (Pin 6):
Feedback Input to Error Amplifier. Connect the VOUT
BURST (Pin 3):
Burst Mode Threshold Adjust. Automatic to ground resistor divider tap here. The output voltage can be Burst Mode Operation: A resistor/capacitor combination adjusted from 2.25V to 5.25V according to the formula: from BURST to ground programs the average load current at which automatic Burst Mode operation is exited, ac- R1 R2 VOUT = + 1.216 • cording to the formula: R2
VC (Pin 7):
Error Amp Output. A frequency compensation RB = 12 network is connected from V I C to ground to compensate the EXITBURST loop. See the section “Closing the Feedback Loop” for guide- where R lines. B is in kΩ and IEXITBURST is in amps
R
C V
T (Pin 8):
Frequency Adjust Input. Connect a resistor to ground C OUT OUT B ≥ • to program the oscillator frequency according to the formula: , 64 000 where CB(MIN) and COUT are in µF. fOSC = 28 RT Please refer to the Burst Mode Output Current Threshold vs R where f BURST Typical Performance Chacteristic curves. OSC is in MHz and RT is in kΩ. Note that during Burst Mode operation the peak inductor
SYNC (Pin 9):
Oscillator Synchronization Input. A clock pulse current will be approximately 600mA and return to zero on each width of 100ns to 2µs is required to synchronize the internal cycle. In Burst Mode operation the frequency is variable, oscillator. If not used, SYNC should be grounded. providing a significant efficiency improvement at light loads.
VOUT (Pin 10):
Output of the synchronous rectifier and The LTC3422 only allows Burst Mode operation to be entered bootstrapped power source for the LTC3422. A ceramic capaci- once VOUT exceeds approximately 2.2V. tor of at least 10µF is required and should be located as close to Manually Implementing Burst Mode Operation: Ground VOUT and the power ground plane as possible. BURST to force Burst Mode operation or connect it to VOUT to
Exposed Pad (Pin 11):
Signal and Power Ground for the force fixed frequency PWM mode. Note that BURST must not LTC3422. This pin MUST be soldered to the PCB ground plane be pulled higher than VOUT. for electrical contact and rated thermal performance.
SS (Pin 4):
Soft-Start. Connect a capacitor from SS to ground to set the soft-start time according to the formula: t(ms) = CSS(µF) • 320 3422fa 6