The SM72485 step-down switching regulator features all of the functions required to implement a low cost, efficient, Buck bias regulator. This high voltage regulator contains an 100-V N-channel buck switch. The device is easy to implement and is provided in the VSSOP and the thermally enhanced WSON package. The regulator is based on a control scheme using an on-time inversely proportional to VIN. This feature allows the operating frequency to remain relatively constant. The control scheme requires no loop compensation. An intelligent current limit is implemented with forced off-time, which is inversely proportional to VOUT. This scheme ensures short circuit control while providing minimum foldback. Other features include: Thermal shutdown, VCC undervoltage lockout, gate drive undervoltage lockout, maximum duty cycle limiter, and a precharge switch.
PART NUMBER | PACKAGE | BODY SIZE (NOM) |
---|---|---|
SM72485 | VSSOP (8) | 3.00 mm × 3.00 mm |
WSON (8) | 4.00 mm × 4.00 mm |
Changes from D Revision (April 2013) to E Revision
Changes from C Revision (April 2013) to D Revision
PIN | TYPE(1) | DESCRIPTION | ||
---|---|---|---|---|
NAME | VSSOP | WSON | ||
BST | 2 | 2 | I | An external capacitor is required between the BST and the SW pins. TI recommends a 0.01-µF ceramic capacitor. An internal diode charges the capacitor from VCC during each off-time. |
FB | 5 | 5 | I | This pin is connected to the inverting input of the internal regulation comparator. The regulation threshold is 2.5 V. |
RCL | 3 | 3 | I | A resistor between this pin and RTN sets the off-time when current limit is detected. The off-time is preset to 35 µs if FB = 0 V. |
RT/SD | 6 | 6 | I | A resistor between this pin and VIN sets the switch on-time as a function of VIN. The minimum recommended on-time is 400 ns at the maximum input voltage. This pin can be used for remote shutdown. |
RTN | 4 | 4 | G | Ground for the entire circuit. |
SW | 1 | 1 | O | Power switching node. Connect to the output inductor, re-circulating diode, and bootstrap capacitor. |
VCC | 7 | 7 | I | This regulated voltage provides gate drive power for the internal Buck switch. An internal diode is provided between this pin and the BST pin. A local 0.47-µF decoupling capacitor is required. The series pass regulator is current limited to 9 mA. |
VIN | 8 | 8 | I | Input operating voltage: 6 V to 95 V. |
Exposed Pad | — | Thermal Pad | NC | The exposed pad has no electrical contact. Connect to system ground plane for reduced thermal resistance. |
MIN | MAX | UNIT | |
---|---|---|---|
VIN to GND | –0.3 | 100 | V |
BST to GND | –0.3 | 114 | V |
SW to GND (steady-state) | –1 | V | |
BST to VCC | 100 | V | |
BST to SW | 14 | V | |
VCC to GND | 14 | V | |
All other inputs to GND | –0.3 | 7 | V |
Storage temperature, Tstg | –55 | 150 | °C |
VALUE | UNIT | |||
---|---|---|---|---|
V(ESD) | Electrostatic discharge | Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) | ±2000 | V |
MIN | MAX | UNIT | ||
---|---|---|---|---|
VIN | Input voltage | 6 | 95 | V |
TJ | Operating junction temperature | –40 | 125 | °C |
THERMAL METRIC(1) | SM72485 | UNIT | ||
---|---|---|---|---|
DGK (VSSOP) | NGU (WSON) | |||
8 PINS | 8 PINS | |||
RθJA | Junction-to-ambient thermal resistance | 139.6 | 42.3 | °C/W |
RθJC(top) | Junction-to-case (top) thermal resistance | 41.8 | 41.4 | °C/W |
RθJB | Junction-to-board thermal resistance | 68.4 | 20.1 | °C/W |
ψJT | Junction-to-top characterization parameter | 4.2 | 0.4 | °C/W |
ψJB | Junction-to-board characterization parameter | 67.5 | 20.3 | °C/W |
RθJC(bot) | Junction-to-case (bottom) thermal resistance | — | 4.1 | °C/W |
PARAMETER | TEST CONDITIONS | MIN | TYP | MAX | UNIT | |
---|---|---|---|---|---|---|
VCC SUPPLY | ||||||
VCCREG | VCC regulator output | VIN = 48 V | 6.6 | 7 | 7.4 | V |
Dropout voltage, VIN – VCC | VIN = 6 V to 8.5 V | 100 | mV | |||
VCC bypass threshold | VIN rising | 8.5 | V | |||
VCC bypass hysteresis | 300 | mV | ||||
VCC output impedance | VIN = 6 V | 100 | Ω | |||
VIN = 10 V | 8.8 | |||||
VIN = 48 V | 0.8 | |||||
VCC current limit | VIN = 48 V | 9.2 | mA | |||
VCC UVLO | VCC rising | 5.3 | V | |||
VCC UVLO hysteresis | 190 | mV | ||||
VCC UVLO filter delay | 3 | µs | ||||
ICC | Operating current | VFB = 3 V, VIN = 48 V | 550 | 750 | µA | |
Shutdown current | VRT/SD = 0 V | 110 | 176 | µA | ||
SWITCH CHARACTERISTICS | ||||||
Buckswitch RDS(ON) | ITEST = 200 mA | 2.2 | 4.6 | Ω | ||
Gate drive UVLO | VBST – VSW rising | 2.8 | 3.8 | 4.8 | V | |
Gate drive UVLO hysteresis | 490 | mV | ||||
Precharge switch voltage | At 1 mA | 0.8 | V | |||
Precharge switch on-time | 150 | ns | ||||
CURRENT LIMIT | ||||||
Current limit threshold | 0.24 | 0.3 | 0.36 | A | ||
Current limit response time | ISW overdrive = 0.1 A, time to switch OFF | 350 | ns | |||
tOFF_1 | Off-time generator | VFB = 0 V, RCL = 100 kΩ | 35 | µs | ||
tOFF_2 | Off-time generator | VFB = 2.3 V, RCL = 100 kΩ | 2.56 | |||
ON-TIME GENERATOR | ||||||
tON_1 | On-time generator | VIN = 10 V, RON = 200 kΩ | 2.15 | 2.77 | 3.5 | µs |
tON_2 | On-time generator | VIN = 95 V, RON = 200 kΩ | 200 | 300 | 420 | ns |
Remote shutdown threshold | Rising | 0.4 | 0.7 | 1.05 | V | |
Remote shutdown hysteresis | 35 | mV | ||||
MINIMUM OFF-TIME | ||||||
Minimum off-time | VFB = 0 V | 300 | ns | |||
REGULATION AND OV COMPARATORS | ||||||
FB reference threshold | Internal reference, trip point for switch = ON | 2.445 | 2.5 | 2.55 | V | |
FB overvoltage threshold | Trip point for switch = OFF | 2.875 | V | |||
FB bias current | 100 | nA | ||||
THERMAL SHUTDOWN | ||||||
TSD | Thermal shutdown temperature | 165 | °C | |||
Thermal shutdown hysteresis | 25 | °C |