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MAX15012BASA+ Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX15012BASA+ Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 14 page 175V/2A, High-Speed, Half-Bridge MOSFET Drivers _______________________________________________________________________________________ 9 Detailed Description The MAX15012/MAX15013 are 175V/2A high-speed, half-bridge MOSFET drivers that operate from a supply voltage of +8V to +12.6V. The drivers are intended to drive a high-side switch without any isolation device like an optocoupler or drive transformer. The high-side driver is controlled by a TTL/CMOS logic signal refer- enced to ground. The 2A source and sink drive capa- bility is achieved by using low RDS_ON, p- and n-channel driver output stages. The BiCMOS process allows extremely fast rise/fall times and low propaga- tion delays. The typical propagation delay from the logic-input signal to the driver output is 35ns with a matched propagation delay of 2ns typical. Matching these propagation delays is as important as the absolute value of the delay itself. The high 175V input voltage range allows plenty of margin above the 100V transient specification per telecom standards. The maximum operating supply voltage (VDD) must be reduced linearly from 12.6V to 10.5V when the maxi- mum voltage (VHS_MAX) increases from 125V to 175V. See the Typical Operating Characteristics. Undervoltage Lockout Both the high- and low-side drivers feature undervolt- age lockout (UVLO). The low-side driver’s UVLOLOW threshold is referenced to GND and pulls both driver outputs low when VDD falls below 6.8V. The high-side driver has its own UVLO threshold (UVLOHIGH), refer- enced to HS, and pulls DH low when BST falls below 6.4V with respect to HS. During turn-on, once VDD rises above its UVLO thresh- old, DL starts switching and follows the IN_L logic input. At this time, the bootstrap capacitor is not charged and the BST-to-HS voltage is below UVLOBST. For synchro- nous buck and half-bridge converter topologies, the bootstrap capacitor can charge up in one cycle and normal operation begins in a few microseconds after the BST-to-HS voltage exceeds UVLOBST. In the two- switch forward topology, the BST capacitor takes some time (a few hundred microseconds) to charge and increase its voltage above UVLOBST. The typical hysteresis for both UVLO thresholds is 0.5V. The bootstrap capacitor value should be selected care- fully to avoid unintentional oscillations during turn-on and turn-off at the DH output. Choose the capacitor value about 20 times higher than the total gate capaci- tance of the MOSFET. Use a low-ESR-type X7R dielec- tric ceramic capacitor at BST (typically a 0.1µF ceramic capacitor is adequate) and a parallel combination of 1µF and 0.1µF ceramic capacitors from VDD to GND. The high-side MOSFET’s continuous on-time is limited due to the charge loss from the high-side driver’s qui- escent current. The maximum on-time is dependent on the size of CBST, IBST (40µA max), and UVLOBST. Output Driver The MAX15012/MAX15013 have low 2.5 Ω RDS_ON p- channel and n-channel devices (totem pole) in the out- put stage. This allows for a fast turn-on and turn-off of the high gate-charge switching MOSFETs. The peak source and sink current is typically 2A. Propagation delays from the logic inputs to the driver outputs are matched to within 8ns. The internal p- and n-channel MOSFETs have a 1ns break-before-make logic to avoid any cross con- duction between them. This internal break-before-make logic eliminates shoot-through currents reducing the operating supply current as well as the spikes at VDD. The DL voltage is approximately equal to VDD, the DH- to-HS voltage is approximately equal to VDD minus a diode drop, when they are in a high state and to zero when in a low state. The driver RDS_ON is lower at higher VDD. Lower RDS_ON means higher source and sink cur- rents and faster switching speeds. Internal Bootstrap Diode An internal diode connects from VDD to BST and is used in conjunction with a bootstrap capacitor externally con- nected between BST and HS. The diode charges the capacitor from VDD when the DL low-side switch is on and isolates VDD when HS is pulled high as the high- side driver turns on (see the Typical Operating Circuit). The internal bootstrap diode has a typical forward volt- age drop of 0.9V and has a 10ns typical turn-off/turn-on time. For lower voltage drops from VDD to BST, connect an external Schottky diode between VDD and BST. Driver Logic Inputs (IN_H, IN_L) The MAX15012A/B are CMOS (VDD / 2) logic-input dri- vers while the MAX15013A/B have TTL-compatible logic inputs. The logic-input signals are independent of VDD. For example, the IC can be powered by a 10V supply while the logic inputs are provided from a 12V CMOS logic. Also, the logic inputs are protected against volt- age spikes up to 14V, regardless of the VDD voltage. The TTL and CMOS logic inputs have 250mV and 1.6V hysteresis, respectively, to avoid double pulsing during transition. The logic inputs are high-impedance pins and should not be left floating. The low 2.5pF input capaci- tance reduces loading and increases switching speed. The noninverting inputs are pulled down to GND and the inverting inputs are pulled up to VDD internally using a 1M Ω resistor. The PWM output from the controller must assume a proper state while powering up the device. With the logic inputs floating, the DH and DL outputs pull low as VDD rises up above the UVLO threshold. |
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