ST L638E Series - User Manual

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Overview

Function Description
Important Technical Specifications (Common to L638xE unless specified)
Usage Features
Maintenance Features

The STMicroelectronics L638xE is a versatile family of high-voltage gate drivers designed for a wide range of applications, particularly those requiring high-voltage shifted control. These devices are built using BCD offline technology, enabling them to operate with high voltage rails up to 600 V. The family includes the L6384E, L6385E, L6386E, L6387E, and L6388E, each offering specific features tailored for different use cases.

Function Description:

The primary function of the L638xE family is to drive high-side and low-side power MOSFETs and IGBTs. They provide the necessary gate drive current capability and incorporate an internal patented bootstrap driver circuit, which eliminates the need for an external bootstrap diode. This internal bootstrap driver utilizes a high-voltage DMOS transistor, synchronously driven with the low-side gate driver, to efficiently charge the bootstrap capacitor.

L6384E: This is a half-bridge driver with an externally-adjustable dead time and a shut-down function. The dead time can be set from 0.5 µs to 2.7 µs by connecting a resistor between pin 3 (DT/SD) and ground. To disable the driver, the DT/SD pin must be pulled below 0.5 V. It features an UVLO (Under Voltage Lockout) on the Vcc supply, with typical thresholds of Vccth1 = 12 V and Vccth2 = 10 V. The low-side and high-side driver outputs (LVG and HVG) can source 400 mA and sink 650 mA, ensuring low impedance in SD conditions. The input (IN) is in phase with HVG and in opposition to LVG, compatible with Vcc voltage.

L6385E: This device is a high- and low-side configurable driver, allowing separate control of HVG and LVG through dedicated logic inputs (HIN and LIN). It includes UVLO functions for both the low-voltage Vcc supply (Vccth1 = 9.6 V, Vccth2 = 8.3 V) and the high-voltage bootstrapped supply (VBSth1 = 9.5 V, VBSth2 = 8.2 V). The driver outputs (LVG and HVG) provide 400 mA source and 650 mA sink current, with a guaranteed maximum of 0.3 V on the pin at 10 mA sink current, removing the need for external bleeder resistors. The logic inputs (LIN, HIN) are compatible with Vcc voltage, with Vil Max = 1.5 V and Vih Min = 3.6 V.

L6386E: Building upon the L6385E structure, the L6386E adds a shutdown function (active low) and a current sense comparator with a 0.5-V threshold, along with a diagnostic output. These additions make it suitable for motion control applications requiring cycle-by-cycle current feedback. The DIAG (pin 5) is an open-drain diagnostic output, and CIN (pin 6) is the comparator input. The SD pin (pin 2) is a shut-down logic input, compatible with Vcc, and can be pulled up with a 5 to 10 kΩ resistor. The UVLO thresholds for Vcc are Vccth1 = 12 V and Vccth2 = 10 V, while for VBOOT they are VBSth1 = 11.9 V and VBSth2 = 9.9 V. It also includes separate ground references for logic signals (SGND) and power ground for the low voltage gate driver (PGND).

L6387E: This device is also based on the L6385E structure, featuring two separate inputs and an interlocking function to prevent simultaneous activation of both power switches. A key difference is its very low UVLO thresholds for Vcc: Vccth1 = 6 V and Vccth2 = 5.5 V. Notably, there is no UVLO on the upper driving section. The logic inputs (LIN, HIN) are compatible with Vcc voltage, with Vil Max = 1.5 V and Vih Min = 3.6 V. The driver outputs (LVG, HVG) maintain the 400 mA source and 650 mA sink capabilities.

L6388E: Similar to the L6385E, the L6388E features two separate inputs that are 3.3-V compatible. It incorporates a fixed dead time of approximately 320 ns and an interlocking function to prevent unintentional simultaneous switching of power switches. The UVLO thresholds for Vcc and VBOOT are identical to those of the L6385E (Vccth1 = 9.6 V, Vccth2 = 8.3 V for Vcc; VBSth1 = 9.5 V, VBSth2 = 8.2 V for VBOOT). The logic inputs (LIN, HIN) are 3.3-V compatible, with Vil Max = 1.1 V and Vih Min = 1.8 V.

Important Technical Specifications (Common to L638xE unless specified):

High Voltage Rail Operation: Up to 600 V.
Driver Current Capability: Typically 400 mA source and 650 mA sink for both low-side (LVG) and high-side (HVG) outputs.
Output Voltage Guarantee: 0.3 V maximum on the output pin (at Isink = 10 mA) with Vcc > 3 V and below the turn-on threshold.
Internal Bootstrap Driver: Patented structure replacing external bootstrap diode, driven by a high-voltage DMOS synchronously with the low-side driver.
Bootstrap DMOS RDS(on): Typical 125 Ω.
Bootstrap Capacitor (CBOOT) Selection: CBOOT should be significantly larger than the equivalent external MOSFET gate capacitance (CEXT). For example, if Qgate is 30 nC and Vgate is 10 V (CEXT = 3 nF), a CBOOT of 100 nF would result in a 300 mV drop.
High-Side Driver Floating Reference (OUT pin): Careful PCB layout is crucial to limit below-ground spikes on this pin.
UVLO Features: Present on Vcc supply for most devices, and on VBOOT for L6385E, L6386E, L6388E.
Input Compatibility: Logic inputs are generally compatible with Vcc voltage, with specific thresholds varying across the family (e.g., L6384E, L6385E, L6386E, L6387E: Vil Max = 1.5 V, Vih Min = 3.6 V; L6388E: Vil Max = 1.1 V, Vih Min = 1.8 V).
Internal Pull-Down Resistors: Logic inputs typically have internal pull-down resistors in the hundreds of kΩs.

Usage Features:

Versatility: Suitable for motor controls, resonant converters, lighting applications, power supplies, and horizontal deflection stages.
Adjustable Dead Time (L6384E): Allows fine-tuning of dead time to optimize switching performance and prevent shoot-through.
Configurable Control (L6385E, L6386E, L6387E, L6388E): Separate HIN/LIN inputs offer flexible control over high-side and low-side drivers.
Shutdown Function (L6384E, L6386E): Provides a mechanism to disable the driver for safety or control purposes.
Current Sense Comparator (L6386E): Enables cycle-by-cycle current feedback for enhanced control in applications like motor drives.
Interlocking Function (L6387E, L6388E): Prevents simultaneous turn-on of high-side and low-side switches, improving system reliability.
Reduced External Components: The integrated bootstrap driver eliminates the need for an external fast recovery diode, simplifying design and reducing BOM cost.
External Charge Pump Option: For very low frequency operation or extended high-side ON times where CBOOT voltage might drop due to leakage, an external charge pump can be added to maintain CBOOT voltage. Signal diodes with low parasitic capacitance are recommended for the charge pump.
Layout Considerations: Attention to power stage layout is important to limit below-ground spikes on the OUT pin. Short connections for dead time setting components (L6384E) are also critical.

Maintenance Features:

Robust Design: The devices are designed for reliable operation in high-voltage environments.
UVLO Protection: Integrated UVLO on Vcc and VBOOT (for some devices) protects the device and external MOSFETs from operating under insufficient supply voltage, preventing potential damage.
Low Impedance Outputs: The gate drivers maintain low impedance in shutdown conditions, ensuring the gate of the external MOSFET is held low, which is crucial for preventing unintended turn-on.
Elimination of Bleeder Resistors: The output stage design guarantees a low voltage on the gate pins when off, removing the need for external bleeder resistors between the gate and source of the external MOSFETs. This simplifies the design and reduces component count.
Internal Bootstrap Driver Benefits: The internal bootstrap driver avoids the high leakage current typically associated with external fast recovery diodes, contributing to better efficiency and reliability. However, it requires that Vout be close to GND (or lower) while LVG is ON for proper charging of CBOOT. The charging time must be sufficient for the capacitor to fully charge.
Diagnostic Output (L6386E): The open-drain diagnostic output can be used to monitor the device's status, aiding in system troubleshooting and fault detection.