SN6505

Part: SN6505BDBVR — Texas Instruments (SN6505B, 420 kHz oscillator option)

Type: Low-Noise Push-Pull Transformer Driver

Description: 2.25–5.5 V supply, 1 A push-pull transformer driver for isolated power supplies with a 420 kHz internal oscillator (SN6505B), spread spectrum clocking, 1.7 A current limit and a 6-pin SOT23 package.

Operating Conditions:

• Supply voltage (VCC): 2.25–5.5 V
• Operating temperature (ambient): -55 to 125 °C
• Output switch current (D1, D2): up to 0.75 A for 2.25 V < VCC < 2.8 V; up to 1 A for 2.8 V < VCC < 5.5 V

Absolute Maximum Ratings:

• Max supply voltage (VCC): 6 V
• Output switch voltage (D1, D2): 16 V
• Peak output switch current (D1, D2): 2.4 A
• Max junction temperature: 150 °C
• Storage temperature: -65 to 150 °C

Key Specs:

• Output drive: 1 A at 5 V supply
• Low RON: 0.25 Ω max at 4.5 V supply
• Internal oscillator: 420 kHz (SN6505B); 160 kHz for SN6505A
• Current limit: 1.7 A
• Shutdown current: <1 μA
• Undervoltage lockout trips at VCC ≤ 2.25 V
• ESD: ±6000 V HBM, ±1500 V CDM (all pins)

Features:

• Push-pull driver for center-tapped transformers
• Ultra-low EMI through slew-rate control and spread spectrum clocking
• Synchronization of multiple devices with an external clock input
• Soft-start to reduce inrush current
• Thermal shutdown, undervoltage lockout, and break-before-make circuitry
• Two integrated 1 A power MOSFET switches

Applications:

• Isolated power supply for CAN, RS-485, RS-422, RS-232, SPI, I2C and low-power LAN
• Low-noise isolated USB supplies
• Process control
• Telecom supplies
• Medical and precision instruments
• Radio and distributed supplies
• Low-noise filament supplies

Package:

• SOT23 (DBV), 6-pin, 2.90 mm × 1.60 mm body

• Push-pull driver for transformers
• Wide input voltage range: 2.25 V to 5.5 V
• High output drive: 1 A at 5 V supply
• Low RON 0.25 Ω max at 4.5 V supply
• Ultra-low EMI
• Spread spectrum clocking
• Precision internal oscillator options: 160 kHz (SN6505A) and 420 kHz (SN6505B)
• Synchronization of multiple devices with external clock input
• Slew-rate control
• 1.7 A Current-limit
• Low shutdown current: <1 μA
• Thermal shutdown
• Wide temperature range: -55°C to 125°C
• Small 6-Pin SOT23 (DBV) package
• Soft-start to reduce In-rush current

• Isolated power supply for CAN, RS-485, RS-422, RS-232, SPI, I2C, low-power LAN
• Low-noise isolated USB supplies
• Process control
• Telecom supplies
• Radio supplies
• Distributed supplies
• Medical instruments
• Precision instruments
• Low-noise filament supplies

1

2 VCC EN 5

3 D2 GND 4

D1

CLK

6

Figure 5-1. DBV Package SOT-23 (6 Pin) Top View

Table 5-1. Pin Functions

over full-range of recommended operating conditions, unless otherwise noted. All typical values are at T A = 25°C, V CC = 5 V.

over operating free-air temperature range (unless otherwise noted) (1) . All typical values are at TA = 25°C, VCC = 5 V.

The SN6505 is a transformer driver designed for low-cost, small form-factor, isolated DC/DC converters using the push-pull topology. The device includes an oscillator that feeds a gate-drive circuit. The gate-drive, comprising a frequency divider and a break-before-make (BBM) logic, provides two complementary output signals which alternately turn the two output transistors on and off.

Figure 9-1. Block Diagram and Output Timing With Break-Before-Make Action

The output frequency of the oscillator is divided down by an asynchronous divider that provides two complementary output signals, S and S, with a 50% duty cycle. A subsequent break-before-make logic inserts a dead-time between the high-pulses of the two signals. The resulting output signals, G1 and G2, present the gate-drive signals for the output transistors Q 1 and Q 2. As shown in Figure 9-2, before either one of the gates can assume logic high, there must be a short time period during which both signals are low and both transistors are high-impedance. This short period, known as break-before-make time, is required to avoid shorting out both ends of the primary.

Figure 9-2. Detailed Output Signal Waveforms

Figure 9-1. Block Diagram and Output Timing With Break-Before-Make Action