ST AN1707 APPLICATION NOTE

APPLICATION NOTE

AN1707

TD220/221 Gate Driver with Vreg and Two-Point Regulator

by Giuseppe Scuderi

1 INTRODUCTION

This application note gives a simple functional description of the TD220/221, which is a standard circuit designed with an industrial application in mind, see Figure 1.

However, the TD220/221, together with other ST components, such as an ST7 microcontroller, and a MOSFET device, can provide a flexible, highperformance, power management solution that may be broadly applied to applications in the industrial fields.

A common problem in such off-line applications is the generation of a low voltage power supply for the various control ICs.

Because of this, the TD220/221 includes a "Two-Point Regulator” that enables control of a switching charge pump connected.

The charge pump diodes are integrated within the TD220/221, and a switch disables the charge pump when the nominal voltage is reached.

The main advantage of the TD220/221 is that it integrates, in a single SO8 package, 3 block functions—voltage regulation, power supply and power MOS driver—at a very reasonable price.

In typical applications, the TD220/221 manages the following functions:

lThe MOSFET gate driver.

lThe microcontroller’s 3.3 V or 5 V supply.

lThe power supply voltage at 13 V.

Fig. 1: Typical application schematic of the TD220/22

October 2003

Revision B

1/5

AN1707

Introduction

Fig. 2: Description of the TD220/221

As shown in Figure 1, the TD220/221 internal blocks are:

lSource—Used in order to bias other blocks in the circuit,

lUVLO—Under Voltage Lock Out,

lVreg—Voltage Regulator at 3.3 V (for the TD220) or at 5 V (for the TD221),

lDriver—Provides the current in order to drive an external MOS,

lTPR—Two Point Regulator,

lClamp—Fixes the maximum Vcc at 22 V.

The UVLO block insures that Vcc is set such that the TD220/221 functions correctly. Two boundary voltages are internally fixed at 14.1 V (UVLOH) and at 8.2 V (UVLOL). If the circuit is in the OFF state, it will turn on when the UVLO voltage reaches 14.1 V. This represents the minimum value necessary to turn the circuit ON, and then

Fig. 3: TPR schematic: LDMOS Off

the Vcc power supply value stabilizes at 13 V. When the circuit is in the ON state, maximum UVLO voltage value that turns the circuit OFF is 8.2 V.

The role of the UVLO is both simple and extremely important: it imposes the voltage range for circuit ignition and blocking.

When the Vcc is at 13 V the Vreg block provides a precise output voltage at 3.3 V (for the TD220) or at 5 V (for the TD221) with accuracy of ±3% at 25°C and for Iout = 10 mA. This Vcc is used to supply power to the driver of an external power MOS.

The Vcc voltage is so exact thanks to the TPR block that allows it to maintain an accuracy of

±300 mV. This variation is measured using the external capacitor C1 = 100 nF as shown in

Figure 3 and Figure 4.

VCC	D1	VCAP
C1			C2
		D2
			Isup
Threshold Comparator High = 13.15V		VSUP
Threshold Comparator Low = 12.85V			t
VCC
	LDMOS
V	13V
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