BTM7811K Datasheet, PDF (8/19 Pages) Infineon Technologies AG – TrilithIC

BTM7811K
4
Circuit Description
4.1
Input Circuit
The control inputs IH1,2 consist of TTL/CMOS compatible Schmitt-Triggers with hysteresis. Buffer amplifiers are
driven by these stages and convert the logic signal into the necessary form for driving the power output stages.
The inputs are protected by ESD clamp-diodes. The inputs IL1 and IL2 are connected to the gates of the standard
N-channel vertical power-MOS-FETs.
4.2
Output Stages
The output stages consist of an low R_DSON Power-MOS H-bridge. In H-bridge configuration, the D-MOS body
diodes can be used for freewheeling when communicating inductive loads. If the high-side switches are used as
single switches, positive and negative voltage spikes which occur when driving inductive loads are limited by
integrated power clamp diodes.
4.3
Short Circuit Protection
The outputs are protected against short circuit to ground and short circuit over load.
In short circuit to ground and short circuit over load situation the HS switches will limit the load current. Due to the
high power dissipation in short circuit situation the junction temperature will rise. The over temperature protection
function will switch off the output transistors if the junction temperature reaches the over temperature shutdown
limit.
4.4
Overtemperature Protection
The high-side switches also incorporate an over temperature protection circuit with hysteresis which switches off
the output transistors and sets the status output to low.
4.5
Undervoltage Lockout
When V_S reaches the switch-on voltage V_UVON the IC becomes active with a hysteresis. The high-side output
transistors are switched off if the supply voltage V_S drops below the switch off value V_UVOFF.
4.6
Open Load Detection
The open load detection of the BTM7811K works in OFF condition and is based on a voltage measurement at the
source of the high side switch. In order to use the open load detection SH2 has to be connected to Vcc via a pull
up resistor. Because this pull up resistor would connect the bridge output to the µC supply it needs to be
disconnected whenever the high side switch is on. This can be done by a transistor as shown in the application
example (Figure 5 “Application Example BTM7811K” on Page 16). To check for open load:
• Set IH1 = IH2 = LOW (both high side switches off)
• Set IL2 = LOW, IL1 = HIGH (only low side switch 1 is on)
• Connect R_ol (open load pull up) to 5V via transistor
If the load is connected properly it will pull down the voltage at SH2 to a value close to 0V.
If the load is disconnected the resistor will pull the voltage at SH2 to value close to Vcc.
If the voltage at SH2 is higher than the open load detection voltage V_OUT(OL) then ST will be pulled down.
Data Sheet
8
Rev. 1.0, 2008-05-15