A5974D

A5974D Up to 2.5 A step-down switching regulator for automotive applications Datasheet - production data Application  Dedicated to automotive applications HSOP8 - exposed pad Description Features The A5974D is a step-down monolithic power switching regulator with a minimum switch current limit of 3.1 A, so it is able to deliver up to 2.5 A DC current to the load depending on the application conditions. The output voltage can be set from 1.235 V to 35 V. The high current level is also achieved thanks to an HSOP8 package with an exposed frame, that allows to reduce the Rth(JA) down to approximately 40 °C/W. The device uses an internal P-channel DMOS transistor (with a typical RDS(on) of 250 m) as a switching element to minimize the size of the external components. An internal oscillator fixes the switching frequency at 250 kHz. Having a minimum input voltage of 4 V only it fits the automotive applications requiring the device operation even in cold crank conditions. A pulseby-pulse current limit with the internal frequency modulation offers an effective constant current short-circuit protection.  Qualified following the AEC-Q100 requirements (see PPAP for more details)  2.5 A DC output current  Operating input voltage from 4 V to 36 V  3.3 V / (± 2%) reference voltage  Output voltage adjustable from 1.235 V to 35 V  Low dropout operation: 100% duty cycle  250 kHz internally fixed frequency  Voltage feed-forward  Zero load current operation  Internal current limiting  Inhibit for zero current consumption  Synchronization  Protection against feedback disconnection  Thermal shutdown Figure 1. Application schematic U1 L1 VIN =4V TO 36V TP1 VCC 6 VREF 2 SYNC 4 COMP INH R3 10K VOUT 1 FB GND 5 A5974D 3 EX-PAD 9 TP2 15uH VOUT R1 5.6K 7 D1 C3 100p STPS3L40U C1 10uF 50V C2 68nF 50V 8 C4 33nF TP3 C9 R2 3.3K 330uF small signal GND TP4 GND power plane June 2014 This is information on a product in full production. DocID018774 Rev 2 1/46 www.st.com Contents A5974D Contents 1 2 Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 Datasheet parameters over the temperature range . . . . . . . . . . . . . . . . 8 5 Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6 7 2/46 5.1 Power supply and voltage reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5.2 Voltages monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.3 Oscillator and synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.4 Current protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 5.5 Error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.6 PWM comparator and power stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.7 Inhibit function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.8 Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Additional features and protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.1 Feedback disconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.2 Output overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6.3 Zero load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Closing the loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 7.1 Error amplifier and compensation network . . . . . . . . . . . . . . . . . . . . . . . . 16 7.2 LC filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.3 PWM comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 DocID018774 Rev 2 A5974D 8 Contents Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 8.1 Component selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 8.2 Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 8.3 Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 8.3.1 Thermal resistance RthJA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 8.3.2 Thermal impedance ZTHJ-A(t) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 8.4 R.M.S. current of the embedded Power MOSFET . . . . . . . . . . . . . . . . . . 30 8.5 Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 8.6 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 8.7 Positive buck-boost regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 8.8 Negative buck-boost regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 8.9 Floating boost current generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 8.10 Synchronization example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 8.11 Compensation network with MLCC at the output . . . . . . . . . . . . . . . . . . . 39 8.12 External SOFT_START network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 9 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 10 Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 11 Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 12 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 DocID018774 Rev 2 3/46 46 Pin settings A5974D 1 Pin settings 1.1 Pin connection Figure 2. Pin connection (top view) 1.2 065   7$$ 4:/$   (/% */)   73&' $0.1   '# Pin description Table 1. Pin description 4/46 No. Pin Description 1 OUT 2 SYNCH 3 INH 4 COMP 5 FB 6 VREF 3.3 V VREF. No cap is requested for stability. 7 GND Ground. 8 VCC Unregulated DC input voltage. Regulator output. Master/slave synchronization. A logical signal (active high) disables the device. If INH not used the pin must be grounded. When it is open an internal pull-up disables the device. E/A output for frequency compensation. Feedback input. Connecting directly to this pin results in an output voltage of 1.23 V. An external resistive divider is required for higher output voltages. DocID018774 Rev 2 A5974D Electrical data 2 Electrical data 2.1 Maximum ratings Table 2. Absolute maximum ratings Symbol Value Unit 40 V V V V8 Input voltage V1 OUT pin DC voltage OUT pin peak voltage at t = 0.1 s -1 to 40 -5 to 40 I1 Maximum output current Int. limit. V4, V5 Analog pins 4 V -0.3 to VCC V -0.3 to 4 V 2.25 W Operating junction temperature range -40 to 150 °C Storage temperature range -55 to 150 °C Value Unit 40(1) °C/W V3 INH V2 SYNCH PTOT TJ TSTG 2.2 Parameter Power dissipation at TA 60 °C Thermal data Table 3. Thermal data Symbol RthJA Parameter Maximum thermal resistance junction ambient 1. Package mounted on evaluation board. DocID018774 Rev 2 5/46 46 Electrical characteristics 3 A5974D Electrical characteristics TJ = -40 °C to 125 °C, VCC = 12 V, unless otherwise specified. Table 4. Electrical characteristics Symbol VCC RDS(on) IL fSW Parameter Operating input voltage range Test condition V0 = 1.235 V; I0 = 2 A Min. Max. Unit 36 V 0.250 0.5  3.1 3.6 4.1 A 212 250 280 kHz 100 % 1.235 1.272 V 3 5 mA 2.5 mA 4 MOSFET on-resistance Maximum limiting current VCC = 5 V Switching frequency Duty cycle Typ. 0 Dynamic characteristics V5 Voltage feedback 4.4 V < VCC < 36 V,20 mA < I0 < 2 A 1.198 DC characteristics Iqop Iq Iqst-by Total operating quiescent current Quiescent current Total standby quiescent current Duty cycle = 0; VFB = 1.5 V Vinh > 2.2 V 50 100 A VC C = 36 V; Vinh > 2.2 V 50 100 A 0.8 V Inhibit INH threshold voltage Device ON Device OFF 2.2 V 3.5 V Error amplifier VOH High level output voltage VFB = 1 V VOL Low level output voltage VFB = 1.5 V Source output current VCOMP = 1.9 V; VFB = 1 V Io sink Sink output current VCOMP = 1.9 V; VFB = 1.5 V Ib Source bias current Io source gm 0.4 190 300 A 1 1.5 mA 2.5 DC open loop gain RL =  Transconductance ICOMP = -0.1 mA to 0.1 mA; VCOMP = 1.9 V V 50 4 A 65 dB 2.3 mS Synch function 6/46 High input voltage VCC = 4.4 to 36 V Low input voltage VCC = 4.4 to 36 V Slave synch current(1) Vsynch = 0.74 V, Vsynch = 2.33 V 0.11 0.21 Master output amplitude Isource = 3 mA 2.75 3 V Output pulse width no load, Vsynch = 1.65 V 0.20 0.35 s DocID018774 Rev 2 2.5 VREF V 0.74 V 0.25 0.45 mA A5974D Electrical characteristics Table 4. Electrical characteristics (continued) Symbol Parameter Test condition Min. Typ. Max. Unit 3.2 3.3 3.399 V Reference section Reference voltage IREF = 0 to 5 mA VCC = 4.4 V to 36 V Line regulation IREF = 0 mA VCC = 4.4 V to 36 V 5 10 mV Load regulation IREF = 0 mA 8 15 mV 18 35 mA short-circuit current 5 1. Guaranteed by design. DocID018774 Rev 2 7/46 46 Datasheet parameters over the temperature range 4 A5974D Datasheet parameters over the temperature range The 100% of the population in the production flow is tested at three different ambient temperatures (-40 C; +25 C, +125 C) to guarantee the datasheet parameters inside the junction temperature range (-40 C; +125 C). The device operation is so guaranteed when the junction temperature is inside the (-40 C; +150 C) temperature range. The designer can estimate the silicon temperature increase respect to the ambient temperature evaluating the internal power losses generated during the device operation (please refer to the Section 2.2). However the embedded thermal protection disables the switching activity to protect the device in case the junction temperature reaches the TSHTDWN (+150 C ± 10 C) temperature. All the datasheet parameters can be guaranteed to a maximum junction temperature of +125 C to avoid triggering the thermal shutdown protection during the testing phase because of self-heating. 8/46 DocID018774 Rev 2 A5974D 5 Functional description Functional description The main internal blocks are shown in the device block diagram in Figure 3. They are:  A voltage regulator supplying the internal circuitry. From this regulator, a 3.3 V reference voltage is externally available.  A voltage monitor circuit which checks the input and the internal voltages.  A fully integrated sawtooth oscillator with a frequency of 250 kHz 15%, including also the voltage feed-forward function and an input/output synchronization pin.  Two embedded current limitation circuits which control the current that flows through the power switch. The pulse-by-pulse current limit forces the power switch OFF cycleby-cycle if the current reaches an internal threshold, while the frequency shifter reduces the switching frequency in order to significantly reduce the duty cycle.  A transconductance error amplifier.  A pulse width modulator (PWM) comparator and the relative logic circuitry necessary to drive the internal power.  A high-side driver for the internal P-MOS switch.  An inhibit block for standby operation.  A circuit to implement the thermal protection function. Figure 3. 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