Voltage regulators AN8014S Step-down, step-up, or inverting DC-DC converter control IC ■ Overview Unit: mm The AN8014S is a single-channel PWM DC-DC converter control IC. This IC can provide any one output type from among step-down, step-up and inverting output. Allowing n-channel power MOSFET direct driving, the AN8014S is ideal for high-efficiency power supplies. 10.1±0.3 (0.15) 9 4.2±0.3 6.5±0.3 16 (0° to 10°) 1 8 ■ Features 1.5±0.2 0.3 0.1±0.1 • Wide operating supply voltage range (3.6 V to 34 V) (The voltage is limited within a range between 3.6 V and 17 V if it is connected to a step-down volt1.27 (0.605) 0.40±0.25 age circuit.) Seating plane • Totem pole output circuit: output peak current (±1 A) SOP016-P-0225A • On-chip pulse-by-pulse overcurrent detection and protection circuit Threshold voltage VCC − 0.095 V typical • On-chip bootstrap circuit (allowing n-channel MOSFET direct driving.) • On-chip under-voltage lock-out circuit (U.V.L.O.) • On-chip on/off function (active-high control input, standby current of maximum 5 µA) • On-chip timer latch short-circuit protection circuit • Maximum oscillator frequency (500 kHz) Seating plane ■ Applications On/off active-high 16 2 CT Triangular wave OSC VREF 2.5V OFF 3 4 1 DTC VREF ■ Block Diagram RT • DC-DC switching power supply R Constant current source 1 µA Latch R Q S 10 µA Boot strap 15 14 Q PWM comp. 13 R Latch Q VCC CB Out S 5 Error amp. IN+ IN− 8 S.C.P. comp. 7 FB 12 PGND 11 6 SGND S.C.P. CLM S Q U.V.L.O. 10 1 AN8014S Voltage regulators ■ Pin Descriptions Pin No. Description Pin No. Description 1 Internal reference output 9 Not connected 2 Oscillator timing resistor connection 10 Overcurrent protection input 3 Oscillator timing capacitor connection 11 Signal ground 4 Dead-time control 12 Output stage ground Capacitance connection for short-circuit 13 Totem pole type output protection delay 14 Bootstrap output 6 Error amplifier noninverting input 15 Supply voltage 7 Error amplifier inverting input 16 On/off control 8 Error amplifier output 5 ■ Absolute Maximum Ratings Parameter Symbol Rating Unit VCC 35 V ICC mA PD 143 mW Topr −30 to +85 °C Tstg −40 to +125 °C On/off pin allowable application voltage VON/OFF VCC V Error amplifier allowable input voltage VI − 0.3 to VREF V DTC pin allowable application voltage VDTC − 0.3 to VREF V Out pin allowable application voltage VOUT 35 V IO ±100 mA IO(Peak) ±1 000 mA CB pin allowable application voltage VCB 35 V CB pin constant output current ICB −100, 150 mA CB pin peak output current ICBP −500, 1 000 mA CLM pin allowable application voltage VCLM VCC V Supply voltage Supply current Power dissipation *2 Operating ambient temperature Storage temperature *1 *1 Out pin constant output current Out pin peak output current Note) 1. *1: Except for the operating ambient temperature and storage temperature, all ratings are for Ta = 25°C. *2: At Ta = 85°C 2. Do not apply external currents or voltages to any pins not specifically mentioned. For circuit currents, '+' denotes current flowing into the IC, and '−' denotes current flowing out of the IC. ■ Recommended Operating Range Parameter Supply voltage 2 Symbol VCC Range Unit Step-up circuit system 3.6 to 34 Step-down circuit system 3.6 to 17 V Voltage regulators AN8014S ■ Electrical Characteristics at VCC = 12 V, Ta = 25°C Parameter Symbol Conditions Min Typ Max Unit 2.522 2.6 2.678 V Reference voltage block Output voltage VREF IREF = −1 mA Line regulation with input fluctuation Line VCC = 3.6 V to 34 V 16 25 mV Load regulation Load IREF = − 0.1 mA to −1 mA 1 10 mV U.V.L.O. block Circuit operation start voltage VUON 2.8 3.1 3.4 V Hysteresis width VHYS 60 140 180 mV VIO −6 6 mV IB −500 −25 nA Common-mode input voltage range VICR − 0.1 0.8 V High-level output voltage VEH VREF − 0.3 VREF − 0.1 V Low-level output voltage VEL 0.1 0.3 V Input current IDTC Low-level input threshold voltage VDT-L Duty 0% 0.45 0.65 V High-level input threshold voltage VDT-H Duty 100% 1.2 1.4 V Error amplifier block Input offset voltage Input bias current Dead-time control circuit block −15.8 −13.2 −10.6 µA Output block Oscillator frequency fOUT CT = 120 pF, RT = 15 kΩ 196 218 240 kHz Output duty Du RDTC = 75 kΩ 47 52 57 % Low-level output voltage VOL IO = 70 mA 1.0 1.3 V High-level output voltage VOH IO = −70 mA VCB −2.0 VCB −1.0 V VINCB ICB = −70 mA VCC −1.2 VCC −1.0 VCC − 0.8 V Bootstrap circuit block Input standby voltage Short-circuit protection circuit block Input threshold voltage VTHPC 0.70 0.75 0.80 V Input standby voltage VSTBY 30 120 mV Input latch voltage VIN 30 120 mV Charge current ICHG VTH VCLM −2.76 −2.30 −1.84 µA V On/off control block Threshold voltage 0.8 2.0 Overcurrent protection block Threshold voltage VCC VCC VCC − 0.115 − 0.095 − 0.075 V 3 AN8014S Voltage regulators ■ Electrical Characteristics at VCC = 12 V, Ta = 25°C (continued) Parameter Symbol Conditions Min Typ Max Unit ICC 5.0 7.0 mA ICC(SB) 5 µA Whole device Total consumption current Standby current • Design reference data Note) The characteristics listed below are theoretical values based on the IC design and are not guaranteed. Parameter Symbol Conditions Limit Unit Reference voltage block Output voltage temperature characteristics 1 VTC1 Ta = −30°C to +25°C ±1 % Output voltage temperature characteristics 2 VTC2 Ta = 25°C to 85°C ±1 % Output short-circuit current IOS −40 mA 8 mA −110 µA 70 dB Error amplifier block Output sink current Output source current ISINK VFB = 0.9 V ISOURCE VFB = 0.9 V Open-loop gain AG Output block Frequency supply voltage characteristics fdV fOUT = 200 kHz, VCC = 3.6 V to 34 V ±3 % Frequency temperature characteristics 1 fdT1 fOUT = 200 kHz, Ta = −30°C to +25°C ±9 % Frequency temperature characteristics 2 fdT2 fOUT = 200 kHz, Ta = 25°C to 85°C ±9 % VRT 0.4 V VTHL 1.87 V 200 ns Oscillator block RT pin voltage Short-circuit protection circuit block Comparator threshold voltage Overcurrent protection circuit block Delay time 4 tDLY Voltage regulators AN8014S ■ Terminal Equivalent Circuits Pin No. I/O 1 O Equivalent circuit Description VREF: Outputs the reference voltage 2.6 V (allowance: 3%) Incorporating short-circuit protection against ground. VCC VREF 1 2 RT: Connection for the timing resistor which decides the oscillator frequency. Use a resistor in the range 5.1 kΩ to 30 kΩ. The pin voltage is approx. 0.4 V. VREF DTC S.C.P. 100 Ω 2 RT(≈ 0.4 V) 3 VREF To PWM input IO CT 3 OSC comp. 2IO 4 VREF PWM comparator input DTC 4 CDTC 2 RT IDTC RDTC CT: Connection for the timing capacitor which decides the oscillator frequency. Use a capacitor in the range 100 pF to 10 000 pF. For the oscillator frequency setting, refer to the "Application Notes, [1] Function descriptions" section. Use an oscillator frequency in the range 5 kHz to 500 kHz. DTC: Connection for a resistor and a capacitor that set the dead-time and soft start period of PWM output. Input current IDTC is decided by the timing resistor RT which controls sample to sample variations and temperature variations. It is approx. −13.2 µA when RT = 15 kΩ. VRT 1 × [A] IDTC = RT 2 5 AN8014S Voltage regulators ■ Terminal Equivalent Circuits (continued) Pin No. I/O 5 Equivalent circuit Description S.C.P.: Connection for the capacitor that sets the soft start period and the timer latch shortcircuit protection circuit time constant. Use a capacitor with a value of 1 000 pF or higher. The charge current ICHG is decided by the timing resistor RT which controls sample to sample variations and temperature variations. It is approx. −2.3 µA when RT = 15 kΩ. VRT 1 ICHG = × [A] RT 11 VREF ICHG Latch U.V.L.O. output S R Q 0.75 V 5 S.C.P. 6 I 7 I 8 O IN+: Noninverting input to the error amplifier. Use the common-mode input in the range − 0.1 V to +0.8 V. VREF 7 6 IN− IN+ VREF Source current 8 FB Sink current 9 10 I 10 CLM CLM comp. 6 FB: Output from the error amplifier. The source current is approx. −110 µA and sink current is approx. 8 mA. Correct the frequency characteristics of the gain and the phase by connecting a resistor and a capacitor between this pin and IN− pin. N.C.: Not connected. VCC 0.1 V 50 µA IN−: Inverting input to the error amplifier. Use the common-mode input in the range − 0.1 V to +0.8 V. 50 µA CLM: Detects the overcurrent state in switching transistor. Insert a resistor with a low resistance between this pin and VCC to detect overcurrent states. When this pin falls to a level 95 mV or more lower than VCC , the PWM output is turned off for that period thus narrowing the width of the on-period. (This implements a pulse-by-pulse overcurrent protection technique.) Voltage regulators AN8014S ■ Terminal Equivalent Circuits (continued) Pin No. I/O 11 Equivalent circuit SGND: Signal ground. 11 12 SGND GND: Output stage ground. 12 13 GND O Out: Totem pole output. A constant output current of ±100 mA or a peak output current of ±1 A can be ob- VCC 14 CB 14 O 13 Out 15 Description I tained. CB: Bootstrap output. Connect a bootstrap capacitor between this pin and the n-channel MOSFET sourceside pin of the switching element when using a step-down voltage circuit. Short-circuit this pin and the VCC pin when using a step-up voltage circuit. VCC: Power supply. 15 VCC 16 I OFF 16 17 kΩ 13 kΩ OFF: Controls the on/off state. When the input is high: normal operation (VOFF > 2.0 V) When the input is low: standby mode (VOFF < 0.8 V) In standby mode, the total current consumption is held to under 10 µA. ■ Application Notes [1] Function descriptions 1. Reference voltage block This block is composed of the band gap circuit and outputs the temperature compensated reference voltage (2.6 V) to the VREF pin (pin 1). The reference voltage is stabilized when the supply voltage is 3.6 V or more and used as the operating power supply in IC. It is possible to take out a load current of up to −1 mA. 7 AN8014S Voltage regulators ■ Application Notes (continued) [1] Function descriptions (continued) 2. The triangular wave generator block (OSC) The triangular wave which swings from approximately 1.32 V (upper limit value, VOSCH) to approximately 0.44 V (lower limit value, VOSCL) will be generated by connecting a timing capacitor CT and a resistor RT to the CT pin (pin 3) and RT pin (pin 2) respectively. Oscillator frequency can be freely decided by the value of CT and RT connected externally. The oscillator frequency fOSC is obtained by the following formula; VCTH = 1.32 V (typ.) 1 IO = t1 + t 2 2 × CT × (VCTH − VCHL) VRT 0.4 IO = 1.7 × = 1.7 × RT RT Because VCTH − VCTL = 0.88 V 1 fOSC ≈ [Hz] 2.59 × CT × RT fOSC = VCTL = 0.44 V (typ.) t1 t2 Charging Discharging Example) An fOSC of approximately 215 kHz will be obtained if CT is 120 pF and RT is 15 kΩ. T Figure 1. Triangular oscillation waveform It is possible to use the circuit in the recommended operating range of 5 kHz to 500 kHz of the oscillator frequency. As the AN8014S is used at increasingly higher frequencies, the amount of overshoot and undershoot due to the operation delay in the triangular wave oscillator comparator increases, and discrepancies between the values calculated as described previously and the actual values may occur. The output source currents of the AN8014S's S.C.P. and DTC pins are determined by the timing resistor RT which is externally connected to the RT pin. Therefore, note that this IC can not be used as an IC for slave when the several ICs are operated in parallel synchronous mode. 3. Error amplifier block Detecting and amplifying DC-DC converter output voltage, the error amplifier with PNP transistor input inputs the signal to the PWM comparator. Figure 2 shows the way to connect the error amplifier. The common-mode input voltage range is − 0.1 V to + 0.8 V, and a voltage obtained by dividing the reference voltage with built-in resistors is applied to the non-inverting input. Connecting the feedback resistor and the capacitor between the error amplifier output pin (pin 8) and the inverting input pin (pin 7) allows the arbitrary gain setting and the phase compensation. Startup overshooting caused by feedback delays will be suppressed by setting the output source current and output sink current to as high as 110 µA and 8 mA respectively. The input voltage VIN+ and VIN− to the error amplifier are obtained from the following formulas. R4 R2 VIN+ = VREF × VIN− = VOUT × R3 + R4 R1 + R2 1 VREF R3 IN+ 6 Error PWM comparator amp. CT DTC 13 IN− 7 VOUT R1 R4 8 RNF FB CNF Figure 2. Connection method of error amplifier 8 R2 Voltage regulators AN8014S ■ Application Notes (continued) [1] Function descriptions (continued) 4. Timer latch short-circuit protection circuit This circuit protects external main switching devices, flywheel diodes, choke coils and so forth from breakdown or deterioration when overload or short-circuit of power supply lasts a certain time. Figure 3 shows the short-circuit protection circuit. The timer latch short-circuit protection circuit detects the output level of the error amplifier. If the output voltage of the DC-DC converter is stable, the output of the error amplifier from the FB pin is stable and the short-circuit protection comparator is well balanced. In that case, the transistor Q1 is conductive and the S.C.P. pin voltage is approximately 30 mV constantly. If the load condition changes radically and output signal voltage of the error amplifier (FB) is 1.87 V or higher, the short-circuit protection comparator outputs low-level voltage. Then, by cutting off the transistor Q1, the external capacitor CS of S.C.P. pin (pin 5) starts charging with the current ICHG which is obtained from the following formulas. tPE VPE = VSTBY + ICHG × [V] CS tPE 0.75 V = 0.03 V + ICHG × CS tPE CS = ICHG × [F] 0.72 ICHG is constant current which is determined by the timing resistor RT . If RT is 15 kΩ, ICHG will be approximately 2.3 µA. VRT 1 ICHG = × [A] RT 11 When the external capacitor CS is charged up to approximately 0.75 V, the latch circuit will be turned on. Then the totem-pole output pin will be set to low level and the dead-time will be set to 100%. When the latch circuit is turned on, the S.C.P. pin will discharge electricity till the voltage on the S.C.P. pin reduces to approximately 30 mV. The latch circuit cannot be, however, reset until power supply to the AN8014S is turned off. VREF ICHG Error amp. IN+ 6 IN− 7 FB 8 S.C.P. comp. S Q Cut output off R Q Latch Q1 Q2 1.82 V 5 S.C.P. CS Figure 3. Short-circuit protection circuit 5. Low input voltage malfunction prevention circuit (U.V.L.O.) This circuit protects system from breakdown or deterioration caused by malfunction in control circuit when supply voltage is dropped during transient time at power on or off. The low input voltage malfunction prevention circuit detects internal reference voltage which changes in accordance with the supply voltage level. When the supply voltage is turned on, it sets the dead-time of Out pin (pin 13) to 100% and keeps the DTC pin (pin 4) and S.C.P. pin (pin 5) low level until the supply voltage reaches 3.1 V. When the supply voltage falls, it will operate even below 2.96 V because of its hysteresis width of 140 mV. 9 AN8014S Voltage regulators ■ Application Notes (continued) [1] Function descriptions (continued) 6. Remote circuit It is possible to switch on or off the IC control by using an external control signal. When the OFF pin (pin 16) voltage is lowered to below approximately 0.8 V, the internal reference voltage goes down thereby stopping the IC control and reducing the circuit current to 5 µA or less. When the OFF pin voltage is increased to approximately 2.0 V or more, the internal reference voltage rises thereby starting the control operation. 7. PWM comparator block The PWM comparator controls the on-period of output pulse in accordance with the input voltage. While the triangular wave voltage on the CT pin (pin 3) is lower than both the error amplifier's output voltage on pin 8 and the voltage on the DTC pin (pin 4), the output on the Out pin (pin 13) will be set to high level. Then the switching element (n-channel MOSFET) will be turned on. The dead-time is set by adjusting the voltage VDTC on the DTC pin (pin 5) as shown in figure 4. The DTC pin has constant current output determined by the resistor RT . Therefore VDTC is adjusted by connecting the DTC and GND pins through the external resistor RDTC . When the oscillator frequency fOSC is 200 kHz, the output duty cycle will be 0% at VDTC of 0.44 V typical and 100% at VDTC of 1.32 V typical. The levels of overshooting and undershooting of the peak value VCTH and the trough value VCTL of the triangular wave vary with the oscillator frequency. CT waveform VCTH VREF DTC waveform VDTC IDTC CT FB VCTL tOFF tON PWM DTC Out waveform Off On Off RDTC CDTC Figure 4. Setting the dead-time Output duty ratio Du and DTC pin voltage VDTC are expressed by the following formulas; tON VDTC − VCTL × 1.1 Du = × 100 [%] = × 100 [%] tON − tOFF (VCTH − VCTL) × 1.1 VRT 1 IDTC = [A] × RT 2 RDTC 1 × [V] VDTC = IDTC × RDTC = VRT × RT 2 Example) When fOSC = 215 [kHz] (RT = 15 kΩ, CT = 120 pF) and RDTC = 75 [kΩ] VCTH is approximately 1.32 V, VCTH is approximately 0.44 V, and VRT is approximately 0.4 V. Therefore, the following are obtained. IDTC ≈ 13.3 [µA] VDTC ≈ 0.99 [V] Du ≈ 52.3 [%] There may be an operational delay of the PWM comparator and a difference in peak and trough values of the triangular wave oscillation. Discrepancies between the values obtained from the above formulas and the actual values may occur, in which case adjust the values on the mounting substrate. In starting, if the capacitor CDTC is added in parallel to the external resistor RDTC , and the output pulse width are gradually widened, the AN8014S will be in soft-start operation. Thus the overshoot at the output of DC-DC converters can be prevented. 10 Voltage regulators AN8014S ■ Application Notes (continued) [1] Function descriptions (continued) 8. Overcurrent protection block Utilizing that the overcurrent of power output is proportional to the current value which flows in the main switch (power MOSFET), the block regulates the upper limit of the current flowing in the main switch, thus protects the parts such as main switch device, a flywheel diode and a choke coil from the damage caused by the overcurrent. The current detection are done by monitoring, at CLM pin (pin 10), the voltage drop in resistor which is placed between the main switch device and VCC pin. When the main switch device (power MOSFET) is switched on and the voltage of CLM pin reaches "VCC − 95 mV", threshold level for overcurrent detection, the output drive transistor is cut off so that no more current flows in the main switch device. This control is repeated at each cycle. When overcurrent is detected once, the transistor remains off during the same cycle, and is switched on in the next cycle. Such an overcurrent detection method is called "Pulse-by-pulse overcurrent detection." (3) Output Off (5) Turned on in the next cycle 1.32 V Triangular wave (CT) 0.44 V Error amplifier output (FB) High Output waveform (Out) Low VCC Overcurrent protection input (CLM) VCC − 95 mV (1) Overcurrent detection tDLY : Delay time (2) Latch set High Latch circuit set signal Low High Latch circuit reset signal Low (4) Latch reset Figure 5. Waveforms of the pulse-by-pulse overcurrent protection operation R2 and C1 shown in figure 6 constitute a low-pass filter to eliminate noise due to parasitic capacitance when the power MOSFET is turned on. The cut-off frequency of the filter is obtained from the following. fC = 1 [Hz] 2πC1R2 C1 R2 Out In R1 V-Out CLM Figure 6. CLM noise filter circuit 11 AN8014S Voltage regulators ■ Application Notes (continued) [1] Function descriptions (continued) 9. Bootstrap circuit of output block If the n-channel MOSFET is used as a switching device for DC-DC converter control of step down method, a bootstrap circuit is required. Bootstrap circuit ensures that the gate-source voltage is gate threshold voltage or higher by going up the high level of the Out pin (pin 13) than VCC voltage when n-channel MOSFET turns on. Figure 7 shows the output of bootstrap circuit including the external circuit. Figure 8 shows the operating waveform of the bootstrap circuit. VS M1 VCC 15 VD1 PWM comparator CT DTC FB V-Out VGS SBD D1 Q1 CB I1 14 CB I2 VCB 13 Out Q2 Figure 7. Bootstrap circuit of output block VCBH VOH Turns off VCC −VDS(ON) [V] VCC − 0.7 [V] VCC CB pin waveform Turns off Out pin waveform 0V M1 source side waveform VOL −VF t1 t2 t3 M1 Off M1 On M1 Off Figure 8. Bootstrap circuit operating waveform The following describes the operation of the bootstrap circuit. 1) N-channel MOSFET (M1) off time: t1 While the M1 is turned off, the choke coil is provided with energy from the schottky barrier diode (SBD) and the source-side voltage VS of the M1 is fixed to −VF. The bootstrap capacitor CB is charged from the VCC pin (pin 15) through the AN8014S's internal diode D1. The voltage VCB on the CB pin (pin 14) is expressed by the following. VS = −VF VCB = VCC − VD1 VF : Forward voltage of SBD VD1 : Forward voltage of D1 Therefore, the charged voltage of bootstrap capacitor CB is expressed by the following. VCB − VS = VCC − VD1 + VF 12 Voltage regulators AN8014S ■ Application Notes (continued) [1] Function descriptions (continued) 9. Bootstrap circuit of output block (continued) 2) N-channel MOSFET (M1) turn-on time: t2 When the PWM comparator output is inverted, the Out pin (pin 13) output changes into a high level. The Out pin voltage VO rises toward the CB pin voltage. VO = VCB − VCE(sat) Then the voltage between the gate and source of the M1 is obtained from the following. VGS = VO+VF When the Out pin voltage VO is the same as or higher than the gate threshold voltage VTH , the M1 turns on. Then the M1 source-side voltage rises up to the voltage expressed by the following. VS = VCC − VDS(ON) The bootstrap capacitor CB is connected to the source side and CB pin of the M1. Therefore, the CB pin voltage rises according to the M1 source-side voltage due to capacitor coupling. VCB is expressed by the following formula. VCB = VS + VCC − VD1 + VF = 2 × VCC − VD1 + VDS(ON) + VF 3) N-channel MOSFET (M1) turn-off time: t3 The Out pin voltage turns off after rising to the saturation voltage of the AN8014S's internal transistor Q1. The M1 source-side voltage drops to −VF . The CB pin voltage drops to VCC − VD1 or below due to capacitive coupling. Then the M1 will be in the state described in the above 1). [2] Bootstrap circuit usage notes 1. Operating voltage range for step-down circuit Just like what described previously, if a step-down circuit is in DC-DC converter control, the CB pin (pin 14) voltage will be approximately twice as high as VCC when the n-channel MOSFET as a switching element is turned on. The allowable voltage applied to the CB pin is 35 V. Therefore the operating supply voltage must be within a range between 3.6 V and 17 V. VCB = 2 × VCC − VD1 − VDS (ON) + VF < 35 [V] 35 + VD1 + VDS (ON) − VF VCC < [V] < 17 [V] 2 2. Value setting of bootstrap capacitor The bootstrap capacitor raises the CB pin voltage to VCC or higher due to capacitor coupling to the source side of the n-channel MOSFET when the n-channel MOSFET is turned on. At that time bootstrap capacitor is discharged by n-channel MOSFET gate-drive-current. If the capacitance of the bootstrap capacitor is too low, an increase in switching loss will result, which will reduce the efficiency. Therefore, the capacitance must be large enough in comparison with the gate input capacitance of the nchannel MOSFET. Refer to the following. CB > Ciss Determine the best value by testing on the printed circuit board for mounting. 3. CB pin connection for step-up circuit If a step-up circuit is in DC-DC converter control, no bootstrap circuit is required because the source side of the n-channel MOSFET is grounded. Therefore, short-circuit the CB pin (pin 14) and the VCC pin (pin15). Thus, the operating supply voltage range in the step-up circuit method is between 3.6 V and 34 V. 13 AN8014S Voltage regulators ■ Application Notes (continued) [3] Timing chart High OFF pin voltage Low 3.6 V Supply voltage (VCC) Error amplifier output (FB) Internal reference voltage 2.6 V Power supply turning on 1.87 V Triangular wave (CT) DTC pin voltage 1.32 V 0.44 V 0.03 V High S.C.P. pin voltage Out pin waveform Low Software start operation The maximum duty Figure 1. PWM comparator operation waveform Internal reference voltage 2.6 V 1.87 V Short-circuit protection comparator (threshold level) 1.32 V DTC pin voltage Error amplifier output (FB) 0.44 V Triangular wave (CT) High Out pin waveform Low 0.75 V S.C.P. pin voltage Short-circuit protection comparator output 0.03 V tPE High Low Figure 2. Short-circuit protection operation waveform 14 Voltage regulators AN8014S ■ Application Notes (continued) [3] Timing chart (continued) Output off Turned on in the next cycle. 1.32 V Triangular wave (CT) 0.44 V Error amplifier output (FB) High Out pin waveform Low VCC Overcurrent protection input (CLM) VCC − 95 mV Overcurrent detection tDLY: Delay time Latch set High Latch circuit set signal Low High Latch circuit reset signal Low Latch reset Figure 3. Waveforms of the pulse-by-pulse overcurrent protection operation [4] PD Ta curves of SOP016-P-0225A PD T a 600 Glass epoxy printed circuit board (50 mm × 50 mm × t0.8 mm) Rthj−a = 263°C/W PD = 380 mW (25°C) Power dissipation PD (mW) 518 500 400 360 Independent IC without a heat sink Rthj−a = 278°C/W PD = 360 mW (25°C) 300 207 200 143 100 0 0 25 50 75 85 100 125 150 Ambient temperature Ta (°C) 15 AN8014S Voltage regulators ■ Application Notes (continued) [5] Main characteristics Internal reference voltage temperature characteristics Oscillator frequency temperature characteristics 225 Oscillator frequency fOUT (kHz) Internal reference voltage VREF (V) 2.63 2.62 2.61 2.60 −50 −25 0 25 50 75 100 215 210 205 200 195 −50 125 −25 0 25 50 75 100 125 Ambient temperature Ta (°C) Ambient temperature Ta (°C) Output duty ratio DTC pin voltage Output duty ratio temperature characteristics 100 56 55 Output duty ratio Du (%) 80 Output duty ratio Du (%) 220 60 40 20 0 0.4 54 53 52 51 0.6 0.8 1.0 1.2 50 −50 1.4 DTC pin voltage VDTC (V) −25 0 25 50 75 100 125 Ambient temperature Ta (°C) Oscillator frequency Timing capacitance Output peak current COut 0.6 10 000 0.5 1 000 RT = 5.1 kΩ 100 RT = 15 kΩ 10 0.4 0.3 0.2 0.1 1 10 100 1 000 Timing capacitance CT (pF) 16 Output peak current IPeak (A) Oscillator frequency fOUT (kHz) VCC = 12 V ROUT = 10 Ω 10 000 0 1 000 5 000 10 000 Value of output connection capacitor COUT (pF) Voltage regulators AN8014S ■ Application Circuit Examples 1. DC-DC converter control (Example of step-down circuit) In 12 V 3.9 kΩ 0.1 µF 75 kΩ 47 µF 3 CT 10 Ω f = 200 kHz Triangular wave OSC VREF 2.5V OFF 16 Constant current source On/off active-high R 1 µA R 10 CLM Latch Q S 10 µA Boot strap U.V.L.O. 15 VCC In 14 CB Q S 33 Ω 0.039 µF 15 kΩ 120 pF 4 DTC 1 VREF 9.1 kΩ 100 µF Out 5V 1 000 pF 2 RT V1 0.1 Ω Q PWM comp. 13 Out R Latch Q S S.C.P. 5 6 IN+ 7 IN− 62 kΩ Error amp. FB 8 S.C.P. comp. PGND 12 SGND 11 0.12 µF 100 kΩ 11 kΩ 2. DC-DC converter control (Example of step-up circuit) Out RT CT DTC VREF In 16 2 Triangular wave OSC VREF 2.5V OFF 3 4 1 V1 Constant current source On/off active-high R 1 µA R CLM Latch Q S 10 µA Boot strap U.V.L.O. 15 VCC In 14 Q S 10 Q CB PWM comp. 13 Out R Latch Q S 6 IN+ 7 IN− Error amp. FB 8 12 S.C.P. comp. PGND SGND 11 S.C.P. 5 17 AN8014S Voltage regulators ■ Application Circuit Examples (continued) 3. DC-DC converter control (Example of polarity-inverting circuit) Out RT CT DTC VREF In 16 2 Triangular wave OSC VREF 2.5V OFF 3 1 4 V1 Constant current source On/off active-high R 1 µA R CLM Latch Q S 10 µA Boot strap U.V.L.O. 15 VCC In 14 CB Q S 10 Q PWM comp. 13 Out R Latch Q 18 Error amp. 6 IN+ 7 IN− V1 8 S.C.P. comp. FB PGND 11 SGND 12 S S.C.P. 5 1 VREF