Voltage Regulators AN8011S 2-channel step-down, step-up, or inverting use DC-DC converter control IC Unit: mm ■ Overview 10.1±0.3 9 4.2±0.3 6.5±0.3 16 (0.15) The AN8011S is a DC-DC converter control IC with two-channel output using the PWM method which allows 500 kHz high-speed control. Respecitve output operation can be completely synchronized with each other by using the same oscillation output. 1 8 ■ Features (0° to 10°) 1.5±0.2 0.3 0.1±0.1 • PWM control frequency of 500 kHz is available. • Wide operating supply voltage range 1.27 (0.605) 0.40±0.25 (VCC = 3.6 V to 34 V) Seating plane Seating plane • Built-in 2-channel of open collector type for output (A single-channel is also usable for inverted SOP016-P-0225A amplification type) • Each output can be stopped independently by the external control . • Built-in on/off function for the operation/stop of IC Incorporating circuit for short-circuit portection and undervoltage lock-out (U.V.L.O.) • The latch circuit is externally controllable. • Low consumption current (during operation: 5 mA, during standby: 2 µA) ■ Applications • LCD displays, digital still cameras, and PDAs 8 VCC 9 Out1 10 7 DTC1 11 FB1 12 IN−1 13 IN+ 14 15 Latch 16 VREF ■ Block Diagram Error amp. Latch VREF PWM1 Unlatch pro. Short pro. U.V.L.O. Unlatch pro. PWM2 OSC GND Out2 6 DTC2 5 FB2 4 Error amp. IN−2 3 On/Off 2 RT CT 1 On/ Off 1 AN8011S Voltage Regulators ■ Pin Descriptions 2 Pin No. Symbol Description 1 CT Pin for connecting the oscillation frequency setting capacitor for triangular oscillation circuit. Frequecy of triangular oscillation is set by connecting a capacitor between this terminal and GND. 2 RT Resistor connection pin for setting the oscillation frequency of triangular oscillation circuit. Frequecy of triangular oscillation is set by connecting resistance between the pin and GND 3 On/Off "On/Off" pin for turning on/off IC. "Low" stops IC (output off) and "High" operates IC. 4 IN−2 Inverted input pin for channel 2 error amplifier 5 F/B 2 Output pin for channel 2 error amplifier. Gain setting or phase compensation is performed by connecting resistor or capacitor between the pin and IN−2. It is also connected to PWM short-circuit protecion. 6 DTC 2 Pin for setting dead-time period of channel 2. The dead-time of channel 2 is set by connecting external resistor. Soft start function can be also given by connecting capacitor in parallel with the external resistor. In addition, only channel 2 output can be turned off by decreasing the pin voltage to below 0.12 V. (short-circuit protection function stop circuit) 7 Out 2 Channel 2 open-collector type output pin. IO = 100 mA maximum 8 GND Grounding pin of signal system. 9 VCC Power supply voltage application pin. It detects start voltage and stop voltages 10 Out 1 Channel 1 open-collector type output pin. IO = 100 mA maximum 11 DTC 1 Pin for setting dead-time period of channel 1. The dead-time period of channel 1 is set by connecting external resistor. Soft start function can be also given by connecting capacitor in parallel with the external resistor. In addition, only channel 1 output can be turned off by decreasing the pin voltage to below 0.12 V. (short-circuit protection function stop circuit) 12 F/B 1 Output pin for channel 1 error amplifier. Gain setting or phase compensation is per formed by connecting resistor or capacitor between the pin and IN−1. It is also con nected to PWM short-circuit protection. 13 IN−1 Inverted input pin for channel 1 error amplifier. 14 IN+ Pin for noninverted input of channel 1error amplifier. 15 Latch Pin for connecting the time constant setting capacitor for timer latch type short-circuit protection circuit. The time constant for short-circuit protection is set by connecting a capacitor between this terminal and GND. 16 VREF Internal reference voltage output pin (2.5 V(allowance: ±3%)). If a load of 20 mA typical or more is applied, the overcurrent protection operates to reduce VREF and switching operation stops. Voltage Regulators AN8011S ■ Absolute Maximum Ratings at Ta = 25°C Parameter Symbol Rating Unit VCC 35 V PD 380 mW Operating ambient temperature Topr −30 to +85 °C Storage temperature Tstg −40 to +125 °C Supply voltage Power dissipation * Note) 1. Do not apply ecternal currents or voltages to any pins not speifically mentioned. For circuit currents, '+' denotes current flowing into the IC, and '−' denotes current flowing out of the IC. 2 * : When using the IC at Ta of 25°C or more, the power dessipation should be decreased 3.8 mW per 1°C. ■ Recommended Operating Range Parameter Supply voltage Symbol Range Unit VCC 3.6 to 34 V ■ Electrical Characteristics at VCC = 12 V, Ta = 25°C Parameter Symbol Conditions Min Typ Max Unit 2.413 2.5 2.588 V Reference voltage block Output voltage VREF Input regulation with input fluctuation Line VCC = 3.6 V to 34 V 3 20 mV Load regulation Load IREF = 0 mA to 5 mA 2 10 mV Output voltage temperature characteristics 1 * VTC1 Ta = −25°C to + 25°C ±1 % Output voltage temperature characteristics 2 * VTC2 Ta = 25°C to 85°C ±1 % ICC −20 mA Circuit operation start voltage VUON 2.8 3.1 3.4 V Hysteresis width VHYS 100 200 300 mV VIN-O1 −6 6 mV IB1 −500 −25 100 nA Common-mode input voltage range VCM 0.5 0.8 V High-level output voltage 1 VEH1 VREF − 0.3 V Low-level output voltage 1 VEL1 0.5 V IB2 25 100 nA Common mode input threshold voltage VIN+ 0.72 0.75 0.78 V High-level output voltage 2 VEH2 VREF − 0.3 V Low-level output voltage 2 VEL2 0.5 V Overcurrent protection drive current * U.V.L.O. block Error amplifier block 1 Input offset voltage 1 Input current 1 Error amplifier block 2 Input current 2 3 AN8011S Voltage Regulators ■ Electrical Characteristics(continued) at VCC = 12 V, Ta = 25°C Parameter Symbol Conditions Min Typ Max Unit PWM comparator 1/2 block High-level input threshold voltage VDT-H fOSC = 200 kHz, duty = 100% 1.2 V Low-level input threshold voltage VDT-L fOSC = 200 kHz, duty = 100% 0.6 V Input current IDTC RT = 20 kΩ −37 −34 −31 µA fOUT1 CT = 150 pF, RT = 20 kΩ, IO = 30 mA 180 200 220 kHz Output 1/2 block Output frequency 1 Frequency 1 fdv VCC = 3.6 V to 34 V CT = 150 pF, RT = 20 kΩ −2 2 % Output duty ratio 1 Du1 CT = 150 pF, RT = 20 kΩ, RDTC = 24 kΩ 40 45 50 % Output duty ratio 2 Du2 CT = 150 pF, RT = 20 kΩ, RDTC = 33 kΩ 65 75 85 % Output saturation voltage 1 VO(sat)1 IO = 30 mA 0.9 V Output saturation voltage 2 VO(sat)2 IO = 100 mA 1.2 V Output leak current 1 IOLe1 VCC = 34 V, when output transistor is off 10 µA Frequency temperature characteristics 1 * fdT1 fOSC = 200 kHz, Ta = −30°C to +25°C ±9 % Frequency temperature characteristics 2 * fdT2 fOSC = 200 kHz, Ta = 25°C to 85°C ±9 % 2* fOUT2 CT = 150 pF, RT = 6.6 kΩ, IO = 30 mA 500 kHz VCC = 3.6V to 34V, CT = 150 pF, RT = 6.6 kΩ ±2 % Output frequency Frequency 2* fdv2 Short-circuit protection block Input threshold voltage VSLTH 1.75 1.85 1.95 V Latch drive voltage VSLON 1.15 1.25 1.35 V ICHG −120 −50 −40 µA VULTH 0.12 V VTH 0.8 2 V VCC = 12 V, RT = 20 kΩ 5 7 mA Total consumption current fluctuation ICC(max.) VCC = 3.6 V to 34 V, RT = 20 kΩ 2 mA Standby consumption current ICC(SB) VCC = 12 V, VREF is down 2 µA Maximum standby consumption current ICC(SB-M) VCC = 34 V, VREF is down 5 µA Charge current Unlatch pro. 1/2 block Input threshold voltage On/off block Threshold voltage Whole device Total consumption current ICC Note) *: These characteristics are theoretical values based on the IC design and are not guaranteed. 4 Voltage Regulators AN8011S ■ Terminal Equivalent Circuits Pin No. Equivalent circuit 1 VREF 16 To PWM input IO CT 1 OSC comp. 2IO 2 VREF 16 OSC PWM Description I/O CT: The terminal used for connecting a timing capacitor to set oscillator frequency. Use a capacitance value within the range of 100 pF to 0.1mF. For frequency setting method, refer to the "Application Notes, [2] Function descriptions" section. Use the oscillation frequency in the range of 1 kHz to 500 kHz. O RT: The terminal used for connecting a timing resistor to set oscillattion frequency. Use a resistance value ranging from 5.1 kΩ to 20 kΩ. The terminal voltage is 0.67 V typ. I On/Off: The terminal for on/off control. High-level input: normal operation (VON/OFF > 2.0 V typ.) Low-level input: standby state (VON/OFF < 0.8 V typ.) The total current consumption in the standby state can be suppressed to a value below 5 µA. I IN−2: The terminal for the inverted input of ch.2 error amplifier. Use a common-mode input ranging from − 0.1 V to 0.8 V. I 2 RT (= 0.67 V) 3 Internal circuit start/stop On/Off 17 kΩ 3 13 kΩ 4 VREF 16 0.75 V 4 IN−2 5 AN8011S Voltage Regulators ■ Terminal Equivalent Circuits (continued) Pin No. 5 Equivalent circuit VREF 16 25 µA typ. PWM2 CT 8 mA typ. Description I/O FB2: The output terminal of ch.2 error amplifier. Its source current is −25 µA typ. and sink current is 8 mA typ. Correct the frequency characteristics of the gain and the phase by connecting a resistor and a capacitor between the terminal and IN−2 terminal. O DTC2: 1) Terminal for connecting a resistor and a capacitor for setting the dead-time and the soft start period of ch.2 PWM output. Input current IDTC is determined by the timing resistor RT so that dispersion, and fluctuation with temperature are suppressed. The input current is −35 µA typ. when RT = 20 kΩ VRT IDTC2 = × 1.04 (A) RT (VRT: 0.67 V typ.) 2) The ch.2 output can be turned off by reducing the terminal voltage to below 0.12 V. (short-circuit protection function stop) I Out2: The ch.2 open-collector type (Darlington) output terminal. The absolute maximum rating of ouput current is 150 mA. Use with an output current under 100 mA normally. O GND: GND pin VCC: The pin to which supply voltage is applied. Use within an operating supply voltage range of 3.6 V to 34 V. 5 FB2 6 VREF 16 IDTC2 CT PWM2 U.V.L.O. output 6 DTC2 7 VREF 16 Out2 7 8 8 GND 9 9 VCC 6 Voltage Regulators AN8011S ■ Terminal Equivalent Circuits (continued) Pin No. 10 Equivalent circuit VREF 16 Out1 10 11 VREF 16 IDTC1 CT PWM1 U.V.L.O. output 11 DTC1 12 VREF 16 25 µA typ. CT PWM1 8 mA typ. Description I/O Out1: The ch.1 open collector type (darlington) output terminal. The absolute maximum rating of output current is 150 mA. Use with an output current of 100 mA or less normally. O DTC1: 1) Terminal for connecting a resistor and a capacitor for setting the dead-time and the soft start period of ch.1 PWM output. Input current IDTC is determined by the timing resistor RT so that dispersion and fluctuation with temperature are suppressed. The input current is −35 µA typ, when RT = 20 kΩ. VRT IDTC2 = × 1.04 (A) RT (VRT: 0.67 V typ.) 2) The ch.1 output can be turned off by reducing the terminal voltage to below 0.12 V. (short-circuit protection function stop) I FB1: The output terminal of ch.1 error amplifier. Its source current is −25 µA typ. and sink current is 8 mA typ. Correct the frequency characteristics of the gain and the phase by connecting a resistor and a capacitor between the terminal and IN−1 terminal. O IN−1: The terminal for the inverted input of ch.1 error amplifier. Use a common-mode input ranging from − 0.1 V to +0.8 V. I IN+: The terminal for noninverted input of ch.1 error amplifier. Use a common-mode input ranging from − 0.1 V to +0.8 V. I 12 FB1 13 VREF 14 13 14 IN − 1 IN + 7 AN8011S Voltage Regulators ■ Terminal Equivalent Circuits (continued) Pin No. Equivalent circuit 15 VREF 16 ICHG 4.2 kΩ typ. Latch S R 30 kΩ 10kΩ typ. typ. 1.25 V typ. I/O Latch: Terminal for connecting the time constant setting capacitor for timer latch short-circuit protection circuit. The charge current ICHG is about −80 µA. O VREF: The output terminal for the reference voltage (2.5 V typ.). Use it with a load current of −1 mA or under. The terminal has a built-in short-circuit protection circuit, and the short-circuit current is −20 mA typ. Use the terminal for setting the reference input of the error amplifier. O Q 1.25 V typ. 15 Latch 16 VCC 9 VREF overcurrent detection Bias to other blocks 16 VREF 8 Description Voltage Regulators AN8011S ■ Application Notes [1] Main characteristics Reference voltage temperature characteristics Maximum duty ratio temperature characteristics 54 Maximum duty ratio Du(45) (%) Reference voltage VREF (V) 2.500 2.495 2.490 2.485 2.480 −40 −20 0 20 40 60 80 53 52 51 50 49 −40 100 209 90 208 80 Output duty ratio (%) Output frequency fOUT (kHz) 100 207 206 205 204 203 50 60 60 80 100 80 100 Ambient temperature Ta (°C) fOUT = 200 kΩ 30 20 40 fOUT = 500 kΩ 40 10 20 40 60 201 0 20 70 202 −20 0 DTC pin voltage Output duty ratio Output frequency temperature characteristics 210 200 −40 −20 Ambient temperature Ta (°C) Ambient temperature Ta (°C) 0 0 0.5 1 1.5 DTC pin voltage (V) Output frequency characteristics Output frequency fOUT (kHz) 500 100 RT = 10 kΩ RT = 5.1 kΩ RT = 20 kΩ 10 0 102 103 104 105 CT (pF) 9 AN8011S Voltage Regulators ■ Application Notes (continued) [2] Function descriptions 1. Reference voltage block This block is composed of the band gap circuit, and outputs the temperature compensated 2.5 V reference voltage to the VREF terminal. The reference voltage is stabilized when the supply voltage is 3.6 V or higher, and used as the operating power supply for the IC inside. It is possible to take out a load current of up to −3 mA. Also, an overcurrent portection circuit is built in for the load, thereby protecting the IC from destruction when VREF terminal is short circuited. 2. Triangular wave oscillation block The triangular wave which swings from the wave peak of approximately 1.4 V to the wave bottom of approximately 0.4 V will be generated by connecting a timing capacitor and a resistor to the CT terminal and RT terminal respectively. The oscillation frequency can be freely decided by the value of CT and RT connected externally. The triagular wave is connected with the inverted input of PWM comparator of the IC inside. 3. Error amplifier block This block detects the output voltage of DC-DC conveter, and inputs the signal amplified by the PNP transistor input type differential amplifier to the PWM comparator. The common-mode input voltage range is − 0.1 V to 0.8 V, and is a voltage obtained by dividing the reference voltage with resistors. Also, it is possible to perform the gain setting and the phase compensation arbitrarily by connecting the feedback resistor and the capacitor from the error amplifier output terminal to the inverted input terminal. The output voltage VOUT, if positive, is obtained by connecting the resistor-divided reference voltage to the noninverted input terminal as shown in figure 1. 1), and the output voltage VOUT, if negative, is obtained by connecting to the inverted input terminal as shown in figure 1. 2). The output voltages in each of these cases are given in the following equations. R1 + R2 R3 + R4 VOUT1 = VIN × VOUT1 = − (VREF − VIN-1 ) × + VREF R2 R3 R1 + R2 R2 VIN−1 = VREF × VIN+ = VREF × R2 R1 + R2 VOUT1 R1 R2 VREF VREF 16 R3 Error amp.1 PWM comparator IN+ input 14 IN−1 13 12 R4 RNF FB1 R1 R2 16 R3 Error amp.1 PWM comparator IN+ input 14 IN−1 13 12 R4 RNF FB1 VOUT1 CNF CNF 2) Negative output 1) Positive output Figure 1. Connection method of error amplifier 1 FB2 VOUT2 5 VREF: 2.5 V CNF R1 RNF The output voltage of channel 2 VOUT2 is exclusively for positive voltage ouput, and method of connection is as shown in figure 2. R1 + R2 VOUT2 = 0.75 × R2 IN−2 4 R2 R3 Error amp.2 PWM comparator input 0.75V R4 Figure 2. Cnnection method of error amplifier 2 10 Voltage Regulators AN8011S ■ Application Notes (continued) [2] Function descriptions (continued) 4. Timer latch short-circuit protection circuit This circuit protects the external main swiching devices, switching diodes, choke coils, and etc. from destruction or deterioration if overload or short-circuit of power supply output lasts for a certain time. The timer latch type short-circuit protection circuit detects the output level of each error amplifier, and when the ouput level of either one or both of the error amplifiers exceeds 1.85 V typical, the timer circuit is actuated, and initiates charging the external capacitor for protection enable. If the ouput of the error amplifier does not return to a normal voltage range by the time when the voltage of this capacitor reaches 1.25 V, it sets the latch circuit, cuts off the ouput drive transistor, and sets the dead time to 100%. 5. Low input voltage malfunction prevention circuit (U.V.L.O.) This circuit protects the system from destruction or deterioration due to control malfunction caused by the supply voltage reduction in the transient state of power on or off. The low input voltage malfunction prevention circuit detects the internal reference voltage according to the supply voltage level, and cuts off the output drive transistor by resetting the latch circuit, thereby setting the deadtime to 100% and keeping the latch terminal low. 6. PWM comparator block The PWM comparators, each has one inverted input, and two noninverted inputs, and controls the on-period of output pulse in accordance with the input voltage. It turns on the output transistor during the period when the triangular wave of CT terminal is lower than either the error amplifier ouput voltage or the DTC terminal voltage. The dead-time is set by the addition of a resistor between the DTC terminal and GND. By the addition of a capacitor in parallel with the external resistor RDTC, the soft start function which gradually extends the on-period of the ouput pulse by the RC time constant when the power supply is turned on starts to work. 7. Output block The ouput drive transistor is of open-collector type output connected in Darlington circuit of emitter common GND. The breakdown voltage of the collector ouput terminal is 34 V and it is possible to obtain up to 100 mA ouput current. 8. Remote circuit It is possible to switch on/off the IC control by an external control signal. When the on/off terminal voltage is lowered to a value below approximately 0.8 V, the internal reference voltage goes down, thereby the IC control is stopped and the circuit current is decreased to 5 µA or less. When the on/off terminal voltage is increased to a value higher than approximately 2.0 V, the internal reference voltage raises and the control operation is started. [3] The time constant setting method for timer latch type short-circuit protection circuit Figure 3 shows the block diagram of the protection latch circuit. The comparator for short-circuit protection compares the output voltage of error amplifier VFB with the reference voltage (1.85 V) at all the time. When the load conditions of DC-DC converter output is stabilized, there is no fluctuation of error amplifier output, and the shortcircuit protection comparator also keeps the balance. At this moment, the switch SW1 will be in the off state, and the latch terminal voltage will be kept at approximately 0.9 V typical. When the load conditions suddenly change, and high-level signal (1.85 V typical of higher) is inputted from the error amplifier to the noninverted input of the short-circuit protection comparator, the short-circuit protection comparator outputs the high-level signal. This signal turns on the switch SW1, and the charging to the capacitor CS connected externally to the latch terminal is started with a current of 80 µA typical. When the external capacitor CS is charged up to approximately 1.25 V typical, the latch circuit is set and the undervoltage lock-out circuit (U.V.L.O.) is enabled, thereby the ouput drive transistor is cut off and the dead-time is set to 100%. Once the under-voltage lock-out circuit (U.V.L.O.) is enabled, the latch circuit will not be reset unless the power supply is switched off. 11 AN8011S Voltage Regulators ■ Application Notes (continued) [3] The time constant setting method for timer latch type short-circuit protection circuit (continued) VREF ICHG 80 µA typ. SW1 FB2 5 Latch comp. 4.2 kΩ typ. 30 kΩ typ. 1.25 V typ. 10 kΩ typ. FB1 12 1.85 V Cut output off S R Latch R U.V.L.O. 4 Latch CS Figure 3. Short-circuit protection circuit When the power supply is turned on, the output is considered to be short-circuited state, so that the error amplifier output becomes high-level, then SW1 becomes on state and the charging starts. It is necessary to set the external capacitor so as to start up the DC-DC converter output voltage before setting the latch circuit in the later stage. Especially, pay attention to the delay of the start-up time when applying the soft-start. [4] Explanation of unlatch protection circuit operation Figure 4 shows the block diagram of the unlatch protection circuit. It is possible to suppress FB terminal, the error amplifier output terminal of the channel, to low by setting DTC terminal to 0.12 V or less through external signal. Consequently, by controlling the DTC terminal voltage, it is possible to operate only one channel, or to start and stop each channel in any required sequence. 5 FB2 FB1 12 Error amp.1 IN+ 14 To PW1 To PW2 Error amp.2 4 IN−2 IN−1 13 IDTC2 IDTC1 DTC1 11 Unlatch protection comp.1 0.12 V typ. 0.12 V typ. Figure 4. Unlatch protection circuit 12 6 DTC2 Unlatch protection comp.2 Voltage Regulators AN8011S ■ Application Notes (continued) [5] Triangular wave oscillation circuit • Oscillation frequency setting method The waveform of triangular wave oscillation is obtained by charging and discharging of the constant current IO from the external timing capacitor CT which is connected to CT terminal. The constant current is set by the externally attached timing resistor RT . The peak value of the wave VCTH and the trough VCTH value of the wave VCTL are fixed at approximately 1.4 V = 1.4 V typ. typical and 0.4 V typical respectively. The oscillation frequency fOSC is obtained by the following formula; VCTL t1 t2 1 IO = 0.4 V typ. fOSC = = Charging Discharging t + t 2 × C × (V − V ) 1 2 T CTH CHL (typ.) VRT 0.67 =2× RT RT Because VCTH − VCTL = 1V 0.67 fOSC = [Hz] C × RT T (typ.) Where IO = 2 × T Figure 5. Triangular wave oscillation waveform The ouput frequency fOUT is equal to fOSC since it is PWM-controlled. [6] Dead-time (maximum duty) setting method The setting of the dead-time is conducted by adjusting the DTC terminal voltage VDTC as shown in figure 6. Since the DTC terminal provides a constant current output through the resistor RT, VDTC is adjusted by attaching the external resistor RDTC. The output duty ratio Du and the DTC terminal voltage VDTC are expressed by the following formula. When the oscillation frequency fOSC is 200 kHz, the output duty ratio is 0% at VDTC = 0.42 V, and 100% at VDTC = 1.35 V. Pay attention to the peak volue and the trough value of triangular wave because the overshoot and undershoot voltages depend on the frequency. CT waveform VCTH VREF DTC waveform VDTC IDTC tOFF tON Off On VCTL IDTC = VRT × 1.04 [A] RT CT FB PWM Out waveform Off DTC tON Du = × 100 [%] tON + tOFF (typ.) VCTH −VDTC = × 100 [%] VCTH −VCTL VDTC = IDTC × RDTC (typ.) RDTC = VRT × × 1.04 [V] RT RDTC CDTC ex.) When fOSC = 200 kHz (RT = 20 kΩ, CT = 150 pF), VCTH ≈ 1.4 V(typ.) VRT ≈ 0.67 V(typ.) VCTL ≈ 0.4 V(typ.) IDTL ≈ 35 µA (typ.) Figure 6. Dead-time setting method When the capacitor CDTC is added in parallel with the external resistor RDTC, the soft start function gradually extends the on-period of the output pulse when the power supply is turned on. This prevents the overshoot of the DC-DC converter output. 13 AN8011S Voltage Regulators ■ Application Notes (continued) [7] Timing chart Supply voltage (VCC) 3.1 V typ. Lock-out release 3.6 V Reference voltage (VREF) 2.5 V Error amplifier output (FB) 1.83 V Power supply on Triangular wave (CT) Latch terminal voltage 1.3 V 0.9 V 0.40 V 0.03 V High Dead-time voltage (VDT) Low Output transistor collector waveform(OUT) Soft start operation Maximum duty Figure 7. Operation waveform of PWM comparator 2.5 V Reference voltage (VREF) Short-circuit protection input threshold level Comparator threshold level 1.85 V 1.4 V 0.9 V DTC terminal voltage Latch terminal voltage Error amplifier ouput (FB) 0.40 V Triangular wave (CT) High Output transistor collector waveform (OUT) Short-circuit protection comparator output Low tPE High Low Figure 8. Operation waveform of short-circuit protection 14 Voltage Regulators AN8011S ■ Application Circuit Examples • Application circuit example 1 SBD 3V 33 kΩ VCC 9 VCC 12 FB1 13 IN−1 14 IN+ 15 Latch 16 VREF 120 kΩ 10 Out1 0.01 µF 0.1 µF 7 kΩ −5 V 11 DTC1 14 kΩ 6 kΩ 23 kΩ VREF 3V SBD f = 200 kHz Duty = 75% Error amp. Latch 7 5V 25.5 kΩ PWM1 Unlatch pro. 4.5 kΩ Short pro. U.V.L.O. To pin 4 Unlatch pro. OSC PWM2 GND 8 Out2 7 DTC2 6 0.01 µF 3V 33 kΩ 120 kΩ 0.1 µF FB2 5 Error amp. IN−2 4 On/Off 3 20 kΩ 2 RT CT 150 pF 1 On/ Off SBD 5V 25.5 kΩ 4.5 kΩ 15 AN8011S Voltage Regulators ■ Application Circuit Examples • Application circuit example 2 500 Ω VIN = 7 V 9 VCC 100 Ω GND 8 33 kΩ 10 Out1 100 Ω VCC = 7 V Out2 7 13 IN−1 14 IN+ 15 Latch 16 VREF 10 µF 12 FB1 120 kΩ 2.5 V 11 DTC1 0.01 µF 0.1 µF 3.3 V Error amp. Latch VREF PWM1 Unlatch pro. Short pro. U.V.L.O. Unlatch pro. OSC PWM2 0.01 µF 33 kΩ DTC2 6 FB2 5 120 kΩ 0.1 µF IN−2 4 On/Off 3 20 kΩ 2 Error amp. RT CT 150 pF 1 On/ Off R 500 Ω VCC = 7 V 5V 25.5 kΩ 0.75 V 4.5 kΩ 16