Voltage Regulators AN8013SH Single-channel step-up or step-down DC-DC converter control IC Unit: mm 6 3.0±0.30 5 0.2±0.1 10 0.625±0.10 1 +0.1 0.15–0.05 0.5±0.2 4.3±0.30 6.3±0.30 0.625±0.10 1.5±0.2 0.1±0.1 The AN8013SH is a single-channel PWM DC-DC converter control IC. This IC implements DC-DC converters that provide a single arbitrary output voltage that is either a stepped-up or stepped-down level. It features a wide operating supply voltage range, low power, and a built-in overcurrent protection circuit to protect the switching transistor from damage or destruction. The AN8013SH is provided in a 0.5 mm pitch 10-pin surface mounting package and is optimal for use in miniature high-efficiency portable power supplies. 0.5 ■ Overview ■ Features SSOP010-P-0225 • Wide operating supply voltage range (3.6 V to 34 V) • Small consumption current (2.4 mA typical) ■ Pin Descriptions • Supports control over a wide output frequency range: 20 kHz to 500 kHz. CLM 1 • Built-in pulse-by-pulse overcurrent protection circuit 2 RT 3 CT (Detection voltage: VCC − 100 mV) S.C.P. 4 • Built-in timer latch short-circuit protection circuit DTC 5 (charge current 1.3 µA typical) • Incorporating the under-voltage lock-out (U.V.L.O.) circuit • Built-in reference voltage circuit (Error amplifier reference input: 0.75 V (allowance: ±4%)) • Output block is open-collector (darlington) type. • High absolute maximum rating of output current (100 mA) • Duty ratio with small sample-to-sample variations (55% ± 5%). • Adopts a 0.5-mm lead pitch 10-pin small outline package 10 VCC 9 Out 8 GND 7 IN− 6 FB ■ Applications • Switching mode power supply units (in portable equipment and other applications) 1 AN8013SH Voltage Regulators 2 RT 3 CT 5 DTC 10 V CC 1 CLM ■ Block Diagram OSC VREF VREF 0.1 V PWM 9 RT Out S R Latch FB 6 VREF RT VREF 8 GND IN− 7 Error amp. 0.75 V S R Latch R S Q U.V.L.O. 1.90 V S.C.P. 4 0.75 V S.C.P. comp. ■ Absolute Maximum Ratings at Ta = 25°C Parameter Symbol Rating Unit Supply voltage VCC 35 V CLM pin allowable application voltage VCLM 35 V Error amplifier allowable input voltage VIN− −0.3 to +2.5 V DTC pin allowable input voltage VDTC 2.5 V Out pin allowable application voltage VOUT 35 V Collector output current IOUT 100 mA Power dissipation (Ta = 85°C) PD 154 mW Operating ambient temperature Topr −30 to +85 °C Storage temperature Tstg −55 to +150 °C ■ Recommended Operating Range at Ta = 25°C Parameter Symbol Min Max Unit Supply voltage rise time (0 to 3.6 V) tr (VCC) 10 µs Collector output voltage VOUT 34 V Collector output current IOUT 50 mA Timing capacitance CT 100 1 800 pF Timing resistance RT 5.1 15 kΩ Oscillator frequency fOUT 20 500 kHz Short-circuit protection time constant setting CSCP 1 000 pF capacitor 2 Voltage Regulators AN8013SH ■ Electrical Characteristics at Ta = 25°C Parameter Symbol Conditions Min Typ Max Unit U.V.L.O. block Circuit operation start voltage VUON 2.8 3.1 3.4 V Hysteresis width VHYS 100 200 300 mV Error amplifier block Input threshold voltage VTH Voltage follower 0.72 0.75 0.78 mV Line regulation with input fluctuation Vdv Voltage follower, 2 8 mV IB −500 −25 nA High-level output voltage VEH 2.0 V Low-level output voltage VEL 0.3 V Input threshold voltage temperature Vdt1 ±1 % ±1 % VFB = 0.9 V 8 mA ISOURCE VFB = 0.9 V −120 µA 70 dB VCC = 3.6 V to 34 V Input bias current Ta = −30°C to +25°C characteristics 1 Input threshold voltage temperature Vdt2 Output source current Open-loop gain Voltage follower, Ta = −25°C to +85°C characteristics 2 Output sink current Voltage follower, ISINK AV PWM Comparator Block Input threshold voltage: high VDT-H Duty: 100% 1.2 V Input threshold voltage: low VDT-L Duty: 0% 0.6 V Input current IDTC −12 −11 −10 A Output block Oscillation frequency fOUT RT = 15 kΩ, CT = 150 pF 185 205 225 kHz Output duty Du RDTC = 91 kΩ 50 55 60 % Output saturation voltage VOL IO = 50 mA, RT = 15 kΩ 0.9 1.2 V Output leak current ILEAK VCC = 34 V, when output Tr is off 10 µA RT pin voltage VRT 0.59 V 500 kHz Maximum oscillation frequency fOUT(max) RT = 5.1 kΩ, CT = 120 pF Frequency supply voltage characteristics fdV fOUT = 200 kHz, VCC = 3.6 V to 34 V ±1 % Frequency temperature characteristics 1 fdT1 fOUT = 200 kHz, Ta = −30°C to +25°C ±3 % Frequency temperature characteristics 2 fdT2 fOUT = 200 kHz, Ta = 25°C to 85°C ±3 % Note) At VCC = 12 V, RT = 15 kΩ, CT = 15 pF, unless otherwise specified. 3 AN8013SH Voltage Regulators ■ Electrical Characteristics at Ta = 25°C (continued) Parameter Symbol Conditions Min Typ Max Unit Short-circuit protection circuit block Input threshold voltage VTHPC 0.70 0.75 0.80 V Input standby voltage VSTBY 120 V Input latch voltage VIN 120 mV Charge current ICHG −1.6 −1.3 − 1.0 µA Comparator threshold voltage VTHL 1.90 V VSCP = 0 V Overcurrent Protection Block Input threshold voltage VCLM Delay time tDLY VCC − 120 VCC − 100 VCC − 80 mV 200 ns Whole device Total consumption current 1 ICC RT = 15 kΩ 2.4 3.5 mA Total consumption current 2 ICC2 RT = 5.1 kΩ, CT = 150 pF 3.4 mA Note) At VCC = 12 V, RT = 15 kΩ, CT = 15 pF, unless otherwise specified. ■ Terminal Equivalent Circuits Pin No. Pin I/O Function 1 CLM I 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 100 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.) 2 RT I Connection for the timing resistor that determines the oscillator frequency. Use a resistor in the range 5.1 kΩ to 15 kΩ. Thus the pin voltage will be about 0.59 V. Internal equivalent circuit 1 VCC 0.1 V CLM comp. 50 µA 50 µA VREF 100 Ω 2 3 4 CT O Connection for the timing capacitor that determines the oscillator frequency. Use a capacitor in the range 100 to 1 800 pF. See the "Application Notes, [2] and [3]" sections later in this document for details on setting the frequency. Use an oscillator frequency in the range 20 kHz to 500 kHz. OSC PWM RT (V ≈ 0.59 V) S.C.P. DTC VREF To PWM input OSC comp. IO 3 2IO Voltage Regulators AN8013SH ■ Terminal Equivalent Circuits (continued) Pin No. Pin I/O Function 4 S.C.P. O Connection for the capacitor that determines the time constant for soft start and the timer latch short-circuit protection circuit. Use a capacitor with a value of 1 000 pF or higher. The charge current ICHG is determined by the timing resistor RT, and sample-to-sample and temperature variations can be suppressed. When RT is 15 kΩ, the current will be about −1.3 µA. VRT 1 × ICHG = [A] RT 30 5 6 DTC FB I O Connection for the resistor and capacitor that determine the PWM output dead-time and the soft start period. The input current IDTC is determined by the timing resistor RT, and sample-to-sample and temperature variations can be suppressed. When RT is 15 kΩ, the current will be about −11 µA. VRT 1 × ICHG = [A] RT 3.6 Error amplifier output A source current is about −120 mA and a sink current is about 8 mA. Correct the gain and the phase frequency characteristics by inserting a resistor and a capacitor between this pin and IN−pin. Internal equivalent circuit VREF ICHG Latch S Q U.V.L.O. 0.75 V R 4 VREF IDTC CT PWM U.V.L.O. 5 VREF 120 µA CT PWM 8 mA 6 7 IN− I Error amplifier inverting input For common-mode input, use in the range − 0.1 V to +0.8 V. VREF 0.75 V 7 8 GND Ground 8 5 AN8013SH Voltage Regulators ■ Terminal Equivalent Circuits (continued) Pin No. Pin I/O Function 9 Out O Open-collector (darlington) output The absolute maximum rating for the output current is 100 mA. Use with a constant output current under 50 mA. 10 VCC Internal equivalent circuit VREF 9 Power supply connection Provide the operating supply voltage in the range 3.6 V to 34 V. 10 ■ Application Notes [1] Main characteristics Error amplifier input threshold voltage temperature Maximum duty ratio temperature characteristics characteristics 60 VCC = 12 V Voltage follower Maximum duty ratio Dumax (%) Input threshold voltage VTH (V) 0.760 0.758 0.756 0.754 0.752 0.750 −40 −20 20 40 60 80 54 100 −40 −20 0 20 40 60 80 100 Ambient temperature Ta (°C) Oscillator frequency temperature characteristics Timing capacitance Oscillator frequency 1M VCC = 12 V CT = 200 pF RT = 15 kΩ Oscillator frequency fOUT (Hz) Oscillator frequency fOUT (kHz) 56 Ambient temperature Ta (°C) 215 210 205 200 195 −40 −20 VCC = 12 V Ta = 25°C RT = 5.1 kΩ 100k RT = 15 kΩ 10k 0 20 40 60 Ambient temperature Ta (°C) 6 58 52 0 VCC = 12 V CT = 200 pF RT = 15 kΩ 80 100 100 1 000 Timing capacitance CT (pF) 10 000 Voltage Regulators AN8013SH ■ Application Notes (continued) [1] Main characteristics (continued) Input threshold voltage line regulation 4.0 Ta = 25°C Total consumption current ICC (mA) Input threshold voltage VTH (V) 0.765 Total consumption current line regulation 0.760 0.755 0.750 0.745 0 5 10 15 20 25 30 Ta = 25°C 3.5 RT = 5.1 kΩ 3.0 2.5 RT = 15 kΩ 2.0 35 0 Timing resistance Total consumption current 10 15 20 25 30 35 Timing resistance Output saturation voltage 0.85 VCC = 12 V Ta = 25°C Output saturation voltage VOL (V) Total consumption current ICC (mA) 3.5 5 Supply voltage VCC (V) Supply voltage VCC (V) 3.0 2.5 2.0 VCC = 12 V IO = 50 mA Ta = 25°C 0.84 0.83 0.82 0.81 0.80 4 8 12 16 Timing resistance RT (kΩ) 20 4 8 12 16 20 Timing resistance RT (kΩ) 7 AN8013SH Voltage Regulators ■ Application Notes [2] Function descriptions 1. Reference voltage block The reference voltage block is based on a band gap circuit, and outputs a temperature corrected reference voltage of 2.5 V. This reference voltage is stabilized once the supply voltage exceeds 3.6 V, and is used as the power supply for the IC itself. 2. Triangular wave generator This circuit generates a triangular wave with a peak of about 1.45 V and a trough of about 0.35 V using a timing capacitor connected to the CT pin (pin 3) and a timing resistor connected to the RT pin (pin 2) respectively. The oscillator frequency can be set to arbitrary value by selecting appropriate values for the external capacitor and resistor, CT and RT. The triangular wave signal is provided to the inverting input the PWM comparator internally to the IC. CNF RNF 3. Error amplifier FB This circuit is an PNP-transistor input error ampli6 VOUT fier that detects and amplifies the DC-DC converter Internal 2.5 V output voltage, and inputs that signal to a PWM comreference voltage parator. PWM R3 R1 A 0.75 V level is created by resistors dividing the Error amp. comparator input 0.75 V internal reference voltage. This level is applied to the IN− noninverting input. 7 R4 Arbitrary gain and phase compensation can be set R2 up by inserting a resistor and capacitor in series between the error amplifier output pin (pin 6) and the inverting input pin (pin 7). Figure 1. Connection method of error amplifier The output voltage VOUT is given by the following formula by connecting a resistor divider to the output as shown in figure 1. R1 + R2 VOUT = 0.75 × R2 4. Timer latch short-circuit protection circuit This circuit protects the external main switching element, flywheel diode, choke coil, and other components against degradation or destruction if an excessive load or a short circuit of the power supply output continues for longer than a certain fixed period. The timer latch short-circuit protection circuit detects the output of the error amplifier. If the DC-DC converter output voltage drops and an error amplifier output level exceeds 1.90 V, this circuit outputs a low level and the timer circuit starts. This starts charging the external protection circuit delay time capacitor. If the error amplifier output does not return to the normal voltage range before that capacitor reaches 0.75 V, the latch circuit latches, the output drive transistors are turned off, and the dead-time is set to 100%. 5. Low input voltage malfunction prevention circuit (U.V.L.O.) This circuit protects the system against degradation or destruction due to incorrect control operation when the power supply voltage falls during power on or power off. The low input voltage malfunction prevention circuit detects the internal reference voltage that changes with the supply voltage level. While the supply voltage is rising, this circuit cuts off the output drive transistor until the reference voltage reaches 3.1 V. It also sets the dead-time to 100%, and at the same time holds the S.C.P. pin (pin 4) at the low level. During the fall time of the power supply voltage, it has hysteresis width of 200 mV and operates 2.9 V or less. 8 Voltage Regulators AN8013SH ■ Application Notes (continued) [2] Function descriptions (continued) 6. PWM comparator The PWM comparator controls the output pulse on-period according to the input voltage. The output transistor is turned on during periods when the level of the CT pin (pin 3) triangular wave is lower than both of the error amplifier output (pin 6) and the DTC pin (pin 5) voltage. The dead-time is set by adding a resistor between the DTC pin and ground. Additionally, the AN8013SH can provide soft start operation in which the output pulse on-period is gradually lengthened according to an RC time constant when power is first applied by adding a capacitor in parallel with the resistor RDTC. 7. Overcurrent protection block Destruction of the main switching device, the flywheel diode, and the choke coil, which are easily damaged by overcurrents, is prevented by limiting the maximum current that flows in the switching device. This is implemented using the fact that power supply output overcurrents are proportional to the current flowing in the main switching device (a bipolar transistor). The AN8013SH detects the current by connecting a resistor with a low resistance between the main switching device and the VCC pin and monitoring the voltage drop across this resistor at the CLM pin (pin 1). When the main switching device (a bipolar transistor) is on and the CLM pin voltage reaches VCC minus 100 mV, which is the overcurrent detection threshold voltage, the AN8013SH shuts off the output transistor, thus controlling the main switching device so that currents in excess of the limit cannot occur. While this control operation is repeated at each period, once an overcurrent is detected the output transistor is turned off for the remainder of that period and is not turned on again until the next period. This type of overcurrent protection is called pulse-by-pulse overcurrent protection. 8. Output block The output drive transistor is of open-collector type output in which transistors are darlington-connected with a grounded common emitter. The breakdown voltage of collector output terminal (pin 5) is 34 V and it is possible to obtain up to 100 mA output current. 3 Output off 5 On at the next period 1.4 V Triangle wave (CT) 0.4 V Error amplifier output (FB) High Output transistor collector waveform (Out) Low VCC Overcurrent protection input (CLM) VCC − 100 mV 1 Overcurrent detection 2 Latch set TDLY : Delay time Latch circuit set signal High Low High Latch circuit reset signal Low 4 Latch reset Figure 2. Pulse-by-pulse overcurrent protection operating waveforms 9 AN8013SH Voltage Regulators ■ Application Notes (continued) [3] Triangular wave oscillation circuit 1. Setting the oscillator frequency 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 pin (pin 3). The constant current is set by the externally attached timing resistor RT. The peak value of the wave VCTH and the trough value of the wave VCTL are fixed at about 1.45 V typical and 0.35 V typical respectively. The oscillator frequency fOSC is obtained by the following formula: 1 IO VCTH = 1.4 V typ. fOSC = = t1 + t 2 2 × CT × (VCTH − VCHL) whereas IO = 1.8 × VRT 0.59 = 1.8 × RT RT because VCTH − VCTL = 1.1 V 1 fOSC = [Hz] 2.07 × CT × RT VCTL = 0.37 V typ. t1 t2 Charging Discharging T Figure 3. Triangular wave oscillation waveform The output frequency fOUT is equal to fOSC since it is PWM-controlled. 2. Usage notes This IC uses the constant current given by the timing resistor RT as the bias current of the triangular wave generator and the PWM comparator for consumption current reduction. The total consumption current is about 2.4 mA typical when RT is 15 kΩ, and it increases to about 3.4 mA typical when RT is 5.1 kΩ. In order to obtain the constant output current of 100 mA at the open-collector output, it is necessary to set RT value to 15 kΩ or smaller. It is possible to use the circuit in the recommended operating range of 20 kHz to 500 kHz of the oscillator frequency. As the AN8013SH 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. See the timing capacitance - oscillator frequency relationship in the "Application Notes, [1] Main characteristics" section of this document. Note that this IC can not be used as an IC for slave when the several ICs are operated in parallel synchronous mode. [4] Setting the dead-time (maximum duty) The dead-time is set, as shown in figure 4, by setting the DTC pin (pin 5) voltage, VDTC. Since the DTC pin has a constant current output set with the resistor RT, VDTC is adjusted by adding the external resistor RDTC. The output duty, Du, and the DTC pin voltage, VDTC, are expressed by the following formulas. For an oscillator frequency of 200 kHz, the output duty will be 0% at VDTC = 0.45 V, and 100% at VDTC = 1.45 V. However, care is required here, since the amount of overshoot and undershoot in the triangular wave peak (VCTH) and minimum (VCTL) values depends on the oscillator frequency. 10 Voltage Regulators AN8013SH ■ Application Notes (continued) [4] Setting the dead-time (maximum duty) (continued) CT waveform VCTH DTC waveform VDTC VCTL tOFF tON Off On VREF IDTC VRT × 1 [A] RT 3.6 PWM CT FB IDTC = DTC OUT waveform Off RDTC tON Du = × 100 [%] tON + tOFF VCTH −VDTC × 100 [%] = VCTH −VCTL VDTC = IDTC × RDTC = VRT × CDTC Example: When fOSC = 200 kHz (RT = 15 kΩ, CT = 150 pF) VCTH ≈ 1.45 V (typ.) VRT ≈ 0.59 V (typ.) VCTL ≈ 0.35 V (typ.) IDTC ≈ 11 µA (typ.) RDTC 1 × [V] RT 3.6 Figure 4. Setting the dead-time Adding the external resistor RDTC and the capacitor CDTC in parallel implements a soft start function that causes the output pulse on width to increase gradually when the power supply is started. Use of this function can prevent DC-DC converter output overshoot. [5] Setting the time constant of the timer latch short-circuit protection circuit The structural block diagram of protection latch circuit is shown in figure 5. The comparator for short-circuit protection compares the output of error amplifier VFB with the reference voltage of 1.90 V all the time. When the load conditions of DC-DC converter output are stabilized, there is no fluctuation of error amplifier output, and the short-circuit protection comparator also keeps the balance. At this moment, the output transistor Q1 is in the conductive state and the S.C.P. pin is hold to about 30 mV through the clamp circuit. When the load conditions suddenly change, and high-level signal (1.90 V or higher) is input from the error amplifier to the non-inverted input of the short-circuit protection comparator, the short-circuit protection comparator outputs the low-level signal. Since this signal cuts off the output transistor Q1, the S.C.P. pin voltage VPE is released, and the externally connected capacitor CS starts charging according to the following equation : When the external capacitor CS has been charged up to about 0.75 V, it sets the latch circuit, cuts off the output drive transistor by enabling the low input voltage malfunction prevention circuit, and sets the dead-time at 100%. tPE VPE = VSTBY + ICHG × [V] CS 0.75 V = 0.03 V + ICHG × CS = ICHG × tPE CS tPE [F] 0.72 11 AN8013SH Voltage Regulators ■ Application Notes (continued) [5] Setting the time constant of the timer latch short-circuit protection circuit (continued) ICHG is the constant current determined by the oscillation timing resistor RT, and its dispersion and fluctuation with temperature are small. ICHO is expressed in the following equation : ICHG = VRT RT × 1 30 [A] VRT is about 0.5 V and ICHO becomes about 1.1 µA at RT = 15 kΩ. Once the low input voltage malfunction prevention circuit is enabled, the S.C.P. pin voltage is discharged to about 30 mV but the latch circuit is not reset unless the power is turned off. VREF ICHG PWM comparator input FB 6 Error amp. IN− 7 0.75 V S.C.P. comp. S R Latch Q1 0.75 V R U.V.L.O. Output cut-off Q2 1.90 V 4 S.C.P. CS Figure 5. Short-circuit protection circuit When the power supply is started, the output appears to be shorted. The error amplifier output goes to the high state, the S.C.P. pin voltage, VPE, is released, and charging starts. The external capacitor value must be set so that DCDC converter voltage output starts before the latch circuit in the later stage is set. If the soft start function is used, special care is required to assure that the start time does not become excessive. 12 Voltage Regulators AN8013SH ■ Application Notes (continued) [6] Timing chart VCC (0 V→3.6 V) rise time tr (VCC) ≥ 10 [µs] 3.1 V typ. Lock-out release Supply voltage (VCC) 3.6 V Internal reference voltage 2.5 V Error amplifier output (FB) 1.90 V DTC pin voltage Triangular wave (CT) Power supply on 1.40 V 0.40 V 0.03 V High S.C.P. pin voltage Output transistor collector waveform (Out) Low Soft start operation Maximum duty Figure 6. PWM comparator operation waveform 2.5 V Internal reference voltage Short-circuit protection input threshold level Comparator threshold level 1.90 V Dead-time voltage (VDT) 1.40 V Error amplifier output (FB) 0.40 V Triangular wave(CT) High Output transistor collector waveform (Out) Low 0.75 V 0.03 V S.C.P. pin voltage Short-circuit protection comparator output tPE High Low Figure 7. Short-circuit protection operation waveform 13 AN8013SH Voltage Regulators ■ Application Circuit Examples 1. Step-down circuit In Out +5 V 62 kΩ SBD 100 kΩ 0.001µF 6 FB 7 IN− 8 GND 9 Out 10 VCC 11 kΩ 15 kΩ 150 pF 0.01 µF DTC 5 S.C.P. 4 CT 3 RT 2 CLM 1 f = 200 kHz Dumax = 80% RDTC = 110 kΩ 0.033 µF 110 kΩ 2. Step-up circuit SBD In Out +12 V 150 kΩ 100 kΩ 0.001 µF 6 FB 7 IN− 8 GND 9 Out 10 VCC 10 kΩ 15 kΩ 14 150 pF 0.01 µF DTC 5 S.C.P. 4 CT 3 RT 2 CLM 1 f = 200 kHz Dumax = 80% RDTC = 110 kΩ 0.033 µF 110 kΩ Voltage Regulators AN8013SH ■ Application Circuit Examples (continued) 3. On/off circuit example 1) Cutting the power supply line Q3 Q1 In VO 6 FB 8 GND CT 3 7 IN− 9 Out ICC RT 2 C10 10 VCC SBD Q2 DTC 5 S.C.P. 4 CLM 1 On/off Standby current ≈ 0 µA 2) Cutting the IC VCC line Q3 In 8 GND CT 3 6 FB 9 Out RT 2 10 VCC ICC 7 IN− SBD Q1 C10 VO Q2 DTC 5 S.C.P. 4 CLM 1 On/off Standby current ≈ 0 µA 4. Usage Since this IC does not include an on/off circuit, an external circuit must be added to implement a standby function. If a switch (Q1) is inserted in the power supply line as shown in on/off circuit example 1, the standby current can be held to 0. In this circuit, a transistor essentially equivalent to the one used for the main switching device (Q3) is required. If a switch (Q1) is inserted between the power supply line and the IC VCC pin (pin 10) as shown in on/off circuit example 2, the size of the switching device (Q1) can be reduced. However, the sample-to-sample variations in the Q1 saturation voltage will result in sample-to-sample variations in the overcurrent protection threshold level. 5. Usage Notes If an external on/off circuit is added, the VCC rise time may become excessively steep and the IC internal latch circuit may be set at that time, causing problems at power supply startup. To avoid such problems, set the value of C10 so that the VCC (pin 10) rise time is at least 10 µs. 15