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Voltage regulators
AN8014S
Step-down, step-up, or inverting DC-DC converter control IC
s Overview
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.
10.10.3 16 9
Unit: mm
4.20.3 6.50.3
(0.15)
0.3
(0 to 10)
s Features
* 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) 0.400.25 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 A) * On-chip timer latch short-circuit protection circuit * Maximum oscillator frequency (500 kHz)
0.10.1
1.50.2
1
8
Seating plane
s Applications
* DC-DC switching power supply
VREF DTC
1
4
3
CT
2
RT
s Block Diagram
VREF 2.5V 16 On/off active-high R U.V.L.O. S R Latch Q S.C.P. 5 S Q Q
Triangular wave OSC Constant current source 1 A 10 A Boot strap PWM comp. Latch R Q S
10
CLM
OFF
15 14 13
VCC CB Out
6 S.C.P. comp. Error amp. FB 8 7
IN+ IN-
11
SGND
PGND
12
1
AN8014S
s Pin Descriptions
Pin No. 1 2 3 4 5 Description Internal reference output Oscillator timing resistor connection Oscillator timing capacitor connection Dead-time control Capacitance connection for short-circuit protection delay 6 7 8 Error amplifier noninverting input Error amplifier inverting input Error amplifier output Pin No. 9 10 11 12 13 14 15 16
Voltage regulators
Description Not connected Overcurrent protection input Signal ground Output stage ground Totem pole type output Bootstrap output Supply voltage On/off control
s Absolute Maximum Ratings
Parameter Supply voltage Supply current Power dissipation
*2 *1
Symbol VCC ICC PD Topr Tstg VON/OFF VI VDTC VOUT IO IO(Peak) VCB ICB ICBP VCLM
Rating 35 143 -30 to +85 -40 to +125 VCC - 0.3 to VREF - 0.3 to VREF 35 100 1 000 35 -100, 150 -500, 1 000 VCC
Unit V mA mW C C V V V V mA mA V mA mA V
Operating ambient temperature Storage temperature
*1
On/off pin allowable application voltage Error amplifier allowable input voltage DTC pin allowable application voltage Out pin allowable application voltage Out pin constant output current Out pin peak output current CB pin allowable application voltage CB pin constant output current CB pin peak output current CLM pin allowable application voltage
Note) 1. *1: Except for the operating ambient temperature and storage temperature, all ratings are for Ta = 25C. *2: At Ta = 85C 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.
s Recommended Operating Range
Parameter Supply voltage Symbol VCC Range Step-up circuit system Step-down circuit system 3.6 to 34 3.6 to 17 Unit V
2
Voltage regulators
s Electrical Characteristics at VCC = 12 V, Ta = 25C
Parameter Reference voltage block Output voltage Line regulation with input fluctuation Load regulation U.V.L.O. block Circuit operation start voltage Hysteresis width Error amplifier block Input offset voltage Input bias current Common-mode input voltage range High-level output voltage Low-level output voltage Dead-time control circuit block Input current Low-level input threshold voltage High-level input threshold voltage Output block Oscillator frequency Output duty Low-level output voltage High-level output voltage Bootstrap circuit block Input standby voltage VINCB ICB = -70 mA VCC -1.2 VCC -1.0 fOUT Du VOL VOH CT = 120 pF, RT = 15 k RDTC = 75 k IO = 70 mA IO = -70 mA 196 47 VCB -2.0 218 52 1.0 VCB -1.0 IDTC VDT-L VDT-H Duty 0% Duty 100% VIO IB VICR VEH VEL -6 -500 - 0.1 VREF - 0.3 -25 VREF - 0.1 0.1 VUON VHYS 2.8 60 3.1 140 VREF Line Load IREF = -1 mA VCC = 3.6 V to 34 V IREF = - 0.1 mA to -1 mA 2.522 2.6 16 1 Symbol Conditions Min Typ
AN8014S
Max
Unit
2.678 25 10
V mV mV
3.4 180
V mV
6 0.8 0.3
mV nA V V V A V V
-15.8 -13.2 -10.6 1.2 0.45 1.4 0.65
240 57 1.3
kHz % V V
VCC - 0.8
V
Short-circuit protection circuit block Input threshold voltage Input standby voltage Input latch voltage Charge current On/off control block Threshold voltage Overcurrent protection block Threshold voltage VCLM VCC VCC VCC - 0.115 - 0.095 - 0.075 V VTH 0.8 2.0 V VTHPC VSTBY VIN ICHG 0.70 0.75 30 30 0.80 120 120 V mV mV A
-2.76 -2.30 -1.84
3
AN8014S
s Electrical Characteristics at VCC = 12 V, Ta = 25C (continued)
Parameter Whole device Total consumption current Standby current * Design reference data ICC ICC(SB) Symbol Conditions
Voltage regulators
Min
Typ
Max
Unit
5.0
7.0 5
mA A
Note) The characteristics listed below are theoretical values based on the IC design and are not guaranteed.
Parameter Reference voltage block Output voltage temperature characteristics 1 Output voltage temperature characteristics 2 Output short-circuit current Error amplifier block Output sink current Output source current Open-loop gain Output block Frequency supply voltage characteristics Frequency temperature characteristics 1 Frequency temperature characteristics 2 Oscillator block RT pin voltage
Symbol
Conditions Ta = -30C to +25C Ta = 25C to 85C VFB = 0.9 V fOUT = 200 kHz, VCC = 3.6 V to 34 V fOUT = 200 kHz, Ta = -30C to +25C fOUT = 200 kHz, Ta = 25C to 85C
Limit 1 1 -40
Unit
VTC1 VTC2 IOS
% % mA
ISINK
8 -110 70 3 9 9
mA A dB
ISOURCE VFB = 0.9 V AG fdV fdT1 fdT2
% % %
VRT
0.4
V
Short-circuit protection circuit block Comparator threshold voltage VTHL 1.87 V
Overcurrent protection circuit block Delay time tDLY 200 ns
4
Voltage regulators
s Terminal Equivalent Circuits
Pin No. 1 I/O O
VCC
AN8014S
Equivalent circuit
Description VREF: Outputs the reference voltage 2.6 V (allowance: 3%) Incorporating short-circuit protection against ground.
VREF 1
2
VREF
RT: Connection for the timing resistor which decides the oscillator frequency. Use a resistor in the range 5.1 k to 30 k. The pin voltage is approx. 0.4 V.
DTC 100 2 RT( 0.4 V) S.C.P.
3
VREF To PWM input OSC comp. IO CT 3 2IO
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.
4
VREF PWM comparator input DTC 4 CDTC 2 RT IDTC
RDTC
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 A when RT = 15 k. VRT 1 x [A] IDTC = RT 2
5
AN8014S
s Terminal Equivalent Circuits (continued)
Pin No. 5 I/O
VREF ICHG Latch U.V.L.O. output
S R Q
Voltage regulators
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 A when RT = 15 k. VRT 1 ICHG = x [A] RT 11 IN+: Noninverting input to the error amplifier. Use the common-mode input in the range - 0.1 V to +0.8 V. IN-: Inverting input to the error amplifier. Use the common-mode input in the range - 0.1 V to +0.8 V.
0.75 V
5 S.C.P.
6
I
VREF
7
I
7 IN-
6 IN+
8
O
VREF Source current 8 FB Sink current
FB: Output from the error amplifier. The source current is approx. -110 A 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.
9 10
I VCC 0.1 V
10 CLM
CLM comp. 50 A 50 A
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.)
6
Voltage regulators
s Terminal Equivalent Circuits (continued)
Pin No. 11 I/O 11 SGND Equivalent circuit Description SGND: Signal ground.
AN8014S
12
12 GND
GND: Output stage ground.
13
O
VCC 14 CB
14 O
Out: Totem pole output. A constant output current of 100 mA or a peak output current of 1 A can be obtained. 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.
13 Out
15
I
15 VCC
16
I
OFF 16
17 k 13 k
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 A.
s 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
s Application Notes (continued)
[1] Function descriptions (continued)
Voltage regulators
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; 1 IO = t1 + t 2 2 x CT x (VCTH - VCHL) VRT 0.4 IO = 1.7 x = 1.7 x RT RT Because VCTH - VCTL = 0.88 V 1 fOSC [Hz] 2.59 x CT x RT fOSC = Example) An fOSC of approximately 215 kHz will be obtained if CT is 120 pF and RT is 15 k.
VCTH = 1.32 V (typ.)
VCTL = 0.44 V (typ.) t1 T t2
Charging Discharging
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 A and 8 mA respectively. The input voltage VIN+ and VIN- to the error amplifier are obtained from the following formulas. R4 R2 VIN+ = VREF x VIN- = VOUT x R3 + R4 R1 + R2 1
VREF R3 IN+ 6 IN- 7 R4 RNF Error PWM comparator amp. CT DTC
13 VOUT R1
8
FB
R2
CNF
Figure 2. Connection method of error amplifier 8
Voltage regulators
s Application Notes (continued)
[1] Function descriptions (continued)
AN8014S
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 x [V] CS tPE 0.75 V = 0.03 V + ICHG x CS tPE CS = ICHG x [F] 0.72 ICHG is constant current which is determined by the timing resistor RT . If RT is 15 k, ICHG will be approximately 2.3 A. VRT 1 ICHG = x [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 S Q1 1.82 V 5 S.C.P. CS Q2 Q Cut output off RQ Latch
ICHG Error amp. IN+ 6 IN- 7 FB 8 S.C.P. comp.
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
s Application Notes (continued)
[1] Function descriptions (continued)
Voltage regulators
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 A 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 DTC waveform tOFF tON DTC Out waveform Off On Off RDTC CDTC VCTH VDTC VCTL VREF IDTC CT FB PWM
Figure 4. Setting the dead-time Output duty ratio Du and DTC pin voltage VDTC are expressed by the following formulas; tON VDTC - VCTL x 1.1 Du = x 100 [%] = x 100 [%] tON - tOFF (VCTH - VCTL) x 1.1 VRT 1 IDTC = [A] x RT 2 RDTC 1 x [V] VDTC = IDTC x RDTC = VRT x RT 2 Example) When fOSC = 215 [kHz] (RT = 15 k, CT = 120 pF) and RDTC = 75 [k] 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 [A] 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
s Application Notes (continued)
[1] Function descriptions (continued)
AN8014S
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 Triangular wave (CT) Error amplifier output (FB) (5) Turned on in the next cycle 1.32 V 0.44 V
High Output waveform (Out) Low
Overcurrent protection input (CLM)
VCC VCC - 95 mV
(1) Overcurrent detection (2) Latch set Latch circuit set signal tDLY : Delay time High Low High Latch circuit reset signal (4) Latch reset Low
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] 2C1R2
C1 In R1
R2 Out
V-Out
CLM
Figure 6. CLM noise filter circuit
11
AN8014S
s Application Notes (continued)
[1] Function descriptions (continued)
Voltage regulators
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.
M1 VCC 15 VD1 I1 14 CB I2 13 Out Q2 VGS SBD D1 CB VS V-Out
PWM comparator CT DTC FB
Q1
VCB
Figure 7. Bootstrap circuit of output block
VCBH VOH Turns off VCC CB pin waveform Turns off Out pin waveform 0V M1 source side waveform VOL -VF t1 M1 Off t2 M1 On t3 M1 Off VCC -VDS(ON) [V] VCC - 0.7 [V]
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
s Application Notes (continued)
[1] Function descriptions (continued)
AN8014S
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 x 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 x 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
s Application Notes (continued)
[3] Timing chart
Voltage regulators
High
OFF pin voltage
Low 3.6 V
Error amplifier output (FB)
Supply voltage (VCC) Internal reference voltage
2.6 V 1.87 V
Power supply turning on Triangular wave (CT) DTC pin voltage
1.32 V 0.44 V 0.03 V
S.C.P. pin voltage Out pin waveform
High Low
Software start operation The maximum duty
Figure 1. PWM comparator operation waveform
Internal reference voltage
2.6 V 1.87 V 1.32 V 0.44 V
Short-circuit protection comparator (threshold level) DTC pin voltage Error amplifier output (FB) 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
s Application Notes (continued)
[3] Timing chart (continued)
Output off Triangular wave (CT) Error amplifier output (FB) Turned on in the next cycle.
AN8014S
1.32 V 0.44 V High
Out pin waveform Low
Overcurrent protection input (CLM)
VCC VCC - 95 mV
Overcurrent detection
tDLY: Delay time High Low High
Latch set Latch circuit set signal
Latch circuit reset signal Latch reset
Low
Figure 3. Waveforms of the pulse-by-pulse overcurrent protection operation
[4] PD Ta curves of SOP016-P-0225A PD T a
600
518 500
Power dissipation PD (mW)
Glass epoxy printed circuit board (50 mm x 50 mm x t0.8 mm) Rthj-a = 263C/W PD = 380 mW (25C)
400 360 300 Independent IC without a heat sink Rthj-a = 278C/W PD = 360 mW (25C)
207 200 143 100
0 0 25 50 75 85 100 125 150
Ambient temperature Ta (C)
15
AN8014S
s Application Notes (continued)
[5] Main characteristics Internal reference voltage temperature characteristics
2.63
Voltage regulators
Oscillator frequency temperature characteristics
225
Internal reference voltage VREF (V)
2.62
Oscillator frequency fOUT (kHz)
-25
220
215
210
2.61
205
200
2.60 -50
0
25
50
75
100
125
195 -50
-25
0
25
50
75
100
125
Ambient temperature Ta (C)
Ambient temperature Ta (C)
Output duty ratio DTC pin voltage
100
Output duty ratio temperature characteristics
56
80
55
Output duty ratio Du (%)
Output duty ratio Du (%)
54
60
53
40
52
20
51
0 0.4
0.6
0.8
1.0
1.2
1.4
50 -50
-25
0
25
50
75
100
125
DTC pin voltage VDTC (V)
Ambient temperature Ta (C)
Oscillator frequency Timing capacitance
10 000 0.6
Output peak current COut
VCC = 12 V ROUT = 10
Oscillator frequency fOUT (kHz)
0.5 1 000 RT = 5.1 k 100 RT = 15 k
Output peak current IPeak (A)
0.4
0.3
0.2
10
0.1
1 10
100
1 000
10 000
0 1 000
5 000
10 000
Timing capacitance CT (pF)
Value of output connection capacitor COUT (pF)
16
Voltage regulators
s Application Circuit Examples
1. DC-DC converter control (Example of step-down circuit)
In 12 V
0.1 F 75 k 1 000 pF 120 pF 15 k 10 0.1 100 F 0.039 F 33
AN8014S
3.9 k
Out 5V
47 F
V1
9.1 k
1 VREF
4 DTC
3 CT
2 RT
f = 200 kHz
Triangular wave OSC
VREF 2.5V
10 CLM
Boot strap
Constant current source 1 A 10 A
OFF 16
R
On/off active-high Q U.V.L.O. S R Latch Q Q
R
Latch QS
15 VCC In 14 CB
PWM comp.
13 Out
S.C.P. 5
0.12 F
S
6 7 SGND 11 PGND 12 FB 8
S.C.P. comp. Error amp.
IN+ IN-
100 k
62 k
11 k
2. DC-DC converter control (Example of step-up circuit)
VREF
In Out
DTC
CT 3
V1
1
4
2
Triangular wave OSC
RT
VREF 2.5V
10 CLM
Constant current source 1 A 10 A
OFF
16
On/off active-high R U.V.L.O. S R Latch Q Q Q
R
Latch QS Boot strap
15 VCC In 14 CB 13 Out
PWM comp.
S.C.P. 5
S
6 7
S.C.P. comp. Error amp.
IN+ IN-
11
12
SGND
PGND
FB
8
17
AN8014S
s Application Circuit Examples (continued)
3. DC-DC converter control (Example of polarity-inverting circuit)
VREF
Voltage regulators
In
DTC CT RT
Out
V1
4
1
3
2
Triangular wave OSC
VREF 2.5V
10 CLM
Constant current source 1 A 10 A
OFF
16
On/off active-high R U.V.L.O. S R Latch Q Q Q
R
Latch QS Boot strap
15 VCC In 14 CB
PWM comp.
13 Out
S.C.P. 5
S
6 7
11 12 8
S.C.P. comp. Error amp.
IN+ IN- V1
SGND
PGND
FB
1 VREF
18

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