NJM A High Power DC/DC Converter Controller IC

Transcription

1 7.A High Power DC/DC Converter Controller IC GENERAL DESCRIPTION The NJM28 is a high power step down DC/DC converter IC. It incorporates 7.A power transistor, ±2% accuracy precision voltage reference, fixed frequency PWM controller with cycle-by-cycle current limit and low power consumption stand by function. The NJM28 realizes a high power step down application with minimal external components. PACKAGE OUTLINE PIN FUNCTION :V FB 2:SW OUT 3:GND 4:V + :STBY (V COMP ) FEATURES Adjustable output voltage more than V Operating Voltage 7.V to 4V PWM form Switching Power Supply Control Internal High Power Transistor 7.A (min.) Fixed Frequency Oscillator 72kHz (typ.) Current Sense Amplifier Under Voltage Lockout Thermal Shutdown Circuit Bipolar Technology Package Outline TO-22(PIN) NJM28TLA2 Pin locates on the left side of the package drawing (top front view). BLOCK DIAGRAM 4 Current Sense Amplifier 7.A Power Transistor Current Detection Transistor 2 Thermal Shutdown Reference Voltage Oscillator S Q ON/OFF VREF R Under Voltage Lockout PWM Comparator Latch Circuit VREF Standby Circuit Error Amplifier 3 - -

2 ABSOLUTE MAXIMUM RATINGS (Ta=2 C) PARAMETER SYMBOL MAXIMUM RATINGS UNIT Maximum Supply Voltage V + 4 V Switch Output Voltage Vo (SWITCH) -. +Vin V Voltage Feedback and Compensation Input Voltage Range V FB,V COMP V Power Dissipation P D TO-22 (PIN) 6(T C 46 C) W Operating Junction Temperature Tj -4 + C Operating Temperature Range Topr -4 ~ +8 C Storage Temperature Range Tstg - ~ + C THERMAL CHARACTERISTICS Thermal Junction-to-Ambient Temperature θja 7 Resistance Junction-to-Case θjc 6. C/W POWER DISSIPATION vs. AMBIENT TEMPERATURE 8 (T opr =-4~+8 C, Tj= ~+ C, P D =6W(T C 46 C)) Power Dissipation PD (W) θ HS = C/W θ HS = C/W θ HS =2 C/W Heat Sink 2 Without Heat Sink 2 7 Ambient Temperature Ta ( C) - 2 -

3 ELECTRICAL CHARACTERISTICS (V + =2V, Ta=2 C) Oscillator Block Frequency fosc V + =7.V khz Error Amplifier Block Voltage Feedback V FB (th) V Input Threshold Line Regulation REG Line V + =7. 4V.3.8 %/V Input Bias Current I B V FB =V FB (th)+.v.. µa Ripple Rejection PSRR V + = 2V 8 db Output Voltage Swing V OH V OL Isource=7µA,V FB =4.7V Isink=.4mA,V FB =.3V V V PWM comparator Block Duty Cycle Maximum Minimum DC (MAX) DC (MIN) V FB =V V FB =.3V 9 % % Switch Output Block Output Voltage Saturation V SAT V + =V,Isource=7.A V V V OFF-State Leakage Isw (off) V + =4V,SW OUT =V µa Current Limit Threshold Ipk (SWITCH) V + =V A Switching Times Output Voltage Rise Time Output Voltage Fall Time tr tf V + =4V,R OUT =7.7Ω,V FB =V V + =4V,R OUT =7.7Ω,V FB =V ns ns Under Voltage Lockout Block Startup Threshold V TH(UVLO) V + Increasing V Hysteresis V H(UVLO) V + Decreasing.3..7 V Total Device Standby-State Power Supply Current Operating-State Power Supply Current Icc (stby) STBY.V 36 µa Icc V + =4V,V FB =V duty cycle=max Keep the limit of maximum power dissipation not to operate thermal shutdown. Low duty cycle pulse test is used to close its junction temperature to ambient temperature. 4 3 ma - 3 -

4 MARKING 28- JRC Product Number (NJM28TLA2) Logo Lot Number TYPICAL CHARACTERISTICS Switch Output Saturation Voltage V (V) SAT Switch Output Saturation Voltage vs. Output Source Current (V + =V, Ta=2 o C) Output Source Current SOURCE I (A) Output Saturation Voltage V (V) SAT(ERROR) Error AMP Block Output Saturation Voltage vs. Output Sink Current (V + =2V, V =.V, Ta=2 o C) 2 FB Output Sink Current SINK I (ma) Standby-State Power Supply Current I (µa) CC(stby) Standby-State Power Supply Current vs. Supply Voltage (Ta=2 o C) Supply Voltage V + (V) Duty Cycle DC (%) Duty Cycle vs. Compensation Voltage (V + =2V, Ta=2 o C) Compensation Voltage V COMP (V) - 4 -

5 TYPICAL CHARACTERISTICS Voltage Feedback Input Threshold vs. Temperature (V + =2V). Voltage Feedback Input Threshold V (V) FB Error AMP Block Input Bias Current vs. Temperature (V + =2V, V =V (th)+.v).4 FB FB Input Bias Current I B (µa) Oscillator Frequency vs. Temperature Current Limit Threshold vs. Temperature Oscillator Frequency f OSC (khz) (V + =2V) Current Limit Threshold Ipk (SWITCH) (A) (V + =V) Under Voltage Lockout Threshold V (V) TH(UVLO) Under Voltage Lockout Threshold vs. Temperature Startup Threshold V + Increasing Startup Threshold V + Decreasing Power Supply Current I CC (ma) Operating-State Power Supply Current vs. Tmperature (V + =4V, V =V, duty cycle=max) FB Ambient Tmperature Ta ( o C) - -

6 TYPICAL APPLICATIONS Step-Down Converter Vin *SBD 4 2 NJM28 L Vout = R2 R + V FB (th) [V] Vout 3 R2 Cin CF SBD Cout RF R ) V and higher converter, the application must be connected R resistor according to above figure. 2) High current converter, the application must be placed Cin capacitor next to NJM28, which avoid the power-line fluctuation. 3) The sharp fluctuation of output load cause reverse voltage for inductance and over the supply-voltage for SW OUT terminal. To avoid this problem, the application must be placed SBD between terminal 2 and 4. TIMING CHART Oscillator ) Compensation Switch output ON OFF ON 2) Current sense OFF 3) ON Thermal shutdown 4) OFF ) The NJM28 generate square waves. The PWM comparator generate PWM signals to compare square waves and compensation voltage. 2) The switching duty is maximum 9%(typ.). 3) Over the 8.A(typ.) current, the output switch will be OFF to operate current limit protection. The NJM28 sense the switching current of power transistor. 4) Over the Tj=8 C(typ.), the switching will be OFF to operate thermal shutdown circuit

7 MEMO [CAUTION] The specifications on this databook are only given for information, without any guarantee as regards either mistakes or omissions. The application circuits in this databook are described only to show representative usages of the product and not intended for the guarantee or permission of any right including the industrial rights