CS2844 CHERRY | Alldatasheet
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Features
S R PWM Latch Current Sensing Comparator R 2 R Error Amplifier 2.50V Set/ Reset VCC Undervoltage Lock-out 34V 16V/10V (8.4V/7.6V) R R VFB VCC Pwr VOUT Pwr Gnd Oscillator Toggle Flip-Flop
5.0 Volt
( ) indicates CS-2845/3845 I Optimized for Offline Control I Temp. Compensated Oscillator I 50% Max Duty-cycle Clamp I VREF Stabilized before Output Stage is Enabled I Low Start-up Current I Pulse-by-pulse Current Limiting I Improved Undervoltage Lockout I Double Pulse Suppression I 1% Trimmed Bandgap Ref. I High Current Totem Pole Output Package Options CS2844/3845 SERIES Current Mode PWM Control Circuit with 50% Max Duty Cycle CS2844/CS3844 CS2845/CS3845Description Block Diagram Absolute Maximum Ratings Analog Inputs (V Lead Temperature Soldering 1COMP VFB Sense OSC VREF VCC VOUT Gnd
8 Lead PDIP & SO Narrow
14 Lead SO Narrow
The CS3844/45 provides all the neces- sary features to implement off-line fixed frequency current-mode control with a minimum number of external components. The CS3844 family incorporates a new precision temperature-controlled oscil- lator to minimize variations in fre- quency. An internal toggle flip-flop, which blanks the output every other clock cycle, limits the duty-cycle range to less than 50%. An undervoltage lockout ensures that V REF is stabilized before the output stage is enabled. In the CS2844/CS3844 turn on occurs at 16V and turn off at 10V. In the CS2845/CS3845 turn on is at 8.4V and turn off at 7.6V. Other features include low start-up current, pulse-by-pulse current limit- ing, and a high-current totem pole out- put for driving capacitive loads, such as gate of a power MOSFET. The out- put is low in the off state, consistent with N-channel devices. 1111 NC NC COMP VFB SENSE OSC NC NC NC V REF VCC VCCPwr VO Gnd Pwr Gnd NC
16 Lead SO Wide
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786 Email: info@cherry-semi.com Web Site: www.cherry-semi.com A Company ® Rev. 3/17/99
CT = 3.3nF for sawtooth mode., unless otherwise stated. CS2844/CS2845 CS3844/CS3845 PARAMETER TEST CONDITIONS MIN TYP MAX MIN TYP MAX UNITS CS2844/3845 SERIES I Reference Section Line Regulation 12 ≤VCC≤25V 6 20 6 20 mV Load Regulation 1 ≤IREF≤20mA 6 25 6 25 mV Temperature Stability (Note 2) 0.2 0.4 0.2 0.4 mV / ˚C Output Noise Voltage 10Hz ≤ f≤10kHz, T J=25˚C (Note 2) 50 50 µV Long Term Stability T A=125˚C, 1000 Hrs. (Note 2) 5 25 5 25 mV Output Short Circuit T A=25˚C -30 -100 -180 -30 -100 -180 mA I Oscillator Section Initial Accuracy Sawtooth Mode, T J=25˚C 4 75 25 74 75 25 7 k H z Voltage Stability 12 ≤VCC≤25V 0.2 1.0 0.2 1.0 % Temperature Stability Sawtooth Mode T MIN≤TA≤TMAX (Note 2) 5 5 % Amplitude V OSC (peak to peak) 1.7 1.7 V I Error Amp Section Input Bias Current V FB=0V -0.3 -1.0 -0.3 -2.0 µA AVOL 2≤VOUT≤4V 65 90 65 90 dB Unity Gain Bandwidth (Note 2) 0.7 1.0 0.7 1.0 MHz PSRR 12 ≤V CC≤25V 60 70 60 70 dB Output Sink Current V FB=2.7V, VCOMP=1.1V 2 6 2 6 mA VOUT HIGH V FB=2.3V, RL=15kΩ to Gnd 5 6 5 6 V I Current Sense Section Maximum Input Signal V PSRR 12 ≤VCC≤25V (Note 3) 70 70 dB Input Bias Current V Sense=0V -2 -10 -2 -10 µA Delay to Output T J=25˚C (Note 2) 150 300 150 300 ns I Output Section Output Low Level I SINK=20mA 0.1 0.4 0.1 0.4 V ISINK=200mA 1.5 2.2 1.5 2.2 V Output High Level I SOURCE=20mA 13.0 13.5 13.0 13.5 V ISOURCE=200mA 12.0 13.5 12.0 13.5 V Rise Time T J=25˚C, CL=1nF (Note 2) 50 150 50 150 ns Fall Time T J=25˚C, CL=1nF (Note 2) 50 150 50 150 ns
CS2844/CS2845 CS3844/CS3845 PARAMETER TEST CONDITIONS MIN TYP MAX MIN TYP MAX UNITS CS2844 CS3844 CS2845/CS3845 PARAMETER TEST CONDITIONS MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS Notes: 1. Adjust Vcc above the start threshold before setting at 15V. 3. Parameter measured at trip point of latch with V FB=0. 2.These parameters, although guaranteed, are not 100% tested in production. 4. Gain defined as: A = ; 0 ≤ VSense ≤ 0.8V. ∆VCOMP ∆VSense I Under-Voltage Lockout Section Voltage Package Pin Description PACKAGE PIN # PIN SYMBOL FUNCTION I Total Standby Current Start-Up Current 0.5 1.0 0.5 1.0 mA Operating Supply Current V FB=VSense=0V RT=10kΩ, CT=3.3nF 11 17 11 17 mA VCC Zener Voltage I CC=25mA 34 34 V I PWM Section Maximum Duty Cycle 46 48 50 46 48 50 % Minimum Duty Cycle 0 0 % 8L 14L 16L PDIP/SO SO Narrow SO Wide 1 1 3 COMP Error amp output, used to compensate error amplifier. 23 4 V FB Error amp inverting input. 3 5 5 Sense Noninverting input to Current Sense Comparator. 4 7 6 OSC Oscillator timing network with Capacitor to Ground, resis- tor to V REF. 5 9 11 Gnd Ground. 8 10 Pwr Gnd Output driver Ground. 61 0 1 2V OUT Output drive pin. 11 13 V CCPwr Output driver positive supply. 71 2 1 4 V CC Positive power supply. 81 4 1 5 V REF Output of 5V internal reference. 2,4,6,13 1,2,7,8,9,16 NC No Connection. CT=3.3nF for sawtooth mode., unless otherwise stated.
During Undervoltage Lockout (Figure 1), the output driv- er is biased to sink minor amounts of current. The output should be shunted to ground with a resistor to prevent activating the power switch with extraneous leakage cur- rents. PWM Waveform To generate the PWM waveform, the control voltage from the error amplifier is compared to a current sense signal which represents the peak output inductor current (Figure 2). An increase in V CC causes the inductor current slope to increase, thus reducing the duty cycle. This is an inherent feed-forward characteristic of current mode control, since the control voltage does not have to change during changes of input supply voltage. When the power supply sees a sudden large output cur- rent increase, the control voltage will increase allowing the duty cycle to momentarily increase. Since the duty cycle tends to exceed the maximum allowed to prevent transformer saturation in some power supplies, the inter- nal oscillator waveform provides the maximum duty cycle clamp as programmed by the selection of OSC compo- nents. Circuit Description Test Circuit Open Loop Laboratory Test Fixture VREF VCC VOUT 1k Ω 0.1 µF 0.1 µF VREF VCC VOUT Gnd VFB Sense OSC COMP 5k Ω 100k Ω 4.7k Ω 1k Ω Error Amp Adjust 4.7k Ω Sense Adjust RT 2N2222 CT Gnd A VCC VON 16V 8.4V VOFF 10V 7.6V CSX844 CSX845 ON/OFF Command to reset of IC <15mA <1mA VON VOFF ICC VCC Figure 1: Startup voltage for CSX844 and CSX845.
Part Number 0˚C to -25 ˚C Description 70˚C to 85 ˚C CS2844LN8 8L PDIP CS2844LD14 14L SO CS2844LDR14 14L SO (Tape & Reel) CS2844LDW16 16L SO Wide CS2844LDWR16 16L SO Wide (Tape & Reel) CS2845LN8 8L PDIP CS2845LDW16 16L SO Wide CS2845LDWR16 16L SO Wide (Tape & Reel) CS3844GN8 8L PDIP CS3844GD8 8L SO CS3844GDR8 8L SO (Tape & Reel) CS3844GD14 14L SO CS3844GDR14 14L SO (Tape & Reel) CS3844GDW16 16L SO Wide CS3844GDWR16 16L SO Wide (Tape & Reel) CS3845GN8 8L PDIP CS3845GD8 8L SO CS3845GDR8 8L SO (Tape & Reel) CS3845GD14 14L SO CS3845GDR14 14L SO (Tape & Reel) CS3845GDW16 16L SO Wide CS3845GDWR16 16L SO Wide (Tape & Reel)
Ordering Information
D Lead Count Metric English Max Min Max Min 8 Lead PDIP 10.16 9.02 .400 .355 8 Lead SO Narrow 5.00 4.80 .197 .189 14L SO Narrow 8.75 8.55 .344 .337 16L SO Wide 10.50 10.10 .413 .398 Thermal 8 L 8L SO 14 L SO 16L SO Data PDIP Narrow Narrow Wide RΘJC typ 52 45 30 23 ˚C/W RΘJA typ 100 165 125 105 ˚C/W Package Specification PACKAGE DIMENSIONS IN mm (INCHES) PACKAGE THERMAL DATA © 1999 Cherry Semiconductor Corporation Cherry Semiconductor Corporation reserves the right to make changes to the specifications without notice. Please contact Cherry Semiconductor Corporation for the latest available information. Rev. 3/17/99 Plastic DIP (N); 300 mil wide 0.39 (.015) MIN. 1.14 (.045) D Some 8 and 16 lead packages may have 1/2 lead at the end of the package. All specs are the same. .203 (.008) .356 (.014) REF: JEDEC MS-001 3.68 (.145) 2.92 (.115) 8.26 (.325) 7.62 (.300) 7.11 (.280) 6.10 (.240) .356 (.014) .558 (.022) Surface Mount Narrow Body (D); 150 mil wide 0.33 (.013) 6.20 (.244) 5.80 (.228) 4.00 (.157) 3.80 (.150) 1.57 (.062) 1.37 (.054) D 0.25 (0.10) 0.10 (.004) 1.75 (.069) MAX 1.27 (.050) 0.40 (.016) REF: JEDEC MS-012 0.25 (.010) 0.19 (.008) Surface Mount Wide Body (DW); 300 mil wide 1.27 (.050) BSC 7.60 (.299) 7.40 (.291) 10.65 (.419) 10.00 (.394) D 0.32 (.013) 0.23 (.009) 1.27 (.050) 0.40 (.016) REF: JEDEC MS-013 2.49 (.098) 2.24 (.088) 0.51 (.020) 0.33 (.013) 2.65 (.104) 0.10 (.004)